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BS BS?



Very simple answer for what I used for Mode-B:  A homemade antenna.
Windload, less than dish, yes.  Not hard to design around though.  Lighter, 
yes. Again, not hard to design around.

Neighbors seeing 3 foot dish.  Ok.  Neighbors seeing 15 foot long antenna:  
Not happy.

Will this matter to me in a couple of months when I move to the country?: 
No.  Will it matter to others in these days of Deed Restrictions (in the US 
anyway)?: Yes.

On a small, 4-5 element 2m, apogee was unreliable.  Once you get up to about 
10 eles, it's reliable again.  Then you are up to the 15 foot long antenna 
again.

As far as expensive stabilization, there is no reason a spin stabilized sat 
like AO-13 can't benefit from the antenna gains at the higher freqs using 
smaller antennas, that can compensate for the "path loss".  Under normal 
conditions the smaller range could compensate for the omni's low gain even 
at the higher freqs.

I agree there are tradeoffs.  I personally like the smaller footprint 
antennas even though the mechanicals are a bit harder.  Why hams accept (I 
own one so I can trash myself) the cheap quality of the rotors that are 
marketed to hams is beyond me?  This is the real problem with dishes.  The 
G5400, G5500 are too wimpy.

My personal concern with mode-S at this time is the cordless phones and 
802.11b devices out there now.  But we can go to higher bands, just like the 
commercial guys are.

You are partially correct on the 2m problem getting better.  The only thing 
that's incorrect is that QRN-type man made noise (the effect "Kelvin" 
temperature level background noise) is still increasing at that band, 
especially in non-rural (suburban and urban) areas.  And face it, the 
bandwidth is limited on 2m for passband ops.  I hope some day we can uplink 
megabaud data through an Amsat sat.  Can't do this on 2m-- not enough room.

So, I think there is a need to continue down the microwave path.
I'm not trashing 2m either.  But to eventually do more than linear 
transponders, we can't forget the microwave bands either.

This is what makes engineering fun, the tradeoffs.  It is impossible to make 
something "perfect".  "Good enough" is often better, but I hope we continue 
to learn something from the endeavor.

BTW, I really like Bob's idea of a 10m PSK-31 up 2m FM down satellite.  That 
could be so much fun and contribute to future "cheap data" initiatives.  One 
of these days I'll keep my promise and submit a 10m SSB receiver design to 
him like I said I would!!!  IF I ever have time... :o(

Fred W0FMS

>From: "Gary \"Joe\" Mayfield" <gary_mayfield@hotmail.com>
>To: "Frederick M. Spinner" <fspinner@hotmail.com>
>CC: <amsat-bb@AMSAT.Org>
>Subject: Re: [amsat-bb] Special Bulletin - new satellite
>Date: Tue, 30 Apr 2002 16:01:15 -0500
>
>I'll let this thread die with this set of comments.  (I believe we are
>beating the grease spot where the horse used to be).
>
> > S1 was quite good before it failed.  B is very marginal with small
> > antennas-- impossible at apogee.  There is a place for both.  AO-40 mode 
>S
> > sounds about the same as AO-13 Mode B did to me.  I think its an apples 
>to
> > oranges comparison.  A 2m transmitter is cheap to build and should be
> > included if the satellite package is big enough to accomidate it.
>
>I'm curious about your AO-13 mode 'B' setup.  There is quite a difference
>from where I sit (many things can very, it is hard to compare apples to
>oranges can't argue that).  I thought small antennas were the big advantage
>of mode 'S'.  The yagi I used for AO-13 was a lot lighter and caught a lot
>less wind than my mode 'S' dish.  It also fit into a 36 inch by 4 inch
>cylinder when traveling.  Pointing the yagi was not terribly critical and 
>it
>worked great at apogee.
>
> >
> > The Mode-S (and higher especially) equipment can be placed on smaller
> > spacecraft due to the smaller antennas, and thus should still be
>persued...
> > imagine if we could get a small sat up in a GTO, but the sat package was
>too
> > small for gain 2m antennas?  Would it be a political decision in this 
>case
> > to forego a mode-B downlink?
> >
> > I'd guess that the motivations are technical and not political when it
>comes
> > to future microwave downlinks.
>
>I'd argue against your guess.  Mode 'S' requires the larger spacecraft.  
>You
>need more power available to get the same power out of the bird (more
>surface for solar cells).  If you plan to add high gain antennas you have 
>to
>stabilize the spacecraft which adds to power consumption and complexity.
>The 9 inch cube spacecraft accommodates 2 meters (it must not take up too
>much room).  As Bob and others have mentioned the main arguments against 2
>meters are vanishing.  Am I against using S band, absolutely not, (I've got
>too much invested in it now, hihi) but I believe promoting it over 2 meters
>is a mistake.
>
> >
> > Fred W0FMS
>
>73,
>Joe
>ka0yos@amsat.org
>
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