Anyone care to listen to this sample created with Unitrunker and offer some advice?

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br0adband

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Got a sample here and it's driving me a bit batty, but before I get into it I need to say it's not what you think in terms of an audio sample like figuring out what type of transmission it is.

I'm using Unitrunker (1.0.27.10, had issues with rev 12 so I rolled back for the time being) and also using two RTL sticks to get a makeshift trunking scanner working. I'm not using SDR# or anything else at this time, just Unitrunker + the two RTL sticks. One is configured as the signal (control channel) receiver, the second is the voice channel receiver. It's working - repeating it to clarify: it does work and it works quite well given the situation and what I'm doing but, there's an issue that's been nagging me for a few days now since I started this particular setup.

Here's the sample file:

Playing: WhatTheHellIsThisNoise.mp3 - picosong

21 seconds, very short sample. At the beginning you'll hear a voice channel broadcast but it seems horribly interlaced with what I can only deem as some horrible crosstalk or bleeding in that particular transmission, so I hit Next (on the Unitrunker radio dialogue) to skip to the next talkgroup and that audio comes in about as clear as one might hope, until about the 16 second point where I end up on another frequency/TG and that noise comes right back. Reminds me of many many years ago when I installed my first car audio system and I'd have massive amounts of alternator whine being picked up by the AM/FM radio - that turned out to be a simple thing to fix but this is driving me nuts at this point.

I have to say that this doesn't happen when I use Unitrunker for just tuning the control channel and then using a debug receiver to pass info to SDR#'s trunking plugin and let that program tune the second system for me - the audio is always clear or as clear as it should normally be.

But when doing this pure-Unitrunker-only analog trunking setup, that noise is just incredibly frustrating to try and resolve. I've done the following in the past week:

- created better cabling
- finally got the MCX to BNC pigtails I ordered in mid-December (thanks USPS, it's only 3 weeks late, no problem)
- built one of those 1/4 wave multiband antennas found at: http://www.qsl.net/n4yek/scanner/antenna.pdf and was pleasantly surprised at just how well it actually does work
- still use my trusty Radio Shack 800 MHz and Diamond RH-C77A antennas when needed (that's how I currently have the Unitrunker setup working, with the Diamond tuning the control channel and the RS 800 handling the voice channels - as a note the signal strength here is more than adequate overall since I'm centrally located from all the repeaters/towers on the mountains that surround my entire area)
- tried leaving the RTL sticks plugged directly into my laptop on different sides with the antennas as far apart as possible
- tried using 10' USB extension cables (with the outer metal shielding removed to cut down on noise, learned that tip from a blog someplace and it does actually help) putting the RTL sticks and the antennas almost in different corners of my room, as far apart as they'll go
- placing the RTL sticks inside metal containers (Altoids tins, cut to fit and with contact on the USB plug's metal shield to lower noise, another tip from that blog and yes that works as well)
- various other things so far

After all that experimentation, whenever I fire up this Unitrunker-only trunking setup, that noise still exists and I can't figure it out at all. Seems like I should be able to figure this out but it's stumping me so, if anyone else is using Unitrunker in this "new" capacity - meaning it can do analog trunking all by itself now, no additional SDR software needed - I'd love to hear your setup and whether or not you're getting that kind of odd noise or "audible interference" that sample above makes fairly clear.

It won't stop me from using it but it sure would be nice to get rid of that noise if I can.

Also, the USB cables are choked with ferrite loops to help keep noise to a minimum also. I think I've done most everything to keep the noise floor around ~-60dB and it tends to stay there no matter what I'm doing so, I don't think is a noise issue directly, maybe it's something to do with Unitrunker's newfangled capabilities of handling RTL sticks simultaneously, maybe? :confused:

Anyway, if anyone can offer any advice I'm all ears... figuratively speaking.
 

slicerwizard

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Sounds like a) intermod, where other signals are mixing with the desired signal, or b) you're landing on dead channels after their comms have ended and again, you're picking up intermod from other signals, or c) a tuning error is landing you on dead channels.

If it's a, there is insufficient (software) RF filtering to block the unwanted signals.

If it's b, there is insufficient (software) RF filtering to block the unwanted signals. And some (software) squelch logic should be muting it anyway, but isn't.

You should pay closer attention to which RF channels are exhibiting the problem; this may let you confirm or rule out c.
 

SCPD

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The software br0adband describes is a preview release.

If anyone wants to beta test any of the preview releases, please sign up on the Unitrunker mailing list on Google Groups. These preview releases are very experimental. Expect them to have all manner of bugs or rearrange your data in a way that isn't compatible should you decide to roll back.

After multiple iterations, a preview release is eventually promoted to an official release. At that time, you'll read about it here.

br0adband - if you post your question on the mailing list, we can take it from there.
 

br0adband

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Location
Springfield MO
Well I was toying around with some ideas this morning and I kept thinking that with an RTL stick and SDR, that works like a virtual discriminator tap of sorts so... I created a new Unitrunker receiver (Signal) using Discriminator for the Model, the audio port being my first VB-Audio Cable, 48000 sampling rate, etc. I then fired up SDR# and tuned it to the control channel for S.N.A.C.C. (854.7125 MHz) and voila, Unitrunker latched right onto it without a single issue.

Then I attached my second RTL stick, fired up a cloned copy of SDR# with the Trunker plugin functional and hit Play and voila a second time, it works great and it doesn't have that weird screwball audio interference that using Unitrunker for both receivers seems to do. In this instance and this different way of accomplishing things it's working better than I thought possible (still can't just hold on a talkgroup but that's a given).

It even works great for trunked P25 monitoring as well since the "Voice" clone of SDR# (for P25 use) is assigned to VB-Audio Cable A and I tell DSD+ to monitor that for the input and, well...

VOILA!!! :D
 
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