[amsat-bb] Re: Polarity switching question
Gordon JC Pearce
gordonjcp at gjcp.net
Mon Jul 13 08:01:06 PDT 2009
On Mon, 2009-07-13 at 14:51 +0000, w6zkh at comcast.net wrote:
> I recently obtained a pair of KLM yagi's for satellite work. They both
> have the KLM polarity switching box mounted and wired up. Since I
> havent put them up yet, and not well versed in the subject, I got out
> my ohm meter just to see what was what on this item. I noticed that
> both driven elements have continuty to the center pin of the coax at
> the same time. I was under the impression that the relay switched back
> and forth the driven elements to give either RH or LH polarity. I
> havent applied the 12 volts to the box yet to check that out, but was
> just curious. One thing I have noticed while using the downlink yagi
> is that I get very little fade due to polarity when I turn the
> antenna. I hope that is a good thing?? I havent checked the uplink
> yagi to see if it has the same results.
> I hope someone can enlighten me abit.
If it's circular-polarised then both elements should be wired, with one
going through a 1/4-wavelength loop of wire. That way, the 90-degree
rotation of the circular polarised signal translates into a 90-degree
phase shift between the horizontal and vertical elements.
Imagine trying to thread a corkscrew through the elements along the
length of the boom, and you'll get it.
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