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hi Rick - when I read Natan's reply, my first reaction was: it wasn't the filter, they probably also removed a coax jumper too, and that also did the trick. I have a similar issue with my JRC JST245 xcvr, which is a wonderful radio, but on 6m looking into a yagi antenna the SWR will shoot off the scale for no apparent reason. If you hook up the antenna analyzer, it shows no problem. If you put the Bird wattmeter in line, the problem goes away! I finally just left the Bird in line so I could continue operating... then one day the problem returned... so I remove the Bird and the problem goes away! My theory, based on this observation and on fuzzy memories of classes taken 20 years ago, is: your coax is not an ideal transmission line, but rather is really a bundle of distributed and lumped capacitances and inductances that do tend to act as an ideal transmission line to a first approximation. The overall circuit that is your xcvr final output, plus your coax, plus your antenna, has resonances and Q factors. What may be happening is that one of these resonances is setting up an oscillation in your finals. (No, I have no idea what the feedback path is that creates the oscillator..). By changing the length of your coax, you change the resonances of this circuit, and therefore remove the oscillation. I have a friend who says he has seen this oscillation in his JRC rig. I have never heard of it happening in other rigs, but it may be a possibility. I expect that the above is not necessarily correct, but may serve as a starting point for discussion - I stand ready to be corrected!-) 73 - vq Rick Lehman wrote: > > I have a C19XR with a high VSWR (when measured at the transmitter end of the > coax) on 10 meters and do not use an LP filter. It was suggested by force > 12 that I add about 5 feet of coax. I did that and to my amazement it > worked. I have been trying to understand why this would work and have not > yet come up with a technical explanation (Force 12 cannot explain it > either). With an ideal line, the length of coax should not make a > difference on the VSWR seen at the transmitter. It instead would only > affect the phase angle from a Smith Chart standpoint. From a real world > lossy line standpoint, 5 feet of coax is not long enough to cause any > appreciable loss or effect on the VSWR. My first thought was that the force > 12 balun was bad as the symptoms suggest that the coax was functioning as > part of the antenna. However, I removed the 5 feet of coax, and replaced > the balun with a current balun from Hygain. The results were the same as > with the force 12 balun... Therefore I have ruled out this possibility. My > coax is new, so I am for the time being ruling out this possibility. The > antenna seems to work fine on 10 meters, but I am bothered that I do not > understand this phenomena. Any ideas? > > Rick WB4EJC > Coconut Creek, Florida > > > -----Original Message----- > > From: Tony [mailto:ad6id@arrl.net] > > Sent: Saturday, June 17, 2000 4:47 PM > > To: force12talk@qth.com > > Subject: Re: [Force 12 Talk] !0 meter VSWR > > > > > > At 01:37 PM 6/17/00 -0400, Natan Huffman wrote: > > ...> > > >Five out of five installations experiencing this high 10 meter > > VSWR problem > > >fixed the problem by removing the LP filter! All of the problem filters > > >were of the same manufacturer. > > > > > >So, if you don't think things are quite right on 10 meters, look > > at your use > > >of a LP filter as a very possible problem initiator. > > > > Thanks for the great detective work. Could you tell us which > > 'same manufacturer? > > Or do you suspect that they all have this effect? > > > > I didn't catch which antenna. I have a C4SXL (without a LP > > filter, so far). > > > > 73, Tony > > > > Tony Armendariz, AD6ID > > ad6id@arrl.net > > FISTS 3535 WPSS ARRL > > > > > > -------------------------------------------- > > Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. > > Force 12 Web site: http://www.qth.com/force12 > > > > Submissions: send to Force12Talk@qth.com > > To unsubscribe: send a blank e-mail to Force12Talk-leave@qth.com > > Force12Talk Message Archive: http://www.qth.com/force12/list/force12talk > > For problems with the list, contact force12@qth.com > > > > > > > > -------------------------------------------- > Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. > Force 12 Web site: http://www.qth.com/force12 > > Submissions: send to Force12Talk@qth.com > To unsubscribe: send a blank e-mail to Force12Talk-leave@qth.com > Force12Talk Message Archive: http://www.qth.com/force12/list/force12talk > For problems with the list, contact force12@qth.com -- jeff stai KQ6VQ DM13 NAR #21059 TRA #3356 L2 jstai@home.com / kq6vq@arrl.net ROC web page: http://www.rocstock.org/ -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. 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