Thanks to Bob, Skip, Jeff and everyone who assisted me with my Circulator question. You have given me much to think about as to "IF" I want to install one on my 2-Meter machine. Let me throw this question out as you guys have been there and done that! Under what circumstances would you use a circulator on your 2-meter repeater? Here is my setting: A strong RF Site with a 152.480 Paging Transmitter,FM Radio Station on 103.5. My ham repeater on 147.210 is getting hit by the Paging and I suspect the FM Station. There is a crystal filter on my ham receiver for 152.480, a good one furnished by the paging company. After going through the duplexers and crystal filter the sensitivity is on the RX is naturally down a little. I also have a VHF Community Repeater that is receiving on 160 MHz and TX on 153. Although that antenna is lower than the Ham Antenna it talks better. I know there are a lot of variables, I have good TX RX Duplexers on both units, a Stationmaster on the commercial and a G-7 on the Ham which hopefully will become a stationmaster soon. I just called the paging company and made them come down as they were splattering a lot of the high band receivers at the tower. They installed another large CAN (Filter of some type on top of the cabinet and it looks like the leads go to the exciter, small RG-58 type cable, compared to the 1/2" hardline on the output. There now that I have rambled on I am trying to figure what I can do to get my ham Mastr II to do as good as the MSF5000. I was grabbing at straws with the circulator thinking that maybe the FM Station was coming back down my antenna although I can't measure it. Any suggestions as everything I do don't make the MASTR II much better.It is the closest freqquency to the paging. Thanks 73 JIM KA2AJH
----- Original Message ----- From: <[EMAIL PROTECTED]> To: <[email protected]> Sent: Wednesday, November 05, 2003 4:17 PM Subject: [Repeater-Builder] Re: Tuning of DB4613-1A Circulator > From: "Jeff DePolo WN3A" <[EMAIL PROTECTED]> > > > > > > >Even pass cavities don't necessarily attenuate harmonics produced by a > >circulator sufficiently. A 1/4 wave cavity will have a very good pass > >response at 3/4 wave (3rd harmonic). > > A long time ago I tuned a 10" diameter Motorola VHF pass can to a 2 meter freq., then tried to use it at exactly 3x that freq. It wasn't even close to resonance. I suspect there was some capacitive loading or overmoding taking place that was pulling the 3/4 wavelength resonance. I'll try repeating that test some evening & report my findings. > > If this is true, that would make a pass cavity more effective at suppressing odd transmitter harmonics than one would normally expect. > > >Even at other harmonics, or between > >harmonics, a bandpass cavity isn't necessarily going to give you adequate > >attenuation of the harmonics. A pass can is always good practice on any > >transmitter, but a one-stop-shopping cure for isolator harmonics it is not. > > Whether the higher-order resonances are pulled or not, I would expect a pure pass cavity to have excellent rejection at antiresonant frequencies such as even harmonics. Yet another evening experiment to try. > > > > >And be careful of the varieties of "harmonic filters" out there. Some of > >the cheaper ones are just 2nd harmonic traps. They'll knock down the 2nd > >harmonic by 40 dB or so, but do nothing for the 3rd and higher harmonics, > >which can really be a problem on highband (3rd harmonic ends up on UHF). A > >real low-pass filter is what you should use. > > Agreed. However, I thought the biggest harmonic threat from an isolator was the 2nd. > > Bob NO6B > > > > > > > > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ > > > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
