At 01:30 PM 6/9/02 +0100, you wrote:
>I was thinking of suspending 2 40m diamond-configuration quad loops from the
>top of an 80' steel scaffold-pole mast.
>Option 1 is put a horizontal 20' length of timber with central pivot at the
>top of the mast, thus spacing the loops correctly, and allowing them to be
>'walked around' to the desired direction.
>Option 2 is to mount the tops of both loops on insulators at the top of the
>mast, and pull the sides and bottoms of the loops away from the mast,
>What are the pros and cons of both options, and which do you prefer for best
>DX performance ?
By coincidence, I just finished modeling both as parasitic arrays for 80m,
with a 48-foot spacing, fairly close to what you're describing. The diamond
configuration, fed at the top, gave at best about 10.5 dBi gain at 34
degrees take-off angle, while the delta at the same apex height gave about
9.7 dBi at 37 degrees, but with slightly higher front-to-back ratio. The
biggest problem with either antenna is that the effective height is rather
lower than the apex, accounting for the relatively high take-off angles,
which are well above what is needed, for example, between Europe and the
US. A 2-element yagi at the apex height would still be a noticeably better
DX antenna. On the other hand, the performance is rather better than a
4-square, and it would be a lot cheaper than a rotary yagi.
73, Pete N4ZR
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