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Motorola Saber 3 UHF - 5.4KHz off frequency- normal drift?

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g8tzl2004
Posts: 1091
Joined: Wed Sep 08, 2004 10:13 am

Motorola Saber 3 UHF - 5.4KHz off frequency- normal drift?

Postby g8tzl2004 » Sat Jun 23, 2018 2:44 pm

I have a UHF Saber 3 which is 5.4 KHz off frequency.

I have had other Motorola UHF stuff such as MCS2000's and MTS2000's which have been 2KHz off frequency and have warped back onto frequency OK....I guess the TXCO crystal has drifted over the years...and the drift is always greater with UHF stuff...600Hz at VHF is 2KHz at UHF etc

But is 5KHz off still "normal" drift for a 25 year old UHF Saber 3 or is there another problem with the radio?

Other than being 5KHz off freq, the radio works OK..RX sensitivity is comparable to other UHF radios as long as the test signal is +5.4 KHz the programmed frequency. I have not yet tried to reprogram/align the radio.

Thanks

Jim202
Posts: 3512
Joined: Sun Sep 09, 2001 4:00 pm

Re: Motorola Saber 3 UHF - 5.4KHz off frequency- normal drift?

Postby Jim202 » Sun Jun 24, 2018 4:31 am

I have two questions.

1. What are you using to determine the radio is 5.4 KHz. off frequency?

2. Has the device your using to measure the radio being off frequency been calibrated recently?

Just because your measuring the radio off frequency doesn't mean anything unless your using a calibrated device. Even service monitors can be off frequency if they are not recently calibrated. I own 3 service monitors and have to calibrate each of them yearly to insure they are on frequency.

Jim

g8tzl2004
Posts: 1091
Joined: Wed Sep 08, 2004 10:13 am

Re: Motorola Saber 3 UHF - 5.4KHz off frequency- normal drift?

Postby g8tzl2004 » Sun Jun 24, 2018 5:55 am

I used a frequency counter to measure the Saber 3's TX frequency. I checked the frequency counter using 3 other radios which are all +/-200Hz.

My frequency counter has not been calibrated but its within a few hundred Hz...the Saber is 5400Hz off frequency (10x more than "acceptable")...weak received signals are still within the Sabers passband but weak signals are not received well...unless you lower the test signal by 5 KHz and then the RX is perfect. I've seen 2-3 KHz drift with a TXCO crystal but I'm not sure if 5.4KHz is too much and whether you can warp it back onto freq using service mode?

RFI-EMI-GUY
Posts: 48
Joined: Fri Jun 02, 2006 7:23 pm

Re: Motorola Saber 3 UHF - 5.4KHz off frequency- normal drift?

Postby RFI-EMI-GUY » Fri Jul 13, 2018 10:18 pm

I have been refurbishing UHF Systems SABER radios for a long time and find that most of them are within 200 Hz of spec. This is pretty good, but they are 2 ppm TCXO's. The regular SABER radios have a 5 ppm TCXO and from the ones I see, they are very good as well. These are surplus radios, probably built 29 years ago and not serviced for past 15.

Being off 5.4 KHz is a bunch. You either have a bad TCXO, a bad 5V regulator or the tuning values are hosed up. I would bet someone dumped a codeplug into it and did not press the right button to retain the tuning values in the radio. I would try retuning it in the service mode. Take note of the original tuning value and then adjust it. If you cannot make spec, revert to the original value and check voltage to the TCXO. REplacing the TCXO is simple, buy another cheap radio and swap it out. They simply plug in.
TV DINNER BY THE POOL, IM SO GLAD I FINISHED SCHOOL. FZ

g8tzl2004
Posts: 1091
Joined: Wed Sep 08, 2004 10:13 am

Re: Motorola Saber 3 UHF - 5.4KHz off frequency- normal drift?

Postby g8tzl2004 » Tue Jul 17, 2018 10:19 am

Thanks RFI-EMI-GUY.

OK on maybe the radio had had a codeplug dumped in but the tuning values of the other radio were retained rather than the tuning values of the actual radio. I checked my notes from years ago and it was an easy mistake to use the wrong tuning values...the RSS wording was not at all clear!! So hopefully that's what the problem is!!


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