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

[Edward Cole]

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
>dealing
>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.

Jonny,

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.


73,
Ed - KL7UW
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