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Re: cost comparisons



Excellent points, Wayne!

2.4 gig and above will have HORRIBLE vegetation loss. It doesn't get better
as you go up.

The only disadvantage to the 2.4 gig downlink is "obstruction and
absorption" losses (leaves and houses). These losses were readily apparent
on Mode J even with 70cm downlink.  They aren't as severe as 2.4 gig, but
they are very obvious, nonetheless.

Mode J was quite instructive in that the obstruction losses on 2m uplink
were a very small problem...which we discovered as people tried to make up
for downlink obstruction losses by cranking up the uplink power on 2m. Also,
we had another similarity with mode S on AO-40...people didn't think they
needed preamps there either (on 70cm downlink). The results were predictable
....signals on the bird were 6 dB above the beacon...and the very same
person couldn't copy his own downlink!

It was a constant battle to get people to understand that the Icom 471,
Yaesu 726R, et al, were basically DEAF on 70cm. It is difficult, at times,
to explain to someone that their 1000 dollar radio is deaf...but the word
finally got around and everyone was buying gasfets like crazy. Those who
did, found Mode J to be pretty much fun. Those who didn't, left frustrated
or in a huff.

The same phenomenon is repeating itself on Mode S. Except this time, a lot
of those who are disappointed have been VERY LUCKY. They didn't spend a
grand...they spent 30 bucks! The 150 dollar preamp solution looks like a
small cost, given dedicated KiloBuck radios had to have the very same
preamps (and antenna mounted in most cases), that the cheap converters need
today.

The more I reflect on what was going on with mode J, the more similar it is
to what we have learned so far for AO-40: RECEIVER, RECEIVER, RECEIVER.

Future birds need to worry about propulsion...the band planning can be every
bit as "complicated" as AO-40 is. The problems with AO-40 are not the design
of the transponders....it's the propulsion. We're not very good at "rockets"
<grin>.

Assuming we get nothing more than U/L uplink and S downlink, and the
antennas get oriented towards us, I'll be pleased as punch, and very
grateful for everyone's efforts.

<Preaching to Converted Mode ON>

Let's not forget...for a while there, we had what appeared to be a dead
bird, period. Now we have parts that work, that we can readily get the
necessary equipment for. Antennas are cheap, downconverters are cheap,
preamps are "reasonable", rotors are quite inexpensive.....what's the
problem? We lost 2m....which other parts of the world have been begging us
to abandon for years. We lost something we thought we had...that makes it
hard to swallow. We didn't really lose anything that we absolutely "had" to
have.

If the only way we could use the bird was to spend a thousand NEW
dollars...yeah...that's not good. But, on the other hand, if we already were
Mode B capable, then we are only an inexpensive downconverter, cheap antenna
and reasonably priced preamp away from Mode U/S.

<Preaching to Converted Mode OFF>

I don't see what the beef is.

73,

hasan schiers, N0AN
schiers@netins.net

----- Original Message -----
From: "Estes Wayne-W10191" <W10191@motorola.com>
To: <amsat-bb@AMSAT.Org>
Sent: Friday, June 01, 2001 12:03 PM
Subject: [amsat-bb] cost comparisons


> Al Lawler wrote:
>
> If I had to summarize AO-40  cost distribution, I'd say that the
> cost has moved from the desktop to the antenna mast, but it certainly
> hasn't increased...  (And the antenna sizes for a GOOD receiving
> setup are approaching what can be successfully loaded on a pair
> of TV rotators...)
>
> Wayne replies:
>
> I suspect that the combination of an 18-element 70cm CP yagi, 1 meter
> crossboom, and a 54-element 13cm loop yagi is a SMALLER LOAD than the
> average TV antenna.  It is entirely practical to use with cheap TV rotors.
>
> A 13cm receiving setup consisting of a 3-foot dish (or loop yagi), preamp,
> and surplus downconverter will COST LESS than the big yagi and preamp that
> most people used to receive the 2m downlink from AO10 and AO13.  And
that's
> not counting the fact that you can get away with much cheaper rotors.
>
> There seems to be nearly universal agreement that 2m is NOT a good band
for
> high-orbit satellites or earth stations.  Antennas are too big, spectrum
is
> limited, noise is high, and there is too much legal and illegal
interference
> beyond our control.
>
> 70cm seems to be the BEST uplink band for the foreseeable future since
> transmitters are widely available, antenna size is reasonable, and cable
> loss is tolerable.
>
> I'm still not sure if 13 cm is the best downlink band.  Antennas are
cheap,
> small, and easy to steer with TV rotors.  Surplus downconverters are
cheap.
> Good preamps aren't really very expensive.  But the signal is absorbed by
> trees, which is a problem for a lot of people.  Also, interference from
> unlicensed wireless devices will be a growing problem over the next few
> years.
>
> Too band 23cm isn't a permissible downlink band.  It probably would have
> been the great downlink band from the perspective of antenna size and tree
> absorption.  Is 10 GHz less affected by trees than 2.4 GHz?
>
> Wayne Estes W9AE
> Mundelein, IL, USA
>
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