Seductive serendipity / Verleidende serendipiteit

January 29th, 2014

CQ160 CW 2014 contest

During the weekend of January 25/26 I participated in the CQ160 CW contest.

A photo impression can be found here.

Top loaded shunt fed vertical T-antenna for 160m.

January 16th, 2014

145 MHz / 2m Moxon

An antenna was needed after building a FOKZBox, a modern 2m fox hunt receiver.
Although HB9CV antennas are popular among ARDF/fox hunt enthusiasts,
more simple/better performing alternatives are available nowadays.

One alternative is the Moxon, described by Les Moxon G6XN in 1993.
elaborates on its effectiveness and ‘unbelievable’ (> 30 dB) F/B ratio.

Moxons (mechanical construction) outperform(s) a HB9CV, and… its width is ~30% less.
Imho the biggest asset of a 145 MHz Moxon is lack of eye poking!

Moxon calculators are online (see Google). However, I used 4NEC2. I found some 5 mm diam
‘scrap’ elements in my shed. One element transformed into the radiating element.
Another element was extended with Al-pipes (after tap wrenching) to serve as reflector.

The radiating element is fed through a common mode choke / 1:1 balun  (~50 cm RG58, coil wound).
The contraption was strengthened using RG213 PE-dielectric.
PE-dielectric may increase (capacitive) ‘Moxon coupling’ somewhat, but.. what the heck ; -)

The result has an excellent VSWR, F/B ratio, and deep notches around + and – 105° azimuth.
Pictures of my 145 MHz Moxon implementation are depicted below (your mileage may vary).

(Click on images to enlarge, open in new tabs)

145 MHz Moxon, top view.

145 MHz Moxon, side view. Notice the hand grip ; -)

Trespa feed point close up. A ~25 uH choke (‘anti static’,

Xl = ~23 kΩ) across the terminals was added later.