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johnjohn
in Signals Received
Newbie can anyone tell me why on the signal bar some times OV. comes up in red

Comments

  • KA7UKA7U
    John,
    Ron - KA7U
    john
  • johnjohn
    Many thanks Ron can you tell me when I'd be able to get one of these RTL-SDR.COM BROADCAST am reject Filters in the UK regards John
  • KA7UKA7U
    John,
    You might not need to filter any complete bands, you might find you have 1 or 2 nearby stations that have strong received signals at your location. I would set the WF max slider for 0dB, go to the MW broadcast band and set the waterfall for "zoom to band". Then turn on the Spectrum switch. I would then look for signals peaking over -30dB and definitely take note of signals approaching or above -20dB. Then I would make a LC series filter from the feedline to ground for that frequency. The greater the L value, the narrower the notch. A LC filter calculator can be found here:

    For example a series LC filter with 3000 picofarads and 4.4 microhenrys should filter 1380Khz down an additional 15dB or more, and if it were a -20dB it would now peak at -35dB. 

    I have not tried this, but I've read that if the input impedance to the filter is increased at the input and then decreased at the output, notch will be deeper. Such as a 1 to 4 step up transformer at the input, and a 4 to 1 step down transformer at the output. (50 ohms to 200 ohms).
    Ron - KA7U
    john
  • johnjohn
    Many thanks Ron for your guidance I will have to experiment with it many thanks again regards John
  • G8JNJG8JNJ
    Hi John,

    Some more notes on the subject can be found here.


    Regards,

    Martin - G8JNJ
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