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Re: Antennas vs future



Rees,

These are questions I've struggled with over the past year as I got my
phase 3B (OSCAR 10) and PACSAT station up and running.  I've read
thousands of postings about satellite antennas, equipment, modems, etc.,
etc., and I can give you the condensed version of my findings.

>1) Is there agreement on which manufacturer makes the best antenna
>with regard to long term durability?  How well it stands up to
>the stresses of being exposed to sun, wind, rain, ice, snow etc?
Yes, most postings agree that KLM and M2 make the sturdiest antennas. 
They are also the most expensive.  You get what you pay for.

>2) Does anyone have experience with the suggestions presented in
>the June issue of CQ VHF with regard to mounting cross polorized
>antennas in a "x" rather than a "+"?  Any comments with regard
>to lightning protection that this affords by using metal vs
>fiberglass masts?

I've tried it both ways, and didn't notice any difference in performance.
 However, this is a very subjective appraisal, since there are many
veriables with satellite reception.  Since you said you were also
interested in 2m and 70 cm terrestrial work, I would recommend you mount
your yagis in the + configuration so you can do both satellite and
terrestrial operation sucessfully.

>3) Would investing in an AZ/EL system merely give access to AO-10 now?
Will you need the amount of gain from a typical AZ/EL configuration to
use the new Phase 3D?  In other words, will spending money now give over
kill capability in the future.

An AZ/EL system is never a waste of money.  It is useful now with AO-10
and all the low earth orbit birds.  It will be useful with phase 3D to
point your 1.2 GHz helix and 2.4 GHz dish at the bird.  One of the
discussion topics brought up in the AMSAT forums at the Dayton Hamvention
was that the 2m and 70cm uplink/downlinks would be "de-emphasized" in
favor of the microwave links.  This would be done by scheduling less and
less transponder time on VHF/UHF bands and more on the microwave bands. 
This has the added advantage of letting us use small microwave antennas
for the P3D satellite and our big yagis would then be free for full time
terrestrial work.

>4) Is an AZ/EL a high maintenance configuration?  I realize it
>depends on how it was put together in the first place, but would
>putting an AZ/EL system on top of a 50 foot tower be crazy?  The
>purpose of doing so would be to use these antennas for long distance
>tropo as well as satellite use.  

I don't think an AZ/EL rotor is higher maintenance than any other rotor
system.  Just buy quality to save yourself a lot of headaches later.

>5) I have read that using a well installed cross polorized satellite
>antenna can and has been used for EME as well.  This depends on 
>working the other ham who uses a very large antenna system on their end.
 What size of antenna (gain) is needed for this for either/both 2 meters
and 70cm?

I have read this too, but never tried it personally.  The type of system
used was an OSCAR 10-class station.  This provided enough gain to talk to
the EME "superstation" on the other end.  I understand EME stations use
linear polarization, not cross yagis as we do with satellites.

>6) I have heard that certain antenna manufacturers antennas are harder
to put together than others.  Hard on the hands and fingers etc.
>Any experiences?  Suggestions?

Personally, I've not had problems with either KLM or Cushcraft.  Don't
know about the others.
>
>7) Knowing that Phase 3D will eventually fly, would a lower tech
>omni antenna system be a more sane answer to the question of what
>antennas to use for satellite usage?  Do you really need the gain?
>
Yes, you really need the gain.  An omni setup will work only for LEO
satellites, and then only with a low-noise preamp at the antenna.  I
would not expect an omni to be successful with any Phase 3 satellite.

>8) If gain is required, how much is needed as a minimum to work
>AO-10/Phase 3D when it is at the furthest distance from the earth? 

A common arrangement currently in use on AO-10 is 40 elements on 70cm for
the uplink, 18 to 22 elements on the downlink, with a 20dB mast-mounted
preamp on the downlink.  Both antennas circularly polarized, with
polarization switching helpful on the downlink.  Most stations I talk to
on AO-10 tell me they're using 50-100 watts on the uplink.  CW is very
helpful when the satellite is at apogee (furthest distance from the
earth).  And don't forget short runs of low-loss coax (9913 or better) is
needed at these frequencies.

>9) Do the antenna manufacturers who supply cross polorized antennas
>for satellite use provide the "switcher box" or just the relay
>configuration on the antenna for switching between left hand and
>right hand polorization?  It is very unclear that one would have
>to build a switcher box to control the relays on the antenna.  It
>would be nice to know who makes them and are they all the same?  Are
>there any software solutions which monitor radio signal polorization
>and provide control options?
>
You provide your own switch and 12 volt power at the station end.  I am
not aware of any software that does the switching automatically, but most
of us just switch the receive polarity when we hear the signal fading on
the AO-10 downlink.
>
>These questions are the result of a couple of months of "looking into"
>the whole satellite antenna issue.  I guess I am in need of
>experienced input.  I have recently joined AMSAT and have explored
>the AMSAT web site.  I also recently purchased a Yaesu FT-847 and
>want to make an informed decision on the issues of antennas for
>satellite usage.  I want to take advantage of the FT-847's multi
>mode capability on the vhf and uhf bands as well as its satellite
>capability.

I read the review of the FT-847 in the June issue of CQ VHF.  Very
impressive.

>
>I realize these issues may have been dealt with before, but I think
>the actual questions posed here would be of benefit to others as
>new users are always coming on board.  My thoughts are beginning
>(after 39 years in amateur radio) to conclude that satellite
>usage is the future of ham radio.  Or at least a large portion
>of it.

Software is the future of ham radio.  Especially DSP programming!
>
>I thank you in advance for taking time to answer these questions.
>Please reply to the bulletin board so others may learn as well.
>
>Sincerely,
>
>Rees Roberts - K9UUT
>Racine, WI

Good luck with your satellite station, Rees.  I'll be listening for you
on the birds!

73,
Jeff Sykes K5VU
El Paso, TX

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