Using BR330T to log in Unitrunker

[bwilborn]

I live in Colorado and I would like to do some control channel monitoring of the state DTRS system, but my 396 currently does not have a discriminator tap. I do however have a BR330T that sits mostly idle on my desk. I was thinking that I could use it to tune to the particular CC frequencies that I would like to monitor, and then feed the audio into my PC and decode the stream using Unitrunker. Can I do it like this?

Here is what I've tried so far:
I can tune to a control channel (853.3125, CO DTRS site 326 in this case), and I can hear audio that sounds like a data stream. I have an audio cable from the headphone output of the scanner plugged into the mic input on my sound card. I then used the oscilliscope feature in Unitrunker, and I'm getting what looks like a clean signal after adjusting all of the levels (no clipping and a smooth waveform). The problem is that nothing is showing up in the log.

Looking through the documentation it suggests using a "small buffer amplifier" between the radio and the PC. Are we talking about, say, running the audio into a home stereo amp, then into the PC?

-- B

 

[SCPD]

I do however have a BR330T that sits mostly idle on my desk. I was thinking that I could use it to tune to the particular CC frequencies that I would like to monitor, and then feed the audio into my PC and decode the stream using Unitrunker. Can I do it like this?

If the '330 is tapped, yes.

I have an audio cable from the headphone output of the scanner plugged into the mic input on my sound card. I then used the oscilliscope feature in Unitrunker, and I'm getting what looks like a clean signal after adjusting all of the levels (no clipping and a smooth waveform). The problem is that nothing is showing up in the log.

The audio has been filtered. The signal transitions that define the boundaries between adjacent bits are distorted - resulting in bad data. You will need to tap the radio to get good results.

Looking through the documentation it suggests using a "small buffer amplifier" between the radio and the PC. Are we talking about, say, running the audio into a home stereo amp, then into the PC?

Again, this is in the context of discriminator audio. Start with feeding the tapped audio directly into the computer (with a capacitor or resistor for isolation) - then see if you need additional isolation in the form of a buffer amp.

You don't want to drive your computer's sound input with a home audio stereo amp. It might damage your computer.

-- B[/QUOTE]

 

[bwilborn]

If the '330 is tapped, yes.

The audio has been filtered. The signal transitions that define the boundaries between adjacent bits are distorted - resulting in bad data. You will need to tap the radio to get good results.

(...)

Again, this is in the context of discriminator audio. Start with feeding the tapped audio directly into the computer (with a capacitor or resistor for isolation) - then see if you need additional isolation in the form of a buffer amp.

(...)

You don't want to drive your computer's sound input with a home audio stereo amp. It might damage your computer.

So, what you're telling me is that I need a discriminator tap? That's a bummer that you can't use the headphone audio at all for this. It'd be nice if you could reroute the audio around the filter and just use the jack, but oh well.

So, since I'm not exactly the greatest at designing circuits, how can I tell how large of a resistor I need to put in-line? Should I connect it to the ground or signal wire? I know how to read resistor bands so I can tell the difference, and my limited knowledge is making me think that it makes the most sense to run it in-line on the ground wire, but I would like someone to reaffirm that for me. I've actually got a cable and jack ready to go for the surgery à la this thread but I've been hesitant to open up my $500 396 and do it. I'd be more willing to do it to my 330, as it wouldn't be as great of a loss to me (although I would still cry).

So, even though the 330 doesn't have the hardware to decode digital, we can still use it to recieve the CC stream from a digital system, because the PC is the one doing the decoding, right?

-- B

 

[SCPD]

So, since I'm not exactly the greatest at designing circuits, how can I tell how large of a resistor I need to put in-line?

Somewhere in the range of 4.7k to 47k ohms - in series on the tip (signal), not the ring (ground) of the audio jack. You start with no resistor or capacitor - straight through. The computer will have DC blocking capacitors so they will at least provide DC isolation. The two problems with this are usually (a) distortion of the signal going into the PC and (b) a "loading" side effect on the scanner that produces wrong squelch levels and prevents it from scanning. Higher resistor values will reduce the current "leached" from the discriminator circuit inside the radio - allowing the radio to operate normally. This also means less current at the microphone input - requiring more gain inside the PC to compensate (which most PCs are able to do).

So, even though the 330 doesn't have the hardware to decode digital, we can still use it to recieve the CC stream from a digital system, because the PC is the one doing the decoding, right?

Right.

 

[FlashSWT]

If you're nervous about opening up your 330 or 396 see if you can find a used Pro-93, 94 or 95 and tap that. I had never soldered anything in my life and got a Pro-93 taped without near as much effort as I thought it would take. It was much less nerve raking since I didn't care if I killed the old scanner.
.

 

[bwilborn]

If you're nervous about opening up your 330 or 396 see if you can find a used Pro-93, 94 or 95 and tap that. I had never soldered anything in my life and got a Pro-93 taped without near as much effort as I thought it would take. It was much less nerve raking since I didn't care if I killed the old scanner.

Yeah, I think that's going to be the route I take. I had a conversation with someone earlier today, and that pretty much convinced me to leave my current two radios alone.

-- B

 

[bneilson]

I have had a small bit of luck using my 330 untapped. My signal strength in Unitrunker is very weak 20-30%.

I went the route of getting a dedicated scanner. I picked up an old Pro-92 on ebay that had a broken screen for practically nothing.

Now it just sits on the CC of one of the local systems collecting data