[Elecraft] Poor Man's Spectrum Analyzer

[K6MR]

If you don't mind degrading the input specs a bit, a minimum loss pad is 
about as simple as you can get.  Two resistors in the input line.  I 
think you lose something like 4 dB when going from 50 to 75 ohms for a 
voltage measurement (you can calculate it exactly).  This trick is used 
in the CATV industry since most test equipment is 50 ohm and they are 
75.  There are commercial versions available with the proper connectors 
on each end, but unless you can find them surplus they would probably be 
pretty expensive.

Ken  K6MR

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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