MTS2000 UHF - 2nd LO crystal off frequency??

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g8tzl2004
Posts: 1128
Joined: Wed Sep 08, 2004 10:13 am

MTS2000 UHF - 2nd LO crystal off frequency??

Post by g8tzl2004 »

Several of my UHF MTS2000's and other Jedi's are a bit deaf compared to my Waris and XTS stuff.

I have often thought that they actually sound a bit off frequency but the TX ref Osc is spot on (say +/- 200Hz)

I'm thinking that the problem might actually be the RX 2nd LO crystal being off frequency.

I checked the service manual and I think the 2nd LO crystal is on 73.35MHz.

I went though several Jedi's with a test receiver and looked for a zero beat on 73.35MHz.....I got the best signal half way up the Jedi on the back of the radio..the 2nd LO is very weak but easy to detect.

The Jedi which sounded most off freq zero beated on 73.351200 MHz. (Others were on around 73.350400 and 73.350200 MHz)

If I am correct, this suggests that the 2nd LO on the above radio is 1.2KHz off frequency..which I guess results in the actual RX freq being 1.2KHz off freq..although the TX will be spot on.

I think a 1.2KHz error WILL be noticeable on a weak signal, especially if the received signal is a bit off freq in the "other direction".

Am I correct in my above assumptions?

Is there any way to adjust the 2nd LO frequency or is this set up in the factory?

Is an off freq 2nd LO crystal a common issue with Jedi radios?

Thanks
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