If you are not using a pll exciter, it's hard to get the isolation.......... Kerry ----- Original Message ----- From: "Kevin Custer" <[EMAIL PROTECTED]> To: <Repeater-Builder@yahoogroups.com> Sent: Monday, May 31, 2004 12:07 PM Subject: Re: [Repeater-Builder] Wacom WP-641, correction on its specs...
> 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 > > > > > > > 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/
