Narrowbanding

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muhockey86

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Does narrowbanding affect CTCSS tones? Here's what I'm getting at. I have a vx 454. Currently our county is still operating under wideband. I updated some things on my radio and went ahead and changed all of my frequencies to narrow, thinking the only consequences would be some coverage loss and minor distortion. I have one channel set up with an MDC1200 identifier. Before switching to narrowband, it would work and transmit the id. After switching, that channel no longer opens up the repeater. Any ideas?
 

12dbsinad

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The quick answer to your question: No, CTCSS and narrowband are not related. In saying that, a CTCSS tone does not need to change when switching to narrow. It is just reduced deviation (from 5 to 2.5 Khz +/-) and has really no relation to PL/DPL other than just that. However, sometimes agencies will decide to change these codes to prevent a non narrowband compliant radio to access the system unless it is reprogrammed, or because of other issues like interference form a co channel user when conditions are just right, or something along those lines.
 

jackj

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I think that CTCSS deviation will have to be reduced also when a radio is narrow-banded. I base that on logic, not direct knowledge. It would make sense that, if the system deviation is reduced, then all aspects of system deviation would be reduced including CTCSS.
 

12dbsinad

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I think that CTCSS deviation will have to be reduced also when a radio is narrow-banded. I base that on logic, not direct knowledge. It would make sense that, if the system deviation is reduced, then all aspects of system deviation would be reduced including CTCSS.
As far as mobile and portable radios are concerned, when selecting between wide/narrow on a particular frequency all audiable and sub audiable (CTCSS) are automatically adjusted to the correct deviation.
 

SCPD

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Your CTCSS deviation is probably not enough to be recognized by the decoder in the repeater
 

Thunderknight

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Your CTCSS deviation is probably not enough to be recognized by the decoder in the repeater
I concur. That is the most likely answer.

In narrowband mode, you are looking at only about 300Hz of tone deviation, where as in wideband it's around 600Hz.
 

muhockey86

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I know the CTCSS hasn't changed. I have the frequency programmed in a few times. One channel as a pager, one normal, and one with a MDC 1200 identifier. The one with the MDC is the only one that has stopped working. I've confirmed that it's still giving the correct code and that the transmit frequency is still correct.
 

muhockey86

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Both, since I've switched that frequency to narrowband, I can't hit the repeater. I haven't noticed if its receiving radio traffic or not. Every time I switch over to it the radio traffic dies down. I know I'm not missing anything due to the fact the base station radio being silent as well.
 

mancow

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Some Vertexes area pain to narrow band. Our VX4000s had to be retuned due to modulation levels being very low for voice and very high for ctcss. Each one needed it after narrow was selected.
 

kruser

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I had a similar issue with three of our VHF PSR400's.
When I changed them for narrowband operation, they would key the repeater just fine but three of the 400's would no longer open the receive audio or if they did, it was very delayed. Like 5 seconds of delay before the receive audio would open.

I use DPL though. On those three radios I just turned off coded squelch on receive as we don't have any other users nearby on the freq anyway but some day I'd like to investigate why they did this.
The repeater was switched to narrowband prior to the portables and those three portables did still work fine at that time so I'd think my problem is in these three portables.
I thought about switching everything over to PL for a short test but there are many radios so not a good option if it worked and I had to reprogram everything.
The receive audio on the three odd portables sounds fine also so this remains a mystery. Switch them back to wide and they work fine again with DPL on.

One think I keep forgetting to check is if the software version on the three troubled radios is different than the others that worked fine.
 
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RKG

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1) The MDC decoder in a radio's receiver requires a certain audio level in the audio available to it, which is tapped before the high-pass audio filter. That level is equivalent to a deviation of nominal 750 Hz in a wide band channel (about 15% of max deviation), though from experience most radios' decoders will work down to an audio level equivalent to about 450-500 Hz (or about 9-10% of full deviation).

2) If you program a subscriber for narrow band and then transmit to a base station that is still programmed for wide band, you are effectively reducing the audio level fed to the station's decoder by half.

3) Theoretically, reprogramming a radio for narrowband causes a shift in the width of the IF filter's bandpass, and if that is properly done, it should compensate 1-for-1 on the reduced RF level of subscriber radios' transmitted PL. That is to say, 300 Hz of PL into a narrow band receiver should still yield audio at about 12% of max deviation, and the decoder should work.

4) On the other hand, if the station's receiver doesn't have an adjustable IF filter width, it may try to deal with narrowbanding by simply changing the amplification factor of the audio amplifier, and if that change is made after the high pass filter (so that it doesn't also goose the audio going to the PL detector), you're going to have a problem.

5) So the bottom line is that for any given combination of station hardware and subscriber hardware, you're going to have to experiment to see how narrowbanding affects PL decoding.

6) For what it is worth, virtually all of my experience involves Motorola equipment: Quantar and MTR2000 stations and Waris/Jedi/XTS or XTL hardware, and we've yet to experience a problem.
 
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