Chuck, Perhaps we're splitting hairs, because the text in that bulletin states "To the spurious, the stub looks like a short..." I agree that my choice of words leaves unclear the difference between "looks like a short" and "is a short." Is it too late to invoke that handy disclaimer of vagueness, "YMMV?"
-----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Chuck Kelsey Sent: Tuesday, July 28, 2009 6:25 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Sinclair Q202 duplexers (frankenstein series) But.... the GE file shows how to make a quarter-wave open-stub filter, not a shorted one. Chuck WB2EDV ----- Original Message ----- From: "Eric Lemmon" <wb6...@verizon.net <mailto:wb6fly%40verizon.net> > To: <Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > Sent: Tuesday, July 28, 2009 9:06 PM Subject: RE: [Repeater-Builder] Sinclair Q202 duplexers (frankenstein series) > Eric, > > I was referring to commercial inline shorted-stub arrestors, such as those > made Huber+Suhner, that typically are intended for use at 800 MHz and > higher > frequencies. I did not mean to imply that home-made quarter-wave stubs > cannot be used. In fact, instructions for fabricating just such a device > are found here: > <www.repeater-builder.com/ge/datafile-bulletin/df-10002-01.pdf> > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > [mailto:Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Eric Grabowski > Sent: Monday, July 27, 2009 10:30 PM > To: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > Subject: RE: [Repeater-Builder] Sinclair Q202 duplexers (frankenstein > series) > > > > Eric, > > Why is a quarter-wave shorted stub impractical at 2m? > > I have been told that a quarter-wave shorted stub would serve two > purposes: > a) provide a dc path to ground for static caused by precip or wind, and > also > b) substantially reduce the strength of a transmitter's second harmonic. > > 73 and aloha, Eric KH6CQ > > --- On Mon, 7/27/09, Eric Lemmon <wb6...@verizon.net <mailto:wb6fly%40verizon.net> > wrote: > > > > From: Eric Lemmon <wb6...@verizon.net <mailto:wb6fly%40verizon.net> > > Subject: RE: [Repeater-Builder] Sinclair Q202 duplexers > (frankenstein series) > To: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > Date: Monday, July 27, 2009, 4:51 PM > > > > > Norm, > > A Polyphaser does not put a DC ground on the center conductor of the > feedline- nor does any other inline arrestor of any brand, except a > quarter-wave shorted stub. But that is impractical at 2m. My point > was > simply that a single bandpass cavity on either the TX or the RX > side, > between the duplexer and the antenna tee, will put a DC ground on > the > feedline at the transmitter end. Most antennas are DC grounded, but > a lot > can happen to that feedline between the antenna and the duplexer. > One 2m > repeater I have on a hilltop suffered a lot from wind-caused static > discharges (aka triboelectric charging) until I put a single > bandpass cavity > on the receive side. My intent was to prevent desense from the > adjacent FM > broadcast station, but the static elimination was a bonus. > > Regarding the determination of high pass versus low pass, this is > usually > determined by the design of the duplexer. Some designs are > symmetrical, > while others are asymmetrical. In most cases, the loop coupling will > be > different between the high side and the low side, so it is > convenient to > simply follow the manufacturer' s settings, and their tuning > instructions. > In the case of the Sinclair Q202-G, the loop assemblies are all > identical, > and the notch tuning capacitors are the same as well, regardless of > which > pass side they're on. > > You're correct about bandpass duplexers being unsuitable for the 600 > kHz > split at 2m. However, I have a 8" bandpass duplexer on a commercial > repeater that is using a 5.26 MHz split on VHF, and it works > perfectly. I > specified it because of the antenna being the high point on the > tower, and I > wanted DC ground at the duplexer for repeater protection. > > 73, Eric Lemmon WB6FLY > > <snip all following> > > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
