[grc] LPFM transmitter advice

[Paul Bame]

1. That Nicom is fairly simple so I've no doubt it can be repaired by Nicom
or by some others who do that sort of work (I don't have names though, and
it's been a while since I had one open).

2. It's not clear to me if "degraded signal or silence" refers just to
audio problems, or to the forward+reverse power as well -- guessing the
former.

3. Problems with audio like that are frequently due to cable+connector
issues. I'm sure you've already checked all the connectors in the audio
path (inside and outside the TX) for corrosion/oxidation, shorts, and
failing solder joints. Those symptoms can vary with moisture or temperature.

4. Mysterious problems in equipment that age almost always demand
evaluation of especially the larger electrolytic caps in the power
supplies. Re-capping is a very common repair, and might be a part of any
"reconditioning" anyway. Easy to DIY too.

5. An easy and sometimes-fruitful check is to put a 'scope (or a voltmeter
set to /AC/) on all the DC power rails (especially near that audio chip).
When power-supply filter caps fail, you can sometimes see it as an
appreciable AC voltage with this test even while a DC voltmeter might also
show the right voltage.

6. The FX-30 I doubt is approved for LPFM, plus the temporarily-lower
power... an engineering STA application might be wise.

7. To fully flesh out an older transmitter like that, I'd add an external
audio processor and a phone and/or web interface to monitor power etc and
do basic transmitter remote control (BT WVRC4, Burke, Sine Systems). New
transmitters put audio processing, RDS, settings, control and monitoring in
one integrated web-controllable package. My current recommendation is the
Ecreso line by Worldcast Systems (given the demise of BW) unless someone
wants to drop another couple $K on a Nautel or something.


##
Paul (he/him) (pablito) Bame
Engineering Director, Philadelphia, Prometheus Radio Project
<http://prometheusradio.org/>
215.727.9620 x2 / 970.988.3849


On Wed, May 25, 2022 at 9:12 AM Robert Park via grc <grc at maillist.peak.org>
wrote:

> For more than a decade WIDE-LP in Madison WI has operated successfully with
> a reconditioned NiCOM NT 250/LCD transmitter. In recent weeks we have had
> an increasingly serious problem with periods of degraded signal or silence
> followed by spontaneous recovery. We have traced the problem up the line as
> far as the audio chip in the transmitter. As a result we have switched out
> the NiCOM for an older FX 30 that now has us reliably back on the air, but
> at half our allowed 100 W ERP.
>
> To return to normal operation we need to decide whether to repair,
> recondition or replace the NiCOM. Advice from this list would be
> appreciated.
>
> Is there anyone in Wisconsin who could determine whether the audio chip in
> the NiCOM is the whole problem? If it is, would repairing the NiCOM by
> replacing that chip be a viable option?
> Is anyone else operating an LPFM station with a NiCOM transmitter?
> If we decide to repair or recondition the NiCOM is there a place in the
> midwest folks would recommend for doing it? Would it be best to ship the
> NiCOM to the company <https://www.nicomusa.com/> in San Diego CA?
>
> Bob Park
> Program Director
> WIDE-LP 99.1 FM
> http://widelp.org/
> email: radio at widelp.org
> https://twitter.com/WIDE_LP
> https://www.facebook.com/WIDE.LP.99.1/
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