[amsat-bb] Re: Station not coming together - the full post (sorry for repost, reply to this)
kl7uw at acsalaska.net
Tue Mar 6 22:07:30 PST 2007
At 08:01 PM 3/6/2007, Jonny 290 wrote:
>Bruce, Gould and Les,
>Sincere thanks for your thoughts so far. I'll let this topic percolate for a
>bit, but I had to comment on one thing:
><<<Unlike in HF, where the RF sometimes just gets through, here you're
>with the Hard Numbers, and they will crush you into silence.>>>
>THIS is why I love satellite operation. It's a huge challenge, and the
>ionosphere largely has NOTHING to do with it. No 'magic' involved. I know
>it's anathema to ye olde Amateur Radio meme of "operating in a dim room with
>a small transmitter", but I am finding that this satellite station is the
>greatest engineering challenge of my life, to date - and I'm going at it
>100% solo NOBODY in my area knows anything gives a rip about the birds. Yet.
As you are discovering, the Amsat-bb is a great source of help for
folks starting out. The others have pretty well pointed out your
receiving system on 435 MHz is not working well enough. I have no
experience with SO-50 so do not know if the K5OE eggbeater has enough
gain. An excellent article was printed about receiving AO-51 in the
latest issue of Amsat Journal. If you are not a member then this is
one benefit of membership.
My impression of Hamtronics equipment is that is better for repeater
use and not optimum for "weak-signal" satellite reception. The
Hamtronics preamps do not have low noise figures. Gain without low
noise figure will not result in bettering your reception. Preamps
must be placed close to the antenna (if not directly to the
antenna). The 2-dB coax loss is directly added to the noise figure
of your preamp (which I estimate is no better than 1.5 dB). You want
to get a 0.5 dB noise figure preamp with a minimum of 15-dB
gain. The IC-208 probably does not have very low noise figure (I
would guess around 10-12 dB).
Line loss is better measured using a power meter and a
transmitter. Receiver S-meter indications are altered by the AGC
action of the radio and not trustworthy for signal level measurements
of any accuracy. But if the coax is new then 2-dB loss for 29-feet
is probably close.
I would try the eggbeater on its own support mast (height is not
particularly important for satellite reception if not obstructed by
hills or buildings. I received AO-51 using a 2m 19-inch high
mag-mount whip on a square of sheet metal and a 0.5 dB noise figure
preamp with very clear signals above 10-degrees of elevation. This
was very early in its history when running very low power on the satellite.
Try these ideas out and let us know how it goes.
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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