VXR-7000 DCS ?

[trlrdrdave]

I am looking at a Vertex vxr-7000 that has a trashy looking DCS wave form. It decodes DCS fine but some model portables will not decode it most of the time. A Kenwood 2180 works fairly well but the newer models just don't want to decode it. DCS level is at .43 khz. Any vertex gurus run into this? I have already thought about outboarding a comspec dpl board on it. All 4 repeaters that were bought at the same time do the same thing. A kenwood in its place works perfectly.

 

[n1das]

I am looking at a Vertex vxr-7000 that has a trashy looking DCS wave form. It decodes DCS fine but some model portables will not decode it most of the time. A Kenwood 2180 works fairly well but the newer models just don't want to decode it. DCS level is at .43 khz. Any vertex gurus run into this? I have already thought about outboarding a comspec dpl board on it. All 4 repeaters that were bought at the same time do the same thing. A kenwood in its place works perfectly.

Maybe try cranking the DCS deviation up a bit and see if decoding improves on the problem portables. Also does the Vertex repeater have a DCS balance adjustment to correct any DC offset in the waveform?

I dealt with sort of a similar problem with an Icom IC-FR4000 repeater I had on GMRS a few years ago. The waveform looked nice and not trashy but the edges were so rounded off that some radios had trouble decoding DCS. Cranking the deviation up as a workaround solved the problem. Fortunately the edges were rounded enough that it didn't cause the waveform to become audible and annoying. The portables having trouble decoding with the deviation set to spec were expecting a waveform having sharp edges. My Kenwood portables always decoded 100% perfect but others had problems until I cranked the DCS deviation up in the Icom repeater's transmitter.

Also check to make sure the Vertex repeaters are operating dead nuts on-frequency. DCS decoding is sensitive to errors in the transmit or receive frequency. Frequency errors introduce a DC offset in the recovered waveform and blocks what the decoder sees for a waveform. It usually shows up as failure to decode or very slow or intermittent decoding. If the frequency errors are greater than a kHz or two, you can expect problems decoding DCS.

Good luck.

 

[trlrdrdave]

I don't see any way to adjust just the DCS at all just an IDC pot. Repeater is right on frequency. I'll play with it, turn it up and down a little and see what happens.

 

[ElroyJetson]

I've set up, programmed, and had to adjust quite a few VXR-7000s. I found that every one of them had, as you say it, trashy DCS waveforms. The DCS circuit is not well designed and implemented in those repeaters.

Those repeaters are also a common factor in several multi-repeater systems that I've worked on that always had interference issues that I was never able to pin down and fully correct.


If I recall correctly, the TIA 603 spec for digital squelch levels is 8 percent of peak deviation.
That'd be 200 Hz for 2.5 KHz deviation.

In practice, it seems to be all over the map. Motorola always said to set for 300 Hz in a wideband channel, and half that for 2.5 KHz deviation narrowband.


Figure me this: I've had radios cross my bench that worked fine with one repeater and wouldn't open PL or DPL squelch with another repeater of the same brand and model. Both repeaters were aligned as precisely as my 250,000 dollar's worth of calibrated, certified test equipment on my service bench would allow.

Same frequencies, same PL/DPL, same modulation levels for audio and tone/DPL. Everything is exactly the same as far as all the test equipment can determine.

But the specific portable radio doesn't play nice with one specific repeater. Consistently.

I was thinking of calling an exorcist.

I called the repeater manufacturer. Their tech support guys asked me to check the repeater firmware
revisions.

They were different.

The problematic one had older firmware.

They sent me the firmware update kit and I updated both repeaters to the newest firmware revision.

Problem solved.

Not even the factory techs could explain why.

There was absolutely no measureable difference in any performance parameter of the repeaters
that I could analyze.

I guess the new firmware had been exorcised. Demon in the machine gone.

It's as good an explanation as any.

 

[trlrdrdave]

May try that. Although 3 of them are brand new under warranty doing the same thing. I never had this trouble with Motorola. DPL deviation on wideband is always 700 hz and narrrow band should be 350 hz.

 

[ElroyJetson]

To add to my previous comments, what was REALLY interesting is that the problematic repeater issue only occurred on certain specific DCS codes. And according to other test equipment, there was nothing at all unusual about any aspect of those DCS pulse trains as compared to the identical pulse train coming from the other identical, identically programmed repeater that didn't cause the problem.

Absolutely mystifying. I can not explain this.

This is the part where being a bench tech can be the most fun and the most annoying.