Friday, May 02, 2008

Is my K9AY working as expected ?

Following is another example of the interest of WSPR and the network of bidirectionnal beacons that is building up. Last night the activity focused on 80m band; a good opportunity to test the RX performance of my K9AY-loop versus my vertical. Once again I used my automatic switching system (see previous posts) to switch from the vertical to the K9 every ten minutes. I inserted a step attenuator in the TX antenna line to the RX, to balance the noise floor on both antennas (and avoid soundcard input overdriving). Following are a few results, based on limited number of spots, but which IMHO already give interesting indications (as for any statiscal method, more samples more accuracy). As for the previous plots published on the blog, all levels are normalized as if the transmitted power was always 1W - Of course it assumes that the operators are honnest, with their claimed power level, but for this particular exercise it does not really matter. The beauty of WSPR is it provides directly the SNR (Signal to Noise Ratio), which is the most interesting parameter when you want to compair receiving antennas.
First is the theoretical pattern of the K9AY, with the direction of the considered stations (I took the station that I copied more often, taking care that I had a balanced number of spots on each antenna). the pattern is for 30 degrees elevation... to be more accurate, the pattern should be considered for the circuit elevation, but this is just an indication. The important follows...

We can see on this first plot that the K9 is much better for G4MQL, while the vertical is more favorable to F1VS, especialy in the evening. By the way we can see the propagation drop at short distance during the night...

The second plot is for SV2BBO... I leave you to make your conclusions...

Finaly are the plots for several US stations, and for VE1RG and VE1VDM ( I put their spots together, as they had equal number of spots, and they are not that far away from each others).
So now, I think that we have the answer to the inital question: Is my K9AY working as expected - YES !
What is the benefit of such a receiving antenna: for my personnal case on 80m, an average 5 to 6dB if the station is in good part of the half-circle. Enough to make a QSO feasible or not ! Not too bad for such an inexpensive antenna which takes very little space ! (mine is a half-size one and only has 1 direction - the least noisy one which is North). Of course in particular DX direction, it won't compete with a long beverage, but I don't have the space for a beverage... ;-)

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