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  • Early demonstration of "channel nulling"

    Here is a very early demonstration of using the Kiwi's synchronous AM detector (SAM) to subtract one sideband from the other. So a strong on-channel signal that is covering up a weaker one (either on-channel or close by) can be attenuated. This is something I'm tentatively calling "channel nulling". There is much work to be done, but this is at least an existence proof.

    In the first image there is a local powerhouse on 882 kHz and a much weaker carrier on 880 kHz can just be seen in the RF waterfall (green arrow).

    In the second image "null LSB" has been selected from the new menu on the SAM line of the audio tab (bottom right). This puts the SAM detector in "SAL" (synchronous AM LSB) mode such that the USB component is not passed through to the audio. However, just prior to that the USB component is subtracted from the LSB, and, given the sideband symmetry of AM signals, the LSB is effectively nulled (to a varying degree). In the spectrum display above the waterfall you'll note the weak station carrier 2 kHz away now appears above the noise and, sure enough, a Spanish language station can be heard which was impossible previously.

    The "spectrum display" in this case is not the usual spectrum data from the RF waterfall but rather a single-sided spectrum of the audio channel (hence symmetry either side of center). Note that an extension called "FFT" has been selected. This is going to be an expansion of the existing "integrate" extension to include more general audio FFT and spectrum capabilities.

    The RF waterfall doesn't change between these two images because it is from the RF/IF path and not the demodulated/nulled audio.

    This technique is not perfect. Due to the subtraction involved It depends on excellent USB/LSB signal symmetry which can be easily upset by frequency selective fading. A very common problem on shortwave and medium wave at night (at a time when you're most likely to want to use such a feature). But in the presence of fading the nulling effectiveness will vary and it just might give you the chance to "bag a new one" on MW if conditions are right.

    As usual, many thanks to Youssef of AirSpy who recently pioneered this idea. A superior implementation is found in SDR# (the "Co-Channel Canceller" https://swling.com/blog/?s=co-channel). Maybe someday I'll understand how he does it (but probably not, lol).

  • v1.352: new time station extension (timecode decoder)

    v1.433 February 12, 2021

      Timecode extension improvements:

        Support for JJY(Japan), RBU(Moscow), RTZ(Irkutsk), BPC(China) added.

        While running AGC delay is temporarily increased to improve noise immunity.

  • Problem with massive RFI after changing router

    Changing the external SMPS is fine. But there is another issue that is more difficult to deal with. The use of internal DC-to-DC converters (that are also SMPS) directly on the PCB of the device.

    These days it seems a lot more devices, including PC motherboards, are powered with higher voltage from the primary supply. Then high-efficiency "point of load" DC-to-DC converters are used right at the consuming load. In the case of your router the external SMPS is now 12V instead of 5V and there is almost certainly a 12V-to-3.3V (or even less) converter internally (chips don't run on 5V these days and in many cases don't run on 3.3V either except maybe for I/O).
  • Command MU

    mu is an alias for make users And doing make -n users reveals that it does a:
    zcat /var/log/user.log.4.gz > /tmp/kiwi.log;
    zcat /var/log/user.log.3.gz >> /tmp/kiwi.log;
    zcat /var/log/user.log.2.gz >> /tmp/kiwi.log;
    cat /var/log/user.log.1 >> /tmp/kiwi.log;
    cat /var/log/user.log >> /tmp/kiwi.log;
    cat /tmp/kiwi.log | grep -i leaving | grep -vi kf6vo | grep -vi 192.168.1
    rm -f /tmp/kiwi.log
    So /var/log/user.* are the log files you'd want to search and copy information from. As usual with Unix there are a dozen different ways of doing this sort of thing depending on the result you want.
  • New KiwiSDR forum: differences and features

    Okay, after way too much effort I think attachment links are working again. There were 584 such attachments in the database and I have been spot checking the comments containing them. If you notice anything amiss please let me know.

  • Two deaths in the family

    Both issues, "cable brownout" and lab-grade power supply voltage drop due to current limiting, have happened to me personally and were totally unexpected at the time. That's why they are documented: http://kiwisdr.com/quickstart/index.html#id-power

  • New KiwiSDR forum: differences and features

    Welcome to the new KiwiSDR forum, hosted on kiwisdr.com and running the latest Vanilla 3.3 forum software.

    All of the forum content from valentfx.com was copied over including attachments, avatars, inboxes etc.

    The most problematic issue will be external links from other places pointing to specific forum posts. Forum links were previously of the form valentfx.com/vanilla/discussion/... and need to be changed to the form forum.kiwisdr.com/discussion/... This is of course impossible for immutable (non-editable) content like links embedded in Twitter tweets. It was not possible to automatically redirect references from the Valent forum for various reasons. So if you have editable links into the old forum please update them. However, links to old posts on Valent will continue to work as long as Valent hosts the old KiwiSDR content.

    Also, the time to edit your posts is not limited on this forum (previously the limit was one day). So if your post contains a link back to Valent you can simply edit it to correct the link per the above. In theory this shouldn't be necessary as the database was scrubbed very carefully to update all the links.

    The forum has a slightly different look but basically the same features. The biggest change is editing posts. There is no longer a "preview" button. When using the new paragraph icon on the left margin, and also when double-clicking on words and making text selections, the formatting changes are immediate. It is a "what you see is what you get" (WYSIWYG) interface. Experiment and you'll see how it works.

    The search box is at top right. Use the "Mark All Viewed" button on the top bar as all the previous viewed information has been reset.

    If you are having any problems (e.g. can't login, can't post, getting error messages, etc.) please email support@kiwisdr.com

  • Kiwi with 2m converter/switch added

    Today's v1.427 release adds a "frequency scale offset" field for each antenna on the admin page, extensions tab, "Antenna switch" entry. After updating to v1.427 you must also install the latest version of the antenna switch extension from github.com/jks-prv/KiwiSDR-antenna-switch-extension

    When any antenna is selected the new offset values will be used and completely override (and overwrite) the offset value from the admin page config tab. A value of zero means no offset, so the usual frequency scale of 0 - 30 (or 32) MHz.

    Any active user connections will get a popup panel requesting a page reload when the offset changes. No offset change is made when "antenna mixing" is enabled because it isn't clear what to do in that case.

  • Early demonstration of "channel nulling"

    From the CHANGE_LOG file. The user interface is definitely rough, but at least you can give channel nulling a try in this update.

    To null, use SAM mode and select the "audio" tab on the main control panel. On the bottom SAM line you should find the "channel null" menu. Select "null LSB" or "null USB". Make sure the PLL carrier is around 0 Hz (+/- 100 Hz maybe). If it's way off then make sure you're tuned to the station center frequency, switch to AM mode briefly, then back to SAM. The PLL should lock.

    Use the spectrum function of the new "FFT" extension to visualize the nulling result. It's best to put the spectrum/waterfall aperture mode on manual so the spectrum doesn't rescale on you when the signal is nulling. You can enable the peak detect ("Pk" button) on the WF tab to see the difference. Because the nulling is happening in the audio path the regular waterfall and spectrum signal levels are not effected. Same for the S-meter. And currently same for the FFT and integrate modes of the FFT extension, although this might change.

    v1.425 November 26, 2020

      Channel nulling, preliminary release

            See forum post: http://forum.kiwisdr.com/discussion/2169/early-demonstration-of-channel-nulling#p1


      Audio FFT extension:

        Rename and expansion of former "integrate" extension.

        Adds continuous audio FFT and audio spectrum modes to existing integration mode.

        The audio spectrum function is particularly useful in visualizing the effectiveness

          of the new channel nulling feature of SAM mode.

      Admin security tab: added option to enable/disable console tab access from the local

        network. This in response to a few Kiwis that still have trouble determining

        their local network address, e.g. when using unsupported WiFi dongles.

      Prevent open menus from unexpectedly closing when colormap averaging event occurs.

      Update embedded URLs pointing to the forum.

  • Hide "in-band-canvas" [partial fix in v1.436]

    Beginning with v1.436 the band identifiers will not be displayed if their frequency is less than the frequency scale offset. But the remaining empty white space is not reclaimed because right now that is difficult to do (for historical reasons). It will have to wait for a major rewrite of that part of the code.