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



U/L would probably techinically be the best.  If I remember correctly, 
doppler vs. patch loss vs. antenna size trade offs converge right at or 
about 1500-1600 MHZ.  I think that's why L band is such a popular band for 
Gov't and military sats.

But unfortunately we can't do an L-band downlink.  I think everyone would be 
happy with U/L up and S/V down.  That's probably the best compromise of 
politics (U/V) and technology (L/S).  I think that's what we should go with 
on Eagle.  For techical reasons, L/S should be primary and U/V secondary, 
but the sat should be designed to have a power budget to run both 
simultaneously.

Fred W0FMS



>From: Jim Sanford <wb4gcs@amsat.org>
>To: "Frederick M. Spinner" <fspinner@hotmail.com>
>Subject: Re: [amsat-bb] Mode-B vs Mode-J VERSUS Mode-S
>Date: Thu, 19 Jun 2003 14:51:16 -0400
>
>Fred:
>I mostly agree.  I don't think S-band is that hard, when all you have to do 
>is plunk down $35 to 50 for an already converted downconverter.  I think we 
>should exploit this in advertising.
>
>And, I'll bet that if there's more L-band up birds, DEM et al will continue 
>developing and we'll have cheaper mast-mounted uplink converters.
>
>I whole-heartedly agree that S-band is easier than the ao-13 2m downlink; 
>and I had a ZRO-8 capable system.
>
>I'm enjoying this discussion!
>
>73,
>Jim
>wb4gcs@amsat.org
>
>
>Frederick M. Spinner wrote:
>>
>>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.
>>>
>>>
>>>
>>>
>>>----
>>>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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>>
>>
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>>----
>>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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>>
>
>

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