Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

G8JNJ

About

Username
G8JNJ
Joined
Visits
373
Last Active
Roles
Member
Points
54
Badges
0
  • How do you use your SDR

    Hi All,

    Mine is fully public 99% of the time.

    I don't think the bandwidth used is excessive, but I'm on a VDSL service with no user cap (as far as I'm aware).

    However it does get very high usage and sometime I have to kick users off so that I can log in and use it myself.

    I have a particular problem in that a lot of Dutch music pirates use my SDR all day long to monitor their own transmissions around 6MHz. 

    What I really need to be able to do is to be able lock out certain frequency ranges or restrict the amount of time individual users can stay on the SDR before getting automatically kicked off. I currently have the inactivity time out set at 15mins but I may have to reduce this still further.

    I now have a second Kiwi on order, so it would be good if I could link them in some way so that they both appear as one Kiwi but with eight possible connections.

    I previously raised this suggestion in this link https://github.com/jks-prv/Beagle_SDR_GPS/issues/48

    I know that there is at least one other station running multiple Kiwis on different ports so I don't think I'm the only Admin who may be interested in this idea.

    Most of the time (when I can log in) I use my Kiwi for general short wave listening and enjoy spotting 'unusual' activity on the waterfall. I also enjoy listening to NDB's, BC stations and Amateur stations. Quite a few of my users seem to listen to HF Aero traffic as well.

    I note that quite a few folks use the WSPR extension (logged as SWUKSDR) especially on the 472KHz band. I've also got antenna switching and this gets used some of the time mainly by the BC listeners in order to try and reduce interference or other stations that are co-channel.

    I think the KiWi has been an excellent purchase and It's certainly re-awakened my interest in Short Wave Listening.

    Well done John, and thanks for all the ongoing support and rapid resolution of any problems that may occasionally arise :-)

    Regards,

    Martin - G8JNJ



    KA7UTonda
  • Noisefloor of my KIWISDR

    Hi Dietmar,

    That looks very good.

    The big test is to see if the antenna you are using is good enough for the KiWi :-)

    The ITU publish a noise / frequency curve (Rec. ITU-R P.372-8) https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.372-8-200304-S!!PDF-E.pdf (figure 2) which shows the variation in natural noise floor with frequency for various locations. 

    As long as you have a receiver and antenna that is slightly more sensitive than the level shown on the graph (best case B <100KHz / >100KHz C <4MHz  / D >4MHz curves), then you don't need to worry about your receiver or antenna. 

    In most cases because of the shape of the curve, this means that you only really need to concentrate on the higher frequencies, as the lower frequencies tend to have a much higher level of natural noise, even in very electrically quiet locations.

    To try this for yourself, pick a suitable clear frequency, perhaps somewhere around 15 - 20MHz, where the natural noise floor is likely to be moderately low and the KiWi has good sensitivity.

    Put a 50 Ohm termination on the KiWi RF input.

    Zoom to level 12 (Z13 has some problems at low signal levels) and increase the WF min sensitivity slider until you can see the KiWi noise floor on the spectrum display at around -150dB.

    Wait a few minutes for the display average to settle and then connect your antenna in place of the 50 Ohm load.

    Make a note of the new level of noise floor on the spectrum display.

    Ideally if the KiWi has enough gain and the antenna is good enough, your noise floor should rise slightly when the antenna is connected (as long as it's not due to unwanted interference). 

    If you find that the noise floor increases by more than 3dB, then the KiWi and antenna you are using are already sensitive enough, as the lowest level signals you will be able to hear are limited by the natural (galactic) noise level

    If the noise floor doesn't rise by 3dB (or at all) then your antenna needs to be improved.

    Generally speaking, when using a good (passive) antenna the Kiwi is usually sensitive enough up to about 25MHz. On higher frequencies the natural noise floor is lower and ideally you need an antenna that has some additional gain in order to achieve a 3dB increase in the noise floor. So if you repeat the same measurement method at for example 30MHz, you may find that you can't see any change in noise level.

    If you are using an active antenna, it's a bit more complicated to conduct these tests, as the amplifier will add it's own noise contribution

    In this case you need to replace the antenna part (whip, probe or loop) with an equivalent terminating impedance. In the case of a whip or probe something like a 12pF capacitor from the amplifier input to the common (ground) rail, or in the case of a loop you need to replace the loop element with a small inductor of equal value to that of the loop (typically 2.5uH). As before look for a 3dB increase in noise when the antenna element is reconnected.

    All of this assumes that your existing noise floor is low, but if it's dominated by local interference (as is the case in most urban environments), then you need to concentrate on reducing the level of interference, rather than worrying about the Kiwi or antenna gain. Although moving an existing antenna to a lower noise location, or using a directional antenna may be at least be a partial solution.

    Regards,

    Martin - G8JNJ
    dl2sba
  • possible feature : TUNING lock

    I think Phil's suggestion of a last used frequency memory would be useful.

    I often find that I listen to one frequency whilst scrolling up or down the adjacent spectrum. If I quickly tune to a new frequency to hear what's been transmitted, it would be good to be able to quickly go back to the previous frequency without having to scroll back or retype the frequency (which I've often forgotten anyway).

    Would it be possible to add something like a browser 'back' and 'forward' function below the frequency entry box, which would allow you to scroll between frequencies that have been entered during the current browser session whilst using the SDR ?

    Regards,

    Martin - G8JNJ



     
    WA2ZKDic8pof
  • Data Signal

    Hi Dave,

    It's a NATO Link-11 data transmission.

    See 


    Regards,

    Martin - G8JNJ






    M0TAZ