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Antenna article
Just found this; looks interesting; no connection with the author;
all in the spirit of free dissemination of knowledge to fellow radio amateurs ... http://www.cvarc.org/tech/antenna_my...enna_myths.pdf |
Antenna article
On Friday, February 14, 2014 1:59:15 PM UTC-6, gareth wrote:
Just found this; looks interesting; no connection with the author; all in the spirit of free dissemination of knowledge to fellow radio amateurs ... http://www.cvarc.org/tech/antenna_my...enna_myths.pdf Several parts of it are pure unadulterated horse doo-doo.. :( I find it to be in very poor taste to post a page claiming to expose and list myths and mysteries, only to replace them with other myths and mysteries. :+ That is akin to chasing one's tail while barking at the moon. |
Antenna article
wrote:
On Friday, February 14, 2014 1:59:15 PM UTC-6, gareth wrote: Just found this; looks interesting; no connection with the author; all in the spirit of free dissemination of knowledge to fellow radio amateurs ... http://www.cvarc.org/tech/antenna_my...enna_myths.pdf Several parts of it are pure unadulterated horse doo-doo.. :( I find it to be in very poor taste to post a page claiming to expose and list myths and mysteries, only to replace them with other myths and mysteries. :+ That is akin to chasing one's tail while barking at the moon. I confess to only have 'scan read' the reference and I thought it was still pretty good. What in particular do you have an issue with, please? -- 73 Brian G8OSN/W8OSN |
Antenna article
On Friday, February 14, 2014 11:21:01 PM UTC-6, Brian Reay wrote:
wrote: On Friday, February 14, 2014 1:59:15 PM UTC-6, gareth wrote: Just found this; looks interesting; no connection with the author; all in the spirit of free dissemination of knowledge to fellow radio amateurs ... http://www.cvarc.org/tech/antenna_my...enna_myths.pdf Several parts of it are pure unadulterated horse doo-doo.. :( I find it to be in very poor taste to post a page claiming to expose and list myths and mysteries, only to replace them with other myths and mysteries. :+ That is akin to chasing one's tail while barking at the moon. I confess to only have 'scan read' the reference and I thought it was still pretty good. What in particular do you have an issue with, please? -- 73 Brian G8OSN/W8OSN Well, I suppose most is OK, but there are a few problems. Take this one.. More recent HF tests by Al Christman - KB8I; "Eleva ted Vertical Antenna Systems," QST, August 1988, p 35; have shown that fewer "elevated" radials will perform about as well as 120 ground mounted ones. A base mounting height above ground of about 1/10 to 1/16 of a wavelength seems optimu m for 4 radials.........but will vary with soil conductivity. I don't know how he ran his tests, but this is not right. 1/10 WL is way too low for four elevated radials to equal 120 on the ground. I was harping about this "myth" in another post not long ago.. There is no free lunch. :| For four radials to equal 120 on the ground, they will need to be nearly 1/2 wave up. Four radials at 1/4 wave up are equal to about 50-60 on the ground. Seems optimum? If the radial system were optimum, it really wouldn't matter what the conductivity of the ground was. This is actually proving my point that four radials at 1/16 to 1/10 WL are not nearly enough to actually equal 120 on the ground. If they were equal, you wouldn't have to raise the antenna and radials. That's the whole point of using so many radials on the ground. So the quality of the ground, good or bad, really doesn't matter. Efficiency will be high either way. Some of his 1/2 vertical design statements could be argued with, but I'll be here all night if I start into that.. :/ Then you have this.. Myth: A 5/8 wave antenna has 3dB more gain than a ground plane. False This can be true in many cases. But it can also be false in many cases. * The losses in the required matching coil at the base of the 5/8 wave antenna reduce the gain difference to a max of about 2dB (with a perfect ground plane) to zero difference in some installations. ** -------------------------------------------------- This is fairly absurd.. The loss of the loading coil is quite negligible. I bet not even enough for most people to accurately measure. The coil has nothing to do with why some types of 5/8 verticals show little or no gain vs a 1/4 GP, or isotropic. Those are a couple of my issues anyway.. The "Free Lunch" elevated radial system being one of my pet peeve myths.. :| |
Antenna article
"Jeff Liebermann" wrote in message ... The coil has nothing to do with why some types of 5/8 verticals show little or no gain vs a 1/4 GP, or isotropic. Just a minor note on this issue. If the coil actually did contribute a 1dB power loss, the lost power would need to be either reflected or dissipated by the coil if it's not being radiated as RF. I haven't seen any high VSWR 5/8 wave antennas, so it's not VSWR. I haven't seen the matching coil on my Larsen 5/8 wave antenna, with a 45 watt VHF mobile, become warm. If it was dissipating 4.5 watts, I should be able to see it get quite warm[1]. I pointed an IR thermometer at the coil and transmitted for about 5 minutes. No change. However, I did see a very slight temperature rise from a mercury thermometer taped to the stainless steel antenna rod (which could be attributable to my sloppiness). The test is easily reproduced. Have fun. Just the same type of easy test that can be done with the old saying of 1 db loss per connector. Connectors have a very small loss in them. If they did have the 1 db or even 1/2 of a db loss and you put 100 to 1000 watts through them you could really feel the heat after a short transmission. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
Antenna article
On Saturday, February 15, 2014 11:39:51 AM UTC-6, Jeff Liebermann wrote:
I haven't seen any high VSWR 5/8 wave antennas, so it's not VSWR. Actually, a 5/8WL antenna is a standing wave antenna. Therefore, there is a standing wave *on the antenna element* no matter what the feedpoint impedance. The SWR on the loading coil will be higher than the SWR on the antenna element. All that a resistive feedpoint on a standing wave antenna means is that the forward wave *on the antenna element* is in phase with the reflected wave *on the antenna element* at the antenna feedpoint. -- 73, Cecil, w5dxp.com |
Antenna article
wrote in message ... On Friday, February 14, 2014 11:21:01 PM UTC-6, Brian Reay wrote: BIG SNIP What in particular do you have an issue with, please? little snip Brian G8OSN/W8OSN Well, I suppose most is OK, but there are a few problems. BIG SNIP I had a question about his j-pole analysis. He says "A J-pole, like ANY end fed antenna, needs radials, a counterpoise or ground plane to work properly." I've never seen this anywhere else, even as a suggestion or hint. I can envision places to fit one but what would it do? As built, both the pattern and the impedance already seem to be what I want. Thoughts? "Sal" |
Antenna article
On Saturday, February 15, 2014 3:27:15 PM UTC-6, Sal wrote:
As built, both the pattern and the impedance already seem to be what I want. And it already has a counterpoise. The counterpoise is where the current flowing on the inside of the coax shield goes when it leaves the coax. The J-pole has a radiation pattern of a 1/2WL vertical, i.e. the lower 1/4WL doesn't radiate (much) and is part of the matching section and counterpoise. Quite often, the outside of the coax braid is also part of the counterpoise. -- 73, Cecil, w5dxp.com |
Antenna article
"W5DXP" wrote in message
... On Saturday, February 15, 2014 3:27:15 PM UTC-6, Sal wrote: As built, both the pattern and the impedance already seem to be what I want. And it already has a counterpoise. The counterpoise is where the current flowing on the inside of the coax shield goes when it leaves the coax. The J-pole has a radiation pattern of a 1/2WL vertical, i.e. the lower 1/4WL doesn't radiate (much) and is part of the matching section and counterpoise. Quite often, the outside of the coax braid is also part of the counterpoise. -----ooooo----- Cecil, I read with interest your critiques of the article. On the basis that you mentioned eznec, I wonder of perchance you are a professional? Gareth |
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