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Re: Beginners questions



On Wed, 1 Mar 2000 SBCmusic@aol.com wrote:

> First, can I expect to work any of the FM birds, reasonably, with a 2 meter 
> vertical or dipole?  (same for 440)

Yes & No.  I have been using a 20.25 inch vertical whip antenna over a
ground plane as a dual band 2m and 440 antenna for the satelites for about
2 months.  It acts as a 1/4 wave on 2m and as a 3/4 wave on 435 MHz with a
good pattern for satellites.  It has low VSWR on both bands.

I have found that using an HT (kenwood with built in 9600 baud TNC), I can
regularly hear every pass as follows:

AO27 above 25 deg
UO14 above 20 deg
UO22 above 25 deg
KO23 above 15 deg
KO25 above 20 deg
TO31 above 10 deg
SO35 above  5 deg

And since my tracking program automatically tunes the radio for doppler
too, its really nice to just let it run all day.  WHen any satellites
meets the above criteria, the squelch opens and I hear the bird and/or the
computer captures any packet data.

Almost all of these satellites have shown to be predominantly vertically
polarized most of the time, so there is no 3dB loss associated with
listening to the horizontal component.  ALso as a 3/4 wave vertical on
435, there is almost 7 dBi of gain above 30 deg, combined with the fact
that the satllite is 6 dB closer than at the horizon, you can see that
this 2m vertical whip antenna performs with almost 12 dB of "relative" 
gain to a typical mobile whip which is maxmimzed on the horizon.
THus, it works very well overhead indeed (but only about 1/3rd of all
passes are in this region)

A comparison of this antenna against others is plotted graphically on

http://web.usna.navy.mil/~bruninga/astars.html 

down near the bottom of the page. 

COAX LOSS:  Also, if you are using this antenna on your car (with only a
few feet of coax, you will see this kind of performance.  If you are using
100 feet of RG8 type coax, to your roof, forget it.  You wont hear the
satellites at all without a preamp.

FINAL COMENT.  But since this antenna only looks UP in a cone above say 25
degrees of your location, it is a waste to put it "high and in the clear".
Height gains you nothing in this case.  SO just mount it on your gutter
just above your window with 10 feet of coax, and then you have good sky
coverage and minimal coax loss...

Just my 2 cents.
Will this work well?  Depends on what you want to do.  Yes, it will let
you monitor the downlink of many satelites every day with a simple
antenna.  No, your station will never compare to a traking pair of yagii
antennas that can give coverage horizon to horizon when mounted well high
and in the clear...

But it also works in your car and thats a great place to just play ham
radio...

de WB4APR, Bob


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