[Moon-Net] new to 3cm eme

charlie at sucklingfamily.free-online.co.uk charlie at sucklingfamily.free-online.co.uk
Fri Nov 25 14:41:27 CET 2016

Hi Greg

A few thoughts-

Some stations use CP, some use linear.  If you look at my paper at EME2016
you will see there are pros and cons:


It kind of depends on what you want to do.  If you want to not worry about
polarision, but at the expense of some system performance then CP is the
way to go.  If you want optimum performance (when polarisation angles are
matched) then LP is better.  A very large proportions of the smaller
stations that you could work with your dish use linear.  Some of the
larger stations use rotatable linear to get the very best performance when
working smaller stations.

If you want to build a CP feed, my paper has a reference in to a very good
design by SM6FHZ.

I've never used a Spid rotator, but you need something that you can move
in small increments smoothly.  Linear actuators (screw jacks) are nice in
this respect.

Re the RX isolation relay (CP) or T/R switch (LP) most stations use
waveguide switches primarily for low loss, but also higher power handling.

Good luck with your project!


Charlie G3WDG

> Hello everyone,
> I have a 3 cm terrestrial dish with 3 watts that I go rover with and
> really
> like it.  Now I want to build a 3 cm eme system and I am looking for parts
> or build plans on making my own gear.  I am learning a lot about eme but I
> would like any advice on the do's and dont's so as to build it right the
> first time.
> I was reading about which feed is most used on 3 cm eme, linear or
> circularly polarized with a septum feed.  I can build my own linear feed
> as
> I have done with my terrestrial dish but a cp feed with septum looks a bit
> more difficult.
> Does anyone have pictures and a detailed block diagram of the circularly
> polarized feed with septum?  I would like to build one or buy one if
> someone makes them.  I also am looking for a waveguide switch as it seems
> its on the tx side.  Can you use sma or type N relays instead of a wave
> guide switch?
> My dish is a 2.4 meter with a shepherds crook prime focus and will either
> be turned with a spid az/el rotor or a ea4tx rotor controller and screw
> jacks.
> Thank you, Gregr/KA9VDU
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