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A PRO-95 Tap
- Thread starter Bucephalus
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nova1010
Member
Nice work 
Thanks
Umm, unless I'm missing something it appears to me as if you have set up a simple RC filter for your tap rather than a DC blocking and load isolation tap that, as I understand it, most use.
Without knowing the exact values you used, that filter may or may not help you depending on the type of signal you are trying to decode. The general idea of a discriminator tap is to eliminate as much filtering as possible so as to allow full bandwidth passband signals through giving you the most options for decoding with appropriate software and sound card hardware. The idea of the resistor and capacitor combination in SERIES is so that the resistor prevents loading down the radio's discriminator circuit and the capacitor provides DC isolation.
What you have is the resistor in series with the cap paralleled to ground thus creating a RC filter. I would suggest that you desolder the cap from ground and move the wire tap to that point on the cap instead; the cap and resistor should be series, no parallel components. Also, rather than a single wire, I would use a shielded cable and solder the center wire to the cap+resistor+discriminator tap and the shield to a ground point as close to the tap as possible. Keep all leads as short as possible, ideally.
So you should have tap point->resistor->cap->center conductor of shielded audio cable and shield of audio cable grounded to a close and good ground point on the radio's PCB.
-Mike
Without knowing the exact values you used, that filter may or may not help you depending on the type of signal you are trying to decode. The general idea of a discriminator tap is to eliminate as much filtering as possible so as to allow full bandwidth passband signals through giving you the most options for decoding with appropriate software and sound card hardware. The idea of the resistor and capacitor combination in SERIES is so that the resistor prevents loading down the radio's discriminator circuit and the capacitor provides DC isolation.
What you have is the resistor in series with the cap paralleled to ground thus creating a RC filter. I would suggest that you desolder the cap from ground and move the wire tap to that point on the cap instead; the cap and resistor should be series, no parallel components. Also, rather than a single wire, I would use a shielded cable and solder the center wire to the cap+resistor+discriminator tap and the shield to a ground point as close to the tap as possible. Keep all leads as short as possible, ideally.
So you should have tap point->resistor->cap->center conductor of shielded audio cable and shield of audio cable grounded to a close and good ground point on the radio's PCB.
-Mike
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Tap is now working.
Thanks to the UniTrunker built in Uniscope program I figured out why the tap wasn't working.
Thanks to the UniTrunker built in Uniscope program I figured out why the tap wasn't working.
After some Mutilation I finally got it right.
Actually it wasn't working until I cut out the 2.2 Micro Farad Cap. It was like a miracle and Trunker88 came to life with 100%. This is a Rad program. After some trial and error I finally got it. The Pro-95 works excellent. Here is the final photo after some butchering. I had some Cat 5 laying around and snipped out the Cap. Hooked up the ground and BAM!
This is my correct hook up for Tapping the PRO-95.
View attachment 28883
Actually it wasn't working until I cut out the 2.2 Micro Farad Cap. It was like a miracle and Trunker88 came to life with 100%. This is a Rad program. After some trial and error I finally got it. The Pro-95 works excellent. Here is the final photo after some butchering. I had some Cat 5 laying around and snipped out the Cap. Hooked up the ground and BAM!
This is my correct hook up for Tapping the PRO-95.
View attachment 28883
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slicerwizard
Member
More like a lose 99.99% of the signal filter!
Never heard of it. Must be new...
More like a lose 99.99% of the signal filter!
Yeah, LOL, I guess if we assume the cap was 2.2uf and the resistor was 10K ohms than you'ld have to be very interested in frequencies less than 7Hz or so...which might be just a wee tad low for trunking control channel decoding I s'pose....:- |...
Well, I guess one person, at least, read my advice, though not really the one who needed it...
Amazing that clipping that nasty ol' cap out created that "miracle" that allowed "Trunker88" to work! Gosh, wow; DC isolation...bah...let the sound card handle that (yeah, I know, most do anyway, mine does, but still...).
Whatever...
-Mike
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