[amsat-bb] Station not coming together - the full post (sorry for repost, reply to this)
jonny290 at gmail.com
Tue Mar 6 18:52:57 PST 2007
LONG LONG LONG post ahead.
OK, the situation is: I'm building up a satellite station to get familiar
with LEO sats and to get ready for the phase 3E fun to start soon. Here's my
station, and I'll post my thoughts after that.
The "too long, didn't read" version: I've built good antennas, fed them with
good feedlines and into a supposedly good receiver, but I just can't keep
solid copy on LEO birds, and cannot get a QSO. I am jealous of the
"Satellites worked with HT and 5/8 wave" articles, and want to figure out
what the weak link in my station is.
Eggbeater II antenna mounted at 15 feet. This is built to the K5OE Eggbeater
II spec (http://members.aol.com/k5oejerry/eggbeater2.htm) using RHCP but
uses a 100 ohm phasing line using two 50 ohm coax lines done in parallel,
used in a balanced configuration, instead of 93 ohm RG-62. Antenna was
'redesigned' in MMANA-GAL to match exactly 100 ohms and to use 6mm diameter
copper tubing instead of AWG 12 house wire. It is peaked for SWR < 1.1 at
436 MHz, and is less than 1.5 at 435.0 and 437.0.
Our lot is lightly treed, but there is no wood (natural or otherwise) within
six feet of this antenna. A good chunk of the sky, mainly northwesterly
looking, is partially obscured by a large tree, but right now the leaves are
off and it shouldn't kill the signal that much...should it?
This antenna is the secondary antenna on this mast and is mounted on a 3
foot PVC stand-off pipe. The primary antenna is a Diamond F22A mounted at
approximately 18 feet. It has a 10 foot vertical element and three 1/4 wave
horizontal radials. It is not used in the satellite station but I wanted to
describe it, in case it is interfering (I suspect it is.)
Eggbeater is fed through29 feet of 213 spec coax (5.1 dB loss/500 MHZ)
terminated in well done PL-259 connectors. I have verified this particular
cable's loss at less than 2 dB at 432 MHz, using my Icom PCR-100's accurate
S-meter and a known signal source.
My latest upgrade: RX chain goes into a homebrew bypass relay / Ramsey
preamp box (the relay is DPDT and switches the preamp in or out of the RX
signal path). The preamp provides approximately 18 dB of gain when inserted
and using a test signal around 432 MHz. It has proven somewhat beneficial,
giving me 2-3 S-units advantage at certain points from the LO-19 CW beacon
(Which I recently received at up to S9 with the preamp on a ~60 degree pass,
a new record so far).
I have tested both with the antenna coax plugged directly in, and through
the relay/switch box, which is connected to the radios through a 3 foot RG-8
patch cable. The preamp box uses runs of RG-174, but all runs are properly
done and less than 2 inches. Telay box and the patch cable has been measured
to have 1-2 dB of loss when bypassed at 432 MHz. I know this can be
improved,but given my tests, I don't believe the plastic case of my preamp
is killing incoming signals or anything (I switch coax lines quickly and it
doesn't kill weak but audible signals at all).
IC-208H dual band radio, rated at <0.18 uV for 12dB SINAD
PCR-100 computer controlled receiver, rated at <0.34 uV for 12dB SINAD
The TX setup is currently an IC-271 pushing from about 4 to 38 verified FM
watts into a simple RHCP turnstile, recently built. It is mounted on a
slightly shorter PVC mast about 10 feet away from the "big mast". It is the
only antenna on this pole, and is fed through 27 feet of 213 spec coax.
Peaked at 145.8 MHz with SWR less than 1.1 . I know the turnstile pattern
has most gain directly overhead and has some shortages towards the horizon,
but I have plenty of theoretical EIRP to get on the LEO sats, I believe, and
I'm not worried about the TX path right now.
I'm just not getting the signal strength and intelligibility that I expect
from this setup. For example, there was a theoretically perfect SO-50
ascending pass today at about 5:15 PM Central, 15 minutes plus duration and
it peaked at almost 80 degrees elevation. I received the signal faintly
starting at 2 degrees, and it steadily improved to a 'fluttering S3" at
about 8-10 degrees. I attempted to come back to a station that finished a
QSO, because I thought it cleared - turns out,the signal DIED. I could just
barely track it for the rest of the pass, even when it was almost directly
overhead at less than 900 miles altitude. Gave up when it was five minutes
before LOS, with no contact made.
So, given my station description, what am I facing? Is my Eggbeater's
'overhead 10dB null' design killing it? I would think that, as designed, the
greatly decreased path loss as the bird comes overhead should compensate for
this shortage, and then some.
As mentioned earlier, I'm also concerned that the Diamond F22's radials are
destroying the radiation pattern of this antenna. I'm in a rent house and
have to conserve masts as much as possible, but if it's killing me, I can
move the satellite antennas to a ~12 foot PVC mast instead of trying to
piggyback them on my metal vertical mast.I've copied beacons and various
carriers from birds as low as 0.5 degrees, so I know the antenna 'gets out'
okay at lower elevations. It's the high elevation periods that are
How does my IC-208H compare to more refined receivers? Is it too deaf? I've
considered feeding my IC-735 HF radio with a 435 MHz receive converter. This
would allow all mode 70cm reception with a very good radio (comments on the
Hamtronics converter boxes would be great). I'd love any comments on the
Hamtronics receive converters from those who have tried them out.
I'd appreciate any comments and advice from the great minds on this list.
Thanks for taking the time to read up and give any advice or comments.
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