G8JNJ

I found some notes on the subject of "New squelch algorithm for the WebSDR" on Pieter, PA3FWM's website - he uses this on his University of Twente WEB SDR

http://websdr.ewi.utwente.nl:8901/

http://www.pa3fwm.nl/technotes/tn16e.html

http://www.pa3fwm.nl/technotes/tn16f.html

Regards,

Martin - G8JNJ

This afternoon I tried using my second KiWi (in 3ch mode) running v1.250 to perform some TDoA runs.

The initial sampling completed OK, but when it tried to process the captures, after a while it came back with an "out of memory: use fewer Kiwis or check signal quality" error message.

Selecting the same TDoA but using my public KiWi running v1.249 in 4ch mode ran OK.

Changing my second KiWi running v1.250 back to 4ch mode and the TDoA ran OK.

Changing my second KiWi running v1.250 back to 3ch mode and I get the same error message.

I have previously used the KiWi in 8ch mode for TDoA and this ran OK, so I assume it's just a problem with the 3ch Mode.

Regards,

Martin - G8JNJ

>
>has anyone attempted to use their PC soundcard microphone input connected to their antenna
>

Yes I have tried receiving several VLF stations using just a PC soundcard.

There is a some very simple receiver software, primarily designed for SAQ transmissions

https://sites.google.com/site/swljo30tb/home/files

But other more sophisticated applications such as spectrum lab have a preset VLF receiver mode.

https://www.qsl.net/dl4yhf/spectra1.html

Mains hum, ground loops and noise pickup from the PC data lines are the main issues when using a sound card.

I got the best results using an Icon Cube Pro USB soundcard 4ch with 196KHz sampling on a USB extender cable. But I find that unless you are really interested in extremely low level sub 10KHz signals the KiWi does a pretty good job.

Regards,

Martin - G8JNJ

Hi Alain,

I think it could be interference from a data over powerline adaptor. Take a look at the spectrum used by this device.



https://www.nikktech.com/main/articles/peripherals/network/powerline-adapters/6854-avm-fritz-powerline-1240e-wlan-set-review?showall=1&limitstart=


They are used to carry ethernet around the home over the mains power cabling. The interference often stops and starts when the ethernet link is being used. Unfortunately they radiate quite badly and can cause interference over a large area. Some manufacturers include notches on specific frequency bands and I think this is what you are seeing.

https://www.frequencycast.co.uk/powerline.html

Regards,

Martin - G8JNJ

Hi Alain,

This circuit may help. It is placed on the KiWi RF input and rolls off the gain at MF and also incorporates a simple MF BC band notch.




The items marked 1 & 2 are the 50 Ohm input and output ports (treat them as coax connectors with a grounded screen). Component legs connected to a common ground are indicated with the triangular shaped three horizontal parallel bar symbols.

The basic circuit is a 10dB Tee attenuator formed by the three resistors.

The values chosen for the attenuator sets the maximum attenuation at the lowest frequency. You can increase or decrease the amount of attenuation by altering the value of the resistors. I chose 10dB as it seems to provide the best compromise in terms of optimizing the amplitude of signal levels VS S/N ratio when using typical antennas.

The 330pF capacitor and 330nH inductor set the frequency at which the attenuation starts to decrease.

The 100pF capacitor resonates with the 330nH inductor at around 30MHz to help reduce any residual attenuation at that frequency.

As the frequency increases the reactance of the capacitor decreases, and the reactance of the inductor increases and this gradually disconnects the attenuator network.

The circuit is typically used in cable TV networks to compensate for increasing coax attenuation with frequency. Amplifiers will have compensation to provide rising gain with frequency in order to offset the cable losses. If you want more background look up Zobel network

https://en.wikipedia.org/wiki/Zobel_network

On the output of the equaliser, a simple series tuned circuit notches out the MF signals centered on approx 900KHz with a notch depth of approx 25dB. The bandwidth and notch depth are determined by the component 'Q' and L/C ratio.

I have built quite a few for various KiWi owners. It usually solves the problem of MF band overload for folks who are using loops without unduly affecting the overall performance.

Regards,

Martin - G8JNJ