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   Home   Help Search  
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Author Topic: sound card output and alc meter  (Read 2796 times)
W2RJJ
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Posts: 5




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« on: April 04, 2003, 03:42:57 PM »

this concerns adjusting the audio output of the soundcard for tx'ing a proper signal with psk31.

what i've read from several sources is that soundcard output should be adjusted until the alc meter just begins to show alc action.

i have an analog alc meter with an area marked "alc." when there is no audio from the soundcard, the meter sits in rest position all the way left. as i begin to raise the soundcard output (windows mixer) the alc meter begins to deflect slowly. does the movement of the meter indicate that the alc has activated? should i stop raising the soundcard output as soon as the alc meter starts moving? is there a chance of underdriving the transmitter if i don't feed it enough audio?

i don't use the mic input for psk31. instead, my soundcard is connected directly to the radio's modulator input which is unaffected by the mic gain control. so an answer that includes information about setting the mic gain will not help here.

Thanks  --ray, w2rjj
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N1ZZZ
Member

Posts: 213




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« Reply #1 on: April 04, 2003, 08:58:59 PM »

Here is what I do.  I leave the RF power at max (100 watts in my case) then vary the AF from the soundcard to the power level desired (usually 5-30 watts).  I never have any deflection of the ALC meter which insures that I am not over modulating the signal at all.  I have never had anyone tell me that I had an overdriven signal.  

Your radio may be different however.

73 Jeremy N1ZZZ
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W2RJJ
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Posts: 5




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« Reply #2 on: April 05, 2003, 05:39:03 PM »

thanks, jeremy. i'll give it a try. i didn't think of approaching it that way. --73, ray
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K0HZI
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Posts: 470




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« Reply #3 on: April 05, 2003, 09:00:18 PM »

Here is a good web page for seting up sound card and rigs: http://www.waypoint.com/users/~discobay/section_7.htm
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VE3WMB
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Posts: 332




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« Reply #4 on: April 05, 2003, 09:20:29 PM »


The best advice I have received wr.t. audio levels for PSK31 is what I call the 50% rule.  If your rig is not rated 100% duty cycle at 100 watts then reduce the drive by 50% to bring it down to 50W. Then adjust the output mixer for your soundcard and/or the pot on your interface so that A) your soundcard slider level is not more than 50% of the way up (overdriving the soundcard is one of the main reasons for non-linearity on PSK31) and B) your power output is 50% of max .. which in this example is about 25W.
I use this trick with my TS-50 which has no ALC indication and I have never had a problem. This simple rule will ensure that you have a good clean PSK signal in the 25W range which is more than enough power.

Michael VE3WMB
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W2RJJ
Member

Posts: 5




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« Reply #5 on: April 06, 2003, 09:49:46 PM »

thank you to n1zzz, k0hzi. and ve3wmb for the answers, which were consistent. my approach was wrong and your recommendations (plus k0hzi's web link) set me straight. this has been very helpful and i greatly appreciate the elmering. thank you. --73, ray, w2rjj.
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