[aprssig] Impedance matching question, not directly APRS

david vanhorn kc6ete at gmail.com
Tue Oct 15 08:59:33 CDT 2013


Feel free to reply off list.
I am on a few ham lists, but most are very low traffic and kind of "dead" :(

I need another set of eyes on an impedance matching problem.
I have a receiver that is 19.3 -113 ohms and I need to match to an antenna
that is 3.8 -13.87 ohms
Both numbers are accurate, the antenna was measured in a lab, and the chip
impedance is specified in the data sheet.

I haven't had a lot of luck finding how to use the smith chart when both
impedances are reactive.
An online calculator tells me that I should use 16nH to ground from the RX
and a series 4.3pF to the antenna (the rx input stage requires a DC path to
ground), but this seems no improvement over pretty much any random L and C,
and the receiver is pretty deaf compared to my HT.

Did I get the matching values right?  Operating frequency is 433.92 MHz.

There is a companion transmitter, which seems to be much improved after a
similar matching exercise, so I think I'm in the right neighborhood sort
of..

thanks
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