Unitrunker popping at end of transmissions

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elliottn

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I keep hearing carrier pops/blips at the end of transmissions if there isn't an immediate reply by someone on the channel. Sometimes it causes bleed over from other locked out channels because unitrunker isn't recognizing that the call is over.

https://www.dropbox.com/s/satemkue5...st (Talon_Viper)_6303-3 Yankee 3_1_1.mp3?dl=0

Is there a way to eliminate this? Are there things that need tuning? My Uniden BCD436HP monitoring the same system doesn't exhibit this behavior at all.
 

AggieCon

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This has been covered before on this forum.

How much did you pay for your Bearcat? How much for UniTrunker?

UniTrunker is primarily for logging information about trunked systems; it's just a nice benefit that he also threw the voice capability in.

Those are the end of transmission messages. Supposedly to tell the radio to go back to the control channel, but likely for some sort of test or just to annoy others monitoring.

I guess get used to it, buy more expensive reception equipment, or lobby the agency to go digital (no, actually, please don't do that).

A quick search shows that people have had the same problem with expensive Bearcats as well.

If you write some code to get rid of the trailing bs, please share it with us.
 

elliottn

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Well I didn't know others had talked about it. I've been googling for awhile (weeks) now but didn't know exactly what to call it so I got a lot of non-relevant threads. I finally broke down and made my first post on this forum.

I appreciate your frustration and defensiveness in the response but it wasn't necessary. I was only looking for information and guidance, not to open any cans of worms on what seems to be a sore subject with you. I only mentioned the scanner didn't exhibit this behavior to eliminate the system as the source of the anomaly if we went down a troubleshooting path.

If there is nothing to be done thats fine. I was just hoping it was a simple setting or adjustment I haven't found yet.
 

AggieCon

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"Unitrunker popping at end of transmissions"

It is not UniTrunker that is popping. The electromagnetic spectrum is "popping" because of intentional emissions by a transmitter.

It is too bad that you mistook my post. I generally am quite patient and helpful, especially with people newer to these programs. But your issue is a bit like whether your peas are too soft or too hard, and we're talking about free software here.

I highly encourage you to use software radio as a tool to explore in learn. For instance, a step you could have taken here would be to use SDR# to observe the frequencies exhibiting this behavior.

The next step might have been to dive in to the specifics of how the system you are monitoring works. The information is all out on the web.

The call might be over, but the transmission is not.

As I was saying, please do develop code to detect the end of message information so that it will mute it.

I am quite confident that--as someone able to configure SDR--you could have reached your own conclusion on this. You just have to spend the time to research and understand. And there is a lot to understand.
 

elliottn

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I did see it in SDR# so I know the system is actually transmitting the series of carrier blips but there doesn't seem to be any blanking logic in unitrunker that's common in commercially available hardware. I was HOPING that there was and it just wasn't configured or misconfigured on my machine.

Is unitrunker open source? On github? I haven't been able to find the actual project just references by usernames or other projects that have plugins. Most google hits bring me to radioreference and not a code collaboration site. I code but have never messed with audio. It would be an interesting problem to try to attack. Need to figure out how to identify it in the signal values measured by unitrunker (RSSI isn't going to work).
 

AggieCon

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I don't understand how you downloaded UniTrunker if not from the UniTrunker website.

UniTrunker is not open source; however, it is freeware.

A solution would have to be along the lines of using a virtual audio cable to pipe the UniTrunker output to a program that listened for the end of message signal. It would then mute the audio until UniTrunker issued a new SDRSHARPTRUNKING.log file, which is where the voice channel activity is printed.

Make sure deemphasis is selected. That might help a bit.

Anyways, UniTrunker is not commercial. We are blessed to have what we have. We should show the utmost thanks.

I think there is probably a fairly straight forward solution for detecting and muting this. I just haven't had time to look into it much.

I certainly am aware of the annoyance. I used to record an entire EDACS system, so the blips and pops were nonstop. Worse is that it extended the recording times. But, like I said, don't look a gift horse in the mouth. Overall, it's an awesome freeware solution.
 

slicerwizard

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A solution would have to be along the lines of using a virtual audio cable to pipe the UniTrunker output to a program that listened for the end of message signal. It would then mute the audio until UniTrunker issued a new SDRSHARPTRUNKING.log file, which is where the voice channel activity is printed.
No. The low speed datastream and disconnect words are not present in that recording, e.g. Unitrunker has already filtered them out. If that filtering can be disabled, then yes, one could take that approach.

Obviously, it would be better to do it in the decoder itself. When the disconnect words are being sent, there is no other audio (other than noise) present, i.e. no user is talking over the disconnect words, so only minimal noise filtering is required (and should be done anyway for audio sent to the speakers) and the processing is simple and audio samples can be directly converted to bits. The data pattern being sent is a repeating 10101100 sequence sent at 300 BPS. To detect it, one can take the noise filtered audio stream and store it in a short circular buffer. Scanning the buffer yields the highest and lowest sample values. Their mean forms an artificial zero line; this negates the effects of tuning errors, which create a DC shift in the FM demodulated audio. Walk through the buffer in steps that match the number of audio samples per low speed data bit. Obviously, the step size is affected by the audio sampling rate in use. For each audio sample stepped on, use the artificial zero line to convert the sample to a zero or one bit and slide that bit into a 32 bit shift register. After 32 bits have been shifted in, if you are processing disconnect words, and if the first bit you shifted in was at the beginning of a 10101100 sequence, your shift register will contain four copies of 00110101 (reversed b/c you left shifted), i.e. the value 0x35353535. If your shift register ever holds 0x35353535, the call is over, mute it. Obviously, you need to deal with misalignment - you may not be stepping on the bit centers or initially stepping on the first bit of a disconnect word, so you have to keep checking as you add new audio samples to the buffer. If you're concerned about false positives (I wouldn't be), use a 64 bit shift register on twice the data. Some efficiencies can be had - use a weighted sum to constantly adjust your zero line and use it to buffer bits rather than audio samples. And instead of a circular buffer, one could implement multiple shift registers (4 are probably enough), each working with the data at different offsets such that one of them will be hitting the bit centers. With them, no circular buffer required - just stuff incoming bits directly into shift registers. If any shift register hits 0x35353535, mute.
 
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AggieCon

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Well the OP couldn't of had better luck than for you to stop by. Thanks for the insight. Awesome!

I think the audio sample was with deemphasis on, or at least that's what it sounds like to me.

So I guess for an external script to work, one would need the "digital" talkgroup output that UniTrunker passes along for DSD+ decoding. Something that isn't processed already.

Well there's all you need right there. I guess I need to hop on that sometime.

And, I agree, I'll take my odds, 8/4.3 billion, that it's the end of message.
 
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