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RE: Power divider for X-yagis



Hi Joop

> When buidling a phasing harness for (switchable) circularly polarised
> crossed-Yagis one needs a device to split the line from the TRX to the
> two legs of the yagi.

Ooh! One of my favourite subjects.

About five or six years ago I spent an enormous amount of time on this very
subject, coming up with all sorts of ideas but often they did not work very
well, especially when trying to measure them up for matching.

Firstly, I used the design here http://www.g6lvb.com/remotepolarization.htm.
this worked well but the N-type coax relays I used were quite bulky. I
originally used it with a pair of Arrows:
http://www.g6lvb.com/ultimate_arrow.htm

I also tried various other switchable polarisation methods including PCB
mounting UHF rated relays with small bits of RG-178 and RG-179
matching/phasing lines: the problem here was that neither the relays nor the
coax was really rated for 50W+ especially at 70cm, and they got nice and
warm! In addition, getting a good match is always a problem.

In the end I got lazy and use the remote Wimo polarisation switchers (models
18080 thru 18083) that can mount, together with a preamp such as the SSB
SP-2000/SP-7000 series, directly behind your cross Yagis' reflectors. This
is the configuration that we use for ARISS contacts in the UK.

To see the importance of proper matching see here:
http://www.g6lvb.com/images/stacking.gif

Essentially what this is saying is that a mismatch that you'd probably not
bother too much about when matching a transmitter to an antenna becomes
important when combining two or more driven elements, so much so that it may
be that there may be little benefit to combining at all.

However once you get it right I am convinced that the benefit of being able
to switch polarisations on an cross Yagi at least saves you the potential
embarrassment of having to explain your massive single linear yagi to the
neighbours ;-)

73, Howard G6LVB
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