Today I decided to take part in the South America 10m Contest… Why? Because it’s a great opportunity to build a custom setup targeted both at a specific geography and band.
The South America 10m contest runs for 24 hours on the 10m band (28.3-29.3Mhz for SSB). The purpose is to encourage radio amateurs from around the world to establish communications with call-signs in South America.
My home is on the South Coast of the UK around 8300km from South America.
The solution – the 10m band is quite wide so to cover the whole band I built a double bazooka diople. The double bazooka dipole is an inexpensive antenna constructed using co-ax cable which should provide a wider bandwidth than a ‘standard’ dipole antenna. The design is very simple as the co-ax ‘legs’ of the dipole also form the balun meaning no windings or torroids are required. The guide I used to build mine is here.
For the center of the double bazooka dipole I built this simple connector block using an old potting box I had lying around. The SO239 connector is for the coax to the radio. The two BNC connectors are for the dipole ‘legs’. Using this arrangement I can change the dipole elements if I want to use a different band to communicate.
The ‘legs’ or dipole elements of the antenna I created using RG-58 coax. I used a high grade of coax because that is what I had available although numerous sources online suggest that the coax grade is not important and some even go as far as to recommend lower grade coax with thinner screening braid. In theory a larger diameter co-ax should provide wider bandwidth although I have not tested this. I accurately cut the screened part of the dipole but left the un-screened sections slightly longer than the calculations, I finished these by folding back the ends with some eyelets so the length can be adjusted for tuning and there is a nice eyelet to clip to supporting ropes. All the joints are waterproofed with heat shrink.
Once completed I put up my 5.5m mast in the back garden and installed the antenna with a broadside bearing of 220 degrees (aimed at South America). The height is just over 1/2 wavelength and there is a reasonably unobstructed path to the South so this is as close to optimal as I can really get! The predictions from VOACAP looked promising….
Here is the end result:
Most importantly was it successful?
I think so. I operated for around 1 hour on the Saturday evening and a couple of hours on the Sunday morning. I’m not a serious contest station, I just like to test new things but plenty of QSOs with South America mostly using just 50w of power into the dipole.
