Bendix King DPH with low transmit audio on analog channel

[dave_n_s]

I've recently taken over comms management for our volunteer fire department, with a good background aviation radio, but there are always quirks that you have to bump into to know about.

While going through my "serviceable spares", I've come across two DPHs that have very low (barely audible) transmit audio volume - as received on various other handsets. Received audio is loud and clear.

That's not an RF problem as these are FM radios and the low level audio was crystal clear. Problem exists with hand mic and internal mic.

I'm perfectly prepared to believe it's an idiot operator problem (me in this case), so anything stupid I could have missed?

Is there an adjustment for transmit audio level? I have a well equipped audio electronics bench for my retirement gig, but I don't mess with things that I haven't got a service manual or good practical knowledge of as it often ends in tears!

Thanks

 

[CCHLLM]

Without a good calibrated service monitor to evaluate what the radio is actually doing with the TX and RX parameters, the best you can do by "ear" is a hack job estimate of evaluating the problem(s). A legitimate service monitor will pretty much indicate where the problems are and give you a good idea of what you need to pursue to solve the problem(s).

 

[mmckenna]

That's not an RF problem as these are FM radios and the low level audio was crystal clear. Problem exists with hand mic and internal mic.

It may be an RF issue. If you've proven that it's not the microphone, and it does it with an external mic, that suggests that it's either an internal failure, or the deviation has way out of whack.

I'm perfectly prepared to believe it's an idiot operator problem (me in this case), so anything stupid I could have missed?

Make sure the radios (both this one and the one you are receiving with) are all set properly on the deviation/bandwidth for the channels. A wide band receiver will hear a narrow band transmission as very quiet.

Is there an adjustment for transmit audio level? I have a well equipped audio electronics bench for my retirement gig, but I don't mess with things that I haven't got a service manual or good practical knowledge of as it often ends in tears!

There is. Deviation, mic sensitivity, etc. But, still may be a failed component or programming issue.

The correct tool for this is a service monitor. Last one I purchased new was $40,000.

When it comes to radios used in any sort of life safety application, you need the right tools and knowledge. The FCC has some specific rules about how radios work, and setting things 'by ear' is not going to fly.
It's one thing to mess around with old radios for amateur radio use, the rules are allow for a bit more slop there. But on the public safety side, any radio that is exhibiting issues deserves a trip into a shop with a knowledgeable tech that can align the radio correctly. When lives depend on it, you want to be 100% sure.

 

[WA0CBW]

Does sound like it could be a deviation issue (wide band vs narrow band). If you could give us the models and frequencies involved that would help. Also you might check your license to see if it reflects the January 2013 FCC mandate for narrow banding.
Bill

 

[dave_n_s]

Apologies for slow response - I thought I'd set alerting for this post and hadn't and much appreciate your responses. With 40+ years in aviation, many of those in flight test as test director in the extremely noisy sector of aviation, I don't mess with anything that I shouldn't, however I am prepared to investigate documented settings that could be incorrect and reprogram correctly. It's just a bit of a learning curve on this particular equipment.

Per the docs I've found, if it is deviation, it doesn't appear that it can be set to say Narrow / Wide without going into Tune mode and having the test equipment I don't have, so off to our repair shop?

This is a GPH5102XP (and it's a GPH Plus of course, not a DPH per the title) and an example frequency is 153.45500, in case that helps someone identify a legitimate non-test set parameter change.

 

[mmckenna]

Depending on the vintage of the radio, wide or narrow should be selectable for each channel via programming software.

If the radio is set correctly and it's still under deviating, then yes, it needs a visit to Mr. Service Monitor.

For -ANY- sort of public safety application, it's a real good idea to have all your radios get benched periodically to make sure they are still meeting factory specs. That'll extend their useful life, and will weed out radios that have no business being on the front lines.

 

[dave_n_s]

mmckenna, thank you, yes these can be selected to Narrow (12.5) or Wide (25) and the channel in question is correctly set on both radios.

I agree on the periodic checks philosophy. Given my aviation background, for equipment that works or doesn't "on-condition" maintenance is the right approach, but where things can drift and particularly with the interesting terrain that we operate in, knowing whether we have a radio or coverage issue in the many nooks and crannies w.r.t. our repeaters or simplex is important.

Two more questions if I may:

Is there an accepted periodicity for bench checks for old BK handsets?

Are there any recommended tools for mapping VHF coverage over terrain?

Thank you.

 

[mmckenna]

Is there an accepted periodicity for bench checks for old BK handsets?

I don't know about anything specific to old BK radios, but...
I ~try~ to do once a year on ours, and will do it specifically if a user complaint matches up with something that could indicate a misaligned radio.

The older the radio is, the more likely you need to check it. As the components age, they drift.

Are there any recommended tools for mapping VHF coverage over terrain?

Yes, from free to very expensive. You get what you pay for. If you have concerns with your system coverage and are considering an upgrade, a professional consultant will have the correct tools and will more than pay for themselves in the long run.

There's some free ham radio oriented stuff out there that will work.

Or, you can go ridiculously expensive but downright amazing software:

Best Radio / Wireless Planning Software - EDX Wireless

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