Radio Shack Pro-97 oddity

[MCWKen]

I realize that it is old and outdated, but I found an interesting shortfall yesterday. We have had severe sub-zero temperatures in the Midwest the past few days. I took that scanner outside for about a half hour. I found it odd that there all of a sudden was no traffic on the 800mhz trunked system we have in the county. I knew the plows were out working, and I knew that the Sheriff's department had a lot of stalled/dead/ditched vehicles out in the County. All I heard in that time the VHF State Patrol.

As soon as I got upstairs, put the scanner on the desk, and turned the Whistler 1040 on in the other room. Sure enough lots of radio traffic on 800mhz , but nothing from the Pro-97. Put the radio over the heater, and in 20 minutes, it came back to life. I thought nothing of it at the time. So today, went out and did my thing, had the Pro-97 in my pocket. After 10 minutes, again 800mhz fell silent while I heard the State Patrol rescuing drivers from dead semi's.

For kicks, took the Whistler with me as I ventured out down the parking lot this evening, then warmed up the van. It did not blink an eye, no noticeable change in performance.

I have had Motorola's and Kenwood's outside in this kind of weather, the only issue was the batteries, but not the radios. Since 2007, never had the Pro-97 give me problems in any weather. I found this odd.

 

[6079smithw]

Sounds like an intermittent caused by contraction... bad trace/solder joint/ribbon connector. Age, wear from vibration. Motos and Kenwoods are built for commercial use; can't say the same for a PRO-97 of which I own 2. Haven't had either of mine outdoors for years though... (Another reason to root for Spring!)

 

[RFI-EMI-GUY]

The reference oscillator that sets the receiver frequency has likely drifted over all these years. Setting it is easy if you know how to do it and have some type of frequency counter or meter. When it drifts, getting either to hot or cold will cause the control channel to be misread.

The other thing to watch for is humidity and condensation on the circuitry. Get it way cold outside, breath on it or duck inside for a cup of coffee and the humidity will short out the workings.

 

[MCWKen]

Both the radio and operator are old, and both do not work as well in this kind of weather (it was -26° with a wind chill).

Since being inside, it has been working as expected. I found it odd that VHF worked fine, but not on 800 Trunked. Next time it happens, for kicks, I will manually scroll down to the control channel, and see what it is telling me. Did not think of that at the time.

 

[slicerwizard]

Wind chill is not relevant for unheated electronics. Reference oscillator drift has far more impact on 800 MHz reception vs VHF; PPM error and all that...

 

[MCWKen]

The -26° was the ambient temperature, not wind chill.

 

[slicerwizard]

Ah, ok - well there you go - goodbye flaky oscillator.

 

[RFI-EMI-GUY]

I was looking at statistics for certain 800 MHz radios that were being PM'd a while back. The data suggested that in the first 18 months the oscillators would drift enough to put them just outside the required NPSPAC band frequency tolerance. They will drift as they age, and in 18 months they drift a lot. If sometime in the second year or beyond they maintained their stability long term.

I ran into this on a 11 GHz digital microwave project. The crystals were "green", not aged and as they aged, there would be errors in the system while, I assume, the receiver AFC corrected. The vendor obtained new crystals that were burned in.

Crystals age and drift. At some point they need to be touched up.



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