Messages

16

Part 15 AM and FM Station Operation / Re: Talking House Transmitter - some spectrum plots

« on: September 26, 2020, 1920 UTC »

Narrowing the bw will also give a slight increase in range, for those stations that can match that bw on rx.

I generally agree with this, but I think it has more to do with packing the audio tightly in that bandwidth than it does simply limiting bandwidth.
I've tried both extensively and found that bandwidth restriction alone doesn't seem to have a huge impact, or any that I can tell at all from practical distances. It does give feel good points though so you know you're not interfering with adjacent stations.

What does matter is really cramming the audio into, as you suggested, the bandwidth of the average radio. Placing the NRSC curve to put some punch out to 5kHz makes a ton of difference, beyond that it's up to the station, and my preference is to ride the bandwidth so that up to 5kHz there is strong presence on soft passages or limited audio range (voice), and push the 5-9.5kHz hard to the standard curve, then drop it with the brick wall after that to comply like the big sticks. That presence around 2-5kHz needs to have its own care though or else it will sound awful on music. Professional audio processors actually treat this range specially with analyzing circuitry (or software) so that voice has punch and music remains full and good, and it's an art.

Remember stories of hot audio processors of yesteryear damaging old radio station transmitters? Running tubes too hot or pounding the mod transformer until destruction? That is what gets loudness and to really get that you need 100% modulation peaks and 95-98% neg. Maybe that is what the talking house transmitter needs? Sounds like a fun project
Not even sure if the thing can do close to 100% positive, or asymmetrical peak riding even though Stereotool can try its hardest to provide it.

17

North American Shortwave Pirate / Re: Damn Skippy 6950 USB 0058 UTC 26 September 2020

« on: September 26, 2020, 1708 UTC »

0251 Gadda da vita
0308 Frog went courting in middle of rock music
SSTV scattered throughout

Great signal from 0240-0320
SIO 544

I think this was the station I heard last night but they went off the air right after those nature sounds turning into some electronic music? Looking to find the actual track they used for that ending segment, never heard it before but through USB it was loud and clear, then off.

18

North American Shortwave Pirate / Re: 80's Forever Radio 6925 usb, 0050 utc, 10 Sep 20

« on: September 11, 2020, 0617 UTC »

Video of the end of MRIs show I took quickly...
https://www.youtube.com/watch?v=vnBSP_FDpt4

Camera audio sucks, but shows the quality of reception last night.

19

North American Shortwave Pirate / Re: Unid 6925 usb, 0050 utc, 10 Sep 20

« on: September 10, 2020, 0134 UTC »

80s Forever Radio (?) ID at 0132UTC, listening on my Tecsun PL880 with solid signal on outdoor Inv. L antenna.
Not sure how to make out the 880s signal meter to S measurement but getting around 50dBu which I know is strong and almost no noise here in the upper midwest.

Glad to see HF band conditions making a comeback since the last few weeks has been completely dead hear on any radio and antenna.

20

The RF Workbench / Re: Tecsun PL-880 external MW antenna idea

« on: August 10, 2020, 1643 UTC »

Update:

I eventually did not like the modification using a coil wrapped around the ferrite bar. It overloaded the radio far too easy with any decent outdoor antenna unless it wasn't much longer than the external wire antenna the radio came with.

After studying the schematic of this radio much deeper I discovered that the ferrite bar and associated JFET transistor circuit is nothing more than a wideband MW amplified ferrite bar, and by wrapping a few turns around like the modification calls for what happens is that any signal is amplified through that first stage (Q26) which can be overkill and cause front end overloading with good outdoor antennas.

There are four wires on the ferrite bar, two for the wideband antenna coil, and two for a smaller sense coil to add positive feedback from the JFET output. At that last point wire 3 goes to the next radio stages just like the shortwave antenna section does. Tapping into this point allows for larger outdoor antennas without the overload issues and sensitivity is on par with my ATS909 radio so I went ahead and did this modification of my own instead...



That is nothing more than a small 0.1uF capacitor wrapped in electrical tape (triangle looking thing) and tapped between the ferrite bar wire 3 and the unused antenna jacks middle ring. I made sure to bend the wires to be near the PCB ground trace so not to cause any capacitive coupling with unwanted parts of the radio.

Tapping the original MW coil at that point does not have any impact on SW reception or FM, or the internal ferrite antenna when ext. ant. disconnected. It is independent of it once the later stages mix the SW and MW/LW antenna inputs together. It is best to only use a TRS "stereo" jack now though to leave the MW middle ring unused if listening to SW.

This allows for much stronger local stations before the radio can overload, and now connected to my 100' outdoor inverted L antenna the performance is identical to my unmodified ATS909/DX398 radio when both radios RF gains are set to high.
Now the radio can be used with external amplified antennas without overload too, and the reception is more evened out across the LW and MW range this way rather than the looped wire modification found online.

PS: I left my original coiled wire modification unsoldered in the radio just in case I ever want to go back to using that instead.

Hope this helps future experimenters

21

Huh? / Re: As if, AM Radio can't sound bad enough, then there's this!

« on: July 30, 2020, 0951 UTC »

Wow now I know what that sound is after hearing the audio example in the link.
Lots of nights listening to Clyde Lewis and Coast to Coast AM and hearing that sound with the regular audio and I thought it was caused by a weird audio phasing issue, like maybe they were mixing left+right stereo together and somehow cancelling the audio material in some odd way since I only ever heard it at specific program points like right after the C2C AM "crash" thunder sound, but turns out I was wrong.
I have only ever heard it on nighttime programming on the major 50kw AM BC stations.

22

The RF Workbench / Re: Tecsun PL-880 external MW antenna idea

« on: July 04, 2020, 0441 UTC »

Well it's night now. Tried comparing radios and though the modification does work okay on the Tecsun, my outdoor antenna is just too much for MW band unless the RF gain is on lowest, but even switched lowest it still is better than the built in ferrite antenna so that's positive news.

I can see how this modification would kick butt for shorter "on the go" antennas to boost MW, but for a full sized inverted L outside and ground radials it overpowers the radio so bad that on high RF gain it just becomes noise, whereas my ATS909 can handle it without issue.

So the mod works, but is a little limited. It is what it is I guess. Still my second favorite radio I've owned so far. It's really hard to find any portable that beats the ATS909/DX398. No matter what radio I use I find myself going back to it for serious DXing with permanent antenna installs, but for a small backpack radio that has incredible audio and battery life the Tecsun wins hands down. Also I can't get enough of that wide open 9kHz bandwidth on the highest setting, makes MW and SW sound so good, and that 500Hz bandwidth for CW is a winner.
Just wish I could slow down the AGC for SSB, but that's a known issue with the radio that eventually someone will find a fix for I suppose.

23

The RF Workbench / Re: Tecsun PL-880 external MW antenna idea

« on: July 03, 2020, 1725 UTC »

Okay jFarley I just opened it up and tried that mod. What a bitch it was to get 5 turns around the loopstick. Seems my recent model places the original coils more toward the end only leaving me a tiny bit of space to add the 5 turns, but it worked.
MW improvement was profound on my longwire, especially through my 9:1 unun. In fact on highest RF gain setting it overloaded it but this is daytime and a local 1kw station isn't far away. Everything else comes in as good as my ATS909 now on MW using the same external antenna.
I swear there is a new birdie at 720kHz though, but maybe it was always there. If I tune to 719kHz it goes away

Might have to make a few special TRS jacks so I can switch between radios easily.

Here is before I added the coil...
https://i.imgur.com/fjaXYsX.jpg

And after..
https://i.imgur.com/Yb3izO8.jpg

I almost wonder if 5 turns is too much being as it's so close to the normal coil, but I'll know for sure tonight when the sun goes down. If anything it will perform wonders on shorter camping wire antennas, but my 130' inverted L is just too much without some padding lol.

24

The RF Workbench / Re: Tecsun PL-880 external MW antenna idea

« on: July 03, 2020, 1519 UTC »

There is a mod for the 880 which allows it to use an external antenna for LW.  It is located here in the NDB Group:

https://groups.io/g/ndblist/message/105858?p=,,,20,0,0,0::relevance,,pl-880+modification,20,2,0,70214479

I have performed this mod on my 880.  It took me about 45 minutes and was pretty easy.  This mod allows me to use my standard NDB antenna - an amplified 96" whip - with the 880.  While I wouldn't call this setup a DX Machine the sensitivity at LF is greatly enhanced.
 
I am not sure if you need to be a group member to access this file, but here is the short form procedure.  It's possible that this was also posted in another group - poss an ultralight group - but I have not been able to fine it. 

1) Open the 880 back. 
2) Wind a few turns (I used 5) of fine insulated wire around the end of the ferrite bar at the end near the Antenna Jack.
3) Tack the wire in place with hot melt or other glue.
4) Solder one wire end to the PCB  pad near the antenna jack which is connected to the jack ground.
5) Solder the other wire end to the PCB pad which is connected to the jack tip; this is not used normally.
6) Button up the back.  Most any antenna can now be plugged into the jack with a mating plug wired to the tip and ground connections.

I did not need to add a LPF between the antenna and RX.  Of course, a winding could be temporarily placed on the ferrite bar and patched to the antenna prior to doing any soldering to estimate the appropriate number of turns required for your setup.

Credit for this mod goes to Steve Ratzlaff AA7U and Geir Laastad LA6LU.

This sounds like a great mod. At this point I don't mind doing the mod either considering the damn radio came defective when I bought it having a rotary encoder not working for the main tuning, I had to open it and reseat the jack going to the tiny PCB to the encoder which was a PITA but it would have cost money to return the defective radio for another one. Works now but ugh.
Makes me wonder if connecting a large outdoor antenna will detune the ferrite bar antenna though?
Might take some thick paper and make a small loop that fits over the ferrite end, remove and tape and wrap the wire around that and then melt some candle wax over it so I can slip it back over the ferrite so I can fine adjust its position and for later easy removal if it doesn't work well.

Anyway, you say the antenna jack tip isn't used but this doesn't make sense to me, the 20' reel antenna the radio comes with is only a TS jack instead of TRS jack, so the ring and the sleeve is shorted and appears to connect to ground, that only leaves the tip of the plug for antenna?
I might still try a decoupled idea too with placing another ferrite bar outside the radio and connecting that to the outdoor antenna to see if it can even work.

edit: just joined and saw the post "The antenna jack on the 880 is really a stereo audio jack, but  it's ring connection point is not used on the radio and can be used as LW/MW antenna input.", solved.

25

The RF Workbench / Tecsun PL-880 external MW antenna idea

« on: June 29, 2020, 1714 UTC »

So this radio does not allow MW external antennas. There is supposedly a menu option by pressing a bunch of buttons like a game
controller to get hidden features including temporary MW antenna jack enable while playing but it does not work on my firmware of this radio which is the newest.
The 880 does have an external jack for SW, but it's disconnected from MW circuitry from the schematic I looked at floating around the internet in russian.

I got to thinking besides the obvious loop antenna and inductive coupling, would it work to loop enough turns around a ferrite bar and match it to my longwire outdoor antenna and grounding and place it near the radio on top where its internal ferrite bar antenna is?
Not sure if this would couple correctly or if it needs to be horizontal to the internal bar antenna?
Just thinking of ideas so that I don't have to modify a perfectly fine working radio.

The only other idea I have without going the loop method is to make a simple box to set the radio inside when listening to MW DX and make a loop around the box and match it to the outdoor longwire.

This is really my largest gripe with this radio. The fact that there is no easy way to connect an outdoor antenna for the 100kHz-1710KHz range. Otherwise this would be a killer on LW and MW.
On SW and FM broadcast bands so far I put this radio as my alternative to my ATS909, it's on par for performance so far, but lacks some RF/antenna features, but God damn the audio out of the 880 is impressive and selective bandwidths up to 9kHz on MW makes the thing a great station monitor compared to anything else I own outside of a TRF barndoor wide set. Then there is down to 500Hz for CW even. So for that it's a step ahead of my ATS909. With both these radios I am setup. They have quirks but make good brothers, one gets the job done when the other doesn't.

26

North American Shortwave Pirate / Re: Pee Wee 6925 USB 0205 UTC 8 June 2020

« on: June 08, 2020, 0300 UTC »

Good signal here on my new Tecsun PL-880, video of a portion I heard...
https://www.youtube.com/watch?v=3KmbpG3Lnkg

Haven't decoded the SSTV yet.

Not too happy with this new radio, out of the box the main tuning rotary encoder was not working, opened it up and resat the plug for it's tiny PCB and then it started working, still slightly erratic though. Kind of sucks to buy a radio for $160 and have to open it up to fix it when it's new, but no complaints now. God damn Chinese QC.

First pirate I picked up on it though, and performance is almost as good as my DX398.

27

10/11 meters / Re: Huge 11m opening Morning 30 May 2020

« on: June 03, 2020, 2006 UTC »

This is making me feel much better about throwing a few bills at an Anytone 5555n with SSB and new antenna. Hopefully conditions pick up once I get everything installed so I can play with my new gear to its fullest potential.

I have a little Anytone "Smart CB" converted to export mode and even that has been lit up the last few days with heavy skip on all 40 CB channels and a ton of freebanders.

28

The RF Workbench / Re: Stretchyman “40W TX” Failure Investigation and Remediation

« on: May 31, 2020, 1650 UTC »

OP definitely doesn't want to investigate the chaos of my homebrew gear without their head exploding lol, but I'm a hobbyist so that's another story.

I want to feel bad for Stretchyman but this could be a learning moment here. Honestly with my own designs I wish I had someone scrutinize my work for free like this, wrong or right, it's still useful to go over things again and analyze. Part of the design process, and why version 2, 3 and so on of a product come to exist.

I do understand just enough about class E/D transmitters and power transients, gate protection, switch-on timing/ramp-up protection (like the big class E ham stuff) and so on to follow along with that long document. So maybe the best idea here is to show how to reproduce the problem easily in the lab, then find a way to quickly fix and put an end to it like the document suggests if this can be reproduced in a similar lab utilizing compatible but other equipment to rule out external faults?
Here I thought my worst fear was switching on a PA FET before the PLL/DSS got running and a pull down resistor on the gate was enough. Ugh, problems show up everywhere even in the most well planned out designs. Then when you think all is working flawlessly something causes a parasitic oscillation where you didn't expect and magic smoke is filling the room.

You know you two might be at odds with one another over this but maybe it would be beneficial to the community at large to work with one another. You're obviously both quite educated by the posts I read like this. Maybe put the egos aside and work together?

29

Equipment / Re: 65 turns loop for vlf reception

« on: May 26, 2020, 1720 UTC »

Just off the top of my head but a 5:1 or 6:1 transformer should get you in the ballpark. 5^2=25*50ohm=1250ohm, or 6^2=36*50=1800ohm. You'd need to pick a toroid core mix that is effective at those low frequencies. Generic ferrite types might be fine or even an old AM radio loopstick ferrite. Maybe something like 4 turns primary and 20 or 24 turns secondary. The ratio is squared and primary turns might require some experimenting.

The other way to go about it is to use the loop itself for the transformation using a few turns around it as a sense wire, then a variable capacitor to resonate the 65 turns. I believe this is far more common, or at least how I built a loop for MW ages ago. It will not be wideband though.

I'm curious how you came to the 1300ohm impedance value? If I remember right loops are often much lower impedance only needing an autotransformer voltage balun or a transformation of 50 to around 450ohms?

Wouldn't mind building myself one again soon.

30

10/11 meters / Re: What the hell is this noise?

« on: May 23, 2020, 1601 UTC »

Maybe its a robot vacuum, it may not be finished in getting set up, so it is sending out a signal. There are alot of bargan no name vacuums made in china. It would be a surprise to me that they are working that low of a freq. From listening to sound, its more like an rc car or a door opener.

That would be funny if that is what it was.

Thankfully whatever was causing it mysteriously vanished the other day after I got fed up and keyed high power of my own over the same frequency a few times. The annoyance hasn't been back since (crossing fingers)