Onondaga County Garbled on BCD996T

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PCN

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Marcellus NY
I'm having a problem in Marcellus at the lower section by the creek with half the transmissions being garbled. I understand this could be a problem of more than one tower being received at once. I had to put an outside antenna up to get any decent signal at all. I think I am getting either Rose Hill, Skaneateles or Stump Road Towers. I read in the minutes on the Onondaga County Radio Web Site that they are in the process of changing licenses to move the Stump Rd. Tower to better cover Marcellus, which should give me a decent signal and might help knock out the weaker ones that I assume are creating the problem..

My radio (BCD996T) does not do this and works fine at the NuTronics store as well as my summer camp on Skaneateles Lake that has a line of site location to the Rose Hill Tower.

About half of the transmissions are garbled and sound like they are off frequency. I monitor the EMT Dispatch and the Fire Dispatch repeater on a seperate scanner (460.025 EMT and 453,850 Fire).

I monitor talkgroups 45,46,48 and 51 on the BCD996T.

Is there another radio available that might handle this problem better than the Uniden?

Normanpc@aol.com
 
D

DaveNF2G

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Short answer: there is no scanner that will work better.

Please search this forum for the other thread(s) about this system. The simulcast problem and its solutions have already been discussed extensively.
 

studgeman

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You pretty much have what you have. My Pro-96 refuses to decode it anywhere I am, and has the same problem on other CQPSK systems. It will take a major design change from the scanner manufactures to correct this. Uniden and GRE do all their digital decoding off an FM discriminator. CQPSK "kinda" works with FM, so you "kinda" get a decode, they have to go to a direct DSP to actually get it to work. To that end a USRP with GNU radio and the OP25 package work quite will when set up properly.
 

KA1RBI

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Portage Escarpment
You pretty much have what you have. My Pro-96 refuses to decode it anywhere I am, and has the same problem on other CQPSK systems.
You would find that if you tapped the 455 KC I.F. of your PRO-96 and fed that I.F. to a DSP receiver such as the one you mentioned below, your DSP receiver would output a clean signal, all the while the PRO-96's speaker was outputting its usual stuttering, popping, mouthful-o-marbles, breaking up, constantly jumping between digital and FM modes, constantly losing sync (etc etc etc etc) in its valiant attempt to copy the sig.

I've actually done this test on a PRO-2096. The 1980's PRO 2006 is even superior still, due to its RF front end.

It will take a major design change from the scanner manufactures to correct this. Uniden and GRE do all their digital decoding off an FM discriminator. CQPSK "kinda" works with FM, so you "kinda" get a decode, they have to go to a direct DSP to actually get it to work.
The OP is exactly correct. They "merely" have to move the DSP signal tap point from AFTER the FM demod (how they do it now) to before it. This is the REAL reason why today's crop of "digital" scanners don't cut the mustard with LSM/CQPSK. The homebrew disc-tap crowd who all hang out on "Trunking Control Channel Decoding" will likewise also have to move upstream someday, to keep up....

Conceptually, it's known as pre-detection sampling or something like that, whereas scanners with the disc taps are in the post-detection category of sampling. In the particular case of LSM/CQPSK, the signal is irrevocably mangled when it passes through the FM demodulator stage...

To that end a USRP with GNU radio and the OP25 package work quite will when set up properly.
Best Regards

Max
 
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DaveNF2G

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Are you saying that we might be able to "tap" a scanner at a different point to acquire the signal where it can be processed better externally?
 

KA1RBI

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Messages
544
Location
Portage Escarpment
Are you saying that we might be able to "tap" a scanner at a different point to acquire the signal where it can be processed better externally?
Yes. And no maybe about it... It does require new skills on both the hardware and software side. In the case at hand the IF to be tapped is generally 455 KC whereas soundcards typically top off at 48 (assuming a 96K samp rate). So typically there's an additional IF down-converter stage. Mine goes from 455 KC to 24 KC. For more info you might check out this page which covers details and links to another page with full plans and diagrams (sigh, I need to spruce these up a bit ... someday)...

LSM Gallery

73

Max
 

MattSR

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Joined
Jul 26, 2002
Messages
395
Location
Sydney, Australia
Are you saying that we might be able to "tap" a scanner at a different point to acquire the signal where it can be processed better externally?
Max is saying that he has done it, tested it and built it, and modelled it in GNUradio, and also compared it to native demod done in a USRP.

And it all works perfectly on simulcast - I've heard the audio. :)
 

SCPD

QRT
Joined
Feb 24, 2001
Messages
0
Location
Virginia
I'm having a problem in Marcellus at the lower section by the creek with half the transmissions being garbled. I understand this could be a problem of more than one tower being received at once. I had to put an outside antenna up to get any decent signal at all. I think I am getting either Rose Hill, Skaneateles or Stump Road Towers. I read in the minutes on the Onondaga County Radio Web Site that they are in the process of changing licenses to move the Stump Rd. Tower to better cover Marcellus, which should give me a decent signal and might help knock out the weaker ones that I assume are creating the problem..

My radio (BCD996T) does not do this and works fine at the NuTronics store as well as my summer camp on Skaneateles Lake that has a line of site location to the Rose Hill Tower.

About half of the transmissions are garbled and sound like they are off frequency. I monitor the EMT Dispatch and the Fire Dispatch repeater on a seperate scanner (460.025 EMT and 453,850 Fire).

I monitor talkgroups 45,46,48 and 51 on the BCD996T.

Is there another radio available that might handle this problem better than the Uniden?

Normanpc@aol.com
Some items of note....

Stump tower is being moved. It is not due to coverage, it is due to location. It is only moving 500 yards down the hill. I highly doubt this will enhance any coverage in the village.

I can talk on a portable from the basement of the village PD and have no issues with garbled audio.

I would suggest trying a yagi antenna pointed to the closest tower site with antenna's pointing to you. What I mean is all sites use directional antenna's. If you point to Rose and Rose is pointed to the East or West it wont give you the signal increase you need to ungarble your scanner. I dont recal what site covers Marcellus the best.

I know there are also some settings in the bearcat that should be looked at.

Hope this helps a bit.
 
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