introduction to 2200m at this qth (qf56ik)

While at the time of writing (23rd December 2007) VK amateur radio operators are not allowed to transmit in the 2200m LF band (except under the LIPD Class Licence), it is certainly possible to 'listen' to this band.

Mind you - 'listening' is not always done in an aural sense.     Because of the narrow bandwidth of this band (2.1kHz), only conventional CW and narrowband digital modes are appropriate - certainly no conventional SSB. 

Although conventional CW is a popular mode in the 2200m band for the above reason, activities that focus on maximising the operating range typically use techniques that employ unusually narrow bandwidth.    The most common of these modes is QRSS or very slow CW (derived from the CW shorthand for 'send slower' = 'QRS').     The extra 'S' in 'QRSS' emphasises the slow speed.    To give an idea how slow - most QRSS is in the range of 3 seconds per dot to 30 seconds per dot.

Such slow CW cannot be readily received by ear so a number of soundcard software programs have been written to display the signals visually so they can be read.

Spectrogram software

The two spectrogram software programs I use are 'Argo' and 'Spectran' available from 'http://www.weaksignals.com' at the time of writing (23rd Dec. 2007).

Conveniently the entire 2.1kHz-wide 2200m band fits snugly into the passband for a receiver in SSB mode.     Typical audio passbands for SSB receivers runs from about 300Hz to 2.4kHz (or about 2.1kHz).    Therefore setting the receiver to USB and tuning to 135.4kHz places the 2200m band (135.7kHz - 137.8kHz) in that 300Hz to 2.4kHz audio passband.

Of even further convenience is that the tuning frequency of 135.4kHz can be entered as an offset into the two spectrogram programs causing the spectrogram scale to display the 2200m frequencies directly.

Information on how to connect the receiver to the soundcard can be found from the internet and so will not be repeated here.

The results of hooking up the two spectrogram programs to an FRG-100 receiver tuned to 135.4kHz in USB mode follows below.

The 2200m lf band in VK2 (qf56ik)

Here below is a spectrogram (via Spectran) of the entire 2200m band at QF56ik (Eastern Australia - west of Sydney area).    The peak at about 136.9kHz is always there at this QTH (at least up until the time of writing and from about a month previous to that time).    I am unsure what it is and if it is local or not.   It appears to be within ground wave range (< 100kms) as it does not show the diurnal changes of a sky wave signal.     Further tests using a portable loop and trips afield might result in an identification.

The spectrogram below shows a relatively quiet period (aside from the 136.9kHz signal).     Quite often there are buzzes of unknown origin - however, one intermittent buzz has been identified as being from our inverter-type microwave oven.

At times there is continual QRN.    These are absent when there are no thunderstorms within ground wave range during the day - however, at night it is possible to hear thunderstorms from a much wider area.    Therefore, for ground wave experiments (< 100kms), middle of the day with no regional thunderstorms is best.

The above graphic has been cropped and shown below with the IARU band plan overlayed and with red vertical lines marking the limits of the 2200m band.   The graphic shows that the unidentified 136.9kHz signal at this QTH is smack in the middle of the 2200m band .

However all is not lost.   Because of the narrow band nature of QRSS signals it should be possible to squeeze into gaps between the interference.

The graphic below is an 'Argo' spectrogram set to read 30 second-dot QRSS.   Note that the frequency scale runs from about 135956Hz to 135962Hz - about 6Hz wide only!    On the graphic above this is represented by the green line.

 Note that although this spectrogram was taken at the same time as the full-band view spectrogram, this narrow 6Hz spectrogram appears nice and clear.

It would be interesting to compare spectrograms at this QTH as time goes by as well as spectrograms from other QTHs.