Is There A Better Way To Find Base Freq.?

[jimlawrence]

On a recent trip to west Texas, I was trying to trunk track the UHF systems in the El Paso area using my Pro-96. I was interested in three UHF systems that can be heard there, all in the 406-420 MHz range.

Here are the systems in question:

http://www.radioreference.com/apps/db/?sid=3906

http://www.radioreference.com/apps/db/?sid=4328

http://www.radioreference.com/apps/db/?sid=3332

I found the info. about the systems here in rr wasn't exactly correct. Specifically, the base freq. for the systems didn't appear to be correct (rr used to show 406.0 as the base freq for the systems, with offset as 380, step as 12.5) As I programmed in the two systems I could hear in the upper valley (west) portion of El Paso, my Pro-96 would show talkgroup numbers and frequencies (all right around 406-410 MHz) but wouldn't produce any audio using those settings. Since my wife was happily shopping at the Outlet Mall of El Paso at the time and I knew I'd have L - O - T - S of time, I decided to try an experiment. I started to program a new base freq. starting with 406.0125 and increasing it in .0125 steps until, finally, the -96 started decoding and tracking the systems properly with base freqs of 406.6125 and 406.1125. I focused on one system's base frequency at a time; I didn't try to work on both systems simultaneously.

Is there a better way to determine a UHF base freq.? Boundary condition: no computer can be used. This all has to be done using only the Pro-96 and the info. the display gives.

Flushed with success, I then turned my attention to another system in the area that also wouldn't track correctly with the info. in the rr database (the Fort Bliss system linked to above). But this one really gave me strange results! No matter what base freq. I used in the 406 MHz range, my Pro-96 showed freqs. in the 472 MHz range. And no audio, of course. This suggested to me that not only was the base freq. incorrect in my Pro-96 but probably also the offset was incorrect as well. Unfortunately, I didn't have enough time to experiment with this system as my wife ran out of money and was hungry and cranky after a long day of shopping (Let that be a lesson to you single men. It's a tough life, gentlemen).

Any suggestions or ideas?

[LEH]

Well, the base for these systems is usually going to be between 406 and the lowest frequency in the system.

Is there an easy way to determine the base frequency? I recall reading, and I think it was on this site, an article (it was) that tells how to determine the base and offset.

I tried working with it once, but math has never been my strong suit, so naturally it didn't work for me.

There was some discussion in the New Mexico forum (maybe the military) on the White Sands system late last year. Seems there have been some changes and no one has (or had at the time) figured it out. You may want to search for that one to see what the story is now.