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Author Topic: Project 775  (Read 4850 times)

Offline Josh

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Re: Project 775
« Reply #15 on: May 14, 2019, 1925 UTC »
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.
« Last Edit: May 14, 2019, 1956 UTC by Josh »
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Offline ChrisSmolinski

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Re: Project 775
« Reply #16 on: May 14, 2019, 1935 UTC »
In the spirit of keeping this rig as "Icom" as possible

And here I thought you were going to talk about low quality audio  :)
Chris Smolinski
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Offline Josh

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Re: Project 775
« Reply #17 on: May 14, 2019, 1955 UTC »
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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Offline Josh

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Re: Project 775
« Reply #18 on: May 16, 2019, 2207 UTC »
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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Offline Josh

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Re: Project 775
« Reply #19 on: August 04, 2019, 1811 UTC »
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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Offline pjxii

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Re: Project 775
« Reply #20 on: October 09, 2019, 0237 UTC »
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.


Offline Josh

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Re: Project 775
« Reply #21 on: October 10, 2019, 1902 UTC »
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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Offline thecolonel

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Re: Project 775
« Reply #22 on: October 19, 2019, 0556 UTC »
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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Wire Loop For 75 Meters to 10 meters as well as verticals and a longwire.

Offline Josh

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Re: Project 775
« Reply #23 on: October 19, 2019, 2005 UTC »
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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Offline pjxii

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Re: Project 775
« Reply #24 on: October 20, 2019, 1819 UTC »
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?

Offline Josh

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Re: Project 775
« Reply #25 on: October 20, 2019, 1850 UTC »
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
« Last Edit: October 20, 2019, 1907 UTC by Josh »
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Offline Josh

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Re: Project 775
« Reply #26 on: October 21, 2019, 2232 UTC »
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Offline pjxii

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Re: Project 775
« Reply #27 on: November 11, 2019, 0108 UTC »
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...)
« Last Edit: November 11, 2019, 0119 UTC by pjxii »

Offline Josh

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Re: Project 775
« Reply #28 on: November 11, 2019, 2323 UTC »
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.

« Last Edit: November 11, 2019, 2356 UTC by Josh »
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Offline Josh

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Re: Project 775
« Reply #29 on: November 15, 2019, 0020 UTC »
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.
« Last Edit: November 15, 2019, 0101 UTC by Josh »
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