[amsat-bb] Re: Station not coming together - the full post (sorry for repost, reply to this)
jonny290 at gmail.com
Wed Mar 7 00:06:39 PST 2007
OK, let's take a bite out of this.
RE, the preamp: I agree that it is likely a weak point. I wanted to check it
out, though, and for $22 I couldn't go wrong. It'll still prove useful at
some point down the road.
If one of the mast mount preamps are what the situation requires, I"m ready
to take that step.
The eggbeater is actually designed with radials to 'pull' the signal towards
the horizon. It almost seems as though the radials may be working too well -
I've got moderate to great copy up to a few degrees, then it falls over
dead. Due to my 'beater's design, it's trivial for me to replace the loops
and/or the radials without messing with the phasing harness or antenna
mount, so I can try an antenna that doesn't have a by-design null at high
elevations. I'd almost like to do this just as a lark, as it'd cost me a
grand total of $7 to go buy another 10 foot piece of 1/4" fridge tubing.
I can also experiment with putting the 435 eggbeater on a nonconductive PVC
mast. Also a cheap experiment, couple of bucks for 15 feet of PVC. That
might get it up high enough with no metal above or near it, save for the
Here's my main issue with the TV rotator, and you'll think this is silly and
trivial, but it's a major sticking point, and why I've been going at this
with omni antennas so far. My main mast sits _directly_ outside my
roommate's window, due to overhead power line and tree location. It's the
only place where I can safely have a structure above 10 feet, that is less
than 75 'coax feet' from my shack window.
I'm concerned that spinning the rotator at night will bother him. If the
mast is solidly mounted to the house just a few feet away, how much will one
of these inexpensive TV rotators conduct into the building? Could I cut that
down by putting some rubber between the mast and clamp, something of that
The next step, and I'm ready to move to this point if I can address the
noise issue to my satisfaction, is to build a small cross yagi, 4 to 7
elements, and mount it at fixed elevation on a small TV rotator. I believe
that an antenna in this size range will prove a big advantage over the
omnis, should have a wide enough beamwidth such that I will get away with
fixed elevation, and should only have to crank the rotator every 60 to 90
seconds, except for the extremely high angle passes.
If that works on receive, but I'm having uplink problems, I can put a 2 or 3
element CP yagi for 2 meters on the same boom, which should let me hit most
of the satellites with 10-15 watts of power, max.
I'm very eager and willing to design and play with antennas - love homebrew
in general, I just can't design a circuit to save my life - and know how to
model and build good quality antennas. I'm fairly certain that I can get
crafty enough to get around what restrictions this environment does have.
So, here's what I'm looking at, I think.
1: Mast mount preamp
2: Beam with rotator
3: Hamtronics downconverter (435.5 - 437.5 MHz, somebody tell me if I'm
getting the wrong frequency range choice - my HF radio stops at exactly
30.000.000 so I want to make sure I can hit the 437+ frequencies)
The beam will require design and construction time (I don't believe in
buying antennas except in rare circumstances); I can throw green paper at
the preamp and get it out of the way, since store-bought is the best option
for that at this time. In addition, I don't want to have to install the beam
and rotator and preamp all at once; it'd be nice to have the preamp ready to
go by the time I put up the beam and rotator.
I'll be honest, I'm generally an impatient person, and I'm busting my chops
and treating this station in a rent house as a challenge. I was serious
about hitting the Phase 3E sats when they go up, but I do _not_ expect to do
it at my current QTH. If all comes together, I move into a house this fall,
at which I hopefully will have clear space and the ability to put up a
"real" antenna support. Once that happens, either a roof mount or small
tower, I'll build a long yagi array and get it under computer control. But
I'm not at that phase yet, and I want to get experienced at this level
before I think about trying to work the high orbit satellites.
I actually grew up a ham in my early teen years back in the early 90's, and
remember poring endlessly over AO-13 articles. It seemed like the zenith of
technical accomplishment in our hobby. I came back to ham radio last year
and was disappointed to find that we had no high orbit satellites currently,
but the LEO satellite 'scene' seemed active and I figured I could get my
feet wet with them before I tackle the big ones when they go up.
More information about the AMSAT-BB