[Antennas] 5 Band Quad's

Mon, 29 Apr 2002 19:34:30 -0400

Dear Randy:

I currently have a six band quad (four elements on 10-20 and seven on 6M) and
have had one at two different QTHs for about 13 years.  I have always used a
remotely controlled switch mounted at the boom in order to switch between
separate feed lines for each of the driven elements.

I had problems similar to yours with my first quad.  The interaction problem was
especially troublesome on 15 meters, but 10 and 12 would cause problems too.
Additionally, I had modeled my quad and the actual antenna's impedance
characteristics did not even remotely correspond to the model.

I subsequently began corresponding with W4RNL (LB Cebik) on the poor modeling
experiences that I had had, and he pointed out that when I modeled the antenna,
the driven element loops for the inactive bands were modeled as closed
(shorted), but when I built the actual antenna, the inactive loops were randomly
opened or closed or somewhere in between depending on the length of coax between
my antenna selector switch terminals and each of the driven elements.  He
recommended that I make each of the coax links between the switch terminals and
the driven elements for each band exactly 1/4 electrical wavelength in length,
and leave the switch end of each inactive coax link open so that the
corresponding element end would effectively be closed and correspond to the
model.

Well, when I rebuilt the antenna here at my new QTH, that's exactly what I did,
and the model and the actual antenna were practically in perfect agreement, i.e.
the SWR minima were within each band or very close.  More importantly, as far as
you're concerned, I have not observed any interaction problems with this
antenna.  If you're not already doing it, it sounds like you might want to do
the switching at the end of each 1/4 wavelength matching transformer and leave
them open when those band are not in use.

By the way, I never attempted to tune my quad, I just relied on the model's
predictions.

I hope this helps.

73, Joe

WX5L wrote:

> I would like to hear from anyone that has successfully tuned a 5 band quad,
> in particular, that has compensated for the interaction that 12 meters has
> on 10 and 17 meters on 15. I use a 5 band antenna switch with 1/4 wave 75
> ohm matching transformers.
>
> I nearly wore a hole in my roof trying to get those bands to cooperate but
> finally gave up. On 12 meters with the driven loop open I had no trouble
> with a properly tuned 10 meter loop but as soon as I hooked the transformer
> up into the switch for 12 meters the SWR would rise to 3:1 on 10. Strange
> thing is that this is an open on 17 meters at the antenna switch on the mast
> but still played games with 10 meters.
>
> Almost the same with 17 on 15 meters.
>
> I'm relocating and will erect the quad from scratch so I'll be able to start
> over but would like any input from anyone that has fought with this
> scenerio.
>
> Thanks,
>
> Randy
> WX5L
>
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