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Re: Mode-B vs Mode-J VERSUS Mode-S




It's very simple and inexpensive to run a hundred or two hundred watts on 
L-band using old 7289 amps.  And a lot of the big guns can afford to shell 
out $1K for the paralleled M57762 bricks as well.  Put that in front of a 10 
ft dish and 25 dB gain.  Hmm.. cooky the front end of the sat fer shure...

I don't personally think it will alleviate the alligator problem at all and 
it will leave the vast majority of us (not me, I do have L-band capability 
in the works) out in the dark for an uplink transmitter.

Technically its a good idea, but I still think most of the AO-40 users do 
not have 1269 MHz uplink equipment.  So this idea, while technically good, 
does place a burden on many in the group.

---On soapbox---

I must be one of the only few people on the amsat-bb that likes the 2400 MHz 
downlink better than the 2m AO-13 downlink.  I built both antenna systems 
from scratch (I've always had a lot of technical knowledge but not a lot of 
money) and I can assure you it was both simpler and cheaper to build the 
S-downlink from scratch using surplus dishes, scrap sheet aluminum/brass, 
than it was to build either uplink/downlink yagi on AO-13.  And my 2.4 GHz 
downlink works better.

Now that I've learned about efficient CP patch feeds on prime focus dishes, 
I have a monster downlink that cost me a fraction of what a good sat yagi 
would (that "except for windloading" takes up much less physical space) and 
I've learned more about antennas and RF on that project than ANY other ham 
radio project I've ever built/worked on.

But if your a appliance operator, I can see how "terrible" 2.4 GHz could be. 
  My goodness, no Yaesu/Icom/Kenwood 2400 MHz rigs.  (Real reason is that 
after a long feedline they wouldn't work)  At the risk of being flamed 
severely, having to have techincal knowledge to operate a HEO bird is part 
of the challenge and fun of it all.  Actually to me, operating is secondary 
(or tertiary even) to the effort building and improving the station--- this 
is the definition of Engineer I guess.   And I've *never* talked to an 
ignornant operator on a HEO bird...I like having the smarter techies on 
AO-40, and they've gotten there by learning when creating their stations.

I'll go as far as saying if Mode S or another microwave downlink isn't 
included, you can count me out.
The technology isn't rocket science anymore guys... Yes it didn't work as 
well as we thought on AO-40, but think of the 2m situation on AO-40.  We 
wouldn't have ANYTHING if S-band wasn't there.  The S-band "weakness" is due 
to physical damage of the 'craft, just like the 2m PA (most probably) eating 
itself due to high SWR from the damaged antennas.  I think many people think 
the S-band and microwave signals are weak because they are not at 145 or 435 
MHz... Not true.

--- Off Soapbox ---

Fred W0FMS

>From: sco@sco-inc.com
>To: Bob Bruninga <bruninga@usna.edu>
>CC: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] Mode-B vs Mode-J
>Date: Thu, 19 Jun 2003 08:16:59 -0400
>
>
>This is why I want L Band (1.2ghz) to be the uplink and U Band (70cm) to be 
>the downlink. It will help allievate the aligator problem. People will not 
>spend the money to have big amps on L band and will most probably have 
>better "ears" than "mouth" so the situation will be better for everyone. 
>LEILA will not be going off all the time. If you can hear your downlink on 
>the sat, then you can talk to it without causing everyone problems. We need 
>to advance the hobby (work in L band) and have something new to work and 
>not just put up old technology (Mode B). If we must put up old technology 
>it should be strickly a second level backup capability in case the primary 
>or secondary systems fail. We should not be encouraging people to use Mode 
>B. But let them have it ... a little, as power budget permits, if we must.
>
>W4SCO
>
>
>>Thus, the typical Mode-J downlink performance is 20+ dB worse than the
>>uplink.  Thus you need beam antennas, skill, and good (not deaf) equipment
>>to hear it.  That is why you hear so many LID's calling CQ who cant hear
>>it.
>>
>>Flip all these around for mode B and instead of having a 20+ dB inbalance
>>in the uplink and downlink, you end up with a pretty well balanced system
>>for the OMNI antenna user.  Everyone can hear the 1W satellite down link
>>10 dB better, and you wont hear so many LID's because now they have to
>>take a little more care on their uplink settings to be heard.
>>
>>Mode-B is really quite a nice way to go.
>
>
>
>----
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