G8JNJ

About

Username
G8JNJ
Joined
Visits
4,159
Last Active
Roles
Member
Points
75

Reactions

212Helpful63Awesome

  • AM Overload Solved

    G8JNJG8JNJ
    Hi James,

    Your notches are doing a great job, as your SDR seems to be a lot happier now :-)

    Regards,

    Martin - G8JNJ
    WA2ZKD

  • GPS Admin screen

    G8JNJG8JNJ
    Hi,

    The patch antenna supplied with the KiWi doesn't seem to be as good as some other GPS antennas.

    A lot of modern double glazing uses a metalised film to provide additional heat retention, but this also has the effect of greatly reducing the strength of GPS signals.

    I rarely used to get two satellites at any time with the supplied patch, but this week I ran in some more cables so that I could split the feed from an existing Trimble GPS antenna and now I'm typically seeing six at any moment with four or more at good strength most of the time.

    Regards,

    Martin - G8JNJ
    M0TAZ

  • External Functions

    G8JNJG8JNJ
    Hi All,

    I would like to be able to switch antenna ports directly from the BB GPIO pins via the web interface and also change some text on the web interface if some of the BB GPIO pins are switched externally.

    Kari, OH1KK, has done a great job in writing the Kiwi extension to drive a MS-S7-WEB antenna switch . But I really don't want to be tied to specific hardware as I've already got a number of different peripherals that I'd like to control & monitor directly from the KiWi.

    Is there an easy way (I'm not a coder) to modify Kari's extension to drive and receive commands from the BB ? 

    Regards,

    Martin - G8JNJ
    ic8pof

  • Local Timeout

    G8JNJG8JNJ
    Thanks John,

    That's really good :-)

    Regards,

    Martin - G8JNJ
    WA2ZKD

  • Strong local signal overloading - any suggestion?

    G8JNJG8JNJ
    Hi,

    Here's my fix.


    Regards,

    Martin - G8JNJ
    WA2ZKD

  • ADC Overload

    G8JNJG8JNJ
    Hi All,

    I notice that one or two KiWi SDR's which are using good antennas (myself included) are suffering from ADC overload due to strong Broadcast stations, especially during the night on the short wave bands.

    I have built a very simple filter that I use to place a very narrow 10dB deep notch on frequencies where I have problems with strong broadcast stations.

    It simply consists of a number of series tuned resonant circuits connected in parallel (shunt) with the KiWi SDR input. The frequencies and number of tuned circuits can be varied in order to suit your own RF environment.

    I used Elsie http://www.tonnesoftware.com/elsie.html and RF Sim 99 http://www.electroschematics.com/835/rfsim99-download/  (both free)  to help design and fine tune the values.

    22uH inductors are used in order to provide the required bandwidth and attenuation for each frequency, but you can change the values as required. 

    Fixed value capacitors with trimmer capacitors connected in parallel were used to fine tune the circuits to the required frequencies. 

    The filters are built into a small metal box with BNC connectors that simply fits in line with the antenna feed. 

    You can tune two or more notches to the same frequency if you have a really strong signal.

    The following diagram shows the circuit and frequency response curves.

    image

    By adding a simple filter like this, it's possible to reduce the level of very strong stations to below -20dB on the spectrum display, which is usually the point at which ADC overload starts to become problematic.

    Regards,

    Martin - G8JNJ
    KA7U