160m Top Loaded Vertical

I needed a 160m antenna in a hurry and this describes the 160m antenna I used for the 160m VK / trans-Tasman SSB Contest in 2011.

I have a 40m Lazy-D in the backyard at about 9m above the ground. I decided to use this as the capacity hat for a 160m top loaded vertical. Lowering the antenna is quite easy. I disconnected the 183Ω feed-line, opened the loop and attached 8.5m of 2.5mm insulated copper wire the loop. Up she went, and a 40 meter long piece of wire got attached as a radial. Here, Pic 1, is a quick view of the geometry of the antenna as modelled. It is not quite correct but good enough to get a rough idea of what to expect.

Looking at the modelled values, approximately 52Ω j+210, I used the build in matching calculator and I was able to calculate a 50Ω match.

Pic 5, above, shows the anticipated vertical radiation pattern and Pic 6, below, the horizontal radiation pattern.

Pic 7, below displays the current distribution on the antenna wire and the radial.

Below are the modelled values, Pic 8.

Using parts from my old PI-coupler, I was able to get the VSWR down to a 1.3:1 at 1.835 and 1.7:1 at 1.875, measured at the output of the network.

The radiated power is approximately 4.87 W of the 5 W injected. And with 25 m of RG-213 between the network and the radio the power-loss should be quite low. Cable attenuation < 0.5dB. The measured loss was it bit more, as the network also has some loses.

So there you have it, it is not that hard to get on 160m from a small backyard block.

Despite poor band conditions, I managed to be heard quite well, getting good signal reports, approx 2 to 3S points less then 100 W stations, and I've heard a few ZL's early in the contest. Of course I had difficulties to get through dog-piles and had to wait my turn, but I managed to work into the north of VK4 (VK4FNQ) and into New Zealand (ZL3UR).

Unfortunately there were no VK6's so no contacts into the West. The next thing to do is to improve receiving, and the plan is to use an active antenna and a remotely tune-able loop.

Update: 14/11/2011, I came fourth in CAT2. Results are here ...