I want to make a four element diamond quad for 28 MHz which can be switched between horizontal and vertical polarization. The spreaders would be made of fiberglass.
The coax for the driven element has to go somewhere, for a standard horizontally polarized quad, most Hams run the coax from the lower point of the driven element up along the spreader to the boom.
Similarly, for vertical polarization, the coax can be run from one side point along the spreader to the boom.
In these instances, how much does the coax affect driven element operation ?
Using series a current feed point with a 1:1 balun, with the balun mounted at the feed point for vertical polarization, the weight of the balun will pull on the wire and make that horizontal spreader droop. If i make that spreader out of aluminium tube, with only a short piece of fiberglass at the end, it will be much stronger, and in terms of how a piece of metal inside the loop affects antenna operation, this is no different than running coax along the spreader right ? I can put the coax inside the aluminium tube.
If there are two feed points for the driven element, one at the side for vertical polarization and one at the bottom for horizontal polarization, with a 1:1 balun at each and coax attached, then two relays can be used, one at each feedpoint, to switch in either one balun or the other while at the same time shorting out the other feed point gap.
Will it be ok to run two lots of coax plus thin speaker wire for the relays, along two of the spreaders, one horizontal spreader for vertical polarization and the lower spreader for horizontal polarization ?
Or is this going to mess up the driven element ?
If that is going to mess up the drive element, it will only mess it up twice as much as the standard practice of running one piece of coax along one spreader for single polarization, right ?
Another idea i had was to use two concentric loops of wire for the driven element, spaced say two inches apart so they don't short on each other, one would have a slightly higher resonant frequency than the other, and just use one for vertical and one for horizontal, each with it's own permanently connected balun and coax. Noting that then the parasitic element dimensions and spacing should be designed to be the in the middle of the frequencies of the two driven elements, unless i doubled those up as well.
Any one got any ideas on this ?
