Hearing 6M Beacon at 16.6032

I have an interesting case to report.

http://kiwisdr.w1euj.com/?f=16603.20cwz9

I am receiving a beacon on the KiwiSDR, iding as K1MS. It's actual transmit frequency is 50.063 MHz. Both the beacon op and I confirmed with a separate receiver (he a PROIII, me a IC-706) that this is not a real signal but more a case of intermod.

My setup is a delta loop antenna down to a PolyPhaser arrestor at the building entry, then an Array Solutions AS-RXFEP receiver protector, then into a shielded enclosure with an additional Mini-Circuits SLP-70+ low-pass filter on Kiwi antenna port. Lambda linear supply. All in a barn with little else.

Looking at the simple sum and difference, its either 33.460 or 66.666 MHz.

Thoughts?

Comments

  • edited December 2017
    Seems to chirp. Is there a chance the beacon is in need of adjustment?
    Screenshot_2017-12-31-09-32-05.png
    1200 x 1920 - 1M
  • edited December 2017
    Hi,

    It could be a Nyqust sampling alias. From memory the ADC clock frequency is somewhere around 66.7MHz.

    So 66.7MHz - 16.6MHz = 50.01MHz which puts it in the same ball park.

    A couple of questions 

    What is the level of the actual beacon signal at the KiWi input ?

    Does the interference go away (or appear at a much lower level) if you install a 30MHz LPF on the KiWi input ?

    Regards,

    Martin - G8JNJ


  • Update.

    The clock frequency is ~ 66.6667MHz

    66.6667MHz - 16.6032MHz = 50.0635MHz = Beacon frequency :-)

    Regards,

    Martin - G8JNJ
  • jksjks
    Accepted Answer
    From the data sheet the MCL SLP-70+ has no attenuation at 50 MHz. So the Kiwi's 32 MHz LPF is the only protection against the alias/image. It would be interesting to know how much power he's running and what sort of antenna gain is pointed your way. In doing the path loss math you might find this is not unexpected at all. S5 does seem like a lot though.

  • With 15 TV and FM stations less than a mile from me, I suppose I should do some math! I would hope that my LF-HF Loop would provide some attenuation though.

  • The beacon is on a hill, about 10-15W into a 3 element beam vertical polarization, oriented such that I'm broadside. Looks like about three and a half miles away.

    The LPF was from the previous SDR, selected to attenuate the FM BCB but leave HF with as little attenuation as possible.

    I'll get back out and check on the beacon signal level. I don't have a LPF right at that cutoff but in light of this I think I'll get one.
  • The beacon is 30db above S9. Wow!

    I've purchased a low-pass with a more appropriate cutoff.


  • Added SLP-30-4 filter, signal gone plus some other background junk.

    Thanks folks!
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