lowband noise on 33.600

jim · Post by **jim** » Thu Jan 15, 2004 7:52 pm

What's with Motorola radios and 33.600? No matter where you go, you get noise on this channel. I assume this is the harmonic of some IF stage? CDMs, Minitor II/III/IV,MT1000s all do this.

I have a CDM1250 that just won't go quiet. Any suggestions to cure this? Can something be changed so I can get this radio to actually work on this frequency?

kc2dla · Post by **kc2dla** » Thu Jan 15, 2004 8:11 pm

I haven't a clue as to your first step with the CDM1250. On the MT1000 however, you may try toggling the RX Injection using the RSS. When you are in the Change/Create/View--> Channel screen, it is F9. IIRC this affects the Injection from the second local oscillator stage.

jackhackett · Post by **jackhackett** » Thu Jan 15, 2004 8:46 pm

That's one of the self quieting frequencies moto says to stay away from. They're all multiples of 16.8Mhz, why does that freq sound familiar? Anyway, since you're warned to not use those freqs I would guess that it's not something changing the injection freq will fix..

jim · Post by **jim** » Fri Jan 16, 2004 6:45 am

Not like the entire county has a choice here- they've used this for fire since the 60's. Problem is, what does Motorola have that works on .600? Nothing!

Kenwood does, however. Imagine that.

jackhackett · Post by **jackhackett** » Fri Jan 16, 2004 7:47 am

Now that I have a chance to look at some books, my suspicion is confirmed, the 16.8Mhz is the synthesizer reference frequency in many of the Moto radios.
I don't think the RF injection setting is going to matter, I believe that just changes it from high side injection to low side, has something to do with it inverting digital data if I recall correctly.
I've seen some radios that have a setting for changing the microprocessor clock frequency in case that causes self quieting, but on the reference oscillator I think you're out of luck.
Some radios had a different freq, GM300s were 14.4Mhz, you'd have to see if there's anything still available from moto that's not 16.8, or go with another brand.