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I am having some issues with my up and downconverter. What I'm trying to do is to receive a 125 kHz signal, upconvert it to 433.125 MHz, transmit it, receive that signal, and downconvert it back to 125 kHz. I have 2 circuits which are shown in the attached images.

I have verified that the mixers are working properly but there's something wrong going on and I can't seem to know what it is. Somewhere along the way the signal either isn't being transmitted or received properly. I would like to get some pointers and also to see if there is something wrong with the design of the circuit that I have missed.


Upconverter Schematic

Upconverter Schematic


Downconverter (U2 is an LT6202)

Downconverter (U2 is an LT6202)

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  • \$\begingroup\$ "Somewhere along the way the signal either isn't being transmitted or received properly." so what about you actually figuring out at least at what point this is the case? \$\endgroup\$
    – PlasmaHH
    Jul 12, 2016 at 14:22
  • \$\begingroup\$ That's what I'm gonna do now. I just wanted to see if there is something wrong circuit-wise that I missed or something. \$\endgroup\$ Jul 12, 2016 at 14:24
  • \$\begingroup\$ How about links to the mixers and antennas? \$\endgroup\$
    – Andy aka
    Jul 12, 2016 at 14:27
  • \$\begingroup\$ @bryan.mitchell If you hover over the downvote button you will see that it says This question does not show any research effort. First you measure, then you ask. \$\endgroup\$
    – pipe
    Jul 12, 2016 at 14:27
  • \$\begingroup\$ I have verified that the mixers are working properly How ? The transmitter is basically only the mixer so if it works it should work. Assuming all the connections are there. \$\endgroup\$ Jul 12, 2016 at 14:36

1 Answer 1

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The FS1000A module you are using as a local oscillator is nominally 433.92 MHz +/- 75 kHz and this can mean that after up-converting the frequency is 75 kHz higher than you thought.

Now, when it comes to down converting the tolerance could work with you and you get precisely your 125 kHz signal from the down-converter but that would be really, really naive.

Whether this is the problem you are getting or not this IS a design problem.

If the net frequency difference between the two FS1000A modules is 20 kHz then your down-converted signal could be 105 kHz or 145 kHz.

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