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A comparison of a G5RV at VK1OD and QW vertical at VK2DVK on 40m over a 14,700km path using QRSS

*** DRAFT ***

This article reports an experiment to compare two antenna systems at nearby sites on 40m over a 14,600km path using QRSS.

The experiment is to compare a temporary 40m quarter wave vertical with a more permanent structure with more radials at greater height, principally to validate the G5RV antenna system at VK1OD (Bowral G5RV for local contacts). The reference antenna system at VK2DVK has previously be validated against several antennas and is taken to perform as well as expected for an antenna of this type.

Configuration

Receiving

The receiving station was W4HBK at Pensacola, FL (USA).

Transmitting

The transmitting stations were VK1OD and VK2DVK located about 100km S/SW of Sydney (Australia), and the antennas were two adjacent quarter wave verticals over elevated ground planes. The two antenna systems are:

At the time of the tests, the path elevation angle at the transmitter is very low, in the range 2° to 6°, and bearing is 78°.

Keyer

A QRSS keyer that facilitates antenna switching based on special characters embedded in the message was constructed. It was used with a quite standard Kenwood TS2000 and Icom IC7410 at each station, in CW mode adjusted for 5W output.

Fig 1:

Fig 1 shows the internals of the QRSS keyer at VK1OD. The keyer is described in detail at Another Morse beacon keyer - A/B RF switching.

Receiver recordings

The receiver used Spectrum Lab to gather and present a view of received signal and noise.

Waterfall charts were used for analysis:

Data is presented below for the hour from 07:00UTC on 16/03/13.

Waterfall charts

Fig 2:
 
 
 
 

Fig 2 shows a set of six graphics cropped from the full waterfall charts.

The top trace in the following clips is VK1OD, the lower one is VK2DVK.

In the last three clips, the power at VK1OD was increased to 10W to help put limits on the difference between the signals.

Conclusions

To the eye, the first three waterfall plots suggest that VK1OD is a little lower in signal level than VK2DVK. As noted, the power at VK1OD was increased by 3dB in the last three plots and VK1OD appears slighly higher signal level than VK2DVK with that power increase. A rough analysis is that VK1OD's G5RV antenna system is 2-3dB lower in EIRP on this path at this time.

The results are quite consistent with previous comparisons of low dipoles with the elevated QW vertical. It has previously been observed that the low horizontal dipole is not as far behind the vertical on such a low angle path as ham folk lore would suggest!

Links / References

Changes

Version Date Description
1.01 17/03/2013 Initial.
1.02    
1.03    

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