jks

v1.318  August 27, 2019
    FAX extension:
        Add LPM (lines per minute) selection. Automatically set 60 LPM for JJC/JSC
        Frequency list corrections; added XSG Shanghai; removed BMF Taipei
    S-meter extension:
        Don't clear graph on frequency change. Instead draw vertical division marker: red when
        frequency change, green when mode change.
    Better detection of missing audio panner API on some browsers.

From the v1.317 CHANGE_LOG file:

v1.317  August 26, 2019
    Added to admin network tab a new switch:
        "Prevent multiple connections from the same IP address?"
        Defaults to NO. The check is bypassed for local net connections and those
        requiring a user password. And also for any admin connections.

v1.316 is out which fixes a bug in the ADC averaging. If the ADC was reporting overflow for *all* samples during the averaging period (severe ADC overload) then the OV indicator would not light up.

You can now set the averaging mask using the development controls extension ("devl" in the extension menu). Set the first field to a hex bit mask as follows: To set OV on every overflow reported by the ADC enter the value 0xffff (a hex number) which represents the old behavior. To set OV if 16 overflows occur out of each 64k samples use 0xfff0. For 256/64k use 0xff00. For 4096/64k use 0xf000 etc. The default is 0xfc00 which is 1k/64k. After some real world testing the default can be adjusted in the next release.

One way to do this now is to bring up the browser debugging window and click the "stop Javascript" button. That will stop the audio and freeze waterfall updates. If you reenable js within a "short" amount of time it will even recover and keep going (otherwise the connection is lost).

The latest release adds some averaging to the overflow signal provided by the ADC. This means the "OV" indicator on the S-meter should now reflect a more meaningful indication of an ADC overload condition.

Previously whenever even a single ADC sample (at 66 MHz) was asserting the overflow signal a latch was set and OV was displayed until the next S-meter update cleared the latch. This logic was simple to implement but for a real signal environment it represented an overly pessimistic reaction. The random instantaneous peaks of strong signals could be adding at the ADC input to cause a single sample to overflow occasionally even though most of the time the vast majority of input samples were within the dynamic range of the ADC input.

Now in the FPGA logic there are two counters. One that counts a for a fixed number of sequential samples (64k at the moment) and one that counts only when ADC overflow is being asserted for a sample. At the end of the 64k period the second counter is checked to see if it is greater than 16k. If so then the OV indication is set. So if more than 25% of the samples are overflowed during the period then the ADC is assumed to be overloaded. Note that it doesn't have to be 16k sequential overflowed samples. Just 16k somewhere out of the entire 64k period. All these values are easily changed.

I ran some tests using an hp8657 signal generator @ 10 MHz. At -13 dBm (S9+60) the OV indicator is never lit. At -12 dBm, just 1 dB more, OV begins to appear. More interestingly IMD products begin appearing in the waterfall which validates that the ADC is indeed in an overloaded condition. When using the old logic OV appears beginning at -14 dBm when there is no IMD in the waterfall. So this seems to confirm that the averaging is doing a better job at representing the true ADC condition. This of course is a single-tone measurement and not the real world.

Note: in the image below the S-meter says -11 dBm when the generator is at -12 because the S-meter calibration (admin page, config tab) needs to be adjusted by 1 dB for this particular measurement setup.