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20m vertical

Antennas are always an issue with neighbours, family, town planners etc. So to date I have limited them to either a) discrete long wire or b) 'TV' like antennas e.g. 2 el band 1 TV antenna for 6metres. However, I had a need for a decent 20m DX antenna and the obvious choice was a vertical. The ideal design was for a full 1/4 wave vertical on the gable end with two 1/4 wave radials sloping down the gable ends. So with the following raw materials:

1) glass fibre fishing pole (7m)
2) 3 x 17ft lengths of 2mm wire
3) Self amalgamating tape
4) 10m UR67
5) 'N' type bulkhead connector
6) chimney brackets and u bolts
7) 2 x dogbone insulators and 2 x standoffs

The vertical wire was run up the inside of the fishing pole and soldered to the N type bulkhead. The two radials were then soldered to the N type and the fishing pole shoved over the vertical element. Self amalgamating tape then sealed the bottom and top of the fishing pole. Initially the top section was left off to enable trimming of the length. Surprisingly, when the final pole section was placed over the top of the antenna the vswr shot up to 3: 1. This was probably due to some strengthening wire in the final section and consequently this section was omitted. Note the SOTA poles are probably ok in that they are glass fibre throughout their length. The antenna was mounted on gable end of house as shown in photos. The 17' vertical and radials were trimmed for best SWR , and a number of different radial angle (to horizontal) were tried. The final best SWR 1.3 : 1 (in 50 ohms) was obtained with the radials actually on the gable ends - which looked best as well. The gable ends being less than 17' required the ends of the radials to be bent down and attached to the drain pipes (insulated from them). With 70 watts CW, the log for the first 2 days included:


RK4HZ Samara 0730hrs
JJ1KXB Tokyo 1200hrs
UT5KTT Zlolbunov 1315hrs
UU9CI Sevastopol 1700hrs
VE2DOH Montreal 2020hrs

RW0BM Dudinka 0810hrs
K1GCD Maine 1938 hrs(UTC)
K2TQC Syracuse 1830hrs
LU2FLN Santa Fe 2100hrs

Note also that the standard length calculation for a 20m 1/4 wave element of 2mm thickness is 16ft 11.5 in at 14.050 MHz.

URM67 Specifications:
Overall diameter: 10.3mm
Capacitance (core to screen): 100pF/m
Max. voltage: 6.5kV
Nominal impedance: 50Ω
Attenuation per 10m: 0.68dB at 100MHz and 2.52dB at 1000MHz.

Say approx 0.2dB at 14Mhz for the 10m run to the antenna. This is a power ratio of 1.047 which equates to a loss of around 3 watts in the 70 from the Tx output. I can just about live with this and the affect on Rx noise figure is a straight 0.2dB which is negligible.
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