Discriminator - UBCD996T

[Scotty]

Going to 'bite the bullet' and finally tap my UBCD996T so I can use UniTrunker etc. There's heaps of info out there on how to do it, but I'm hoping somebody on here can confirm some info for me.

The discriminator point is easy to find on the circuit board, and it seems like it is as easy as soldering a 10uF tantalum capacitor inline to a shielded cable to a 3.5mm mono plug. The problem is that I don't know what 10uF tantalum capacitor to use - there seems several types available in varying voltages.

Hoping somebody can advise, or even better post a Jaycar part number or link.

Thanks,
Scotty

[rustynswrail]

Going to 'bite the bullet' and finally tap my UBCD996T so I can use UniTrunker etc. There's heaps of info out there on how to do it, but I'm hoping somebody on here can confirm some info for me. The discriminator point is easy to find on the circuit board, and it seems like it is as easy as soldering a 10uF tantalum capacitor inline to a shielded cable to a 3.5mm mono plug. The problem is that I don't know what 10uF tantalum capacitor to use - there seems several types available in varying voltages. Hoping somebody can advise, or even better post a Jaycar part number or link. Thanks, Scotty

Scott,

There is considerable opinion on this, so I will add mine. The discriminator can be tapped from a point on the circuit board without heating up the audio chip. Remove the top cover, look for a solder pad marked DISC. Attach your wire to this pad. Rather than use a cap, I use a 10K ohm resistor. It seems to filter things providing a very clean waveform for digital GRN decoding for example. Also seems to make the sine wave nice for the analogue GRN as well.

As to the type of socket, I used to use a 3.5mm audio socket, I now use RCA's. They are easier to install in some equipment and produce a better contact.

The only other advice, use a clean fine tip soldering iron, make sure it is hot. Otherwise it is easy to do, so don't be afraid. I have done dozens.

As I said my opinion, no doubt others will have differing ones.

Russell

[Scotty]

Scott,

There is considerable opinion on this, so I will add mine. The discriminator can be tapped from a point on the circuit board without heating up the audio chip. Remove the top cover, look for a solder pad marked DISC. Attach your wire to this pad. Rather than use a cap, I use a 10K ohm resistor. It seems to filter things providing a very clean waveform for digital GRN decoding for example. Also seems to make the sine wave nice for the analogue GRN as well.

As to the type of socket, I used to use a 3.5mm audio socket, I now use RCA's. They are easier to install in some equipment and produce a better contact.

The only other advice, use a clean fine tip soldering iron, make sure it is hot. Otherwise it is easy to do, so don't be afraid. I have done dozens.

As I said my opinion, no doubt others will have differing ones.

Russell

Thanks Russell, indeed there are several differing opinions - it's not possible at all to get an easy answer! I've made the decision to put both the cap and resistor in place. Both serve slightly different purposes and it seems neither will have a detrimental effect on the signal output - plus, for $2 it's cheap insurance.

I'll be using a 3.5mm plug only because I have plenty of cables available, and I have an old Realistic scanner with a tap that uses the same plug. Horses for courses I guess.

Many thanks for your comments though.

[rustynswrail]

Scott,
There is considerable opinion on this, so I will add mine. The discriminator can be tapped from a point on the circuit board without heating up the audio chip. Remove the top cover, look for a solder pad marked DISC. Attach your wire to this pad. Rather than use a cap, I use a 10K ohm resistor. It seems to filter things providing a very clean waveform for digital GRN decoding for example. Also seems to make the sine wave nice for the analogue GRN as well. As to the type of socket, I used to use a 3.5mm audio socket, I now use RCA's. They are easier to install in some equipment and produce a better contact. The only other advice, use a clean fine tip soldering iron, make sure it is hot. Otherwise it is easy to do, so don't be afraid. I have done dozens. As I said my opinion, no doubt others will have differing ones. Russell

Thanks Russell, indeed there are several differing opinions - it's not possible at all to get an easy answer! I've made the decision to put both the cap and resistor in place. Both serve slightly different purposes and it seems neither will have a detrimental effect on the signal output - plus, for $2 it's cheap insurance. I'll be using a 3.5mm plug only because I have plenty of cables available, and I have an old Realistic scanner with a tap that uses the same plug. Horses for courses I guess. Many thanks for your comments though.

Scott,

You are welcome. The main advantage of the cap is filtering, particularly any 455 KHz IF that maybe present in the signal.

R

[Scotty]

Just added the tap - getting fantastic results using UniTrunker (1.0.0.7, as the latest version kept crashing) and the standard soundcard. I really can't believe it has taken me this long to do it.

Now I just need to find a way to record the audio at the same time without the 'hiss' of the control data.... might be time to hook up that second computer.

[Bigfella237]

You might want to look at installing a second sound card or even a USB sound card on the same computer for recording audio?

Andrew

[Scotty]

You might want to look at installing a second sound card or even a USB sound card on the same computer for recording audio?

Andrew

Thanks Andrew, a second sound card would certainly be an easier option and something I shall look at doing.

[Scotty]

I got myself an 'el-cheapo' ($3.99) USB sound card from eBay on Tuesday and it arrived yesterday. I set it up and have the discriminator audio through the on-board soundcard (better decodes than the USB, up to 100%) and have the scanner audio through the USB card, along with my speakers. Can now record/log conversations through bcTool and analyse sites at the same time using Unitrunker - brilliant!

I might look at getting a PCI sound card at some later date, but I'm more than happy with the setup now. Thanks for the suggestion Andrew.

[soupbones]

Thats the same setup I use. works a treat. Just keep the drivers up to date on the USB sound card. Not an issue if you run win7