[amsat-bb] Re: Crossbooms ... my pennyworth.
howard at howardlong.com
Tue Jan 9 19:36:09 PST 2007
Firstly, I am so glad to hear from you on the BB after a long time.
> In my humble opinion, on LEO's the squint experienced just doesn't
> warrant the effort of being (theoretically) correct. It did make a
> difference on AO-10 and AO-13 (HEO's) but still hardly worth the effort of
> "technically correct".
> Others may have a different opinion ... which of course, they have evey
> right to have.
No, I am sorry but I have to _agree_ with you! There is some time spent on
squint in the bible (Martin Davidoff's superb Radio Amateur's Satellite
Handbook and previously known as the Satellite Experimenter's Handbook).
What's not discussed extensively is the differences operating-wise between
LEO and HEO for this phenomenon.
In practice, squint presents itself on LEOs differently to HEOs. Squint on
amateur LEOs is very temporary and can largely be corrected, during a pass,
by changing polarisation (H,V and/or R,L) on the fly by the operator. For
HEOs, due to the increased distance and longer term power and attitude
constraints, squint is usually an issue to do with the long term positioning
on the satellite's downlink antenna in relation to the Earth, and unless
you're a command station, and the HEO's power budget is good, you can't fix
that from the ground.
For a couple of years prior to AO-40 when only LEO's (plus a tiny bit of
AO-10) were running, I ran for a year or so a pair of Arrows phased on a 6'
cross boom. I spent _many_ evenings messing about placing all the elements
of the 70cm on one boom and all of those of the 2m on another boom but I
could ever get a great match, particularly on 70cm. So I resorted to making
circular polarisation work with the 2m and 70cm planes separated, and remote
preamps and remote polarisation switches.
This worked _very_ well, and the gain you achieve by being able to manually
switch polarisation during a null when working LEO's cannot be over
One final point, radio amateurs have been doing antenna diversity for a very
73, Howard G6LVB
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