jks

I should have done this long ago, but I finally figured out a simple way to implement CIC filter compensation by empirical measurement. The before and after pictures below show the result. No more 10 to 15 dB roll-off at the ends of a wide passband. This will improve wide-band AM frequency response and more importantly wide-band IQ mode uses. DRM in particular might have an easier time without the roll-off (see DRM PSD plots below).

IQ mode, 12 kHz passband, 10 dB/div:
(display is from the new audio FFT)



With CIC filter compensation. Note flat passband:



DRM PSD before and after compensation:

The new 8-channel Kiwi configuration mode trades two of the zoom waterfalls for the ability to have an extra 4 audio-only receiver channels. I.e. the original RX4/WF4 mode, where each receiver channel was paired with a waterfall, can be replaced by an 8RX/2WF mode where only the first two channels have a waterfall. The other 6 channels get a “blank” waterfall and spectrum display (see this post: http://forum.kiwisdr.com/discussion/1233)

The v1.221 release now adds an audio FFT in place of the zoom waterfall / spectrum for those channels that were formerly blank. This is possible because all the FFT processing is done in Javascript on the browser. No additional FPGA, Beagle or network bandwidth resources are required.

However, this scheme has its limitations and also a number of known bugs that are being worked on. When I have a little more time I will list them. Until then please give the audio FFT a try.

Added in v1.222

Added in v1.222

I found that it almost invites a different use of the radio when listening to Morse as the signal become visible before the audio so it is easier to find and settle on a signal (with arrow keys) than blind the audio overshoot. Not being synchronized to the audio is one of the current problems. But If you actually like this behavior note that you can delay the regular waterfall using the "wfdly" URL parameter (not yet documented). Say something like my_kiwi:8073/?wfdly=1000 to get the waterfall to appear 1 second (1000 milliseconds) before the audio. You can specify negative values also.