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Re: Re: Re: was TS-2000X, now AO-40 lids



Hi Fred,

How long have we been on amsat-bb answering this same question?  He! He!  I
guess it will never end as long as newcomers come along.  I wanted to
respond to a couple of your comments (I generally agree with what you have
said).

At 04:51 PM 2/5/03 +0000, Frederick M. Spinner wrote:
>
>Egads.. what a political debate.  Let me state this a little more 
>practically...
>
>All I can say is I've tried both, and yes I use crappy "surplus" 
>downconverters.  I also drive a
>1988 vehicle because at present I can't afford or need better.  And it works 
>75% as well as a new $35,000 one.
>
>I'll bet you my <$100 cheap downconverter/surplus dish combo side by side 
>with your $300 UEK and high priced Hyperlink BBQ
>I'd do better.  Would it be bigger?  Yes.  In my case I'm on 36 acres, I can 
>care less.
>
>I don't think anyone is saying your system is a problem.  But there are many 
>people out there trying to use a Drake with a BBQ.  It works only well 
>enough to hear the beacon.
>
>But I have to strongly disagree with the following comment:
>
>>I can't tell you the number of people I work using surplus D/C's that can't
>>hear worth a darn when connected to moderate receiving antennas. Connect
>>them to a 3 meter TVRO dish and they "seem to work really well", but it is
>>an illusion. They still don't work worth a darn, but the massive antenna in
>>front of them lets the "system" work well.

Well I can relate how my initial "experiments" using a "bare" Drake went.
Using an 18-inch DSS dish, 5-1/4 turn helix, and an unmodified Drake...it
was near impossible to hear AO-40.  I did finally hear it but barely over
the noise.

Next I stepped up to surplus Andrew 4-foot commercial dish with everything
else the same...I could hear the beacon sort of good (not satifactory
compared to what I have now) and barely hearing one conversation (couldn't
make out the words though).

I finally received shipment of my low noise preamp and mounted that on a
33-inch version of of the DSS dish and the whole world came in!  So it took
6 dB more dish gain, plus reducing my NF from the Drake's 5-6 dB to the
MKU-232's 0.6 dB, to accomplish this.

I understand that some of the AIDC convertors are much better NF than the
Drake so they can be successfully used by themselves with a 36-inch BBQ
(sorry if I have the size wrong) or better dish.

So, hold on, I'm not saying you MUST spend lots of money.  A Downeast
Microwave preamp works (specs not quite as good) with a Drake at $100 less
than the MKU preamp.  Even the cheap ($15 if you can still find them)
Conifer preamps have been reported to work OK with a Drake downconvertor.
Note that I am using the Drake as an example sice it is probably the worse
downconvertor for low noise figure (also I know first hand about
them...what I am using).

>ITS NOT AN ILLUSION.  AS A SYSTEM, THEY HEAR VERY WELL.  This is an 
>acceptable set of trade offs.  I am getting a
>bit tired of you UEK-3000 people saying that spending $300+ dollars on a D/C 
>is the only way to get good signals on AO-40.
>(And I've heard plenty of that, and you are certainly implying that here, 
>and its BS).
>
>As you yourself said, put the numbers into the spreadsheet.  If the final 
>S/N ratio is good it really doesn't matter how you get there.
>Yeah, your beamwidth is smaller with the larger dish.  Unless it's too 
>small, who cares?  Gain, noise pickup, efficiency all are better.
>These are tradeoffs.

To really see what a difference changing your dish size, noise figure,
cable loss, etc. this software is indispensible.  Otherwise you can guess,
hope, spend some money, try it, get frustrated, and try again...wondering
what is helping and what is not.  The software lets you play on paper with
these factors before you decide what to get and how to proceed.  Marcus has
given you the engineering tool without you needing to know the engineering.

But also realize that how well you put together you dish and equipment will
affect how well it will perform.  The computer model is a nice goal to
strive for...whether you achieve it will depend on your skill as a builder,
troubleshooter, and....operator!

It seems most everyone getting on AO-40 must pass thru the same
evolutionary process..its called a learning curve!  But there are folks
here that have "been there, and done that"...that can help you thru the
process!  GL all newcomers!

Oh and disregard some of the on-line flame wars!  In time you will figure
out who really knows stuff and who is BS!

>My point is that if you have a BBQ and can't hear well (and it is obvious if 
>this is the case) try getting a *FREE* Primestar or other VSAT, MUZAK or 
>similar dish-- they are all over the place.   Or a larger prime focus.  If 
>it's a offset, use a 5.25 turn helix, if it is a prime focus, a
>patch.  G3RUH patches are expensive.  W0LMD designs are almost as good and 
>are free with a weekend of effort.  The difference between my BBQ and even 
>my 2 foot prime focus w/patch is about an S-unit.  An S-unit is a lot on 
>AO-40.  For me that was the difference between
>struggling to hear the bird and having enjoyable copy.
>
>Could I make that up by getting myself a sub 1dB converter?  Yes.  It is 
>worth $300 to me to do this?  No.
>
>The logic of spending $300 for a D/C and then going minimal on the antenna 
>is like spending $300 on a stereo system and then hooking 3" speakers to it! 
>  It could work, but is this an optimal setup?
>
>If you don't have an AO-40 setup already, skip the $%#$ BBQ's altogether.  
>Or don't listen to the (radio engineers in the) group and waste $75+ on 
>something that is marginal.
>
>The BBQ's would have worked GREAT if $hit didn't happen with AO-40.  It did. 
>  What is you system going to be like if the transponder loses another 3-6 
>dB over the years?  This is a common occurance with commercial sats....

It is too bad that newcomers still have the pre-launch information for
deciding what is needed to work AO-40 (oh I know some articles have been
published to corrrect this, but it is not reaching the new folks).  The
satellite didn't come up to expectations due to the equipment failures that
occured, so you MUST compensate by building a better ground station if you
want "good" operation on AO-40...as Fred says...its just a fact of life!
Be sure to build something that will work at maximum range and large squint
angles with a little extra performance in case things start to degrade up
there over time!  Engineers call this designing in tolerances for reality!
They  also call it CYA!  
 
>>
>>I really can't emphasize strongly enough sitting down with Gene's
>>spreadsheet and "playing" with all the variables, especially the "front 
>>end"
>>ones like antenna gain, circularity, coax losses, D/C NF and Gain, etc.
>>
>
>>(Much snipped and attribution removed to protect the guilty.)
>>
>
>I agree.  Try more dish gain versus NF improvement.  Things move the same 
>way...

>
>I'm probably one of the leaders in the "try and use what you have" camp in 
>ham radio.   But even in the AO-13 days, hearing the transponder noise floor 
>was a goal of a good system.
>
>It frankly scares me that so many people think its actually good to have a 
>system with no overhead margin.  And for that matter
>how do you know you are not hearing the noise floor by only 0.5 dB if you've 
>never heard it?  A spreadsheet and models are very good
>and necessary engineering tools, but are only approximations of reality.  It 
>ain't gospel until its actually measured.

Absolutely correct.  How to tell if you can hear the satellite receiver's
noise floor...tune to a unused frequency while tracking and note your noise
level.  Now swing the antenna off from the satellite...did the noise level
drop?  YES...you can hear the noise floor of AO-40.  NO...then you are not.
 Do this with your elevation angle above 15-degrees so ground noise doesn't
confuse your observations. 

The ZRO tests could provide that without political interpretation...either
you hear it or you don't and need not take anyones else's opinion!

Later, 
Ed - AL7EB

>
>Fred W0FMS
>
>
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