[Elecraft] Poor Man's Spectrum Analyzer

[Gregory P Daly]

Matt:

     If you can't tolerate the loss of the minimum loss pad,
Mini-Circuits makes a little transformer for just such emergencies

http://www.minicircuits.com/

search for the ADT1.5-1

 they're about $3 each and work from about 500 KHz to 650 MHz. I've used
them measuring noise figure in CATV line amps. and a few other spots
that can't stand the pad

     Most of the time, the pad is the way to go, simple and broad band,
but once in a while the 4 dB loss is too much.

     Mini-Circuits also has nicely packaged Minimum loss pads, with
"official" 75 ohm connectors, and your choice of which end gets what sex
connector. If you do get "real" 75 ohm N or BNC female connectors, be
careful not to damage them with 50 ohm males, the 75 ohm pin is smaller,
and it only takes once (don't ask how I know this :-)

     Mini-Circuits is reasonably nice to hams, look around in their web
site, there's all kinds of RF goodies to keep a ham entertained. I don't
know their minimum, I've bought as little as $25 from them and they
haven't gouged me too bad for it.

73 AND GOOD DX DE WB7RSG

Greg



On Sun, 2005-10-09 at 21:42 -0500, Matt Osborn wrote:
> The Poor Man's Spectrum Analyzer I'm building uses a varacter driven
> cable tuner as its front end.  The cable tuner has an input impedance
> of 75 ohms. Most instruments have 50 ohm input impedance and my usage
> will be primarily with 50 ohm devices.
> 
> Maybe it isn't worth worrying about, but I'm looking for a convenient
> way to convert from 75 ohm to 50 ohm input impedance.  I've seen some
> writeups on building a 50 ohm to 75 ohm broadband unun, but the
> articles were incomplete (or my knowledge level is too low to
> recognize a complete article).  The analyzer covers 5MHzto 500MHz.
> 
> Does anybody have any advice?  Leave it alone, build an unun, buy an
> unun, any other options?
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