Vic, For those bands, I would recommend that you use a higher frequency adaptation of the DXPeditioner's Battle Creek Special antenna (see ON4UN's Low Band DXing). Add a 30 meter trap in the vertical section and put a 40 meter trap at the top, then use a wire from the top of the 40 meter trap to create an inverted L antenna for 80 meters. Since the base is already above ground, I would believe you should be successful with elevated radials - but they have to be tuned to the vertical portion to work properly - use 2 (or 4) diametrically opposed radials each for the 30 and 40 meter bands to cancel the horizontally polarized component of the radiation and on 80 meters you can get away with one because the horizontal portion of the antenna already has some horizontal radiation to its pattern, so a bit more horizontal polarization won't hurt. You can instead install a very good on (or in) ground radial system, but that will likely take a minimum of 16 radials to perform as well as the raised radials. With the raised radials, experiment with and without an actual connection to ground to see which gives the better results - often it is better to keep the elevated radials isolated from earth ground (except connected through an RF Choke to keep things at DC ground potential).
Tune the radials one at a time until you get the reactive part of the feedpoint impedance at zero, then observe the resistive part after all radials are in place - you can accept the resulting SWR or install a matching network at the antenna base to bring it into line with the feedline losses you are willing to accept. Good luck with it. 73, Don W3FPR > -----Original Message----- > > > OK, here is what I want to do: > > I have a 33' (10m) vertical with the base about 10' (3.3m) above ground. > It has four 8' (2.4m) radials which are connected to the feedpoint > through a coil which resonates the system on 7 MHz. It works as well or > better than any vertical that I've used on 40m -- low SWR and good > results. It's fed through a relatively short (20', 6m) length of RG-213. > > I would like to use it on 80m and 30m as well. My first try was to > simply use the KAT100 to tune it. It tunes fine on both bands (1:1 at > the rig), but results are fair-to-poor on 30 and poor-to-worthless on 80. > > On 30m, the coax losses are reasonable (the SWR on the coax is about 8 > to 1, but it's very short). I suspect the problem is that the radial > ground system is very poor on this band (on the other hand, the long > vertical radiator should provide a slight amount of gain). So I may try > paralleling a set of radials tuned for 30m. They will also be short, > but resonated with a coil or stub. Does this sound like a good > analysis/solution? > > On 80m, it's more complicated. The ground system is terrible, the > radiation resistance of the vertical very low, and the SWR and losses on > the coax very high. No wonder it's a dummy load! I guess the way to > deal with it is to add more tuned radials in parallel and a switchable > base network, but I would like to avoid any more control wires that have > to go through my lightning suppression panel (I can't pass DC through > the coax, either). Does anyone have any suggestions? > > -- > 73, > Vic, K2VCO > Fresno CA > http://www.qsl.net/k2vco > _______________________________________________ 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
