Problems with DCS Decode and scanning

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Brian7M3

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I submitted a ticket to GRE regarding this problem and wonder if anyone else with a PSR-500 is having the same problems or has any suggestions.

Thanks ...

"I just bought a new PSR-500 and received it last Friday. I am very happy with the unit, however I am having a few problems...

1) On frequencies with DCS enabled and the code specified, I am having issues with the audio dropping out for a brief time during the transmission (less than .5 to 1.5 secs). I changed the HD5 Fade from 2000 to 2500 and this helped quit a bit. Unfortunately, I can't increase the value past 2500. If the unit let me, it might resolve the problem entirely. I tried adjusting some of the other settings (HD2 Qualify and HD2 Holdoff) but that didn't seem to help so I put them back to default.

2) When scanning, the unit will make several passes over an active conventional object before stoppiing on it. It usually misses the entire transmission. I do have either CTCSS or DCS selected for these and the exact tone is specified. I can transmit for 10 seconds or more with the scanner going right past the object before it finally stops on it.

Thanks,
Brian"
 

Viper43

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If your transmitting near the scanner your probably overloading it which is why it won't stop on that channel.
 

wmbio

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I had this problem with my Pro-97 but never with my PSR-500! DCS is perfect and it never skips a transmission.
Make sure you have all Priority scans turned off, also make sure your not scanning for a SAME alert on the weather frequencies.

Speaking about overload, that can happen, try turning ON the ATT for the channels your having trouble with....that sounds crazy but it does work.

73's
Wmbio
 

RoninJoliet

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On my PRO96 and 2096 on signals that the dispatcher is "LOUD" and a DCS active both scanners "Clip' the audio on peaks, i have to just use them with DCS search and it does not happen...However ido have a GRE500 and have not really seen this problem on the 500....I think this was a problem noticed by many 96/2096 users??...
 

Brian7M3

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Thanks, I tried the attenuator but it was still happening. No priortiy or WX priority set. The only thing that makes it not drop out (when stopped on the channel or in manual) and makes it stop on the channel properly when scanning is to set the Sq Mode to "search" for those channels. This of course defeats the whole purpose of having the scanner decode CTCSS or DCS.

BTW, this happens even if no one is talking on the frequency so I don't think it is voice peak related in this case.

Brian
 

xpawel15x

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Yes this happens to the Pro-97 with freqs programmed with the DCS code. Don't know about the PSR-500 though.
 

Brian7M3

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GRE Response

I will try their suggestions and post the results.

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With regard to your DCS question, the PSR-500 will work properly on the vast majority of stations that are using DCS squelch encoding. Unfortunately, every once in the while we see a transmitter where the PSR-500 exhibits dropouts during the transmission. It's hard to say why this happens, but there are some things that are outside of our control, such as the deviation of the DCS encoded signaling and the deviation of the voice modulation. There are three events that can cause an audio dropout. The first is a deep RF fade that is long enough and deep enough to make the radio think that the transmission has ended. This should only occur if the signal has a significant amount of noise present. The second is the loss of the DCS signaling while the RF carrier is still active, such as what might happen if the voice deviation is strong enough or has the frequency characteristics to cover up the subaudible DCS signaling. This is where the HD5 Fade parameter can help performance. When HD5 Fade is set for the default of 2000, the scanner must lose DCS signaling for two full seconds (while RF is still present) before the scanner decides that the signal is really gone and mutes the radio. Two full seconds is a LONG time to lose DCS signaling and still have RF in the vast majority of cases. Even if DCS returns for an instant after it is lost, the timer is reset and DCS must be lost for a full two seconds again. You should not get an audio hole unless DCS signaling is lost for longer than the period defined by HD5 Fade. The third event is the detection of the DCS turn off code that is sent at the end of just about all DCS encoded transmissions. The turn off code tells the radio that the transmitter is ending the transmission, and the radio mutes the receiver immediately so that the squelch tail is not audible. Occasionally, again, with certain transmitters, we have seen a falsing of the turn off code that causes the receiver to mute briefly. This can be mitigated to some extent with the HD2 Qualify setting. HD2 Qualify requires that the turn off code event last at least as long as the setting of HD2 Qualify in order for the radio to consider the turn off code to be valid. Values greater than 100 will likely not have any beneficial effect on a problem like this. You might try running the radio while connected to a computer running the Demo Application that came with the radio on the CD. While monitoring this problem signal, you can watch the HD2 and HD5 states on the screen while the audio dropouts are happening. This will tell you if the dropouts are the result of loss of DCS (HD5) or detection of turn off code (HD2). Once we know what is causing the dropouts, we might be able to experiment with a new version of firmware that allows a longer HD5 Fade value. At the end of the day, we might end up just recommending that you not use DCS on the problem channels if that's possible. I know that's not ideal, but as I mentioned sometimes we just can't get this to work right with certain transmitters. With regard to your other question, please check the PGM FUNC GLOB Sq Wait 1 parameter and ensure that it is set to the default of 10. If the problem still occurs, try raising this in increments of 5 until you get good performance. If you have to set it higher than 20 to get it to work right, I might suggest that we replace your radio with a new unit.
 

n4jri

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Very interesting. I think that the turn-off tone is around 130-140 Hz. I wonder if male voice components could be part of the problem.

73/Allen (N4JRI)
 

Brian7M3

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Update on DCS Issue

On the repeater that was dropping parts of the transmission, I know some work was done on that repeater and now it works fine every time even with the default HD5 value!

On the other DCS UHF repeater that was getting passed by several times during a scan, that still seems to be a slight issue but not as bad. I noticed that while scanning there was a VHF low band frequency with CTCSS that was getting an S3 noise level during my scan. When I locked that frequency out, it seemed to catch the DCS UHF frequency A LOT more on active transmissions. I don't know why that is but I'd rather hear the UHF one, so I keep the low band one locked out now.
 

ScanTheFreqs

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i too have a similar problem, however im not sure if its a problem or if its suppoed to work like this. when i listen to a channel that has a ctcss/dcs tone, my psr 500 NEEDS to be in search mode, or have that code programmed in for me to hear the transmission. if i have the scanner set on "none" (i believe is the setting) and the channel has a tone, i dont hear the channel. is that a problem or is it supposed to do that?
 

RKG

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On the repeater that was dropping parts of the transmission, I know some work was done on that repeater and now it works fine every time even with the default HD5 value!

On the other DCS UHF repeater that was getting passed by several times during a scan, that still seems to be a slight issue but not as bad. I noticed that while scanning there was a VHF low band frequency with CTCSS that was getting an S3 noise level during my scan. When I locked that frequency out, it seemed to catch the DCS UHF frequency A LOT more on active transmissions. I don't know why that is but I'd rather hear the UHF one, so I keep the low band one locked out now.
For what (if anything) it may be worth (and having nothing to do with PSR-500s):

1) We have found that in order for DPL to work reliably, the station sending the DPL must have its deviation nearly perfectly symmetrical and the resulting wave form sharp shouldered, with minimal slump. This is something the tech responsible for the station should check at install and every once in a while thereafter. It is nothing that subscribers (or non-subscriber listeners) have any control over.

2) We have a funny situation in my area where two co-channel users share a frequency, one using a PL of 131.8 and the other using a DPL. Whenever a subscriber of the DPL licensee unkeys, it falses falses a pulse on the PL station, which is apparently falsely detecting the 134 MHz turn-off code as 131.8 PL. And every once in a while, when the station on the PL licensee unkeys while the station on the DPL licensee is transmitting, the phase-shifted PL turn-off code is detected by the DPL station as a turn-off and causes a short drop in audio. The solution, of course, is for the PL licensee to select a different PL.
 

RoninJoliet

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The Kendall County Sherrif here in ILL is on 460.525 and uses a PL, there also "over-modulated" and constantly "CLIP" so i just leave the PL in "search", this happens on the PRO96,2096,GRE500....Ron in Joliet
 
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