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Major RFI/Grounding Problem

 
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Draxx
Voodoo Audio Head


Joined: 16 Oct 2014
Posts: 15

PostPosted: Wed Oct 29, 2014 10:57 am    Post subject: Major RFI/Grounding Problem Reply with quote

Hi. I seem to be having a problem with either RFI or grounding with my TS 440. For matters of simplicity I'm only using my Ultragain Pro 2200. I will eventually be hooking complete rack to ACC2. I thought I'd start with the front mic to get an idea of how it sounds in general. When I turn up the mic gain on the 440 I get a bad internal squeal. Everything is grounded to the radio and I'm using all balanced xlr's. If the audio line is not connected, there is no squeal upon transmit no matter how high the mic gain is turned up. When the audio line is connected, even with the mic gain and the output gain on the preamp turned completely down, I still get the squeal turning up the mic gain on the radio. All equipment is powered thru a Furman Power Conditioner, including the power supply for the 440. I don't believe RFI is getting in thru the ac lines. Any ideas? I thought since I don't have any Ferrite Cores on hand I might wrap the xlr cables in foil temporarily and see if this eliminates the squeal. Any ideas as to determine whether it's a grounding issue or RFI?
Thanks for any and all ideas......
KB6ZYJ
Scott
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BillPaul
Digital Voodoo Guru


Joined: 19 Jan 2011
Posts: 66

PostPosted: Wed Oct 29, 2014 3:31 pm    Post subject: Reply with quote

I have a couple of questions:

1) How are you connecting the output of the MIC2200 to the radio? I know you're connecting to the ACC2 port on the back of the rig, but what I'm asking is how exactly did you cable up the MIC2200 preamp to the ACC2 plug?

2) What band(s) does the squeal occur on? I don't know what bands you tried.

3) Do you have a separate ground for your shack? (I.e. do you have a separate ground wire leading to a pipe somewhere?)

4) What power supply, exactly, are you using with the TS-440? In particular I'm trying to ascertain if it has a 2-pin AC plug or 3-pin.

5) What mode are you transmitting in, SSB or AM? You should only get RF feedback when there's actually RF coming out of the radio, and there wouldn't be any if you turned the output gain on the radio all the way down.

6) Do you have the same problem with a dummy load?

I'm not sure what an "internal squeal" means. I'm assuming you're sure it's not just audio feedback. I think RF squeals often sound more like a howl than anything else.

One of the big problems I ran into with my setup was ground loops. I live in a 2nd story apartment, and the only thing I had that I could use for a ground bus was the pipe for the steam heater. (My building is very old.) The problems I had were due to conflicts between that ground and the AC electrical ground.

Both the TS-950SDX and the PS-51 power supply for my TS-850S have only 2-pin AC plugs. This means they're isolated from the AC electrical system ground. I have the ground lugs on the back of both rigs wired to the heater pipe. By themselves they work fine.

As soon as I tried connecting up my audio gear though, I had an awful 60-cycle hum in my audio.

It turns out this is because the Behringer audio gear uses 3-pin AC plugs. This means the audio gear was all connected to the AC ground. As soon as I tried to cable the audio gear to the radio, this created a ground loop, because the AC outlet and the heater pipe take different paths to the ground.

To fix this, I went to the hardware store and bought some of those 3-pin to 2-pin adapters that they sell to help you connect modern appliances to AC outlets in old homes that don't have 3-pin outlets. They break the ground pin out to a separate terminal which you're supposed to screw to the outlet plate. I soldered a copper wire to these ground terminals and wired all of them to same ground bus as the radio and used them to plug in the audio gear. This put all the equipment on the same ground bus and got rid of the ground loop. Now the hum is gone.

Also, to connect the audio gear to my radios, I use a Radial Engineering J-ISO transformer box. This allows me to electrically isolate the audio gear from the rig, convert from low impedance audio gear output to line level and to convert from balanced XLR to the unbalanced input on the ACC2 port. Unfortunately this stupid thing was expensive. It may be better to just buy a single Jensen transformer and wire it up yourself. It works well for me though.

Sorting out these problems can be a big headache, but don't let it get you down.

-Bill, N1GPT
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Draxx
Voodoo Audio Head


Joined: 16 Oct 2014
Posts: 15

PostPosted: Wed Oct 29, 2014 11:02 pm    Post subject: Reply with quote

Hi Bill,

I am currently connecting the outboard audio input to the front panel mic. I plan to use the ACC2 connector in the near future. Everything is grounded to the radio and the radio is grounded to a grounding rod outside. I am currently using an Astron 20 amp power supply. All the rack equipment has 3 prong plugs, including the power supply and everything is plugged into a Furman power conditioner which filters for RFI and EMF. All equipment is plugged into the Furman. All connections are using xlr's and are balanced except where the audio is connected to the mic jack.

What I've seen is when connected, and I key up (in am mode), as soon as I start to turn up the mic gain using the mic gain control on the radio, I can see the power meter go up to full wattage, and I can physically hear an internal squeal in the radio. This happens on all bands currently. I'm not sure whether it's a grounding problem or perhaps RFI getting into the system perhaps through one or more of the connecting cables, even though all are quality xlr cables utilizing premium shielding. I wanted to try this out on the front panel mic jack first to see how it would sound and I figured it would be easier to wire this up first as opposed to the ACC2 jack in the back. Those pins are so small on the ACC2 plug....lol.

Anyway, no matter which piece of equipment I run first whether it's the preamp or the compressor I get this "squeal". I've been testing with only one piece connected at a time so I could see if I was getting the same results with all equipment. So far it has been consistent. The only thing I don't have in the mix is an isolation transformer before going to the radio's mic jack. I did try running a Direct Box just prior to the mic jack which has a transformer inside it, but still had the same results. I hate to take the time to solder the ACC2 jack on and have the same results. And, you're right...... It is very frustrating but I refuse to let it get the best of me.....lol. I'm hoping someone else on this forum might have had the same experience and will see something I have missed. Sometimes we're too close to see simple mistakes.

Thanks for the reply and I hope I answered all of your questions and thanks for the encouragement.
KB6ZYJ
Scott
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Draxx
Voodoo Audio Head


Joined: 16 Oct 2014
Posts: 15

PostPosted: Sat Nov 01, 2014 7:03 am    Post subject: Reply with quote

*******UPDATE********
Yesterday I wired the ACC2 connector and tried that out. No more problem with the internal squeal. I believe the problem was a "gain" problem going thru the front mic jack. Since the front mic uses a built in preamp stage I think there was too much gain no matter what I tried. Going thru the ACC2 jack now, I am not having the problem I was having previously and i'm getting great audio reports. I think I will still do the C131 mod to add a few more lows and look to see what I can do to add a few more highs. Of course that may mean switching out the IF Filters, but we'll see. My thanks to this website and it's moderators for providing so much wonderful information on the "VooDoo" sound. I only wish there was more information regarding the 440 but I also realize this unit came well before DSP and some of the more advanced features that exist now.

Thanks again to all!!!

KB6ZYJ
Scott
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BillPaul
Digital Voodoo Guru


Joined: 19 Jan 2011
Posts: 66

PostPosted: Mon Nov 03, 2014 6:16 pm    Post subject: Reply with quote

The "C131 mod" only applies to the TS-870. You can likely to something conceptually similar to the TS-440, but it will likely involve more than just one cap, and the part numbers will be different. Start with the schematics in the TS-440 service manual and just follow the audio path from the ACC2 port.

It's still not entirely clear to me where the squeal was coming from, but I'm glad it went away when you connected the gear to the ACC2 audio input. I know those pins are tiny. You should probably order a couple of the 13-pin DIN plugs for it if you haven't already. DigiKey has them for something like $2.

http://www.digikey.com/product-detail/en/SD-130/CP-1013-ND/252010

You said: "Everything is grounded to the radio and the radio is grounded to a grounding rod outside." This may not be enough to eliminate the potential for ground loop hum, because you also said: "All the rack equipment has 3 prong plugs, including the power supply and everything is plugged into a Furman power conditioner which filters for RFI and EMF."

The power conditioner is good to have, but it doesn't have any effect om the grounding situation: the ground pins on all the outlets are still all wired together and lead to the ground pin on the AC outlet where the conditioner is connected.

The problem here is that there are two paths to ground:

1) The ground line run from the rig to the rod outside
2) The path from the ground pin on your AC plugs to your electrical ground bus in your fuse box (which may then lead to a different ground rod)

Both of those lead to ground, but the resistance of the two paths is not equal. It depends on how long the ground wire runs are, what gauge wire was used, and so on. The greater the difference, the louder the hum will be.

Each piece of audio gear is connected to ground via the AC outlets while the radio is connected through a separate wire to your ground rod. You end up joining these two paths together when you connect the audio gear to the rig.

You need to factor one of those paths out of the equation: there should be just one path, and all the gear including the rig should be bused together. But as I said in my original reply, that can be tricky to arrange. I had to resort to a bit of a hack to break the AC ground path used by my audio gear and re-route it to the radio ground. As the quote goes, I had to take off and nuke the site from orbit; it was the only way to be sure. Smile

-Bill, N1GPT
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Draxx
Voodoo Audio Head


Joined: 16 Oct 2014
Posts: 15

PostPosted: Tue Nov 04, 2014 12:52 am    Post subject: Reply with quote

Hi Bill,
I see what you mean about the different potentials. I have no AC hum at all right now. I found out the RFI leak I had was coming from a watt meter I had in line that was too close to the 440. I eliminated that meter (it was very old), and I completely lost the squeal I was hearing when transmitting. I also put Ferrite Chokes on all cables interconecting all the audio gear including the mic cable.

After looking at the schematic for the 440 I see only one cap prior to the balanced modulator which rolls off the lows starting at around 200 hz or so. The cap is actually C135 I believe if memory serves me correctly, and at my age that's a big "if"....lol. Either way, the audio sounds great right now. Of course it could sound even better if I changed out the IF Filters and some other caps but I don't really want to do major surgery on it at this point. I'm currently getting great audio reports so I'm leaning more towards "why fix it if it ain't broke"....lol. Thanks for all the info and the insight, it is greatly appreciated. I love this hobby. Kinda fun to "Frankenstein" equipment to improve it. Take care and 73's......

kB6ZYJ
Scott
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BillPaul
Digital Voodoo Guru


Joined: 19 Jan 2011
Posts: 66

PostPosted: Tue Nov 04, 2014 2:26 pm    Post subject: Reply with quote

I got curious so I dug out my PDF of the 440 service manual and took a look.

From what I can tell, the audio input from the ACC2 port (pin 11) goes to J25 on the IF unit. From there it goes through J23 to the mic gain knob on the front panel. Then it returns back to the IF unit before going to C133 and then into the base of amplifier transistor Q44. From there it goes from the collector of Q44 through C135 and then into pin 1 of the balanced modulator IC5.

It looks like C133 and C135 are both 1uF 50v electrolytic caps.

NOTE: Q44 also has an emitter shunt capacitor, C136, which is 47uF at 6.3 volts.

Without the emitter shunt cap, the amplifier formed by Q44 would have constant gain at all frequencies. With the cap, the gain drops off as frequency decreases, meaning that the amp will tend to have a low end roll-off. The mic and ACC2 pre-amp circuits in the TS-950SDX are the same way, though the ACC2 pre-amp in the SDX has an even smaller cap than the mic pre-amp which cuts off the low end even more. (This was intentional: the ACC2 input is meant for data, i.e. packet radio, not voice.)

Since Q44 is in the audio path for both the ACC2 and mic connector cases, all of these caps affect both cases. However for the mic connector path, there are additional caps that would need to be changed too. The ACC2 path is simpler.

So what I would do is:

- Change C133 and C135 from 1uF to 4.7uF
- Change C136 from 47uF to 220uF (or maybe even 470uF if you can find one that fits)

So, basically, it looks like 3 caps instead of just 1, but still pretty straightforward. Of course, this only restores some of the bass response. For treble you're back to dealing with the filters in the IF stages. So it goes. Smile

-Bill, N1GPT


Last edited by BillPaul on Wed Nov 05, 2014 1:51 pm; edited 1 time in total
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Draxx
Voodoo Audio Head


Joined: 16 Oct 2014
Posts: 15

PostPosted: Tue Nov 04, 2014 8:48 pm    Post subject: Reply with quote

Thanks for all the info Bill.... You ROCK. I don't care what your wife says..... I think you're all right....lol. With the research I've done on the iF Filters, it looks like the only down side of changing them is a much wider receive than you may actually want or like. I think for the time being I may just leave well enough alone. I'm getting great audio reports.

If I wanted to sample the transmit audio where do you think I could do that from to get an accurate representation of the output audio? I was thinking of building maybe a small audio amp or a demodulator I could possibly install inside the 440 and route it to the RCA Jack (ACC3 I believe) to act as an audio sampler. Just a thought and not even sure it would be practical to do. What are your thoughts? Let me know when you have a couple of spare minutes, and again, thanks for your willingness to share your knowledge and your insight.
KB6ZYJ
Scott
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BillPaul
Digital Voodoo Guru


Joined: 19 Jan 2011
Posts: 66

PostPosted: Wed Nov 05, 2014 2:33 pm    Post subject: Reply with quote

If I really did rock, I wouldn't have botched the part number for C136, twice. (Once I called it Q136 and the second time I called it C147. This is what I get for typing too fast at work. I went back and fixed things up.)

As for sampling the audio, I'm not quite sure. I mean, you can sample the audio alone right before it goes into the balanced modulator, but that's not a good representation of how you sound on the air. (For example, it doesn't take into account the bandwidth limiting by the filter stages.

Also, the process of demodulation is different for AM and SSB. For AM, it's easy. For SSB, not so much. I think the TS-950SDX actually uses a portion of the sub receiver for the monitor circuit for SSB. For AM you can create a simple diode detector. For SSB, you'd have to re-inject a carrier somehow to turn it into something that looks like AM again. I don't have any good recommendation for that.

If you have a computer, you might want to look into a cheap USB sofrware-defined radio dongle. Some of them are very cheap, though they tend to only tune down to 25Mhz or so unless you add an up-converter. The RTL-SDR software for them is pretty spiffy and will let you receive yourself in SSB or AM with very wide bandwidth.

-Bill, N1GPT
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Draxx
Voodoo Audio Head


Joined: 16 Oct 2014
Posts: 15

PostPosted: Thu Nov 06, 2014 12:59 am    Post subject: Reply with quote

I think I'll look into an SDR solution for sampling audio. Probably the best and most non invasive way to go. If it's sampling my signal, or actually receiving it, isn't there a chance of front end overload due to close proximity of my antenna, or does it have built in attenuation? We'll either way I think I'll look into something like that. Thanks for the suggestion and all your help with this project..... 73's.

KB6ZYJ
Scott
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Dave457
Voodoo Audio Head


Joined: 24 Jan 2012
Posts: 27

PostPosted: Mon Dec 29, 2014 2:16 pm    Post subject: Reply with quote

I run a Ts440 with the audio piped in the Acc2 port, with just one cap change, C135, Try just that! I get some excellent results with a little bit EQing, compression and limiting
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Draxx
Voodoo Audio Head


Joined: 16 Oct 2014
Posts: 15

PostPosted: Wed Dec 31, 2014 8:56 pm    Post subject: Reply with quote

Thanks Dave457. Going thru the ACC2 port now and get very good audio reports although I haven't tried the c135 mod yet.
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Draxx
Voodoo Audio Head


Joined: 16 Oct 2014
Posts: 15

PostPosted: Sun Jan 18, 2015 8:56 pm    Post subject: Reply with quote

******UPDATE******

Got the squeal down to a bare minimum but was still experiencing a very slight squeal internally with carrier and audio all the way down. I could just barely hear it and could see it on my scope. After struggling to eliminate it I almost gave up. Then I decided to move things around a bit. I moved the 440 to the top of my radio bench all by itself. This completely eliminated any and all rf getting into the transmit circuitry. Am getting great audio reports and am thrilled with how the rig is working. Thanks to all for ideas and suggestions..... The gremlin is finally gone....lol.
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