Very nice to read this material on the bb....brings back some of the excitement of building a first station.....
73 de Tim, K4SHF
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jonny 290 Sent: Wednesday, March 07, 2007 7:16 PM To: [email protected] Subject: [amsat-bb] Re: Station not coming together - the full post (sorryfor repost, reply to this)
Yeah, I think the next paycheck's fun money is going to an AMSAT membership and a stack of 1/4" aluminum rod, heh!
I'm designing the beam on paper, and as per your suggestion, I'm attempting it with a single beam. So far, it looks great - folded dipole element, about 11db forward gain, exactly 50 ohms impedance, great bandwidth and at 30 degrees elevation, the horizon is 1.5db off peak response, and the -10db response on the upper side should be around 75 degrees.
I recall that satellites spend only an infinitesimal amount of time above 75 or 80 degrees elevation, and though it'd be ironic that I'd lose the satellite directly overhead, when it's at lowest path loss, I can deal with that for 30 seconds in one out every 20 passes I work, by my estimation.
If the single one works and I want to improve upon it, it'll be trivial to build another and phase them up.
Question:, for linear polarized antennas, am I going to see any benefit by orienting it any particular direction? I ask because I remember that horizontally polarized signals 'bend' a little bit more over the horizon, though admittedly this effect will be very small at 435 MHz; I also believe most man-made noise is vertically polarized, so I'm thinking that keeping it horizontal would be the best course of action.
Should I go Arrow-style and design a 3 element 2 meter beam at right angles to the 435 beam? If the more important 70cm antenna is horizontal, this would put the 2 meter beam vertical - and even though it'll be at a 30 degree elevation, that would give the uplink antenna a little bit of 'downtime' utility as an FM simplex antenna. That's a very minor issue, but I like to lay it all out as it zips through my head - due to my QTH constraints, antennas that can do 'double duty' are especially valuable to me.
I suppose I could just buy an Arrow....but that's the easy way out (not that those aren't great antennas!)
The Yaesu 817 is a great radio, but I am an irrational brand loyalist for some reason, and I can't help but be obsessed with Icom gear. My big decision is "435 downconverter or Icom 706mkiig" this spring. The downconverter would come about $700 earlier, but the 706 would give me the all-important all-mode 70cm receive as well as 70cm all mode transmit if I want to play with VO-52 or AO-7 in B, etc. My 735 is a hot radio and I believe it'd work very well with the downconverter and an ARR preamp, but the 706 is very tempting.
If the IC-703 had 70cm coverage, I'd have picked one up three months ago. It'd be perfect for this application - I wish they'd realize that and add it. They'd gain a lot of satellite operators with a rig you can snag for $450 or so - and it seems as though you can get by on 5 watts usually!
On the downconverter - mast mounting - good idea, bad idea? I see the upside of "28 mhz cable on RG213 = good", but the downside of "environmental factors/temperature on a crystal oscillator = bad." Thoughts? I'm confident that I can weatherproof, but I'm mainly concerned about the temperature changes.
Well, I think that's all for this evening - back to antenna building :)
73, Matt (or Jonny, whichever :) ) _______________________________________________ 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