Short base loaded vertical Efficiency analysis.

Some power efficiency analysis on one of our fastest to deploy antennas in the field.



Hi Roberto,
Impressive good work, it covers some of the questions I had and didn’t know where to read about it.

I find interesting the fact there’s no huge variation between the radial on ground or elevated (appart from the resistance values variation): I was expecting a larger difference.

Thanks so much for sharing.

73, Ignacio

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really good work! I have been thinking about this very subject over the last couple of weeks, but not done any experiments. I do not have a AX1 and AXE1! I have been through your paper and agree with your workings and results. I used formulas from ON4UN’s Low Band Dxing to give similar results on 40m

I calculated the Rrad as 0.41 ohms, as included an extra foot in the radiator length by including the coils. I estimate the Q of the base loading coil with AXE1 to be a bit higher at 260. But I think ground losses on a typical summit could be more like 15 ohms giving an efficiency of 3.6%

To get any further than this I would need to build a test 40m AX1 with a similar coil, then take my N2PK VNA and laptop up a hill!

I challenge someone with a AX1 + AXE1 to do a 40m RBN test, a few CQ’s with the 33ft single radial. Then repeat with the AX1 disconnected, in its place a second 33ft wire lying on the ground. In other words a dipole lying on the ground. I am confident the results will be several dB better with the wire on the ground!

IMO short whips like this work ok down to 20m, below that we are verging on a dummy load.

73 Gavin

PS I have been round the houses with short verticals over the years and learned what works along the way. My current 160m antenna at home is a T hanging between trees with 18m vertical and about 3.5Km of ground radials :slight_smile:

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Good work. Many years ago I looked at mobile whips and figured that on 7 MHz an 8 ft whip with a large diameter coil could muster roughly 10% efficiency.

Your analysis is completely consistent with that.


The ground is a very lossy dielectric that happens to have some conductance. In the report, the ground loss measurement was done in a park, which I suppose is not a rocky ground like a typical summit. So, the advantage of elevating the radials is expected to be greater in poorer ground like summits.

Typical skin depth in the ground in HF frequencies is a few meters, so surface water has little effect. So, the light rain probably had little effect, but if any, it probably had slightly more impact on 10m due to shallower skin depth.

One way to minimize the ground loss is to increase the radiation resistance. I routinely use 3/8 and 5/8 wavelength verticals on HF from summits with good results. Yes, that is the opposite approach to short, loaded antennas, but it’s nice not having to worry about radiation efficiency in suboptimal radial placements. (Current imbalance among radials is another radial-related concern, and starting with higher radiation resistance minimizes that problem.)


Another possible approach to increase the efficiency of a loaded antenna is to use a center-load configuration. It requires a larger inductance higher up, so it is mechanically more challenging to construct but worth considering.


This exactly the Buddistick antenna design.

This works for 40m and up

For 80m and 60 I am using the tank antenna the Ranger80 by Rez antennas

It’s very heavy so shipping to EU may be pricey
John ve3ips

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