[amsat-bb] Re: Station not coming together - the full post (sorry for repost, reply to this)

Edward Cole kl7uw at acsalaska.net
Wed Mar 7 02:10:20 PST 2007


You can't go wrong with the ARR P432 GasFet preamp ($79).  I used one 
on 2m for eme until getting my current preamp.  Be sure to remember 
that you do not transmit into it...just once and the transistor is 
history - no second chances.

At 11:06 PM 3/6/2007, Jonny 290 wrote:
>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 think you may find that the antenna works much better when you get 
the preamp hooked there.

>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.

Mount the mast/rotator/antenna on a $33 Radio Shack tripod (Buy a 4x4 
foot square of plywood to bolt the legs thru and weigh down with 
rocks or something heavy on three sides.  I used 3 cinder blocks and 
the antenna survived 50-mph winds.

>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

Most LEO satellite passes last only 20-30 min.  You will probably 
have to move the antenna about five times for a pass (max) - or 
computerize it.  Check out WB4APR, Bob Bruninga's cheap radio shack 
rotator system with software (free).  Very simple and cheap!

>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.

Naw.  More like every 3-5 min.

>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.

3-elem 2m + 6-elem 70cm fits on a 3-foot boom.  Google WA5VJB for 
simple/cheap home built yagis.  Mount elements a right angles and no 
interaction.  You have basically built an Arrow.

>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.

Buy the preamp first!  You should get it in 3-days ground-UPS.

>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.

Go for a short ground mount as you will want easy access to tinker 
with things, often.  On a pitched roof will become a pain!

>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.

P3E may only be a year or so off.  Get started with LEO and add 
better antennas, later!  For HEO you will need SSB, so the 435/28 
xvtr is a better investment for the future.  Then all you need is a 
2m SSB radio.  You will want 11-elem 145-MHz and 16-20 elem 435-MHz 
for mode-U/S.  You will need a 2m preamp for that mode and at least 
10w on 435-MHz (50w is better if you have a long coax run).

Ed - KL7UW
  BP40IQ   50-MHz - 10-GHz   www.kl7uw.com
144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
DUBUS Magazine USA Rep dubususa at hotmail.com

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