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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