Discriminator audio over ethernet

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Markb

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Don't know if this is the best place to post this question but here goes.

My only computer is a laptop and I am trying to set things up so I don't have a bunch of USB and other devices tethered to the computer. The project is going well, but the last thing I'm trying to solve is how to make Unitrunker work on my laptop without having a radio attached directly to the computer.
I mounted my wireless router and all the other devices on a wall in a closet, where I'd also like to mount one of my discriminator-tapped radios. I bought a cheapie USB soundcard (like 99 cents cheap) on Ebay and attached it to a Lantronix Ubox (USB over Ethernet) and then attached the discriminator audio output to the soundcard. I get audio to trunker, but it doesn't look right on the scope and the best decode rate I get is in the 40-50 range, obviously not enough to bring up my local TRS. I don't know if it would be a matter of buying a better USB sound card or if discriminator audio won't be reproduced properly over Wi-Fi. I know that there are a lot of places where this could get fouled up, but I think it would be sweet to be able to make this work. My other thought was bluetooth between the scanner and the Ubox.
Anyone have any setups like this or any ideas?

Thanks,
Mark
 

RKG

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Trunking control channel data is digital data in analog audio form (AFSK). In order to transmit analog audio over IP, you have to digitize it, which is done by sampling the analog audio, converting the samples to a digital voltage value, transmitting this digital information, and then reconstructing a facsimile of the input audio at the other end via the transmitted data. If the reconstructed wave form deviates too greatly from the input wave form, the reconstructed AFSK data will be corrupted.

Doing this is not impossible; at least one company I'm aware of has done it (the CTI MCN IP interface), and we have had pretty good luck transmitting AFSK data generated by Zetron Station Alerting panels over fiber optics (which, while not in IP format, do involve vocoding). However, you need some pretty good equipment to make it work.
 

spadoinkle

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Interesting solution you have there. I checked the specs of the UBox, there seems to be two models. The 2 port model is "high speed" which means it supports 480Mbit. The 4 port model is deceptively called "full speed" which actually means 12Mbit. While I think both should be able handle the full sampling rate of your sound card, it could be an issue to check into. One thing I think you should try is to connect the USB sound card directly to your laptop and see how that works. If you get the same symptom then you know it's the sound card, try a better one. If it resolves the issue, then try connecting the UBox directly to your laptop with a cross-over cable. If you get the symptom there, then it's the UBox causing the problem. If it works, then hook the UBox back up to your wifi network and try again from there.

Hope that helps.
 

spadoinkle

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I stumbled across the UBox 2/4 port manual and it confirms the low I/O rates of these devices.

From the manual: http://www.lantronix.com/pdf/UBox_UG.pdf
"The UBox 4100 can sustain, depending on conditions, approximately 5-6 Mb/sec
throughput. The UBox 2100 can sustain, depending on conditions and transaction
types, approximately 12-15 Mb/sec."

The other issue is that the UBox driver on your laptop may also be a bottle neck. Again, since these things seemed to be primarily aimed at use with printers it might not be able to keep up with streaming data like an audio feed. However, the highest data rate you should be able to get from your discriminator input is around 150Kb/s (with a sampling rate of 44k), and that is well within the stated capability of this device.
 

js_scan888

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The signal data has already been sampled with the USB soundcard. This data is being transfered to the laptop. The UniTrunker program is then trying to re-sample the data that has already been sampled in the first place, causing the problems. If you have to, sample with the USB soundcard as fast as you can (192 Kbps), this will help when the data is re-sampled in the UniTrunker program (48 Kbps or 96 Kbps). I think the best solution is getting the UniTrunker program updated to accept an internet UDP socket connection as an input data option.
 

Markb

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I have been having issues with this sound card. Here's the link to one on ebay - USB 2.0 to Mic/Speaker 5.1 Audio Sound Card Adapter NEW - eBay (item 250550162291 end time Feb-15-10 07:33:10 PST)
I installed this one and it shows as an option on trunker and I do get audio passed into trunker, but not out the speakers of the laptop.Finding a better sound card is my next step in troubleshooting the problem, but I was hoping to see if it's even possible before I drop any more cash on the experiment.
I'm also running an Airnav Radarbox though the Ubox, so maybe I'll double check and see if that is too much for the ubox to handle.
Thanks for the Ideas so far.

Mark
 

gmclam

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I have been having issues with this sound card. Here's the link to one on ebay - USB 2.0 to Mic/Speaker 5.1 Audio Sound Card Adapter NEW - eBay (item 250550162291 end time Feb-15-10 07:33:10 PST)
I installed this one and it shows as an option on trunker and I do get audio passed into trunker, but not out the speakers of the laptop.
I bought these cards from eBay. I am using them to stream some scanners around the house here right now (but not discriminator audio). You have to realize that these are SEPARATE sound cards, so there is no "path" for the audio from the USB sound card to the sound card your speaker is connected to.

One comment on your original question/issue; I'd use the highest sample rate supported to get the discriminator audio from the laptop to your PC with UniTrunker. I'm thinking something like DVD audio quality (96kHz).
 

Markb

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Success!!!!

Well, I went out this morning and bought a Soundblaster external sound card and after a little bit of tweaking, I have Unitrunker decoding my local Smartzone system with a 96% decode rate and I'm wireless!

The only problem I have to figure out is why the Ubox appears to be dumping all the connections to it periodically (started prior to the Unitrunker setup)..... Other than that, things are looking good! Thanks for all the advice.

Mark
 
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