Built the up-converter from January 2013 QST

Show off any of your RTL-SDR or cheap SDR related projects.
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Joined: Tue Apr 17, 2018 2:01 pm

Built the up-converter from January 2013 QST

Post by wa5bdu » Wed Apr 25, 2018 7:59 pm

I built the converter so I could copy the HF and MF bands from 1.8 MHz to 30 MHz. It's a fairly simple circuit with an NE612 or NE602 mixer chip and a 125 MHz clock oscillator chip.

I felt the need to keep local AM BC and FM BC out of the mixer so I included a VHF filter on board for FM and used an external HPF for AM BC. This meant that I needed to match the input Z of the chip (to properly terminate the filter) which the original author didn't do. Later I also added a matcher for the output Z when I was having problems with low sensitivity. But they turned out to be unrelated to impedance matching. Fixed now.

It seems to be working pretty well with the dongle and SDR#.

It does produce a lot of spurs as signal levels rise up to -60 dBm and greater. A switchable attenuator might be good.

-Nick, WA5BDU

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