At 07:59 AM 27/10/2007, you wrote: >Did you order the receive crystal for high side injection? A radio >starting in the range you have usually will tune right up with no >oscillation problems if the crystal is on the high side of the >receive frequency. No mods are usually required at all for moving a >radio into the ham band if high side injection is used. I have seen >sensitivity of . 7 to 2 uV show up with a low side crystal (with no >mods) and have seen the sensitivity come to the .35 uV range by >shifting to a high side crystal. > >The high side injection keeps the oscilator/multiplier chain in the >normal range for the radio and keeps things tuning to actual >resonance and not just close to resonance. > >73 - Jim W5ZIT ------- Hello Jim. Yes I did consider high side, but when I read the article in the Repeater Builder about modifying the local osc chain, I decided to go that way so everything was "normal" . It was very easy to do and took very little time. Prior to the modification, I did attempt to tune the unit "as is" and it seemed to tune ok, but I could not get a quieting signal through. As soon as I modified the local osc chain, I had signal. The helical tuning screws were pretty well all in, so I decided to change the helicals from the G8 to the G7. After this, they looked a little more normal and tuned ok except for the instability. I believe it is an interaction the mixer and the last stage in the local osc chain. That transistor gets very hot!! I plugged in a Exec II which has a similar set up and it gets warm, but not hot... The instability seemed to be more pronounced with the G7 coils then the G8, but I think that was because there was more tuning range with the G7 unit. If I don't like it I may try high side injection.
Thanks Doug
