HFU HF Underground
General Category => Amateur Radio => Topic started by: Josh on March 21, 2019, 2115 UTC
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We should share our HAM projects to encourage (or enrage) one another! Mr Smolinksi, plz consider making a sub forum in HAM radio for that!
Tother day I saw an advert for a likely rig at The Ham Station, called upon said proprietor, and with a deal being struck, I ventured homeward with a Icom IC-775DSP for a pittance.
The upside is the pittance, the downside is the rig needs a lot of repair and an entire makeover, this thing looks like it was dragged behind Brunson's (AE4N SK) golf cart at a hamfest.
A bit about the 775;
The 775 were the flagship of the Icom HF line back in the day, just after the glorious 781, but before the 756 original flavour.
The 775 brought DSP to the line and oddly enough it was an option, an option unlike the typical add in DSP cards as it was more or less IF DSP rather than AF DSP. What this means is there are two distinct modulation and demodulation paths for the 775 - one provided by the add in DSP card, the other by the onboard analog hardware. My guess is it was one of Icom's most costly rigs ever, as far as parts and design. It will produce some 200w of output power with a 28v pa featuring transistors that are rated at 150w each so I might be tempted to run it at 300w if the waveform's clean.
The 775 also has option slots for multiple xtal filters in the 9 and 455 IF lines, some of wich are already populated by high quality filters.
It's also a huge radio, behold;
https://www.youtube.com/watch?v=TiZxQCv4m04
Look at those buttons and knobs!
Come in Tokyo!
HAM nerdvana!
Now about that downside;
The 775 has a known issue with the display backlight cfl circuit where the solder cracks and arcing occurs on the hv secondary xformer, another is it was dropped in transit to a repair shop for the display issue, said repair shop refusing to touch it. It seems most delivery services have instilled a "drop it or you're fired" mentality at their hubs.
Anyway, I'm confident I can overcome the xverter cable connector issues (damaged in shipping) and can have the top and bottom covers bead blasted and powder coated locally, and live with the face if I can't source another, the face is kinda beat up but it's all there. It kinda looks like the HAM only operated the rig when he ate fried chicken, thank god he didn't smoke too.
Project 775
A few years ago I was into the R71 in a big way, with mods and historical notes and everything as it was used by many US gov agencies as well as sigint outfits around the world for many uses, from sigint missions to training. It was often paired with the glorious R7000 to add V/UHF coverage. Even today they're a worthy hf rig.
As I was all about the R71, I came up with some mods and replacements of my own and have parts left over that are perfectly suited for the 775.
One of the mods was to employ the MI204 PIN diode for all input bandpass switching in the front end up to 11MHz, that diode being the one chosen by Icom for use in several hf receiver front ends for VLF to MW. The reason this diode is choice is due the carrier lifetime of said diode, they're simply a much better performer down on the low bands than the typical front end diodes, however they're much more expensive and very hard to find, got mine from Icom years ago. Below about 8MHz these diodes are the cat's ululation, above 8MHz the standard Icom 1SS53 is an outstanding performer even though it's not a PIN diode. The following url has images showing how poorly chosen front end diodes contribute to IMD;
http://jking.000webhostapp.com/TS-940/TS-940_02.htm
What this should lead you to suspect is I have a lot of crap left over from my R71 rage days.
So I'm contemplating replacing the standard front end diodes with the MI204s I have on hand, and perhaps in the 455 IF switching lines too but those lines see only controlled and tightly bandwidth limited rf.
Another mod is replacing the FL80 2.4KHz ssb filter with a FL70 2.8KHz filter, a direct pin for pin swap. The FL80 is choice when you run the FL44A 455KHz ssb filter as their bandwidth matches, however the 455KHz ssb filter in the 775 is the FL96, a 2.8KHz wide filter. Not only will I enjoy much better audio from the 2.8KHz pair, I can sell the FL80 as it's a sought after premium part and as the 775 was one of the last to use the FL80, the one in the rig is fresher than many of the others found on epay.
Also have a 6KHz wide AM filter that can be spliced into the IF strip for better selectivity on SWBC AM and ECSSB.
There's a lot of possibilities to the rig as it stands, if I can get the core sections up and running. If I can't, there's more than enough filters and the DSP module that will make me a profit over the current outlay if placed on qth or epay. That being said, I'd really like to get it going and modded to my likes, a super R71 of my dreams that can transmit.
nerdstuff;
https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/radcom/1995/12/page72/
https://en.wikipedia.org/wiki/Carrier_lifetime
https://www.alldatasheet.com/view.jsp?Searchword=1SS53
http://www.arrl.org/files/file/History/History%20of%20QST%20Volume%201%20-%20Technology/QX01-03-Rohde.pdf
http://www.ab4oj.com/icom/filters/list.html
https://www.hamstation.com/
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Isn't the "black arts" board about projects, ham or otherwise?
EDIT, looks like that board was renamed "The RF Workbench" at some point.
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I googled the rig. It's a great looking radio. I can see how it was the Icom flagship at that time. Wish it had a FL-25 500hz filter in it? I need one.
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I googled the rig. It's a great looking radio. I can see how it was the Icom flagship at that time. Wish it had a FL-25 500hz filter in it? I need one.
Did you mean FL52A? The 775 has one, and a matching 9MHz IF 500Hz filter too for utter dual IF filtration goodness where the adjacent stopband attenuation is down around the 80 to 90 dB mark. Had FL52A in the IC703 qrp rig, lovely filter for anything that fit in that passband, mebbe HAM Station has one, can't remember but he had a pile of Icom filters last time I was there. Think I have a FL32A 9MHz IF xtal filter around here somewhere, but that's a filter with the older style of pinout used by the 751 and earlier rigs, can be soldered in or drop in. The newer style filters are close in size but the in/outs are spaced differently... thanks Icom! Sadly, I cannot use the illustrious MI204 diodes in the input bandpass filtering, they're all smt devices and the MI204 is leaded! Now to look for some likely PIN diodes of the smd variety.
Inoue-san interview;
https://www.icom.co.jp/world/news/004/
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Yes you are correct. Must have had numerical dyslexia a the time
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I see you've a 718, nice rig, kinda a grandchild of the 775. I was going to offer a cw filter but the 718 doesn't have a 9Mhz IF strip, just 455Khz and all I have to spare is the 9MHz filter, if I come across one for 455 I'll let you know.
So far in Project 775, Icom parts has the relays I need to replace those popped off in shipping, but the display tube's no longer available, neither is a face plate. The external cable with the broken connectors isn't a xverter jack, it's for an external receiver and I never use those, so as the solder points on the pc boards are broken I'll just link the two points internally with coax.
Some HAMs have used leds to replace the problematic display tube;
https://www.youtube.com/watch?v=jp5qyuBeIdA
What the original looks like;
https://www.youtube.com/watch?v=0z4hd0LSFho
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Oh well, I'll come across one somewhere. Yes I really like the 718. Its a simple rig with a nice screen and easy layout.
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Starting the cleanup and disassembly as well as perusal of service manual. One nice feature noted in said manual is the IF strip is an honest 15Kc wide in wide filter am mode, freaking ossum for ambc audio quality. In ssb you can go 3.3, 6Kc total but it's dsb, not ssb then. The medium filter setting nets you 6Kc width in both 9MHz and 455Kc IF strips, the 9MHz IF filter being optional, and I have one on hand, perfect for swling.
(These wider bandwidths are why I miss my TS870, the 870 ambc audio sounded like you were in the studio, the downside to the 870 is the filtering isn't very sharp.)
Then the 775 detracts from that potentially ossum audio quality by not employing dsp to demodulate that am signal, it uses a diode, and diodes are noisy. Dsp can produce mathematically perfect modulation and demodulation sans distortion = why you want dsp for this. The 775 dsp only modulates and demodulates bfo modes; ssb, cw, and rtty, not am or fm. Oh well, diode rectification can sound good, just replace the diode with a schottky/hot carrier type, bias it a bit perhaps, adjust the output capacitances to recover lows and there you are with studio quality audio out.
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Recalled that some Italian HAMs took their 775s to nerdvana with some serious mods;
http://www.pensioneitaliacapri.com/ham/IC775-Progetto-Modifiche-2009_Finale.pdf
You can translate it online if you wish;
https://www.onlinedoctranslator.com/translationform
Gian and Nick carved up their 775 and replaced or modded quite a lot of the inners of the 775, to include mixers, active vco filtering, roofing filter swaps in various IF strips, etc, read the pdf if you want to know more.
One of the takeaways I got from the pdf was the 9MHz IF roofing filter I'd not noticed. This filter sets the 9MHz IF bandwith to 20KHz right after the mixer, they replaced it via a factory Icom part that was only 6KHz wide. This is great if all you want to pass thru that IF strip is 6KHz wide or less, in itself this should greatly increase tolerance to strong nearby signals while not compromising the desired signals.
Having a filter right behind a mixer is a good idea, because in most mixer cases you send in two frequencies to mix and you get four out (due to images) when you only wanted one freq.
The way to properly terminate a mixer is with a diplexer circuit that terminates the undesired product freqs gracefully. The filter is a brute force means to that end, as well as reducing noise in the IF strip as a typical IF strip can be 10s or hundreds of KHz wide.
The 6KHz wide 9MHz IF filter is too restrictive for someone who wants to have a truly wide bandwidth like 10 or 15KHz, but Icom has other filters of the same case and pinout design and the same center frequency but with different bandwidths. 9M6A1 FL-116 is the 6kHz BW filter - the Icom IC706 employs these for wide am, part number 201 0000 950 if you want one from Icom. The standard IC706MKIIG has a 15KHz filter, this is the one to order from Icom if you want to pass ambc sigs yet still get some tighter filtering over the standard 20KHz wide filter. I'll install a 15KHz filter here, so glorious wide ambc and hfbc sigs can flourish. Flourish I say!
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Preliminary inspection complete.
First off, I'm not set up to work on a rig this massive! Good thing homes have floors.
This thing's missing a lot of case screws, mostly for the faceplate, wich can be an indication people have been rooting around inside and not bothered to replace the screws. Simple enough to remedy and Icom has the screws, I checked. Icom likely still uses many of the same screws in all its rigs.
On the shipping damage front, I was very worried there would be broken boards due the connectors soldered to said boards being pushed in and broken off. Boards are fine, just the leads to the components have sheared off, an easy fix. The external antenna connector jumper apparently hit the floor, broke off two different boards, and in one board pushed two relays far enough that their leads were broken. So far I need 3 relays that Icom says are 11 bucks each, will try to find them cheaper. I suppose I could repair the relays easily enough but the leads are really thin so new is likely best.
On removing the bottom cover, I noted some weird buildup that at first reminded me of mud dauber wasp activity, but tasting it revealed a distinct waxy flavour. Na jk, I touched it and it's wax. So where does wax come from in a 775? As expected, the stalagmites of wax (or are they stalactites?) emanate from the pll and dds area, as provenanced by replacing the cover and seeing how the wax stalagmites and vco/dds openings aligned. This indicates the rig either ran for long periods of time, or the wax wasn't very temp stable. The worst part of this will be everything inside the vco/dds cans might be wax covered due to capillary action, to include the vco tuning caps, then again this wax just might be a beneficial preservative in nature. Have to open them cans and find out.
The reason companies apply literal gobs of wax to vco/pll/dds circuitry is due the nature of solid wax; easily applied in liquid state and then hardens to a stiff support structure. The reason we want to stiffen the vco/pll/dds circuitry is to keep mechanical but not electrical vibration to a minimum. Another issue some waxes and glues present in electronic circuits is that they can become hygroscopic over time, meaning they can absorb humidity from the air and retain it, causing changes in the tuned state of nearby electronics. The Kenwood TS 440 and 940 were/are notorious for this. Removing and replacing this wax is a common procedure in hf rig repair, often hot glue or epoxy is used to replace the wax. I prefer to use something that can be more easily removed than epoxy.
This secret and forbidden love for water that wax seems to have is one of the reasons why one must replace every wax capacitor inside old radios, the wax has had decades of absorbing moisture, and the acids in the paper the cap dielectric's made from have come out and are all combining to transmogrify (lol "transmogrify" is actually in the spell checker!) those caps into a very poor form of resistor.
On the vco/dds front, have to get the rig fired up and warmed up before vco/dds tuning can commence, as well as a complete alignment as a rig this glorious warrants. Every used rig I've ever had needed at least vco/pll.dds alignment, and many could use a full alignment. These full alignments can take hours, but are kinda satisfying to see a rig that before seemed a mite deaf come out with much better than than published sensitivity and selectivity.
Here we should have a talk about manuals since we talked about vco/dds.
To do any real service work on these rigs you need a service manual. simple as that.
I've had about every Icom hf rig, and since getting involved in the madness that is personal computing, have aggregated gigs of user and service manuals on pdf. If you have a rig, its service manual is likely out there on the web for free. If you want a hard copy, it's so easy to take that manual via flash drive to your friendly local printers and have them do one up for you, complete with holes for your three ring binder. Try to splurge and get full color rather than black and white as some schematic overlays use two or more colors to show underside traces and so on.
This faceplate really needs replaced, it's scarred and scratched and looks like someone spilled milk on it. I suppose a trip to the bathtub with hot soap and water will make it look as best it can, considering. I don't trust chemical cleaners such as the spray on types people use to clean electronic devices other than say bar soap. hot water, and a dish rag anymore for cleaning items like radio faceplates due the chance the chems might wipe away printing, or eat plastics.
On checking the various board screws for tightness, almost all of them so far have proven to be about finger tight or loose. The inside is very clean overall other than the wax issue wich is contained to the bottom cover and the insides of the vco/dds cans, so I wasn't expecting every fing board to be loose but that's trivial to deal with. Every rig I get, new or used, has all the screws loosened and tightened or at least checked for tightness. I guess after traveling across the ocean from Japan in some huge creaking container ship and decades of use have temperature cycled the rig, causing the screws to be loose, at least that's my fantasy.
On the top and bottom covers, no spraycan from walmart will be restoring the deep gouges and rusted spots, these things will have to be bead blasted and powder coated or spray painted.
This has been cathartic and fun so far, that's it for now!
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Why alignments are wonderful things;
https://www.youtube.com/watch?v=3MpP1K2pbSA
This vid's from the TRX Bench, a great channel for those interested in HAM radio repair.
Most sdr rigs will never need aligned, they align themselves every time you fire up the app. With analog rigs, the older the rig, the more likely it could use an alignment.
Most rigs made by Icom have a Japanese version not sold outside the home islands. In some of the youtube vids for the IC775 you will see rigs with a black display border and illuminated nomenclature, this is likely the home islands version known as the ICOM 775DX2, same as the euro or American version but with the display oppositely polarised and in some cases 100w out rather than 200w. There is or was a Japanese regulation where all HAMs were allowed on hf with 10w or perhaps more regardless of license class, they considered the low power a limitation on what damage new HAMs could do to the hf bands. When the IC751A ruled the land, Japan had a 10w qrp version for their lowest license class, everyone else got 100w versions. Most lcd displays can be changed from illuminated nomenclature and dark background to the reverse, you'd need to peruse the service manual for said display to see how.
Now back to the home islands Icom naming convention, most Icom rigs sold in the US and the eu are also sold in Japan, just with different names. For example, the IC746 Pro known around the world is the IC-7400 in Japan.
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Relays and case screws ordered and on the way, so stoked!
The kind lady at Icom Parts who took my order discussed the glorious 775 at length with me, and made mention of ebay perhaps being a source for parts Icom no longer had on hand. Must admit hadn't considered ebay as a parts source and checked them out.
Suddenly there's several 775 parts/modules on the screen! You need a pll board? Got one working pull for $100. Need at tuner unit? Got one too. The further I looked into what the seller had on hand raised my hopes greatly. Here was a top cover in very good condition for only $30 ($34 shipping), and its mate for another $30. He had several other parts modules for similar HAM rigs that made me wonder if he buys HAM rigs then vivisects them to sell off the harvest, not sure how to feel about that practice but if it gets me a new faceplate I am all for it I guess. I followed his list to the end and no joy, no face plate for me! Where did it go to? He had to have it if he has the rest of the rig.
The covers can be bead blasted and either powder coated or spray canned into niceness, not gonna shell out 30 a piece and another 34 shipped when rustoleum can do wonders for pennies.
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Follow along as the surgeon makes the first incision;
http://photos.meekfarm.us/GalleryThumbnails.aspx?gallery=4862380
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Relays and new rca jacks installed, checked settings and powered it up.
https://www.youtube.com/watch?v=0VkrUG3OrPc
Bands checked, power out is good, controls seem responsive, dual watch works, all with a face only a mother could love!
Now on to the self dimming display!
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Self dimming display is no longer an issue, now on to tuner motors that seem to be frozen.
(https://cache.nebula.phx3.secureserver.net/obj/QUFBQzg2OTE0QzJGQ0VBNEIzOTQ6ODY4NjgxOGY2NTBkNDZiN2JiZDQ0OTI1ZWRjNjhjYjE=?uid=d0e7be53-d7f4-4270-800e-19d47b169e37)
A fix for Icom tuner motors;
https://www.youtube.com/watch?v=UdY6RhNOCWg
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In the spirit of keeping this rig as "Icom" as possible, it has been festooned with authentic Icom parts; from repair parts to modification parts, keeping with Icom quality standards has been a major consideration.
To wit;
The ac line input connector was replaced with the ac line filter from an Icom IC-765. The 765 had/has a noisy internal smps so Icom filtered it at the line cord. Replacing the internal smps with an external linear psu, I had the 765s ac line filter in the parts box for decades, knowing one day it'd be put to good use. The smps in the 775 is fairly quiet as smps go, I just want to make sure no rf makes its way into the rig via the ac line, and to make the smps as quiet as possible. This is especially important when tuning in the vlf band, as most smps spurs are strongest in the vlf band. Line filters like these can also be retrofitted to pc systems psu to reduce their emi footprint.
The DUALWATCH vfo tuning knob as featured on the 775 is a tiny affair, well weighted for tactile response but minuscule in diametre, and with no means to alter the tuning drag.
Pondering the tiny wheel one afternoon, I removed the existing knob and closely examined the vfo encoder shaft, it was the standard D notched affair with no set screw. Where had I seen this size control shaft before? Oh I know! The Icom IC-706 MKIIG! I had replaced the vfo knob on a 706 years ago as the shiny black finish had been chipped, and tossed the chipped but otherwise perfectly usable tuning knob into the parts bin.
Small as the tuning knob on a 706 is, Icom still included a freely rotating finger dimple, as well as a rugged rubber ring around the circumference of the knob, desirable features in any size tuning knob. The original DUALWATCH knob has no dimple, and as a dimple connoisseur, I demand dimples.
I fished the 706 knob out of the parts bin, gently affixed it onto the vfo shaft, and presto, a 775 with a 706 DUALWATCH vfo knob that looks like it belongs there, you can even see the skirt molded into the front panel behind the knob. And as the Handsome Al Fansome will tell you, knobs are important.
The FL23 9M20 9mHz IF xtal roofing filter, a device inserted shortly after the 775's 9mHz IF mixer to reduce IF bandwidth, will be replaced with an 9M15 xtal filter from an IC-706, passing 5kHz less bandwidth than the stock filter. This is a compromise between a 9M6 6kHz wide filter - wich would result in spectacular close in signal handling ability for ssb, cw, and digital mode work, but would more or less disable fm and am wide mode, so the 9M15 was chosen. This 15kHz filter still increases signal handling ability to a degree while passing am wide and fm signals.
The FL80 2.3kHz wide xtal filter in the 9mHz IF strip will be replaced with an FL70 2.8kHz wide filter that was excised from an Icom IC-R71A receiver. Icom, for whatever reason, paired the FL96 with the FL80, I assume they did this as the FL80 is considered a premium filter according to the shape factor, the FL30 used in most every other Icom hf rig was not in keeping with the flagship status of the 775. The existing (and desired) FL96 455kHz IF xtal filter is 2.8kHz wide, so the FL70 is a perfect match.
The FL80 is a premium part normally paired with the legendary FL:44A filter in Icom rigs of yore, but I've grown fond of wider bandwidth over time for being able to recover more intelligibility from a given signal.
Now to find a factory Icom tcxo!
Add some Icom MB19 rack handles, an unblemished front panel, bead blasted and powder coated cabinet, and a tuneup, and I'd consider this a project for the history books.
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In the spirit of keeping this rig as "Icom" as possible
And here I thought you were going to talk about low quality audio :)
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In the spirit of keeping this rig as "Icom" as possible
And here I thought you were going to talk about low quality audio :)
This rig's got fair rx audio, compared to a lot of Icoms I've had in the past. Pair it with a glorious Heil HC5 "Ragchew" cartridge, set the dsp bandwidth on tx appropriately and it will have the iComest of iCom audio!
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In the spirit of keeping this rig as "Icom" as possible
And here I thought you were going to talk about low quality audio :)
On a serious note, Icom has long had a rep for poor audio quality.
The phrase "Icom audio" is well known by HAMs, especially those that run hf. I feel that the FL30 filter, wich is used to create lsb and usb signals before sent to the final amplifier is more to blame than the microphone and further audio processing. The FL30, present in millions of Icom hf (and other) rigs, is 2.4kHz wide at 6dB down, not wide enough for good audio quality in my mind. So take that poor audio bandwidth and splice on top of it poor microphone quality and audio processing and you have a textbook case of bad audio.
In the case of those stuck with xtal filters and no dsp modulation, replacing the filter is the only option for wider bandwidth tx.
If you have dsp modulation, you can open the dsp up to 2.8 or 2.9kHz lowpass in some cases, in other even more such as 6.6kHz wide, and 80 or 50Hz for the highpass side.
In testing, the 775 running dsp modulation, has 10dB more opposite sideband rejection than in analog modulation mode, so along with creating more mathematically perfect modulation, dsp can clean up your signal greatly.
Then there's the issue of filter faults, where an internal part loses contact with the rest of the circuit or changes value. This is often noted in the FL30 and FL80 filters, especially the FL80, where one sideband seems to pass much more audio than the other, even though these filters are designed and constructed to be as symmetrical as possible. Some HAMs have unsoldered FL30 and FL80 cases, found the culprit part, and resoldered or replaced the offender, rendering the filter fit for service once again. This is a tough nut to crack when the case is hermetically soldered along its entire seam and likely comprises an inert gas environment.
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A face plate in almost perfect condition has been sourced, and negotiations are ongoing for clean top and bottom cases. Could always bead blast and powder coat the case halves but it'd never be the same as the original Icom finish, same goes for the chipped tuning knob. Meanwhile, Project 775 sits here quietly monitoring hf utes and the occasional privateer.
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Josh, I just found this thread. Great stuff and I'm glad you're posting these updates! I'm learning a lot from them.
I just bought an early 775DSP but won't get it for a couple of weeks. It was finally time to upgrade my Kenwood TS-130V (yes, I said V).
Can I ask what the stock 9 MHz and 455 kHz filters are in this rig? Mine will have originals but I would also like the wider SSB filters, but with the option to go narrower (like 1.8 khz) when needed. What filters can I fit in the 775 and what would you suggest? CW using 500 hz would be fine for me and I wouldn't care about AM on this rig, already ordered the Inrad Roofing Mod. I have my other receivers for AMBC.
I always loved the receiving ability of my (now gone) R-70 but the audio was indeed lacking. The 775 has a very good reputation though.
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Glad I could help! Also, Wally, my eyes, ears, and steady soldering hands in this project, also is glad you find this interesting. Everyone wave hi to Wally!
On the 455kc and 9mc filtration front, you have several options built in, and some can be retrofitted.
If you are unconcerned about wideband am or nbfm, one thing you can do is change the filter that sits in the output of the 9mc IF amp from 20kc+ to 6kc or so, this alone will do wonders for close in sigs and IF noise getting to the next stage. Just look at my notes where the filters are mentioned and you will get the idea. This filter swap should help approximate the Inrad front end. I got a replacement filter for this position from a HAM radio repair shop and he may have several of each bandwidth, $20 shipped. Pm me for details.
Also, you have to read the manual closely as you have 3 filter settings buttons and one dsp filter setting set via menu, then you have twin pbt and the like on the front panel.
The FL80 9mc IF filter that is present in all 775s is a high quality 2.4kc filter, great for dx and possibly ecssb, poor for audio reproduction of wider signals. It's a pin for pin swap with the older 9mc IF Icom filters such as the FL70, the FL70 matches the FL96 @ 2.8kc wide sitting in the 455kc IF strip. You can find FL70s on ebay, qth, etc, also they are present in any Icom IC-R71 - wich is where I got mine.
The FL96 doesn't need any replacement unless you can find one of the FL257s, I think it is, a 3.3kc wide filter for the 455kc IF and is a drop in replacement but these are scarce and pricey.
If you're a dxer/intend this rig to be a dx machine, you might be interested in swapping the FL96 for a FL44A, wich matches the FL80 in bw and is the dxer sought after xtal filter pairing for the older Icoms, this pairing was standard in the illustrious IC-751A and optional in many other like era Icoms. The good news is these filters can still be found and are in most cases a lot cheaper than back when everyone was looking for them.
I like the filters to match, doesn't make much sense to run a narrow filter before a wider one or vice versa when you desire wider bandwidth audio.
On the narrow mode filters, you can go 300hz or 250hz for the option slot and that might help in cw work and perhaps weak signal modes like ft8 and psk31, keep in mind with the Icom narrow filters, the more narrow you go the worse the shape factor becomes as is usual for very narrow analog filters, but this should be of little concern for HAM work.
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That was an excellent radio for the 1990s time period that it was produced and it cost a pretty penny back then from what I recall. It was in the range of your Yaesu FT-1000D type of transceivers or the equivalent of buying a couple of FT-1000 MP transceivers. I didn't have one at the time as I was as poor as a church mouse but I did have plenty of opportunities to work people that did on my entry level FT 840 etc which was a well known rig for that time as well and relatively inexpensive at about $750 USD around 1997 or so. Then over the next few years I was able to do much better financially and moved up to IC-746 and Kenwood TS-570D and IC-746 PRO etc before I sold a few of them off and bought some other equipment. The IC 746 and the PRO model was a fine radio but the problem was when the LCD screen went out it was about a 400 dollar repair at the time and I didn't think I was technically savvy at the time enough to actually fix it back into perfect working order. I was more of an operator then versus more of a technician now which came with age and experience.
Icom had a lot of nice and semi basic radios going back to that time period such as the IC-738, 728, 729 etc and they weren't horribly expensive its just that I seemed to gravitate to Yaesu gear and such in the mid 1990s plus I had and still have a working FRG-100B that was one of my first REAL radios after I got a real job and bought more than the few portables I had for most of the 1990s. However, I still like playing with portables or just taking my Eton Executive Elite or my Tecsun PL 880 to the park with me when I go to exercise and take a small 20 to 30 foot roll of automotive wire for use as an antenna which is still fun listening at times.
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A lot of the ft1000 is inside your frog100, they're a very worthy sw set.
:D
I'll do up a Project 775 Care Package with pertinent pdfs and notes and post it at some file host for those interested.
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Yes, a PDF report of your work would be a great idea! The more information readily available always helps.
I got my 775DSP a few days ago (without the manual) and have been web searching for some answers to a question with no real luck. I understand the DSP HPF/LPF set up for TX/RX, but regarding the analog crystal filters:
Does the 775 use one set filter bandwidth (and IF frequency) to transit in SSB (such as the FL-80) and use the others for receiving only, or does the front panel selector allow using the different filters for transmit? In other words, would I have a choice of using both an FL-70 AND something narrower (like an Inrad 2.1 kHz) filter for transmiting if desired? If only one is used for transmit, which filter position is in line during transmit?
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Going from memory, everything txwise starts at the dsp if you have the dsp unit installed, some 775 did not come with the dsp card. The dsp will set the high and low ends of the tx (and rx) bandpass as you've noted. On rx you can pass ssb mode sigs through some very wide filters in both the 455 and 9 IF strips, say 6 to 14kc wide for each filter and the dsp unit will allow for up to 3.3kc rx bw. I'm unsure if tx is allowed via these wide filters, the filter truth table should show us what filters are used in ssb tx, I presume the FL96 and the FL80 to help suppress the lsb and carrier artifacts summing up to about 2.8 total bw. That being said, I saw some video or pdf of a guy opening the dsp unit and defeating the high and lowpass filtration for singlewideband (lol), so I suppose then the analog filters would set the overall bw per the switch matrix. There's a whole genre of HAMs trying to get wide audio on ssb, the ones I used to listen to were on 3630 at nite, 14178 days.
On the filtering, make sure to enable the FL80 and switch betwixt upper and lower, listening for tonal change.
Many FL80 filters fail in a way that causes their pb to shift a bit, say upper sounds pinched and peaky while lower sounds dull and smothered. There should be no substantial difference in audio passband going from upper to lower for any filter. I think all the FL80s that have passed by here have showed that issue to one degree or another, makes sense to spend on the inrad filters or do like me and swap in an FL70.
As stock I figure the dsp develops the mathematically perfect ssb signal, passes it thru the two xtal filters in the respective IFs on the way to the driver and pa, and then out to your antennae to be released to the world. Fly away little signal, fly away! Be free! The service manual will go into much greater detail, just look under the circuit descriptions and you'll get the facts.
For the Project 775 Care Package I've a copy of the extended qst review, an English translation of the Italian 775 mods pdf, and some other tidbits found along the way, just have to get them all into a zipped folder and sent to innernets for distribution. You mention a early 775, this can be good and it can be bad, in the sense of service updates and so on. I found the repair faq from Icom on the 775 and will include it - these are getting hard to find anymore, these faqs have service bulletins on the most common faults in Icom rigs, I've used them countless times to diagnose and repair issues in multiple iCom rigs with just the new part and faq alone.
Also, and I never saw this in the service or user manuals, cpu reset to factory defaults is; power off, press and hold "clear" button, and power on. This also nicely cleared up some odd glitch I had in the dsp and always wondered if I was going to be stuck with it. Before you clear it, make sure to look at the other guys saved memory freqs, might be some interesting stuff.
In your case with the inrad mod, you're not going to get much beyond about 6kc through the rig from antenna jack to speaker so the 6kc wide 9mc IF strip filter mod will definitely make sense, the one present in your 775 right now is 20kc wide, Icom did this to allow for am and fm use.
Dunno if I mentioned this before, but sherweng's never tested a 775 for whatever reason but has tested about every other solid state HAM rig. Apparently the Yaesu
FTdx-101D is a freaking amazing rx.
http://www.sherweng.com/table.html
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775 Care Package
http://s000.tinyupload.com/index.php?file_id=30671678912658575388
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I found a 775 group and read these posts:
"You must bevare of the fact that FL80 (3.if 9MHz 2,4Khz) is bypassed when COMP is off.
In transmit that filter only works with COMP ON.
Else, the TX limit of 2,8KHz is in the FL96 (455Khz 2. if) and PSN is OFF in the menu.
With PSN ON you use the CWF455HT 6KHz filter + DSP settings to set the TX bandwidth."
"The FL-80 (with printed 2.4Khz on it) is more like 2.7Khz filter.
Even in the servicemanual it is called a 2.7MHz filter.
I replaced with FL-70 and made measurements and recordings before and after
replacement. Almost no difference.
And..also have in mind that during transmit the FL80 is bypassed when
compressor is off. (Stated in servicemanual too.)
I never use the compressor if I want good TX audio. (External rack.)
The DSP bypass-mod is more funny if good sound in SSB is the issue."
I don't understand that last line...anyone? That talk about the FL-80 is news to me.
I agree with you that matching filters makes a lot of sense when you have Twin PBT, so it'd probably be better for me to find an FL-44A to replace the FL-96, as DXing is far more important to me than ragchewing, or...would using an FL-70/96 and narrowing with Twin PBT be the equivalent?
I can just use DSP tx to go wider if I use the narrower crystal filters.
Along those lines, would it even be worth getting SSB filters for the narrow slots if it has Twin PBT? I'd probably get the Inrad 1.8s but that's another $250. Would the selectivity over PBT with the FL-80/44A be worth it?
This is getting confusing. Maybe I should have stayed with a simpler old rig, like upgrading my TS-130V to a TS-130S...
Thanks for the link to your "775 Package," I can't open it on my iPhone though. Maybe when I finally get a laptop (radios come first...)
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Icom has made 1.9kc wide ssb filters for the 9mc and 455kc IFs for a while now, if you want narrow, those are the ones to go for. Easiest would be the FL44A swap for the FL96, outstanding filter and matches the FL80 if you want no narrower than 2.4kc. My current understanding is for real narrow ssb work you want the FL222 and FL223 filters for 1.9kc width in each IF strip, a bit narrower when they are paired and aligned, meaning no pbt or IF shift activated.
The FL80 is a true 2.4kc filter, a bit wider at the top than the FL30, however the skirts are much steeper and likely go much deeper than the FL30, wich is why everyone wanted the FL80 to begin with, also there may be more poles in the FL80.
I'm gonna have to reread the service/user manuals to get a good grasp of what filter is allied with what buttons combination for rx and tx both.
Also if narrow bw operation's your goal, swap that 20kc wide second IF roofing filter with a 6kc one from a IC706, that might make for a worthy mod and is a drop in part.
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If modding the 775 for dx work and not wanting to do welding or other intensive surgeries on the 775 such as replacing an entire mixer circuit, meaning drop in, pin for pin, dx enhancing parts swaps, here are some ideas;
1 - Reduction of the noise floor and balance of the AGC gains
In the search for reduction of the total noise of the apparatus and improving the linearity of the amplification stages, the most critical stage is the result Dual Gate MOSFET Q15 3SK131.
This amplifier, placed at the end of the 1st IF chain, has a high gain of 24 db, and in the presence of strong signals loses its linearity. In order to reduce this gain and "lower the NF" said component has been replaced with a BF998R.
In view of its lower gain, about 4dB, the signals detected by the S'meter will be lower so it will be necessary to adjust the
trimmer relative to the total of the AGC loop gain, R198 (IF UNIT). Although there is a loss of 1 dbm on MDS, being the very sensitive IC775 receiver (MDS approximately -130 dbm), this loss is not appreciable although a lower NF makes it more pleasant listening. Probably the loss of gain could be compensated for if it were possible to weld two BF998R in parallel (one above the other), the configuration that would provide us with a higher transconductance and therefore higher gain, but the SMD components are not easy to a simple parallel-to-pin -pin.
NOTE
It is not recommended to introduce this change if you implement the changes occur repositioning of the roofing filter Inrad.
5 - ROOFING FILTER REPLACEMENT ON 2 ^ IF
Premise
To further reduce the intermodulation, NF, increase selectivity and MDS, could be replaced, the roofing filter post 2nd IF called FI1 (9.0115 MHz with BW over 20kHz), with a lower bandwidth. The choice fell on two ICOM commercial filters called FL102 6 kHz BW and / or BW FL103
2.8kHz. The first has a Fo = 9.0100 as originally used in AM, this filter having a different Fo will produce an asymmetry of the passband, although it is more than enough for the purpose.
FL103 ensures excellent selectivity at the expense of a lower audio bandwidth, if you are the SSB Hi-Fi enthusiasts do not use this second solution.
I'd replace the filter with a 6kc wide one from the 706mkiig as it's a pin for pin drop in instead of something that has to be spliced in with minicoax and have traces severed. Also since the filter is of the same design it should have the same in/out z and attenuation. That being said, the skirts will not be as narrow as if one spliced in a FL102 or oither 6kc wide multipole filter. The original filter for this position is one of the monolithics with only a few poles of selectivity.
Here's some info on monolithics;
https://www.electronics-notes.com/articles/electronic_components/quartz-crystal-xtal/monolithic-crystal-filter.php
The mods devised and discussed here stem from this pdf;
http://www.pensioneitaliacapri.com/ham/IC775-Progetto-Modifiche-2009_Finale.pdf
you can translate it into your lang of choice online
I recently noted that you can't really get a 3.3kc width on ssb rx unless you've installed a FL10X 6kc wide am filter in the 9mc IF optional filter slot, otherwise you get only the sum of the present 9mc IF and 455kc IF ssb filters.
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Josh, I can't believe how well you've gotten to know this transceiver! Thanks for all your work, it's greatly appreciated
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Thanks, kinda a icom rx nut from way back (arigato Inoue-san!) and they all seem to share a lot of the same design philosophy so you get to know part numbers, expected gain, etc. Started out with an R70 in '89 and a few months later with a 751. Had 735, 745, 751 and 751A, 765, 761, 756Pro and ProII, and lastly the 775 for tx, R70 and several R71s plus the R7000 for rx.
I wonder why the Italian HAMs who devised the 775 mod pdf don't recommend replacing the 3sk thingy with the bfr thingy for lower nf in the IF amp if you splice in a inrad roof. Pretty sure you can come up with an additional 3 or 4db gain with the inrad roof filter amp (let alone a spot on alignment) so could make up for the lost gain. I'm in a quandary over mine, should I forsake the am rx side and mod for ssb work or leave it possible to rx wide sigs like am and fm? This thing sits on ssb all day day in day out and I've several other rigs that sound better on am.
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I wonder why the Italian HAMs who devised the 775 mod pdf don't recommend replacing the 3sk thingy with the bfr thingy for lower nf in the IF amp if you splice in a inrad roof. Pretty sure you can come up with an additional 3 or 4db gain with the inrad roof filter amp (let alone a spot on alignment) so could make up for the lost gain. I'm in a quandary over mine, should I forsake the am rx side and mod for ssb work or leave it possible to rx wide sigs like am and fm? This thing sits on ssb all day day in day out and I've several other rigs that sound better on am.
Can you give me details about that mod regarding the Inrad roofing filter, please?
Personally, since I have other receivers that sound great on HF I'm not worried about how AM sounds on the 775. I would think that if you aren't using it for AM or FM tx optimizing it for SSB would be the way to go.
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Here's a link to the pdf on the mods, I translated it into English and it came out very well;
https://www.filemail.com/d/vdwnpnjhonrxdbl
You can open a pdf right?
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Yes, got it. Thank you!
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Sometimes one comes across a bad FL80.
These filters are found in the 751, 751A, and 775 as well as other Icom rigs, and any that have a FL80 installed as an option.
The FL80 was sold as an upgrade option for any rig that had a FL30; same pin out, IF, and similar bandwidths but the FL80 skirts went deeper and steeper than the FL30.
A simple way to check for a bad filter is to note the passband response of the rig in ssb mode, then flip to the other sideband and note the response, they should be similar if not identical. Perform this test with no optional filters enabled or the results will be for those filters and not the FL80/FL96 pair.
A bad filter will display a markedly asymmetrical response, I note in most cases usb is pinched while lsb is fine to a bit too bassy. Never seen a bad FL96 or FL70, but surely it can happen, almost always a bad FL80 is lurking in that Icom.
A specific part in the FL80 goes stale over time and changes the passband. For all I know there's only xtals, caps, and inert gas inside one. A HAM opened one to fix it and found a bad silver mica cap (dread silver mica disease!), replacing it brought the filter back into spec. FL30s also fail in a very similar manner, some even stop working altogether.
The FL70, wich matches the illustrious FL96 in bandwidth as well as steep and deep skirts, is a choice option to replace the FL80, unless one wants a narrower passband.
The shame of it all is Icom went with plug-in optional xtal filters in the rigs newer than the 765 series, meaning Icom don't make a pin for pin solder in replacement for the FL80, one has to use up an optional filter slot to run a Icom narrow ssb filter if so desired. And the solder pins of the current plug in filters do not match up with the traces/holes on the circuitboard, so one is obliged to use jumper wires to splice in a newer filter.
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Monitoring weak (realllllllllllly weak) cw sigs has allowed me to test if an 80Hz filter helps or hurts weak cw signal detection. Some weak sig cw enthusiasts say "find your weak sig, then open the filters up wide".
That may work for some ops but when I tried that on some truly weak cw today they melted into the band noise and the cochannel crap, enabling the 80Hz filter made them pop back into detection, time and again on every sig coming in.
And they were just at the perception level in the 80Hz filter.
I don't recall the narrow filter I normally set in the 756 Pro2 (100Hz) being as effective, mebbe it has more ringing, will have to compare both rigs at the same time same signal.
The diff is the 775 has high quality matched 500Hz xtal filters in the 9mHz and 455kHz IF strips that then feed the dsp demodulator/filter unit.
The 775 has 5 frequency mixes/conversions from antenna jack to audio out. A ADC16071 16bit adc does the a/d conversion in the 775.
The Pro2 has a several kHz wide 455kHz IF ceramic filter it passes all sigs through prior to the mix down to 36kHz and right into the adc and dsp. The Pro2 has 3 frequency mixes/conversions from antenna jack to audio out.
The DSP in the IC-756PRO/756PROII employs a 24-bit A/D
converter. The logical value of the dynamic range of a 24-bit A/D converter is 144dB, however the actual value of the analog performance is smaller than this and performance may differ considerably, depending on the type of A/D converter used.
An interesting effect I noted with the dsp filtering in the 775 is you can open the IF filters wide as in ssb wide and the dsp filter does almost as good a job despite no longer having the protection afforded by the preceding narrow xtal filters, despite being a 16bit adc.
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Was wondering how to fill the option filter slots for the 9mHz and 455kHz slots. Already have narrow filters to pass anything 500Hz and narrower. Wanted something for wide ssb, but Icom branded filters for such are rare or unobtainable.
Then I recalled I have a FL-33 6kHz wide xtal filter I can splice in the 9mHz slot, but what about the 455 slot?
Hoarding parts saves the day once again!
Back in the 80s a customer (I used to build and sell ambc and 160m tabletop loops) gave me something from his Icom IC745, a small pcb with caps and xformers that held a 455kHz ceramic IF filter in the slot of a 455kHz xtal filter.
To install a optional xtal filter, you remove this pcb/filter assembly and discard it.
The caps and xformers on the pcb are to match the different in and out z of the filter itself to the IF circuit as it expects to see a xtal filter in that slot, not a ceramic with different characteristics. Mismatches lead to spurs, attenuation, and uncharacterised bandpasses as well as loss.
Much rather have a FL-257 3.3kHz wide xtal filter but those are rare and costly.
So since I have the pcb to swap in a ceramic filter, as well as several ceramic 455kHz filters to choose from, I decided to run with that.
The filter of choice is a Murata CFR455H, a 6kHz wide, 9 pole, metal cased affair that is perfect for wide ssb and narrow am, this will match up with the FL-33 for use in hfbc am listening too, not just ssb.
Best part is all are Icom original parts, continuing with my all-Icom parts theme/fetish.
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Thanks, kinda a icom rx nut from way back (arigato Inoue-san!) and they all seem to share a lot of the same design philosophy so you get to know part numbers, expected gain, etc. Started out with an R70 in '89 and a few months later with a 751. Had 735, 745, 751 and 751A, 765, 761, 756Pro and ProII, and lastly the 775 for tx, R70 and several R71s plus the R7000 for rx.
Not a ham here, obviously, but I see the famous IC-701 is missing from that list of Icoms. What's your opinion on that? I remember seeing the ads for it when it was a new thing, and it looked so cool. Almost made me want to become a ham to get one.
Interesting thread also.
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I never got to play with a 701 but had its power supply and wish I'd not bought it. You see, the 701 rig itself does psu regulation internally, the psu has none. Not knowing about the missing regulation I paired that psu with a TS440 and let some smoke out as the psu was sending more volts than the TS440 likes.
The 701 put Icom on the hf map for the most part and was a good seller, still used by many ops. Haven't seen one for sale in years oddly enough.
I doubt Icom looked like this back when the 701 was king;
http://wiki.oevsv.at/images/5/56/Icom_factory_tour_2010.pdf
The kanban and kaizen of Icom;
https://www.youtube.com/watch?v=Kx1br6CvJNc
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I read somewhere -- probably one of the ham forums -- that the 701 has some issues that have to be fixed when bought used. Some part that's hard to obtain, or one has to come up with a workaround. I don't recall what it was...
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I've never heard of any common issue with the 701, the 720A however has a few that must be remedied before they take place, or hard to find parts will be needed.
Seems an internal rotary relay (used to switch front ends) has far too much tension on a spring and causes the part to beat itself to death, reducing the tension eliminates the problem.
I can remember crap like this I heard decades ago, but not what I had for lunch yesterday.
:D
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Breaking Quarantine
I found someone local to bead blast and powder coat the 775s poor cabinetry. At first I tried to find my goto place where I'd had a Romanian AK74 blasted and powder coated several years ago but couldn't remember where it was, mebbe they gone under. But fb, as much as I dislike anything zuckerberg, revealed a proprietor with a home blasting/coating shop, called and made arrangements for said blasting/coating.
Ran into a snag as the inside of one cabinet half has a large sheet of what I assume is sound deadening material of a synthetic felt nature, glued firmly over a substantial area of said cabinet. It also had a clothe-like sound passing baffle over the speaker port. Both of these would be ruined by the heat of powder coating, or misapplication of the bead blasting process.
So it was decided to simply glass bead the exterior of the cabinetry, the insides of wich are coated in a type of bluing or similar that is conductive, where powder coating is usually a insulator. In consideration of the above, spray bombs were the only recourse.
So while the cabinetry was undergoing the bead blasting, I vetured forth to Lowes only a few miles away and found they were indeed doing business during thapocalypse. Got some dark grey texture finish rustoleums and went back to the bead blasters.
Blasting took off all exterior coating and greatly reduced the apparent scratches and all traces of rust and corrosion! Inside, the cloth materials were unhurt.
Took all home and set up operations in the porch to keep dust and pollen off the surfaces post and ante spraybombing runs. Cleaned the surfaces to be painted with alcohol to remove any oils or other crap.
Holy crap this stuff is vile smelling. Spraying a few light coats, varying the pass direction and angle of attack made for a nice uniform coat, and the longer it dried the better it looked. I didn't like it at first when it was still wet, but now think it looks great, something Inuoue-san might be proud of.
Anyway, it looks like something the factory would have done, can't wait to put it together with the less blemished front panel and see how it looks.
73's and best regardses!
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Just found this interesting forum / discussion group and as I was wondering how to fill the option filter slots for the 9mHz and 455kHz slots as well.
As I would like to "improve" my Tx/Rx audio on SSB having the 3.3khz wide SSB filter FL-257 availabe at my desk I wonder if it would be worthy to go ahead with the FL-96 stock filter replacement for the 455khz IF and try to replace de FL-80 with the FL-70 or FL-103 on the 9mhz IF.
Would one expect the FL-257 be efective for better audio intelegibility on RX and TX (when installed on the FL-96 slot) even for dx? or for dx it would be better install the FL-44A instead pairing it with the stock filter FL-80? :-\
I read a 775DSP thread on eham stating a "neat mod for the IF board that opens up the restricted transmit audio a bit. This is done by replacing the soldered-in stock FL-80 and FL-96 filters (2.4 and 2.8 kHz, respectively) with the FL-103 and FL-257 (2.8 and 3.3 kHz, respectively)".
Also someone shugested "On the reciever end of it i took out the FL-222 1.8 455khz SLOT and replace it with the FL-257 3.3khz" but this suggest that it would be only on RX side thus not improving TX side.
Will thank you in advance any thoughts you may share.
73 pedro