Rotating polarization on HF, as you surmise, does seem
quite fast. In my microscopic city lot, I have
managed to implement both a horizontal wire (with
tuner, ergo pseudo multi-band) and a multiband
vertical. With two radios, I can listen to a signal
on both antennas simultaneously. When DXing I often
do this - what would simply be out-and-out fading if I
used only one antenna turns into a back-and-forth
trading of the signal strength from one antenna to the
other, and there's never a time when the signal is
absent from both antenna/RX combinations at the same
time.
Dave W8NF
>Date: Tue, 8 Feb 2005 22:46:01 EST
>From: TexasRF@aol.com
>Subject: Re: [Amps] 10dB and propagation
>
>I don't recall any mention of polarization changes in
>this discussion.
>Being
>an EME operator I am keenly aware of the faraday
>rotation problem at
>VHF. As
>the frequency is lowered the rotation speed increases
>dramatically. The
>lowest frequency that I have personal experience with
>is 50 MHz and the
>rotation
>there is typically about one fourth degree per
second. >At times of
>disturbed
>(by the sun) conditions the rotation speed can be
much >faster.
>
>I have not seen any data for 40 or 20 meters but if
it >scales like VHF
>could
>be on the order of 3 or 4 degrees or more per second.
>A time interval
>of
>several seconds could make quite a difference if the
>polarity of the
>antenna is
>not adjusted. The difference in signal strength at
VHF >and UHF between
>matched
>and mismatched polarity can approach 20 dB.
>Interestingly, for some
>unknown
>reason there are periods that the polarity smears
>enough that the
>problem
>disappears. We know this because quite a few 432 MHz
>EME operators have
>polarity
> rotators on their antennas and can receive at any
>polarization angle.
>
>73,
>Gerald/K5GW
__________________________________
Do you Yahoo!?
Yahoo! Mail - Find what you need with new enhanced search.
http://info.mail.yahoo.com/mail_250
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|