Squelch opening problem when scanning

g8tzl2004 · Post by **g8tzl2004** » Thu May 04, 2006 7:15 am

I have a 4 channel (no scan) GM350 , a 10 channel LCS2000 (LCD with scan) and a 128 channel GM950 (LCD and scan). I am using carrier squelch. CTCSS is not an option.

With the "no scanning" GM350 , I can lower the squelch in RSS to just above threshold and it works great - opens on the weakest of signals.

With the LCS2000 and GM950 , I can also lower the squelch to just above the noise threshold - again , the squelch will open on very weak signals and works well . BUT if I then start scanning with either the LCS2000 or the GM950 , the squelch keeps opening every few seconds. As I increase the squelch level in RSS , the frequency of the "false" squelch openings is reduced ( ie once every 60 seconds) but I have to increase the squelch threshold right back to the "factory level" before the false squelch openings stop. At this level , I miss weak but readable signals.

I think the false squelch openings is due to internally generated hash when scanning - if I remove the antenna , the squelch still opens - so it must be linked to the scan function?? Also , its not an internal "birdie" as the squelch opens on different channels each time , not the same channel. Also there is no problem on any channel when NOT scanning - infact , you can lower the squelch back to the noise threshold and it works well when not scanning. There is also a big difference between the squelch RSS settings ie threshold is around a setting of "17" but you have to increase this all the way to "34" to stop the false openings when scanning.

Anybody else experienced this problem - I am getting it on 2 "similar" radios so I don't think its a fault condition?

jackhackett · Post by **jackhackett** » Thu May 04, 2006 9:00 am

Congratulations, you've discovered that Moto radios are not ham radios designed for weak signal work.

During scan the radios is changing frequency quickly and sampling each scan channel for a very short time, it doesn't have the luxury of sitting on a single channel where it can constantly sample the noise level, so the squelch level isn't going to be able to sit just above the noise and not false periodically.

If you turn the squelch below the factory default you're going to get false unsquelching during scan, especially on CSQ, that's probably why they set the default where they do.

g8tzl2004 · Post by **g8tzl2004** » Thu May 04, 2006 4:10 pm

I actually find my various Moto radios better for weak signal work than most of the "so called" ham radio sets - most of which are built with wide open front ends and poor intermod performance. Infact , most of my Moto sets also have better front end sensitivity!!! Its just the squelch circuit on some models which play up when scanning at the noise threshold

However , I have other Moto sets , such as a GM900 which scans great right on the squelch noise threshold with no false openings!!

I am just setting up a Moto MC Micro which does not have scanning but the squelch can be set to open on the weakest of signals and rejects wideband computer hash etc - 20 channels , LCD display and only cost $3 - these older sets are basically being given away but can outperform most of the modern expensive ham radio sets!!!

RKG · Post by **RKG** » Thu May 04, 2006 4:29 pm

One thing to remember--though this won't be of much comfort--is that Motorola stuff was never designed to win DX awards. There are standards in the public safety world that, if successfully applied, tend to set a minimum signal strength that public safety receivers can expect to see.

g8tzl2004 · Post by **g8tzl2004** » Thu May 04, 2006 4:44 pm

I have numerous (too many to count !!!) , LMR and ham radio rigs. I still find the front end sensitivity of most of my Motorola sets to be better than an equivalent ham radio set - something like 124 dBM for 12dB SINAD which is very very good. I have done numerous real world weak signal tests and the Motorola always wins!!! Its only when you have to program a Motorola "out of band" that you loose a few dB's eg programming a 438-470 Mhz GM300 programmed down to 433 Mhz for the UK 70cms allocation - but its still in band for the US 440Mhz allocation!!!

jackhackett · Post by **jackhackett** » Thu May 04, 2006 6:39 pm

Hmmm.. maybe I've just come to not expect good equipment from Moto anymore. I always figured amateur radios would be better performers, I stand corrected.

Post by Pj » Thu May 04, 2006 9:58 pm

I find with the older M radios that putting radio's into scan "increases" its sensitivity with weak signals (spectra's/syntors etc) if thats sorta the correct wording.

With the newer ones and the ASTRO's, I find no difference..other than a slower (and annoying) scan speed.

(No, the radios are not scanners, but when there is a significant lag in scanning 16 channels when you miss a good deal of conversation its an issue)

g8tzl2004 · Post by **g8tzl2004** » Sat May 06, 2006 7:28 am

I originally thought that the squelch threshold in scan mode was lower than in non-scan mode - but then when the squelch opened with no antenna connected , I assumed that it was due to internal noise or something.

It would be very useful if you could actually alter the squelch threshold in scan mode - so I could keep the squelch at the minimum threshold for "non-scan" monitoring but then be able to scan at a higher squelch threshold to prevent the false openings.

I have other makes of LMR sets where you can do this - maybe there is an option in Moto LAB RSS which enables the seperate setting of scan squelch levels?