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Author Topic: SSB interfacing problem (PC/rig)  (Read 1940 times)
WS4T
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Posts: 179




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« on: October 22, 2012, 03:52:53 AM »

I'm preparing for CQ WW SSB. I have a Heil headset and have recorded my CQ message on the computer using N1MM software. When I play it back on the computer, it sounds fine. However, when I connect it to the microphone input of the rig (Yaesu FT-897D) and key the rig  (microphone PTT input), the on-the-air audio has a very high background noise level.

I'm using an FT-817 to monitor the signal. The normal background noise level is S0, then I key the rig and it jumps to S9. I've walked around the house with the FT-817 listening to the radio output but the noise is constant.

Any ideas on what the problem could be? I'm using a standard interface circuit into the microphone jack through a 600 Ohm audio transformer (circuit here: http://www.dxmaps.com/wsjtinterface.html).

I've tried running N1MM on two different computers and get the same noise. This is driving me crazy.

Any thoughts?

Tnx + 73,
Gary, ES1WST
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G4LNA
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Posts: 26




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« Reply #1 on: October 22, 2012, 04:40:00 AM »

Can you describe the noise? Is it something like a humming sound or a hissing noise, if it is a hissing noise it sounds like the gain into the rig needs to be reduced, if it is the former then it could be what's called a hum loop which might take a little more to get rid of.
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KA4POL
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Posts: 1853




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« Reply #2 on: October 22, 2012, 05:14:37 AM »

It could be the ground loop as mentioned. Another possibility is your connection catches something like a switching power supply. I'd try a ferrite choke close to the rig. I guess you have adjusted the output voltage down to match the microphone input.
I'd also try just hooking everything up with the computer being off. What happens then?
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WA3SKN
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Posts: 5419




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« Reply #3 on: October 22, 2012, 06:26:53 AM »

What kind of levels are we talking about?
The computer card is usually set for line levels... or about 0 dBm of audio power input to the card.  Your headset may be adjusted for that level, or designed around a radio microphone input level... about -60 dBm... this low level would be near your noise level at the computer input.  So when recorded you would hear noise along with the recorded audio.
How do you have the audio going into the computer vs how do you have the audio going into the radio?  Do you have any measurements or impedances for either?

-Mike.
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WS4T
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Posts: 179




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« Reply #4 on: October 22, 2012, 09:34:48 AM »

Thanks for all the replies.

I did some more on-the-air testing (tnx to ES1TU). ES1TU says the audio sounds fine from his QTH (6 miles away).

Right now my interface is sitting on a breadboard and I'm wondering if the noise is some sort of RF that is getting picked up by the cables. It sounds like a buzzy noise. I moved the breadboard a bit further away from the computer and the noise level did drop a little. Maybe I should just solder it all together and stick in a metal box. I have an Altoids box I can use.

I've thought about eliminating the computer entirely, but then there's no way to send the audio from the computer. I have trying disconnecting everything else.

Unfortunately, I don't have any gear to measure the levels but I have adjusted the computer audio output to make sure I'm not overdriving the rig. I'm monitoring that using the FT-897's ALC meter.

73,
Gary

PS: I wish the FT-897 had a way to record an SSB CQ. That would be very useful.
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G4LNA
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« Reply #5 on: October 22, 2012, 10:41:50 AM »

I agree with Mike, I think your levels are too high, once you get those sorted out then you can start looking at the rest of the set-up.

I think you really do need to get hold of some test equipment to measure your levels, an oscilloscope would be useful if you can borrow one, a lot of amateurs use them and if you are not sure how to use them I sure they will gladly show you. You can't really use the ALC meter, that is quite meaningless for what you are trying to achieve.
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KA4POL
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Posts: 1853




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« Reply #6 on: October 22, 2012, 11:27:58 AM »

Right now my interface is sitting on a breadboard and I'm wondering if the noise is some sort of RF that is getting picked up by the cables. It sounds like a buzzy noise. I moved the breadboard a bit further away from the computer and the noise level did drop a little.
Of course a missing shielding is bad to start with. And when you can see an effect from moving the interface around you got proof of the influence. Put the interface in a metal box which is connected to ground. Let us know of the results.
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KB3LIX
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Posts: 1094




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« Reply #7 on: October 22, 2012, 11:59:48 AM »

Sounds like the levels are too high.

Try using the DATA jack on the rear of the 897.
It is designed for LINE LEVEL inputs rather than
a microphone input that has pre-amplifiers
to amplify the very low levels from a headset.

Don't remember the pins on the DIN jack, but they are
described in the manual.
I use this input (and data output) on this jack for
all my DIGI modes and they work just fine.


BY THE WAY...

I just found your other post about not being able to
use the data jack on an FT-897D.

I just tried it here on MY FT-897D, and IT WORKS FINE.

Set it up on the data jack input, mode USB/LSB
and try adjusting the DIGI gain. Extended menu # 37.

It works for me here.

I do not use this method for phone, I prefer to actually
push the PTT and speak, I feel more "in control"
that way.

Good luck !

bill
« Last Edit: October 22, 2012, 12:09:36 PM by KB3LIX » Logged
WS4T
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Posts: 179




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« Reply #8 on: October 24, 2012, 12:37:57 PM »

Ugh...I still can't get it right.

I put in a bigger resistor (in the voltage divider) to lower the input level to the mic and now the levels are too low. Plus using a splitter with the Heil headset in parallel doesn't seem to work too well. The headset output level drops with the other circuit connected. How could I connect the computer audio and headset both to the mic input and keep them isolated? Is there a simple circuit to do that?

Also tried going through the rear data jack again. All I hear when I monitor the signal is a weird noise -- sounds like some strange digital mode (or feedback!?).

Maybe I'll just use the headset, but it's hard to imagine calling CQ for long without a recording.

I found an interesting article here: http://audiosystemsgroup.com/HamInterfacing.pdf

73,
Gary
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STAYVERTICAL
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Posts: 854




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« Reply #9 on: October 24, 2012, 01:12:57 PM »

Sorry to hear about your ongoing saga.

Here are a few things I have learned (the hard way) about interfacing with my FT897D.

1. Notebook computers can give a buzzing noise into interfaces if the audio transformer is close to the LCD screen.
    I assume it has something to do with the flourescent backlight inverter - move the transformer/wiring well away.
    The same is true of monitors LCD or otherwise.

2. Ground loops will cause noise - an audio transformer will normally solve this.

3. Put a 1K resistor across the audio output from the PC headphone/audio out jack to damp this output or you can get unstable audio levels.
    It may sound crazy but I have solved 3 guys problems with this simple hack.

4. Use shielded cables throughout or you will likely get RF back into your interface causing all sorts of different problems.
    These problems will vary by band and power.
    To see if this is a problem, run very low power 5W and see if your problem persists.
    This problem is particularly acute with verticals or antennas close to the shack.

5. If you are using radio control (CAT port) you can still get a ground loop even if your digital interface is isolated.
    I solved this by buying a cheap RS232 optoisolator "dongle" which electrically isolates the radio control port.
    The dongle just plugs between the computer and radio CT62 cable.

I ended up using my existing USB-Signalink which uses the 6 pin "Data" port for my SSB work.
Works fine and no problems at all.

Good luck, I have been where you are and know how frustrating it can be.

73 - Rob
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KA4POL
Member

Posts: 1853




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« Reply #10 on: October 24, 2012, 09:55:59 PM »

Ugh...I still can't get it right.

I put in a bigger resistor (in the voltage divider) to lower the input level to the mic and now the levels are too low. Plus using a splitter with the Heil headset in parallel doesn't seem to work too well. The headset output level drops with the other circuit connected. How could I connect the computer audio and headset both to the mic input and keep them isolated? Is there a simple circuit to do that?
Do you remember Ohm's Law? You just see it at work Grin
I recommend using a simple switch to switch from one input to the other, i.e. computer and headset.
Quote
Also tried going through the rear data jack again. All I hear when I monitor the signal is a weird noise -- sounds like some strange digital mode (or feedback!?).
This will never work. It is designed for a digital input.
Quote
Maybe I'll just use the headset, but it's hard to imagine calling CQ for long without a recording.
How do you think we have done that before computers and speech memory units?


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W8JI
Member

Posts: 9304


WWW

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« Reply #11 on: October 25, 2012, 07:37:30 AM »

You probably have a ground loop. This is very common with wiring errors on unbalanced audio lines, and sounds like you describe.

You might read this:

http://www.w8ji.com/cables_and_wiring.htm
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W8NF
Member

Posts: 53




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« Reply #12 on: October 25, 2012, 08:56:43 AM »

I don't think you have a problem.

Listening to your own audio using an adjacent receiver is difficult.  You're simply coupling too closely to the FT-817.  If you had no input to the radio's mic jack at all, keying the rig would probably give you a significant rise in background noise.  Then, when you do add audio, you're overloading the FT-817, which is easy to overload anyway.

The way I listen to my audio is to build up a little frequency translator...if I'm TXing on 20 meters, I'll use an RF sig gen into a mini-circuits mixer to translate to some other ham band.  Now I can add attenuators into both the input and output of the mixer to drop the levels into my RX down to something reasonable - I like to see the levels peak at 20dB over S9 maximum.  I attach two very small antennas to the mixer system.

If a ham six mile away can't hear the background noise problem, AND your FT-897's transmit AGC meter is staying within reasonable limits, then I'd say you're ready for game date.

Dave W8NF
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STAYVERTICAL
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Posts: 854




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« Reply #13 on: October 25, 2012, 01:02:41 PM »

One little correction - the rear "DATA" jack is for digital modes, but used in AFSK mode.
It will work fine with voice or AFSK data.

It is not a "true" digital input in that it switches binary states or anything like that.

The labelling on the FT897D data jack is a bit misleading, the DATA-OUT for example could be labelled AUDIO-OUT just as accurately.
Similarly, the DATA-IN could be labelled AUDIO-IN, since this is what you are doing when running PSK31 or other AFSK digital modes.

If this were not true, using the PC headphone/microphone or a USB-Signalink as a modulating source would not work.
You can send voice by the DATA jack, but you would have the same problems with filter settings which one gets when generating CW by audio tone in SSB mode.
All these things are adjustable however in the FT897D menu's (see USER-U etc), and filters can be moved by menu setting.

73 - Rob
« Last Edit: October 25, 2012, 01:08:11 PM by STAYVERTICAL » Logged
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