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South West UK
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  • QRM: Radio China International - From Albania - OV +++

    Hi Giulio,

    Adding a series tuned notch filter across the KiWi RF input will help reduce the problems on 7345KHz.

    These values give the bets compromise between notch depth and attenuation on the adjacent 40m amateur band.

    For this simulation I have used an inductor with a Q of 50. But if you can use a better inductor, it will provide a deeper and narrower notch.

    31 turns wound on a T50-2 iron powder core would be a good starting point, but you would have to add or remove turns in order to tune the notch to the exact frequency.

    It will attenuate signals on 40m to a certain extent, so the signal levels will drop slightly, however as the natural noise floor is usually the limiting factor on the lower frequency bands, I don't think it will harm the Signal to Noise ratio.

    As a test you could run the WSPR decoder with and without the notch in circuit, and compare the average S/N before and after, but always compare reports of the same transmitting stations, don't compare different stations with each other.

    The other interference is something local to you, but sort out the 7MHz overload before investigating the other problems.


    Martin - G8JNJ
  • Last Spectrum persists when all signals removed [fixed in v1.279]

    Hi John,

    Brilliant :)

    Makes spotting and determining the amplitude of fleeting signals much much easier.

    Thanks for this (and all the other stuff too).


    Martin - G8JNJ
  • On-Line frequency database

    Copied from UDXF@groups.io

    "You may or may not be aware that the ITU monitoring stations publish their
    listening logs on their public website:


    This page describes the purpose of the monitoring activity as well as
    allowing you to download the logs as Excel spreadsheets; there's also a
    search tool so you can search for logs by frequency and date.

    The spreadsheets often include DF bearings with an accuracy indication and
    signal strength as well as time, frequency, mode, comments etc.

    They often mention the kind of things we like listening to!"

    I've previously taken a look at the ITU loggings but they always tended to be a bit of a pin to trawl through.

    However the new database search tool is very good. Especially if you are careful about what search parameters you set. You can then click on a individual log entry for even more detail.

    It would be even better if you could download the searched results, but maybe someone will get around to writing a scraper tool :-)


    Martin - G8JNJ
  • Ethernet filters

    Hi All,

    I see that DX Engineering are now offering Ethernet filters.


    "DX Engineering ISO-PLUS Ethernet RF Filters are very effective EMI Suppressors that are quickly and easily connected inline on Cat5e or Cat6 network cables. Their patent pending design provides common mode RF interference and EMI noise filtering of radio frequencies from well below 1 MHz to over 100 MHz. DX Engineering ISO-PLUS Ethernet RF Filters are bidirectional (input and output is interchangeable) and they have no effect on digital throughput; Ethernet data signal levels and speed remain unchanged."


    Martin - G8JNJ
  • Seeed Metal case and GPIO connector

    Hi All,

    Just some brief notes regarding the installation of a 15 way D connector on the Seeed metal case in order to bring out the GPIO port for use with an antenna switch.

    The ventilation slot cuts out very easily and only required a small amount of filing in order to make the connector shell fit.

    First the pinout I used

    End view of case

    Top view of connector

    Wiring to GPIO ports

    Side view

    Hope this is of some use to others.


    Martin - G8JNJ