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On Thursday, June 27, 2013 1:34:20 PM UTC-5, seediq wrote:
I do not doubt your information here. However, it seems to conflict with my experiences working 75 meters. I work 75 each day using a 75 meter horizontal loop. I hear the same characters on each day. Often a newbie pops up with a poor signal. He is in the same area as "the gang" and yet his signal stinks. Almost invariably we ask him about his G5RV. "Gee guys how did you know I was using a G5RV?" Poor signals shows up every time. He is using a dipole that is way too short to resonate on 75 meters. I think they are 82 feet long. It seems to me if VSWR made little difference, then his 82 foot long dipole on 75 meters should work just fine. Not trying for a fight, just want an opinion about why we are hearing this effect. Of course they are using tuners to make a match to their transceivers. A high SWR on it's own is not always bad news. It depends on the feed line used, freq, etc. The main reason the G5RV's don't do so hot is the goofy method of feeding most seem to use. IE: a length of twin lead to a choke, to coax. And then some add insult to injury and run a tuner at the shack. A good amount of power is turned to heat. But if you feed the same antenna with ladder line the whole route, the losses are not so bad, even with a high SWR. If you tune the line and use no tuner, fairly low losses. If you use a tuner, not quite as good, but not too bad if you use the least amount of inductance needed to get a usable match. All antennas will radiate nearly all power applied to them. The trick is getting it from the rig to the antenna without turning some into heat. This is where the usual G5RV is failing. Some of the power is not making it to the antenna due to obtuse lossy methods of feeding. Same issue with some of the windoms, etc that are sold. |
#2
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![]() wrote in message ... A high SWR on it's own is not always bad news. It depends on the feed line used, freq, etc. The main reason the G5RV's don't do so hot is the goofy method of feeding most seem to use. IE: a length of twin lead to a choke, to coax. And then some add insult to injury and run a tuner at the shack. A good amount of power is turned to heat. But if you feed the same antenna with ladder line the whole route, the losses are not so bad, even with a high SWR. If you tune the line and use no tuner, fairly low losses. If you use a tuner, not quite as good, but not too bad if you use the least amount of inductance needed to get a usable match. All antennas will radiate nearly all power applied to them. The trick is getting it from the rig to the antenna without turning some into heat. This is where the usual G5RV is failing. Some of the power is not making it to the antenna due to obtuse lossy methods of feeding. Same issue with some of the windoms, etc that are sold. I have not used the g5rv except for some the club uses at field day. From what I understand about them, they were designed to work on 20 meters. It was just luck that they will have a reasonable low swr on other ham bands. If the swr goes up over 3 or 4 to 1 I can see lots of power being lost in the coax part. I use a home made version of the off center fed. I can compair it to an 80 meter dipole and a triband beam. It usually matches the dipole or is sometimes beter depending on the direction of the other stations on 80 meters. On 20 and 10 meters the beam is usually much beter, but if a station hapens to be in certain places there is not too much differance . The ocf does not work very well on 15, but it is not suspose to. All antennas are fed with Davis Bury flex rg 8 type which does not have too much loss. |
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