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.
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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

Thanks Bob!!!!

That is extremely helpful, and most likely what I will do. Now, is there a computer interface somewhere for these RS rotators?

Lee W5LMM

Bob Bruninga wrote:

...

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

Thanks, Ted, and that's fine if I have to do that, but all the RS rotators are 110v with no 12v option. I have searched, but can't seem to find a small 12v rotator. I'd hate to use an inverter just for that, seems silly.

73 Lee W5LMM

Ted wrote:

Lee, there is a construction article in Chap 6 of the ARRL Satellite Handbook (too complicated for me)

But the reality is that it is easy to manually turn the RS rotor with the control box from the comfort of your chair just following the azimuth showing on your sat program and listening with your ear...this will get you close enough. I have the Elk on a RS rotor with Bob's fixed elevation. (Worked good enough for VUCC #226)

Of course, the original question was about mobile installation, so unless you have a long extension cord or a generator....... hi hi

73, Ted, K7TRK

On 5/24/2012 9:15 PM, Bob Bruninga wrote:

...

...

all the RS rotators are 110v with no 12v option I'd hate to use an inverter just for that,

But a 100W inverter that plugs into a cigarette lighter is only $24 or less at Walmart. That is much less than you would pay compared to trying to find a 12v rotator system.

I agree. I have built a couple of 12V satellite tracker servo systems, and the cost is too high in small quantities to ignore the efficacy of the inverter solution.

Please visit http://www.lostfrogs.com/SatTrack.htm .

My first system was in the AMSAT newsletter of July/August 2009. That system worked OK, but my last system was much improved with dual antennas and by beefier motors and gearing, and was used to make numerous contacts during the 2010 Field Day.

I sold that system to a eager Satellite Ham for $400; that included hand made gear boxes and supported by the Parallax BASIC Stamp. I broke even in materials, that is all.

My current plans are for an improved system (in terms of speeds and accel/decel issues) based upon the Parallax Propeller. As a hobbyist I will buy what I need to put the system together, but if someone is interested in funding an endeavor I am open to that prospect!

Incidentally the inverter problems are maybe less than the RF into the servo controller problems, hence the 8' boom in the current version to get greater distance from the antennas and the servos.

Dave KI4PSR

On 5/24/2012 9:15 PM, Bob Bruninga wrote:

...

all the RS rotators are 110v with no 12v option I'd hate to use an inverter just for that,

But a 100W inverter that plugs into a cigarette lighter is only $24 or less at Walmart. That is much less than you would pay compared to trying to find a 12v rotator system. I had similar designs for 12v rotator systems, but just got lazy and realized it is easier to simply use these cheap inverters that are 95% efficient and just use whatever I need in the car for playing ham radio wether it is 12v or 115v, dosn't matter.

Though watch for RFI from the inverter?

Bob, Wb4APR

Ted wrote:

...

Lee, there is a construction article in Chap 6 of the ARRL Satellite Handbook (too complicated for me)

But the reality is that it is easy to manually turn the RS rotor with the control box from the comfort of your chair just following the azimuth showing on your sat program and listening with your ear...this will get

you

...

close enough. I have the Elk on a RS rotor with Bob's fixed elevation. (Worked good enough for VUCC #226)

Of course, the original question was about mobile installation, so unless you have a long extension cord or a generator....... hi hi

73, Ted, K7TRK

---

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