Hello Niel I'd like to talgate Don's comments with a small one of my own. If you should use just a single radial, you may or not be able to see the little bit of directivity the antenna will develope in the direction of the single radial away from the vertical.
I did a quick check with EZNEC on a 40m vertical with one radial. There is a 5 dB front-to-back ratio, with the best signal in the direction of the radial. The flip side of this is that the antenna gain is only -1.6dB in the favored direction, and even less in other directions. You might be able to take advantage of this, if your property is aligned in desireable directions. Good luck and 73 Bob N6WG ----- Original Message ----- From: "Don Wilhelm" <[EMAIL PROTECTED]> To: "Niel Skousen" <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]>; "Elecraft Reflector" <[email protected]> Sent: Wednesday, August 20, 2008 1:29 PM Subject: [Elecraft] Re: LONG: Background info on Re: WTB: CPK for ButternutHF-6V > Niel, > > Fine on your constraints. > Remember that a vertical with raised radials is just a dipole 'on its > side' with one leg (a single radial) bent at 90 degrees to the radiating > element. > > So how does only the vertical part radiate you may ask. That happens > because you add another radial physically opposite the first one, and > the radiation of one radial is 180 degrees out of phase with the > radiation from the other, so they cancel leaving only the vertical > portion to radiate a signal. > > If the pair of radials are not symmetrical, then you may be just as well > off with only a single radial per band. > > The radials must each be tuned (just like one end of a dipole) with the > vertical radiator. The radials must be an *electrical* quarter wave > long at the band of operation - they can be loaded with inductors near > the junction with the coax shield, or they can be end loaded with a "T" > wire, or some combination of both, but they must be resonant. > If they are placed close to the ground (4 feet is close for the HF > bands), there will be some effect from ground coupling that will de-tune > them, so the easiest is to cut them long and do the trimming with the > aid of an antenna analyzer (if there are several radials for each band, > they must be tuned one at a time - connect only one and tune it, then > connect only the next one and tune, etc. until done. > > Remember that the radials will not be 'radials' unless they are > symmetrically placed around the vertical, it is of no use to run two > radials for any one band out in the same direction for they will produce > the same radiation pattern as a single radial. > > Another 'solution' is to trade that antenna for one that is an > electrical half wave - which does not need radials being an antenna > complete within itself. > > > 73, > Don W3FPR > > Niel Skousen wrote: > > Hi Don (and all who have offered advice & help) > > > > Thanks to all for the input that has been offered. Based on some of the > > comments, I thought I might share the 'rest of the story', both to seek > > additional input, and to show the technical trade off's associated with > > a compromise antenna environment. > > > > I'm installing a used HF-6v in a CCR environment, so I have some > > environment limitations. The CCR 'enforcement' committee is not > > horribly aggressive, but if I don't aggravate the situation, I'm much > > better off. > > > > > > So, the HF6 will be mounted about 4' off the ground, a full elevated > > radial system is not possible. Choices seem to be the CPK solution from > > Butternut or a modified radial system. Two options are being considered > > on the modified radials. > > > > First, 3 tuned radials (either individual wires for 40/15, 30, 20, 15,10 > > or the Butternut tuned twinlead variety) could be connected at the base > > of the antenna, then run down (hidden in the bushes) at a 60 degree > > angle to ground level, then run under/around the rocks. Performance is > > expected to be better than the CPK, but still a compromise. Routing is > > not linear. Tuning of this radial environment is expected to be a bear ! > > > > The second, the CPK, is expected to be enhanced by the low elevation, > > but NOT as effective as a good ground radial system. I might be able to > > enhance this configuration by laying out a psuedo radial set of 6-10 8' > > wires at the base of the 4' mast, which would more accurately be a > > surface capacitive element to enhance the CPK's effect. > > > > In neither case will the near field ground losses be impacted. There > > are some spiral wound counterpoise idea's out on the web, as well as > > some thoughts on constant angle spirals, which are tempting, but at this > > juncture, I expect to lean to the CPK to get it up and running, with > > spirals and experiments to follow... > > > > So any additional input, idea's, are solicited and welcome > > > > Thanks again all, > > > > Niel > > > > > > > > Don Wilhelm wrote: > >> Remember (or understand if you did not before) that elevated radials > >> should be tuned (pruned for length) just like a part of the antenna > >> (they *are* part of the antenna). > >> > >> So get out your antenna analyzer and cut one radial a bit on the long > >> side - attach only that one radial to the vertical and shorten it until > >> you have the correct readings on the antenna analyzer. Cut the second > >> radial to the same length - move to the next band and do the same thing > >> until you are done. Note that the radials can interact on a multiband > >> setup (just like parallel dipoles), so tune the lowest bands first and > >> move upward in frequency one band at a time. > >> > >> The twinlead solution does work, but suffers badly from interaction. > >> > >> 73, > >> Don W3FPR > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
