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Author Topic: PSK31 - Low Modulation  (Read 3372 times)
KD5JDG
Member

Posts: 36




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« on: April 06, 2002, 10:47:39 PM »

I built a homebrew interface kit for my soundcard to my radios and I hardly get any modulation. I have it interfaced to a RCI-5054DX or a Kenwood TR-9000 and they both have the same problem. All the controls on the radio are up and same for the computer. I am using a circuit that looks a little like this:

From Line Out                 To Mic In (On Radio)
----xxx--------|--------------
    100k       x
               x 1k
               x
------------------------------

Very simple circuit, so whats wrong? I am running Windows 2000 on a Compaq Presario 5015, and a built-in soundcard (SB compatible), and either WinPSK, WinPSKse, MMSSTV, or MMRTTY. Any ideas?

TNX & 73's,
Fabian C.
KD5JDG

Email: FCeagle@hotmail.com
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KF4HEY
Member

Posts: 172




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« Reply #1 on: April 07, 2002, 08:56:02 AM »

Hello Fabian,

There is not enough information in your message to decide where your problem may lie.  What is the Volume Control output?  Check the sliders on the mixer window for both Play Control and Wave/Direct output.  You may simply not be driving the soundcard output enough.

Also you may want to change the 100K resistor in the T-pad to 50K.

73,
Mike KF4HEY
 
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KD5JDG
Member

Posts: 36




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« Reply #2 on: April 07, 2002, 03:32:56 PM »

All the mixer controls on windows are all the way up. I'm going to try a 50k resistor today. Actually, i tried a 4.7 k in parallel with the 100k and it did nothing. However, if I put a 1k resistor parallel with the 100k the radio goes back into recieve mode, making me guess that its allowing too much voltage through. Both radios require a low impedence mic, the RCI-5054 needs a 400k mic, and the TR-9000 needs a 600k mic i believe.

TNX & 73's,
Fabian C.
KD5JDG

If anyone wants to sked, I'm on 50.290 BPSK, QRP (well, 25w but with PSK its only putting out 3-5 watts - low modulation) with a really crappy temporary antenna (my 20ft mast and 8ft ground loaded up with a 6m random-wire antenna tuner haha!)
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KD5JDG
Member

Posts: 36




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« Reply #3 on: April 07, 2002, 09:45:16 PM »

Ok, I think I figured some of it out. I can't hear anything when I plug my speakers into my line out port. However, my radio bearly picks up a signal (I suppose) hence the very weak modulation. Why no output on my sound card's line out? tried a multitude of different PSK31, SSTV, and RTTy programs all same result. See my post under: http://www.eham.net/forums/Digital/565

TNX & 73's,
Fabian C.
KD5JDG
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AD5DR
Member

Posts: 8




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« Reply #4 on: April 08, 2002, 07:43:33 AM »

You had replied to my "No Output From Sound Card" post so I thought I'd get back to you here.  I gave up on the Compaq after trying both the motherboard sound as well as a new Soundblaster PCI16 card.  Similar to your problem, receiving on the computer worked but I couldn't get out.  It wouldn't drive speakers either.  If your computer will drive speakers, you might go by Radio Shack and get an "attenuating patch cable" to reduce the drive level - but I guess your voltage divider circuit's probably already doing that.  I hope you can work this out and am sorry I wasn't any help.
73s de AD5DR
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KD5JDG
Member

Posts: 36




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« Reply #5 on: April 08, 2002, 08:59:18 AM »

Well, sorry to hear that your having the same problems. I think I'm just gonna buy a Y connector and plug the radio into one of those and the speakers into the other. I'm hating on Compaq right now, everything is proprietary, and you only have something like 3 PCI slots and 2 ISA slots, definetly not enough. And the Intel Celeron proccessor leaves much to be desired, especially on Windows 2000 (Hell, even a slim OS like Linux - I dual boot). Next time, I'm definetly building my own and selling my Compaq haha. Anyway, right now I have everything hooked up to my Ranger RCI-5054DX (6m) rig, and if I overdrive it it goes back into receive mode and starts doing some real funny stuff, so if I'm not careful I'm gonna really fry this rig lol! Hope to work everyone, I'm only a tech right now but gonna try to upgrade very soon; hope to catch you on 50.290 USB BPSK (when no one's watching TV) or 144.144 USB BPSK (All QRP with really crappy antennas haha)! Maybe some SSTV too!

TNX & 73's,
Fabian C.
KD5JDG

P.S. If anyone has any idea why our computers aren't utilizing the line out port please feel free to help us, 'cuz I can't figure it out!
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NB6Z
Member

Posts: 550


WWW

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« Reply #6 on: April 08, 2002, 11:26:02 AM »

The "line out" on a PC audio port is for high impedance devices, like power speakers. It should NOT provide enough power to drive speakers directly. However, this is the correct line to use for driving the MIC or AUX input of a radio. You can try to go directly from the "line out" to the radio audio input with no interface attenuation (just use a shielded cable) and see if you get enough drive level. You will need to turn down the sound card output for this. If you still don't have enough drive to the MIC circuit... time to get a new PC. Make sure you don't over drive the radio! Keep ALC low or at zero... I was able to drive my new FT-920 directly this way with no trouble. However, using a HB variable attenuator pad, I could bring up the sound card level so that it was acceptable for both the radio and for normal PC work.
The answer is out there... ;-)
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KD5JDG
Member

Posts: 36




Ignore
« Reply #7 on: April 10, 2002, 09:17:21 AM »

Actually, if you buy a Y splitter you can just plug it into your speaker port (along with your speakers) and it works great! The line-out port just doesn't cut it.
Hope to work ya'll on PSK31 on the TVI band 50.290 or the short-range band 144.144!

TNX & 73's,
Fabian C.
KD5JDG
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