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



Not all systems that use a BBQ dish are alike and not all BBQ's appear to
work the same. I've been using a HyperLink 39" with a UEK-3000 from day 1 on
AO-40 and comparing my results using Gene's spreadsheet shows exactly what I
experience. I have made many measurements with a step attenuator and I get
precisely (or at times a bit better) SNR on the Beacon and on my signal that
I should. It is readily apparent what difference I would get by going to the
patch feed with 1 meter dish.

For all this crazy discussion, how about simply plugging in the values of
interest into Gene's spreadsheet and reducing all the speculation?

The BBQ dish I use has 24 dBi linear (horizontal polarization). The 1 meter
dish and patch feed produces 26 dBc, this is a net difference of 5 dB
(correcting for linear to circular loss). Gene's prediction software shows
how well I hear with the BBQ and I have verified it. Can I hear the passband
noise floor at apogee? No. I do see the beacon at a 20 dB SNR. I produce a
signal of 12 dB SNR with 12 w output power into my 14.2 dBc uplink antenna
(assuming 2 dB of coax loss, 80' of LMR-400).

So...what's the problem?

Whatever system one is using as long as you can copy yourself at 8 dB BELOW
the Beacon, your set for a LOT of contacts.

Can you hear everyone on the bird? No. Can you hear the vast majority with
this kind of setup, absolutely!

With the BBQ Dish:

Rx Noise Power -145 dBm
Passband Noise Floor -145.487 dBm

The passband noise floor cannot be heard by about 0.5 dB...these is pretty
darn respectable. 0 Squint, 50,000 km

With the 1 meter dish and circular patch feed:

Rx Noise Power -145 dBM
Passband Noise Floor -140.487 dBm

The passband noise can easily be heard by about 4.5 dB....this is really
good. 0 Squint, 50,000 km

===================================================================

>From the analysis above, I don't  think I could agree that we should be
throwing away the BBQ dishes. That's just too harsh a judgement IMHO. If you
have a really good D/C and a good BBQ dish, you are going to hear very well,
with squints < 30 degrees. That is my direct experience. You won't hear
nearly as well as with a 1 meter dish/patch, but to carry the point further,
the 1 meter dish isn't going to hear "nearly as well" as a 10' TVRO either.
Where do we stop?

The assertion that I should throw my BBQ dish away, based on FACTS (both
theoretical and empirical), not a bunch of speculation, is just not
supportable.

This discussion could take on a lot more variables such as manipulating
squint, etc. The point being, put up the very best receiving setup you can
afford and physically manage, as it will always benefit you. However, don't
throw away your BBQ dish, IF Gene's program shows that you will get
performance similar to mine.

The problem may be two-fold (the apparent good performance of some systems
using BBQ dishes)

1. Lousy downconverters. If you have a top of the line D/C, you may find
SOME BBQ's quite sastisfactory.
2. Poorly performing BBQ Dishes. Not all of them are equal, that is quite
apparent.

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.  They are cheap, but good ones
are not necessarily "automatic performers" upon purchase. Some are fairly
decent, many are very marginal performers. Put these on even the best BBQ
dishes and you get a lousy overall system.

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.

You can then "see" exactly what effect various antennas and d/c's are going
to have on your ability to hear the passband noise at apogee and under
various squint conditions. The same analysis can be done on the uplink, with
very little effort.
===========================================================================

Bottom Line: Don't throw anything away until you use an objective tool to
analyze what is going on, and then verify the predicted performance with
some real "measurements". Then we can tell what should and shouldn't be
"thrown away".


...hasan, N0AN

(Much snipped and attribution removed to protect the guilty.)

>
> You don't know what you are missing because you've never heard it. And you
won't realize this fact until you throw that BBQ in the trash. I have used
that setup, and lots of other guys have and either moved to something
bigger, or gave up. I prefer they move to something bigger.
>


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