[updated 22 nov 2021]
Thanks to the recent excellent open source work of Tomasz (github.com/szpajder/dumphfdl) the Kiwi now has an HFDL extension. Although it will always be less capable and up-to-date than what the original dumphfdl offers (this is true of practically all Kiwi extensions). Note that in the dumphfdl README and kiwiclient README/Makefile are detailed instructions for using dumphfdl directly with a Kiwi IQ stream via kiwi_nc ("netcat"). This is similar to how some people prefer to use Dream DRM + Kiwi IQ stream rather than the Kiwi DRM extension directly due to Dream's features and their familiarity with that application.
There are definitely some problems with the extension. But I wanted to make it available on more Kiwis to make testing easier. In particular there seems to be trouble getting any message decodes initially. For stubborn cases re-opening the extension and clicking the "test" button until you get a decode helps. There may also be issues when multiple channels are running the extension although it works fine in some cases.
Since the EiBi database has labels for most of the HFDL channels a good way to visualize activity on a particular band is to switch to using EiBi (control backslash), select only HFDL, and adjust the zoom until all the HFDL labels of that band fit the waterfall. In the "Bands" menu clicking on the blue band entries selects EiBi labels and automatically sets the optimal zoom. The same happens when clicking on one of the ground station active frequency table (AFT) icons on the map [as of v1.478]. This makes it easy to see which channels have activity. Then you can shift-click a particular HFDL label to bring up the extension on that channel. Shift-click on other labels or use the HFDL extension menus from there.
The "display" menu changes the format of the decoded messages displayed. "DX" shows an abbreviated two-line message per transmission (similar to the ALE 2G extension). "Squitter" is an HFDL term for ground stations transmitting the dynamic "active frequency table" (AFT). Squitter mode will limit the messages to the AFT so it's easier to see which ground stations are using what frequencies. "ACARS" shows only messages containing ACARS message data.
You might also want to reduce the waterfall update rate to "slow" so that you can see more evidence of channel transmission.
The help button has more information on URL parameters. So a compact URL to monitor a particular band might be:
my_kiwi:8073/?ext=hfdl,8977,d:1,l:10&wf=s Adjust as required.
A Kiwi that has poor frequency calibration (because it's not using GPS correction and is in a particularly cold/warm room) will exceed the ability of the HFDL decoder to lock to the signal. This has been observed. In the absence of GPS you can do a Kiwi manual frequency calibration against a time station (e.g. WWV/H, BPC etc.) as described in the Kiwi documentation. The header of each HFDL message (highlighted in yellow) shows the frequency correction. Anything more than about 50 Hz won't decode.
From the CHANGE_LOG file:
v1.471,472 November 12, 2021
HFDL extension preliminary release.
Because the decoding happens entirely on the Beagle, and due to the buffering delay of
delivering audio and waterfall to the browser, you will see the decoded text before the
BBAI performance improvement. Specify correct compiler cpu type (cortex-a15) and
vector floating point version (vfpv4) for the TI AM5729 cpu chip used by the BBAI.
This causes the fused multiply-add instructions available in vfpv4 to be used.
By comparison the BBG (TI AM3359 cpu chip) uses cortex-a8 and vfpv3.