Steve, just changing crystals should not create this problem, and should not require modifications. If the spurs are making it out with significant amplitude, they're probably being generated in a later stage.
If the frequency was just changed, how was the transmitter and power amp tuned? (Or, were they?) Some Spectrum PAs were known for becoming unstable if they were "peaked," rather than aligned exactly as specified in the docs. Some were also prone to modulation by any noise on the PTT line. Make sure whatever switching device is being used by the controller does not have any digital noise superimposed. If it's instability in the PA, the spurs may occur at odd frequency spacing and move around. If it's digital noise, a spectrum analyzer will often show the spurs at a consistent frequency interval which bears some relation to the controller's clock frequency or output of a divider chain. I'd check the easy stuff before I modified the oscillator - that's a real minefield. 73, Paul, AE4KR ----- Original Message ----- From: sdenny61 To: Repeater-Builder@yahoogroups.com Sent: Monday, March 16, 2009 11:28 PM Subject: [Repeater-Builder] Spectrum Transmitter Noise... Hello all, This is my first post to this website, and I must say, I have found a vast amount of great information here. Please continue your great work and thanks to all! Here is the situation, I have a Spectrum SCR-1000 220mhz repeater. The transmitter is very noisy (spurious) that is causing us lots of problems. What we're thinking is the newer ICM crystal is actually overdriving the first multiplier stage, cuasing problems on down the line. The tuning coils on the 1st stage have very little if any response. The repeater is located at my QTH for testing and tuning purposes. When transmitting, it wipes out my TV, VHF, and 6M receivers, so it is pretty broad. Our thought in solving this overdrive is to "knock down" the crystal by placing a resistor (10K or so) in series with the crystal. Has anyone else experienced this or a similiar problem? Any ideas or suggestions, short of replacing the transmitter with something newer. Oh, and the PA was removed from the transmitter box and placed in it's own shielded enlosure to eliminate some problems we thought it was creating, so that is/can be bypassed, we are sure it is the actual transmitter/exciter board causing the problems. Thanks all! 73 de Steve KD8BIW sdenn...@yahoo.com www.kd8biw.com
