VK3MO vs VK3QN

Initial work to determine whether there is a difference between world-class antenna systems VK3MO and VK3QN (the latter is VK3MO's wife's callsign) has shown interesting results.

If you've ever read the late Les Moxon's excellent 'HF for all Antennas' book, you will have come across Ian, VK3MO, mentioned (during his much younger days!) in relation to low-angle radiation on p168.

The VK3MO, non-low angle optimised array.  Image: VK3MO.

VK3MO is a stack of  four, 5 element 14MHz Yagis with no particular optimisation for elevation of radiation. The (rotatable) tower height is 200 feet.

VK3QN, meanwhile, is an array of two, 6-element Yagis at one and two wavelength height, fixed on LP to Europe and optimised for very low radiation.

The question Ian, VK3MO had was whether the low angle radiation is actually important, and whether it's detectable at distant receivers.

Output for both systems was 5W via QRPLabs transmitters connected to a QRPLabs 5W linear amplifier (in the case of VK3QN (2x6 ele array)), the total system gain is computed by HFTA as 24.5dB at 3 degrees' elevation, or an ERP of 1.4kW.

This apparently simple question hides a plethora different possible answers.

Over the course of a full day, the answer for most receivers is that the difference between the two set-ups tends towards zero. Mind you, this is an important result, because a 66 foot tower with a 2 x 6 ele array, though extensive by most people's standards, is a lot less complex than a 200 foot, rotating tower with twice as many antennas on it, if it is achieving the same result!

But, at long path time, differences tend to be revealed, especially if the receiver has a good location and access to very low radiation angles (and very, very few have that).

Even with a simple Ampro stick on the car, I was already seeing a significant difference of up to 10.5dB between MO and QN when I was located at the coast.

This difference was not evident at the delta loop back home, which also heard both stations less often, despite being in a very good location, only a few km inland for the LP path.  That is almost certainly because the delta is hearing somewhat higher angle signals, where the two signals seem to take a much more similar path (as happens, in all likelihood, during daylight hours, bringing the median difference to an apparent, but ultimately misleading, zero value).

Unfortunately, I am not currently able to set up antennas directly on the beach to access ultra-low angles, due to the virus restrictions.  I suspect there would be a significantly greater difference shown, if I could do this.

Reception of VK3QN (low angle 14MHz) by MW1CFN (vetical delta loop).  The peaks represent the long path period, ca. 07:30UT each day. 

I then consulted the outstanding results given by OE9GHV, who I think operates an 80m-cut delta loop, very high up in the mountains.

I was delighted to see that OE9GHV was also seeing a signficant and, more importantly, consistent difference across three days, of up to 7dB between MO and QN, favouring the latter call (the low angle-optimised antenna array).

So, the overall story for now seems to be that yes, the low angle-optimised antenna in VK3 does result in real and significant differences in received signal strength at the distant receiver, provided the receiver can access incoming low angle radiation.  Those who can't access low angles will generally see no significant difference.

More work to confirm will follow...