A series of polarisation tests was performed on 144 MHz in December 1995 and May 1996 with 3 different stations. Both back and forward scatter was utilised with signals sent using horizontal, or circular polarisation, while the receiving antenna had both vertical and horisontal polarisation.
The list below shows how the reflections were received using horizontal and vertical polarisation. The signal strengths and duration was determined from each reflection. Limit of acceptance was drawn to -6 dB of the stronger polarisation channel signal peak strength, or less than 50% of duration compared to the better polarisation. Signals of the two different polarisation deviating less that were marked as "both polarisations received".
On some combinations due to unsuitable antenna illumination pattern and poor S/N ratio, waning meteor activity, only one, or a two samples were analysed. This caused small number statistics, which unfortunately makes data less accurate for evaluating the differences. Automatic set-up would have been better for more accurate results.
The test arrangements included a preparation of equal-gain preamplifiers and driver software switching between the polarisations and A/D converter. Finding the willing stations proved also to be time consuming. Noise from the computer, limited transmitting power and stormy weather during Geminids shower hampered the effort.
The results suggest, that while vertical polarisation does provide fair amount of reflections, by no means it can be said to be superior on a typical meteor scatter path. In fact horizontal polarisation seems to work a little better in most cases.
Before setting up a space diversity receiving system, one could try polarisation diversity first. On a few occasions, the signal fading on overdense trails was out of phase; when the signal disappeared to the noise on H polarisation, it came up on vertical and then again the other way around until the trail decayed.
|Path||H Bursts||V Bursts||H Pings||V Pings|
|Forward scatter, TX horizontal polarisation, PA3BIY-OH5IY, 1650 km path:||35 % +-26 %||65 % +-38 %||75 % +-22 %||25 % +-7.5 %|
|Forward scatter, TX circular polarisation, DL8YHR-OH5IY, 1487 km path:||55 % +-16%||45 % +-13 %||70 % +-22 %||30 % +-9 %|
|Back scatter, TX circular polarisation, OH2TI-OH5IY:||70 % +-22 %||30 % +-9 %||nil||one|
|Back scatter, TX horizontal polarisation, OH2TI-OH5IY:||50 % +-35 %||50 % +-35 %||50 % +-35 %||50 %+-35 %|
I would like to thank F. Hobelmann, P. Hoefsloot and J. Sirviö for taking part in the test.
References: See the Compact MS-Soft's documentation's reference section.