At 4/28/2005 11:26 AM, you wrote: >Hmmm, > >11.2 * 2 * 10? > >or 11.2 * 20? (*40 for UHF) > >What about changing the IF crystals to 10.7? Then you should be ok >until you hit 214 or 428 MHz?
You may be able to make it work so that the TX will not directly desense the RX. However the TX carrier will still be rattling around the RX, making it susceptable to IMD from seemingly unusual sources. Take for example a G.E. mobile repeater on 447.00 RX, 442.00 TX using the usual low-side LO. It will be susceptable to interference from any signals present on 442.245 or 441.755; see the article at http://www.repeater-builder.com/ge/mvp/no6bmvpconversion.html for an explanation of how this happens. If you don't believe me I can drive within 20 miles of your repeater & make it belch all day without transmitting on or near your input. In this case, switching to high-side LO eliminates this known problem, but it doesn't eliminate the intermingling of the TX & LO signals within the radio. In all likelihood the TX carrier is making the RX "soft" in other places. I'm not saying that the G.E. Mastr II/Exec II/MVP mobile radios are unsutiable for repeater use. After all, I have about half a dozen in service right now. What I am saying is that if you start to run into seemingly weird IMD problems with these radios (particularly with several repeaters on the same band at the same site), your easiest course of action in the long run may be to extract the RX & put it in an RF-tight enclosure. Not pretty, but it works. In my case, we made a win-win situation out of it by leaving the RX in the mobile package & switching the main repeater RX to a boxed G.E. RX. The RX left in the mobile became a link RX. We noticed some low-level junk on that link RX at times, but since the link signal was much stronger it didn't matter. Bob NO6B 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/
