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Re: LEO's




On Jun 18, 2008, at 5:38 PM, i8cvs wrote:

> ----- Original Message -----
> From: "Mark Vandewettering" <kf6kyi@gmail.com>
> To: "AMSAT-BB" <amsat-bb@amsat.org>
> Sent: Wednesday, June 18, 2008 9:49 PM
> Subject: [amsat-bb] Re: LEO's
>>
>> On Jun 18, 2008, at 2:46 AM, i8cvs wrote:
>>
>>> Hi Art, KC6UQH
>>>
>>> You are correct 100% because the HEO AO40 was very easy to work
>>> using any old TX capable to run about 50 to 100 watt into 70 cm CW
>>> and SSB
>>>
>>> A 3 to 4 foot dish with a 2400/144 MHz downconverter in the focal
>>> point and
>>> connected to any old 144 MHz CW/SSB receiver mounted on the balcony
>>> was
>>> sufficient to receive a nice downlink from all over the world by
>>> many users
>>> at the same time for many hours every day.
>>>
>>> No complicated TX/RX radios and special software was necessary to
>>> compensate
>>> for doppler just made by hand.
>>
>> Well, sure, if you want to reduce ham radio to just keying the mic,
>> leisurely yapping along for hours at a time, then by all means, let's
>> have more satellites in HEO.  But where's the skill in that?
>>
> Hi Mark, KF6KYI
>
> The skill is in building about everyting by yourself like low noise
> preamplifiers for 2 meters, 70 cm, 13 cm and  high dinamic range
> downconverters for the above bands plus an Automatic Noise Figure
> Meters to get the best Noise Figure, build transverters from 2  
> meters up
> to the MW, build different type of feed for dishes having hours to  
> test
> their efficiency through the HEO satellite in cooperation to many and
> many experimenters worldwide and discuss the problems with them
> improving your knoledge in radio-technique.

I can see that my attempt at sarcasm was apparently lost on some  
people.  I suppose I'll have to explain more plainly.  I suppose that  
means my little joke wasn't funny, since I have to explain it.

It's become trendy on this list to criticize LEO or FM sats.  That's  
okay, as far as it goes.  Yes, they are frequently congested.  Yes,  
they have operators on occasion who are inexperienced, or what's  
worse, just don't care very much about operating reasonably.  And they  
aren't up for very long, which often makes QSOs short.  All of those  
are at least to some extent somewhat reasonable criticisms.  They are  
reasonable in part because we can do something about them: we can  
encourage better operating procedures and work to educate people on  
the proper use of these satellites and thus ameliorate most of the  
problems (except, perhaps the most basic ones: the satellites orbits  
and transponders are what they are, and no amount of good operating  
procedure is going to change that).

Which brings up the first _unreasonable_ criticism.  Complaining about  
either a) the fact that they are FM or b) the fact that they are LEO  
satellites.   No amount of complaining will make this fact change.   
Ever.  They are what they are.  Those of you who would like to  
endlessly revisit this question can point out, again and again if they  
like, about how such FM/LEO birds are a waste of time.  That has  
served been at least one "benefit": AMSAT-NA isn't the least bit  
interested in doing another FM satellite, or even a satellite in LEO.   
You guys won!  It's over!  AMSAT-NA won't be sending any of those  
birds up again, probably for my lifetime.  Whether you thought ECHO  
was a waste of time or not, at least it ruined the entire notion of  
LEO permanently for AMSAT.

The second _unreasonable_ criticism is to complain about how anyone  
with an HT can push a button and work the FM satellites.  That's not a  
problem: that's a feature.  Not everything that is easy is pointless,  
and not everything that is hard is worthwhile.  It's damned cool that  
I can hit the ISS with 5w into an omnidirectional antenna on my car  
roof, and use it for APRS messaging.  It's cool that I can work  
Hawaii, or Alaska, or the East Coast or deep into Mexico using my HT  
and a handheld antenna, stuff I could toss into a backpack and go  
hiking.  Is it hard?  No, not especially.  It's not a snap though,  
since I am operating with such low power.  I find it kind of neat to  
talk to NH7WN in Hawaii, each of us standing outside in the wind  
holding handheld antennas and HTs on 5 degree passes.  I could make it  
harder.  I could use smaller antennas or less power.  I've had QSOs  
over SO-50 with the lower power setting on my VX-3R before (300ish  
mw).  That actually wouldn't be that hard either, except for the high  
power stations which like to transmit over others.  But it isn't _hard_.

The fact is that there is _no actual reason_ that working linear  
transponders in LEO need be hard either.  It's hard mostly because  
satellite communication is a niche market, so we have to make due with  
what we can get.  So, we cobble together downconverters, amplifiers,  
preamps, computers and rotor controls together.  Instead of a single  
box with a microphone attatched, we have two separate radios, perhaps  
each with their own amps/preamps and down/upconverters, and perhaps a  
computer to drive it all and aim the antennas.  It _could_ be in one  
box.  It _could_ use keplers to automatically correct Doppler for you,  
so that tuning would be no more difficult than spinning a dial.  But  
nobody builds that box, and as near as I can tell, nobody in amateur  
radio is really interested in building that box, because they think  
that _the difficulty of something is what makes it valuable_.  We see  
this all the time, when people talk about Morse code and criticize  
digital modes like PSK31 or the like.  As engineers, we should be  
_ecstatic_ that using radio is simple, but instead, we choose to laud  
the efforts of doing things the same old hard way.

And here is the important thing that the AMSAT guys have discovered:  
it's hard to convince government agencies like Homeland Security to  
fund our launches in exchange for providing emergency communications  
of we can't demonstrate that we can build _reliable, consistent ground  
stations in reasonable numbers_.  They aren't really interested in  
helping you learn about radio or to talk to your friend in New  
Zealand.  They want a system for emergency communications.   And if we  
want their money, we are gonna have to _make_ satellite communications  
easy.

Oh, and if we don't want their money?  We aren't gonna get a launch.   
We can't hold enough bake sales to make it happen.


> Probably to build about everyting by your self for a satellite for all
> like an HEO make you a real experimenter because if you are not
> succesfull you cannot send the equipment to the manufacturer but you
> are obliged to study your problem by your self looking and reasoning
> over your own schematic diagrams.
>
>
> When OSCAR-10, OSCAR-13 and AO40 where alive and well we all
> were assisted in solving our technical problems by some well know  
> teachers
> and radio scientists every day on this BB like James Miller G3RUH,
> Charles Suckling, G3WDG and Tom Clark W3IWI now K3IO but
> unfortunately they actually desappeared from  this BB because they are
> not anymore interested to discuss about the technical level and  
> matters
> actually seen on this BB.

I suspect they are very interested in such things.  I have great  
admiration for all of these gentlemen.  I first learned Tom Clark's  
name when I found his Totally Accurate Clock project (GPS and  
timekeeping are other interests of mine).  James Miller's nifty Plan  
13 paper led me to write my own satellite tracking code in Python, and  
I'm working on a nifty idea to extend it.  I'm less familiar with  
Suckling's work, although I know he's a pretty familiar name in the  
microwave community.

I suspect that what each is not interested in (and, in case you hadn't  
figured it out, neither am I) is listening to a bunch of pointless,  
idiotic complaining.  Amsat-bb is incredibly high noise to signal  
ratio.  Complaining is a significant portion of that noise.  It serves  
no purpose at all.

> Read please into the AMSAT-BB archive and compare the importance of  
> both
> technical and operating contents of messages at time in wich OSCAR-10
> OSCAR-13 and AO40 were operational and I am sure that you will learn
> more and more about the purposes of the Satellite Amateur Radio for  
> the
> benefit of your own skill.

It's not a bad suggestion, but it doesn't really justify the current  
level of complaining we see on the list today, does it?   It would be  
great if AO-10, AO-13 and AO-40 were still in operation, and we had a  
platform upon which to explore the various modes and capabilities they  
had.  But we don't.  They are dead.  And, barring an AO-7 like  
miracle, they aren't coming back.  You seem to imply that because they  
are gone, there is nothing better for us to do than complain.  I think  
otherwise.

For instance, here's a little thought experiment I've been running.   
I've been monitoring SEEDS telemetry.  I've written a very simple  
tracking application that drives my little FT-817 to track the signal  
in doppler, and then just examine the telemetry.  There are some  
interesting bits inside: notably the various voltages, the current  
produced by each of the six solar panels, and four different  
temperature measurements.    I noticed that the temperature swings are  
fairly large depending on whether the satellite was illuminated or  
not.   That's hardly a profound observation: it's rather obvious.  But  
imagine you were designing a satellite, and wanted to know what the  
likely swings in temperature were, and how that effected both battery  
and solar panel performance.  Well, that's a bit deeper question, and  
it requires some careful thought and (for those like me whose training  
isn't in spacecraft design) a bit of research.  Phil Karn hinted at  
some of the differences between LEO sats and HEO sats regarding  
thermal control on the namaste-dev list which I found interesting.

I'm also _really_ anxious to hear how DELFI-C3 works out once it  
shifts over to open amateur use.  I am interested in what can be done  
in these small form factor sats, and I think engineering a system  
which runs without batteries on purpose (as opposed to AO-7) is really  
intriguing.

That's what I'm having fun with.  That's how _I_ am justifying my ham  
radio license and its mandate to self train.  And I wouldn't have  
likely gotten here without the FM sats and cubesat launches.  Indeed,  
without those launches, we wouldn't have much to listen to AT ALL.    
And, unless there is some news deep in the innermost chambers of the  
AMSAT leadership that we are unaware of, it doesn't seem to be the  
right time to start holding your breath for an HEO launch anytime soon.



>
>> Hell, you don't even need to know what Doppler is with these easy HEO
>> satellites.  If you want to take the easy way out though...
>
> Every experimenter know what the Doppler is but if you like to make  
> your
> life difficult with Doppler for a few minutes QSO having the time to  
> only
> say.......Five.......Nine.......class.......class !
> and then come into this BB asking for the call letter of the guy you  
> suppose
> have made a QSO then it is better to stay with the FM satellites !

Sigh.

Luckily, I don't need to take your advice about what I should or  
shouldn't "stick with".


	Mark KF6KYI

>
>
>>
>> Mark KF6KYI
>>
>
> Best 73" de
>
> i8CVS Domenico
>
>
>
>
>
>

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