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Re: TH-D7A(G) vs W32-A for Easy Sats?



Edward R. Cole wrote:

> I think this debate originally had to do with HT radios so probably preamps
> would not be needed since one has little or no feedline.  A home-based
> station with roof-top or tower-top antennas and longer coax lines will
> generally (almost always) do better with a mast-mount preamp (e.g.
> connected as close to antenna connector as possible).  You can prove this
> to yourself on very weak signals like from repeaters more than 100-miles
> away or operating FM simplex.  Of course if you operate VHF/UHF-SSB it will
> make a world of difference having a good low-noise preamp (0.5 dB or so is
> low enough).

Yes, agreed Ed.  I was on an airplane and my laptop battery was dying 
when I wrote that, so I forgot to qualify the statements as being for a 
V/U HT.  But your follow-up is right on.

I didn't see this as a "debate" so much as an "exchange of information" 
about receiver specs, and was just reminding everyone that all receiver 
measurements have to be in reference to "something" or a relative 
measurement like 12 dB SINAD.  I hope no one seriously thinks there's a 
debate going on!

Both radios originally being discussed in the thread are excellent 
choices for the proposed type of operations (satellite), as evidenced 
both by the bench numbers and also the fact that so many successful 
operators are using both, without any major complaints!

A couple people pointed out the ARRL Labs measurements -- the numbers 
they provide on popular radios are mind-bogglingly, complete.  Anyone 
can learn to understand the important ones and also understand that 
sensitivity and selectivity are always a trade-off in modern multi-band 
radio design.

With those key concepts in mind, one can end up coming away from reading 
them with a MUCH better understanding of the capabilities of the radio 
being measured/tested.  I'm glad they do those tests!

Repeatable tests for usable sensitivity are fairly easy with a 
fixed/known injection point and level... having the equipment to do that 
is a bit more difficult, depending on one's budget for our hobby!  (GRIN)

Telewave makes a nice wattmeter with built in -40dB injection port built 
in... cheaper than a Bird with all the slugs for the ranges the Telewave 
will cover by a long shot, and an accurate place to inject a weak signal 
into your antenna system as well.  Very nifty product.  Not inexpensive 
for most people, though.

You can also use known good directional couplers from quality 
manufacturers with fixed input levels.  Worst, but not completely 
useless, maybe a "lossy-T" type "make your own" injector, but the 
repeatability of the measurement is very coarse and not good with those.

Add a calibrated signal generator, mix well, and bake -- and you're up 
to quite a few bucks just to measure an antenna system -- but it's still 
cheaper than a network analyzer!

Accuracy = Money, in the "high end" of the hobby, to some extent... but 
it sure can be fun to measure stuff and KNOW what a particular receiver 
will do when hooked to a particular antenna.

And I guess that was my final point I was making... 0.02 uV isn't enough 
of a difference to go hunting for with test gear on the bench... that 
elusive 0.02 uV for this type of operation won't make any difference, so 
no one should think they need to run out right this minute and start 
buying test gear!

Ahh, toys... here's hoping we all get a few more radio toys for 
Christmas this year.  ;-)  (Or at least our friends will so we can stop 
by for coffee and measurements!)

Now I'm off to go look at your website... the low signal levels of EME 
and the deep space birds is fascinating stuff... to read.  I definitely 
don't have the real estate for that type of setup!

(Having read some articles last year about how the Deep Space Network 
cools (freezes?) feedhorns with cryogenics to get the thermal noise 
floor down on receive... wow... chilled antennas!  Now THAT's a RECEIVER!)

Fascinated by the details, as always...

Thanks for the additional info and the hint to go read your website -- a 
little Oscar Zero reading!  A nice way to end the weekend for any radio 
buff.

Nate WY0X
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