[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

RE: circular polarized Arrow antenna



Hello Tim

> In my own personal opinion, a portable CP antenna may not be worth the
> effort unless the satellite antennas are pointed toward earth to create
> an ideal situation to realize the extra gain. A linear Arrow antenna
> requires no polarity switching hardware since you can rotate the axis of
> the boom to compensate for the relative change in polarity. Hopefully
> this does not start a big debate on CP versus linear as I am only
> talking in terms of practical real world applications for portable
> operation.

Whilst I certainly agree with what you're saying for LEO's, there's a couple
of things I'd like to comment on regarding my personal experiences of
operating AO-40 portable & use of a linear or CP antenna on the uplink.

For the majority of the time, over say 10 degrees above the horizon, and at
reasonable Squint Angles (say under 20 degrees), both of which under
'normal' conditions would be at least 85% of the time AO-40 is above the
horizon, I find RHCP is beneficial for two reasons:

o Holding an Arrow up in the air by hand so that you can twist the axis
would be very tiring for the length of time AO-40 is above the horizon - not
to mention a potential risk to one's health if you work out the emissions as
per FCC recommendations at 50W (I did this about six months ago and
calculated that with 50W of SSB you need to be at least 50cm away from the
rear lobe and 2m away from the front lobe).

o Empirically I find RHCP _is_ audibly beneficial on AO-40 by far _most_ of
the time. Only under extreme situations during large squint and/or at
perigee do I find any benefit in switching to vertical/horizontal/LHCP.
Normally all polarisations other than RHCP are audibly worse.

But you're absolutely right about the Arrow when operating LEO's.

73 Howard G6LVB


----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home