John and all,

I mean no disrespect, and I'll apologize now if what follows offends you or anyone. I agree - to a point - about pointing accuracy. Let's face it - of the three FM satellites currently available to us, SO-50 is the largest target we have. It is a 35mm (13.78-inch) cube. We're shooting signals at it from hundreds of miles away, so even the most accurate of pointing likely is a little of dead-center ... hihi.

That fact notiwthstanding, however, I remain convinced that each individual station has its own sensitivity to pointing accuracy relative to effective communications. Stations running relatively high power levels and well-calibrated motorized antenna systems likely can be less accurate and still be effective. I don't believe I and others enjoy that luxury when we set out to work the satellites on handheld stations running lower power levels - in some cases, much lower power levels.

The International Space Station provides at least a partial illustration. Here, I don't worry about Doppler tuning with the ISS because (1) it's orbit is lower (thus, it's closer) and (2) its radio runs significantly more power than any of our other smateur satellites. Even at a "low power" setting of 5 watts out, it is 20x more powerful than SO-50 and 10x more powerful than AO-27. I don't have to be as careful with pointing or Doppler tuning to enjoy a good experience on an ISS pass. Not so when trying to capture and keep, for example, AO-27's half-watt signal.

Before I started working the amateur satellites about 14 months ago, I had spent several years enjoying visible passes of the ISS whenever I could. As I learned of the available amateur satellites and decided to give them a try with a handheld station, it became apparent to me very quickly that my "practice" on the ISS would be helpful. I use a compass to match AOS/mid-pass/LOS positions with known landmarks here, and then I visualize how a satellite will arc across the sky relative to my location on a given pass. I believe that has improved my pointing accuracy significantly, and I further believe that accuracy makes a difference at times in whether I make a successful contact.

This morning on AO-51, I made contacts with KB1RVT in Maine and WA3SWJ in Maryland. Those contacts provided the 29th and 30th states I have worked on the FM satellites using my Yaesu VX-7R HT set at 50 milliwatts (.05-watt) output. I have used either an Arrow dual-band yagi or my current Elk dual-band log periodic to make all of those "flea power" contacts. I don't believe any would have been possible without pointing and tracking that is as accurate as I can make it, given my hand-holding and manual tracking.

That being said, I believe your creation of an antenna bore sight is an outstandning idea - one that will help anyone improve the effectiveness of stations using tower/mast-mounted antennas with motorized Az/El rotation systems. Congratulations on that, and thank you for sharing it with the BB.

73 to all,

Tim - N3TL Athens, Ga. - EM84ha

________________________________ From: john heath g7hia@btinternet.com To: amsat amsat-bb@amsat.org Sent: Thursday, August 13, 2009 1:16:33 PM Subject: [amsat-bb] Antenna pointing

Hi,

I agree with the comments that  high degrees of pointing accuracy are not required for satellite work. However, if you are super keen to improve your pointing accuracy then you may like to consider the modern version of the "bore sight" method.

A bore sight is basically a length of tube, you look through, you only get a view of the target when you are accuratly lined up with it. The longer the tube the greater the pointing accuracy.

For an antenna boom mounted bore sight I used about six inches of  15mm copper water pipe with a stop end soldered onto it. I drilled a 1/8" hole in the stop end and  fixed  a light dependant resistor in the "eye end" Attached to the boom and ran wires to the shack where I had a battery and voltmeter.

Point your antenna at where the Sun should be then "hunt" backwards and forwards, up and down until you see a peak reading on the meter = the sun. Its a bit of work but the benefit of this method is that its on the tower and you can check it anytime the Sun is out.

Practical problems, waterproofing and true alignment to the boom.

It was a lot of work but a fun project, eventially destroyed by water penetration.

73 John G7HIA _______________________________________________ Sent via AMSAT-BB@amsat.org. 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