[amsat-bb] How low can you go?
n3tl at bellsouth.net
Fri Oct 10 08:08:49 PDT 2008
This weekend, AO-51’s operations team is giving all of us who work the FM satellites a chance to answer the question in my post's title to our own satistaction.
Here, I’m reaching for a fresh set of Duracells! I’ll be running QRO on them this weekend, though – pumping all 300 milliwatts out of my VX-7R HT into the new Elk log periodic antenna I’ve been running through the ringer for a week – with really good results.
I challenge all of you who will be working the “QRP pair” on AO-51 this weekend to see how low you can go with the RF out and work the satellite. As many of you know, the Satellite Communications Achievement Award (No. 473) that just got posted to the AMSAT Web site for N3TL was earned solely on the basis of confirmed contacts I made while running 50 mW rf out of the VX-7R – on the same set of 2 AA Duracells. I’ll use the other alkaline-battery power setting this weekend, which is 300 mW.
One of the elements of this very low power work I find most exciting is trying to “reach out” as far as I can. For me, it’s not the distance from N3TL in EM84 to the other station I’m working on fractions of a watt that is important. Rather, it’s the range from my location to the satellite at the moment of contact. That tells an interesting story, I think.
Example – During my Duracell Experiment, I worked Jim, KC9ELU, on AO-51 when the satellite was at 8.6 degrees elevation to my west. I use Orbitron to keep track of upcoming passes, and its simulation mode lets me go back, after a pass, and check stats from contacts. When Jim and I worked, my 50 mW traveled 2,482.003 km (1,542.245 miles) to the satellite. Do the math – that’s 49,640.06 km (30,844.9 miles) per watt. I don’t expect to get close to those numbers at all on 300 mW this weekend, but I’m anxious to find out.
I will post my farthest to-the-satellite distance that resulted in a two-way contact early next week. I hope others will do the same, including rf out and distance to the satellite during the contact. Not only is this fun (for me, at least), but it also provides a great test for our respective stations, letting us know “how low we can go” in, say, a true emergency and still complete effective communications.
FYI – I always err on the side of caution when posting numbers like those above. That is, I always use the highest elevation/shortest range to my location. Even a few seconds during a contact has the satellites moving ever closer or ever farther from us, depending on which part of the passes our contacts occur. I use the highest angle/shortest range because I know it was no higher or no closer to me during the contact.
I hope to try some SSTV reception, but probably on the higher angle passes here because I have no experience at all with SSTV. On the lower angle passes, however, I hope to work many of you on the QRP pair while I’m wearing out another set of Duracells – and in between passes of AO-16 (more about that in another post).
73 to all,
Tim – N3TL
AMSAT Member No. 36820
Athens, Ga. – EM84ha
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