BCD996T Discriminator Tap Question

[Dewey]

Just curious... what are those of you who are having good decodes from a BCD996T discriminator tap using in the wiring? I recently tapped a '996T using a 10uF tantalum cap at the tap point, but my decodes don't go over 3%-5%. Fortunately, I didn't have a 10k resistor on hand because I was going to add it also. Since my decodes are so low, I'm thinking about pulling the cap and running a straight line, but I know that will expose the 996T to damage from stray voltage. So again, I am just curious to what is being used on any 996T that is giving good decodes.

Dewey

 

[gary123]

add the resistor and doble check the cap. such low decode can either be a bad cap or your input levels are way out. the line/mic input setting on the computer should be about 20% of the total range offered.

 

[N9JIG]

Mine works just fine with the tantalum capacitor, I agree with Gary that it is possible that there is a different issue.

 

[Dewey]

Mine works just fine with the tantalum capacitor, I agree with Gary that it is possible that there is a different issue.

Thanks much Rich. Are you using the cap and resisitor, or just the cap?

add the resistor and doble check the cap. such low decode can either be a bad cap or your input levels are way out. the line/mic input setting on the computer should be about 20% of the total range offered.

Thanks much Gary. In my very limited thinking, I don't see/understand how a resistor can help boost/improve a low signal. The two just seem so contrary to each other... resistor - boost. I do have some more 10uF tantalum caps on hand, so I think I am just going to go ahead and replace the cap and add a 10k resistor while I'm at it and see what happens.

Again, thank much to both of you,
Dewey

 

[N9JIG]

I am using just the capacitor. I have upwards of 20 radios with a discriminator tap and the cap has worked fine for both Trunker type applications as well as PL decoders.

Thanks much Rich. Are you using the cap and resisitor, or just the cap?
Dewey

 

[Dewey]

I am using just the capacitor. I have upwards of 20 radios with a discriminator tap and the cap has worked fine for both Trunker type applications as well as PL decoders.

Thanks again Rich. I've tapped my share of scanners since my Pro-2004 also, but I seem to remember somewhere that the BCD996T had a weak discriminator output. I know there was a thread a good while ago about this very subject, but it ended with no real consensus on what type of "protection" to put in the line.

Dewey

 

[gary123]

Thanks much Gary. In my very limited thinking, I don't see/understand how a resistor can help boost/improve a low signal. The two just seem so contrary to each other... resistor - boost. Again, thank much to both of you,
Dewey

Your welcome. The resistor acts as a buffer. It prevents the output of the discriminator from being loaded. Think of the discriminator as a door and the computer as the ground. the resistor acts as stairs. that way you dont end up with a door 10 feet off the ground or 10 feet below the ground. A poor analogy but it shows the basic concept,
another thing I am thinking of is many computers use stereo inputs be sure that you are keeping the pin outs correct. ground (the outer shank) and the center (the pin) strait and that they are not mixed up. THe middle shank on the stereo plug is not used in this aplication.