jks

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Username
jks
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Member, Administrator, Moderator
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Location
Tauranga, New Zealand RF82ci
Callsign
ZL4VO/KF6VO
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KiwiSDR support email: support@kiwisdr.com
  • 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.


    KA7Ubenson
  • 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).

    ChrisSmolinskinjcrz3dvpcathalferrisfractional_n
  • 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

    ChristophJimo
  • v1.419,423: added non-NBFM squelch

    v1.419  November 8, 2020
        Added a simple RSSI-based squelch for the non-NBFM modes.
            See audio tab of control panel. Based on Christoph's squelch from kiwirecorder.
    
    Don't expect too much from this squelch implementation. It's not a VAD or anything. On the audio tab move the squelch slider fully left to disable (default). Two squelch values are stored separately: one for NBFM and another for all other modes (except DRM which doesn't need it).

    For the non-NBFM squelch the slider represents dB above the median of a number of past RSSI (S-meter) values. There is also a menu of "tail" times -- additional time the squelch is held open before being closed.

    The speaker icon now has a third color, white, indicating the squelch is closed (hence no audio). This in addition to red (muted) and green (squelch open or disabled).
    Powernumptydl7awlWA2ZKDbensonCommSigmaChrisSmolinskinjccathalferris
  • v1.419,423: added non-NBFM squelch

    v1.419  November 8, 2020
        Added a simple RSSI-based squelch for the non-NBFM modes.
            See audio tab of control panel. Based on Christoph's squelch from kiwirecorder.
    
    Don't expect too much from this squelch implementation. It's not a VAD or anything. On the audio tab move the squelch slider fully left to disable (default). Two squelch values are stored separately: one for NBFM and another for all other modes (except DRM which doesn't need it).

    For the non-NBFM squelch the slider represents dB above the median of a number of past RSSI (S-meter) values. There is also a menu of "tail" times -- additional time the squelch is held open before being closed.

    The speaker icon now has a third color, white, indicating the squelch is closed (hence no audio). This in addition to red (muted) and green (squelch open or disabled).
    Powernumptydl7awlWA2ZKDbensonCommSigmaChrisSmolinskinjccathalferris