I have a similar problem on the Hamtronics REP-200 6m repeater. It is constantly swamping the receiver. I tried a antenna tuner in the transmitter line as well as the antenna line; trying to "make the PA Happy".
The TX light will go out,. and there will still be power going through the meter, at a higher SWR. It will occaisionally key the 2m repeater which is about a mile away. When the receiver actually is sensitive enough to produce static with the squelch completely open, you can hear it clearing the runway and preparing to take off as the PA decides to sweep the RF spectrum. Some times it just likes to output power after the exciter drops out. Touching the stud nut on the bottom of the chassis while it is transmitting results in RF burn; so it is no wonder it swamps the Receiver; even with a dummy load on the Duplexer at the antenna port. ----- Original Message ----- From: "Bryan Fields" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, December 19, 2005 4:55 PM Subject: [Repeater-Builder] Hamtronics T301 220 exciter Final and microphonics > well I have a T301 on 220 that has some serious power drop off and > microphonics issues. I had thought the microphonics were generated in the > VCO, and while some of them are, i have traced most down to the final amp. > > It looks like just a bad amp design as the transistor has the collector > commen > to the case, putting RF on the Heatsink. the heat sink seams to form a > capacitor between it and the shield so any movement or heating modulates > the > signal. > > We also have seen the output power go from 4 watts down to 1.2 watts as it > heats up. If we put a fan in there the output is stable at about 2 watts, > but it modulates the signal with a hum from the moving air. > > So I was thinking to replace the output transistor with a MRF237 which has > the > case tied to ground(emitter) which would seam to be a better idea. > > For the time being we removed the final and are using a small brick amp > that > puts out 3 watts stable, with no microphonics. > > So anyone tried this or have a better fix for the issue? > > -- > Bryan Fields, KB9MCI > ____________________ > 15:28:02 up 2 days, 14:35, 2 users, load average: 0.85, 0.61, 0.52 > > Health is merely the slowest possible rate at which one can die. Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
