Thu 13th Jan 2011, 15:43
I just built an EB that should be resonant at around 435 but has high swr (6:1 or more) right across the band. It receives very well on the sats and I heard lots of activity on AO51 with full quieting for almost the entire pass from around Arizona up through Saskatchewan and over the NW Territories. I used 1/4 in Cu tubing for the elements (circular) and RG58u for the Q section, phasing lines and balun. From there I run a 20 ft length of LMR400 into the Yaseu8900r. The mast is 2" black abs plastic 20' off the ground. My question(s) are about the radial system: I can't find any good explanations of reflector/radials for UHF anywhere. I'm fairly new to antenna construction and would like to know;
What does changing the diameter of the reflector (round or rectangular) or length of the radials (8 - 1/4wave radials at present) do to the signal?
Does the reflector/radial system have to be connected to ground like it is on a quarter wave vertical? If not why not?
How will changing the distance of the reflector/radial system from the driven elements change the signal, receiving characteristics or swr the driven elements?
Can you use a reflector surface without the radials or vise versa?
Does it matter how close to the mathematically vertical axis of the mast that the reflector/vertical system starts? (For example should you punch holes in the mast and push the radials right inside near the coax?)
Sorry for all the questions: Any opinions would be welcome!
Fri 14th Jan 2011, 12:10
not built one of those, but there's some good info here:- http://vu2ivv.blogspot.com/2010/07/e...mateur_26.html
Did you use an insulator between the elements at the top?
Black plastic pipe uses carbon as the colouring agent, making it partially conductive.
At H.F. this doesn't bend the signal much, but at U.H.F. the signal suffer more.
Looks like you don't need to use a reflector, only to increase sensitivity.
Sorry I can't give you more info, but this antenna is new to me...
Fri 14th Jan 2011, 14:26
Thanks Dem: Especially for that info about the pipe. I'll switch to the grey or white pipe if nothing improves. And yes I do have a rubber grommet separating the two elements at the top.
Ya it's a little confusing for me. I got my license 25 years ago and after a year or so of experimenting I never used it for anything but FM in the truck so I've forgotten a lot of stuff. I can't figure why some one would want a reflector and a radial system and I'm finding a lot of contradictory data on the web about "counterpoise", "radials" and "reflectors". I remember I built a 432helical for my brother and the reflector was tied to ground: With this antenna the ground side of the coax doesn't appear to play any role in the propagation from the elements at all (which also puzzles me).
I think I have been to that website and he uses rg62 if I'm remembering it right. I can't find rg62 so I'm using the original "version 2" from "http://on6wg.pagesperso-orange.fr/Page%201.html" in which the author switches from one rg62 to 2 parallel rg58's for phasing instead.
If I can't get this thing to work I found another version with rectangular elements that I might try next..
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