Neal Newman wrote: >I am Getting only 83 db Isolation usning My 641's.. >funny thing. I cannot get it to work with my MastrII repeater. But it >works great with the Spectrum.. >
The obvious question is, is it tuned properly? The Wacom 641 is very simple to get close with nothing more than a handheld and a signal generator. I prefer to tune the pass under low power, like one watt from the handheld. It makes the pass more precise, as tuning it with a spectrum analyzer usually won't yield as good a loss. I have always been able to hit the 1.5 dB loss mark by using this method. PLEASE spare me the "Don't tune the duplexer under power BS" These cavities are rated at 350 watts intermittent, and 275 continuous and you won't be able to arc the fingerstock with a few watts of power, especially if you get it close to resonance with a signal generator first. After getting the pass frequency 'correct' you will find that obtaining the stated isolation is easy. One thing that happens is if the cavity is not tuned correctly on the pass frequency, the reject amount will suffer. Why? As the spacing between pass and reject frequencies decrease, so does the ability for the cavity to provide the rejection response. With this cavity, the lowest loss and best return loss appear nearly on top of one another, so match is at its best when the cavity is properly tuned for lowest insertion loss. Here is more on pass and reject response with one cavity from a WP-641 duplexer: http://www.repeater-builder.com/rbtip/wacombpbrnotes.html Another thing that happens commonly with a duplexer and a radio set that was converted from commercial service to amateur, is the actual terminal impedance will not be 50 ohms. A duplexer that has been optimized on a piece of 50 ohm test equipment *may* not perform very well in practice. There are a few things that can be done to help this problem, like using a matching device (Z matcher) on the transmitter. Some prefer to match the duplexer to the transmitter by adjusting cabling lengths. Either method can substantially improve the operation of the duplexer. Sure, it would be nice or best if the radio set presented a perfect 50 ohm match, but many we convert do not. Wacom had written a dissertation on optimizing the duplexer interconnection cabling lengths. That information, as well as duplexer tuning, is available here: http://www.repeater-builder.com/pdf/wp6xxVHFtuninginstructions.pdf Look on page 4 under the section "Cable length between transmitter and duplexer" Hope this helps... Kevin Custer 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/
