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Re: preamps



At 08:42 PM 5/27/2005 -0700, Emily Clarke wrote:
>Without making any judgements about things I just posted an article on 
>Preamps on the Project OSCAR website.  See the article "Improving Satellite 
>Reception Pt 2" at:
>http://www.projectoscar.net/beacon.php
>
>73,
>
>Emily

Very good article, Emily.  Jack realizes the impossiblity of his question,
I think.  Sort like asking what is the best car to buy!
But I think the ones offered by folks so far make up a good list.

Emily gives the reason for a preamp as overcoming coax line-loss, but that
is really half the story.  At HF sky-noise and man-made noise overshaddows
the performance of receivers.  But as one goes up into VHF and higher
frequencies the sky-noise drops and hopefully your man-made noise drops
too.  This then makes possible receiving much weaker signals, if your
equipment does not produce too much internal noise.  This is the other
important function of the preamp...to provide low-noise amplification.

A general rule might be (for up to 436-MHz): 
1) For strong signal Leo sats one should get a preamp with under 1-dB noise
figure (NF).
2) For weaker signal Heo sats one should get a preamp of no more than 0.5
dB NF.

At 2.4-GHz it gets harder to make low-noise preamps but gets even more
important.  I would try to get one less than 1-dB NF.
I bought a preamp for 10-GHz which is 0.8 dB NF with 23-dB gain (Kuhne
MKU-102-EME but cost me over $300 incl. shipping from Germany).  OK, I
think you get the picture...you get what you pay for.

Preamps must have gain to overcome coax line-loss and the high NF of your
transceiver (Yes, they are high).  A general rule would be to add the coax
loss to your transceiver NF in dB's and then add 10-dB more to arrive at
how much preamp gain you need.  e.g. you have 5-dB coax loss and your xcvr
NF = 10-dB, then you should try to get a preamp with 25-dB gain.  This may
require a two-stage preamp.

Many super low-noise preamps exhibit lower gain like 16-dB (or less).  You
can add a second preamp of 3-dB and say 15-dB gain to  achieve an overall
NF nearly equal that of the first preamp...but I won't go into the math of
that, here.

ARR, SSB, Downeast Microwave, Kuhne Engineering all make good preamps.
Some offer RF-switching to bypass the preamp in transmit, others do not.
Some offer wx-proof enclosure models.  Many offer super low-noise for such
operation like eme, but offer slightly higher NF models that are more
immune to interference from strong signals out of the band.  Some offer
protection circuits to protect from tranmitting into the preamp (acccessory).

Interestingly, I was just looking on-line for good eme preamps.  I have a
super-low NF 144 preamp (0.15-dB with 16-dB gain), but it is custom made
(one of a kind) and I probably will not be able to get the builder to make
another.  I found a company called LNA-Technology which looks promising for
ultimate but high-cost preamps:  http://www.lnatechnology.com/

As I said, high-cost, but look real nice.  If cost is a consderation then I
would suggest Hamtronics or ARR.

I have three ARR preamps for 144-MHz.  I have a custom-made 144 preamp
(WA5VJB) and a custom-made 432 preamp (N9MKC).  I have several DEMI preamps
for 1296, 2400, and 10-GHz.  I have a WD5AGO 2-stage 1296 preamp and I have
Kuhne preamps for 2400 and 10-GHz.  I started with the ARR and progressed
to Kuhne.  There are a lot more ham preamps available than have been listed
here.

If you are interested in evaluating your overall station NF you might find
my eme calculator of interest:
http://www.qsl.net/al7eb/eme144.htm
click on the the link "system NF" found half-way down the page.  This is an
excel spreadsheet.




73's,
Ed - KL7UW  <new call>
=================================
http://www.qsl.net/al7eb
144-MHz EME - BP40iq:
FT-847, mgf-1801/1402, 4xM2-xpol-20, 170w
=================================
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