The company that comes out with an AZ/EL unit that is about $200 is going to sell a million.
Radioshack already does. Its called a TV rotator, and I would buy one before they are no more!. For LEO satellites one does not need elevation 98% of the time and with a modest beam (ARROW type) you can have a $70 system. Tilt the beam up about 15 degrees so that you still have max gain on the horizon where satellites spend 1/3rd of all their pass times below 20 degrees. Track then in AZ only.
As the satellite gets above about 30 degrees and starts to roll off a dB or so of beam gain, remember that at that elevation the satellite is HALF as far away so it is now 6 dB stronger! This remains true up to over 45 degrees, where you may be down 3 dB on the beam but the signal is 10 dB closer to you! The break-even point is above about 70 degrees. BUT! Remember, the satellite is only above 70 degrees less than 2% of all pass times. Simply not worth spending another $700 for an elevation rotator for 1 minute a day of better access.
Also, do NOT be tempted to tilt above about 15 degrees or you are going to lose gain on the horizon where you need it most. Lots of folks put it up higher because it seems logical, but they are ignoring the very significant DISTANCE factor at low elevations (sketched to scale on the web page).
Please take a look at the plots on http://aprs.org/rotator1.html
Its an old page, but the drawings are always valid.
Bob, WB4APR
----- Original Message ----- From: "Lee Maisel" [email protected] To: "amsat-bb" [email protected] Sent: Thursday, May 24, 2012 1:02:39 PM Subject: [amsat-bb] Re: Antenna suggestions for mounting on vehicle for sat work.
Thanks Clayton!
Now if I could find a small commercial az-el rotator for an Arrow, that would be ideal!
Lee
Clayton Coleman W5PFG wrote:
Lee,
I have yet to find a better solution for FO-29, SO-50, and AO-27 mobile than a combination of small UHF yagi with preamp for the downlink and a VHF vertical for the uplink. While the quadrifilar helix, eggbeaters, and 19" whip all work, nothing gives me a 100% copy of all the LEO's from AOS to LOS like the yagi/preamp combination.
I've tested the above mentioned fixed antennas for downlink across a variety of Texas terrain and surrounding noise environments. They all work, some better than others, but are no where near the performance level of a directional antenna. Since I'm a firm believer that hearing the bird is #1, I do not compromise with a vertical. It's safer for me to pull my vehicle over to a parking lot or rest area to work passes. I have done a few passes "in motion" with both the quad and the 19" whip and quite frankly terrain/obstructions play such a huge role I hardly recommend even attempting to do it unless you are on a flat, high plain.
73 Clayton W5PFG
On Thu, May 24, 2012 at 3:02 AM, Lee Maisel <[email protected] mailto:[email protected]> wrote:
Any ideas on a good antenna combo for mounting on a large vehicle? Possibly roofrack, specifically for satellite work? Thanks! Lee W5LMM _______________________________________________ Sent via [email protected] <mailto:[email protected]>. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
_______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb