9 Oct 2012

Improved Software VLF Receiver

SWL Roland's enhanced SM6LKM software VLF receiver
An SWL called Roland from Germany has produced an enhanced version of SM6KLM's software VLF receiver, originally designed to allow reception of SAQ on 17.2kHz CW. The new version has:
  •  44.1k/48k/88.2k/96k/176.4k/192k sample rate support
  • More CW filters, SSB filter and AM filter added
  • Spectrum display for audio frequency
  • File-I/O for *.wav format (16bit)
  • Left/Right channel select
  • RMS signal level bar for audio level
  • Muting (M) key
  • Time+Date display, UTC or local time
This now makes the "enhanced" SM6KLM software receiver a superb tool for VLF use. Information and downloads are available at Roland's website https://sites.google.com/site/swljo30tb/

To use the receiver all that is needed is a VLF signal feeding into the mic input of the PC. Be sure you know what you are doing: the usual safe thing to do is to put a couple of back-to-back diodes across the DC isolated VLF input to prevent damage to the sound card. With an E-field probe antenna this receiver is capable of receiving many VLF transmitters from around the world. I shall be using it in future to monitor my 8.97kHz earth-mode CW beacon when out in the field testing.  


TiƩgui said...

This is great. But instead of using diodes, why not using a neon lamp ?

Diodes can create intermodulation products and or detect AM signal.

A neon lamp should be quick enough when an ESD surges.

73, from Thierry.

Roger G3XBM said...

Agreed Thierry. Anything that prevents damage to the sound card and minimises the risk of IM2/IM3 products.

Anonymous said...

I'm not so sure about either neon lamps or spark gaps a.k.a gas arresters used for protection ALONE.
First, the voltage has to reach the ignition level, which is at least 70V (neon lamp), or 327V (spark gap) for the device to ignite. Second, before the protection device gets into the arc discharge stage (the "protection" mode) the voltage climbs up to the so called impulse breakdown level. Both, the timing and exact level of which depends on the rise time of the stimulus but a range of 600-800V is typical for spark gaps. Yes, it means a nasty, nanosecond spike that is destructive for a typical, low input capacitance FET/MOSFET device if not filtered out by additional measures.
Several diodes in series might be a better choice...
Janusz, VE3ABX