I’ve been thinking for a while about discrete HF communications. I often read about issues in the UK with radio amateurs falling foul of local government enforcement action: Radio enthusiast at risk of losing lifelong hobby – BBC News
In the UK most amateur radio antenna’s do require planning permission although this is rarely enforced. In the US the situation is much worse for those living under Home Owner Association rules (HOAs) which seem very restrictive on amateur radio antenna’s particularly for the HF bands where large size antennas are the norm. Planning guidance for most domestic property in the UK can be found here.
This weekend was the ARRL 10m radio contest. The 10m band is at the top end of the HF spectrum and is a great band for long distance communications. I decided this would be a great opportunity to experiment with some ideas for ‘covert’ HF communications. Given the short wavelength and the challenge of long range I wondered could I build something that could be hidden but communicate with the US (over 5000KM)?
I tested two ideas – the first on the Saturday was an inverted vee antenna attached to the back wall of my house. It’s not covert as such but it’s below the roof line of the house and cannot be seen from anywhere apart from my immediate neighbors property. Even with a drone it would be hard to spot! In order to give some separation from the wall I have made the vee shape point towards the west (ideal for communications to the US).
The results were not bad – I was able to communicate with stations in North America, Canada, Brazil, Romania, Bulgaria, Greece, Serbia and Turkey using 25w of RF power.
For the Sunday I decided to push the envelope further – a fully covert dipole antenna in my roof-space and a reduction to QRP power to see how far I could push the concept. The antenna in the roof-space has no visual compromise from anywhere outside of my property and reduction of the power levels to QRP will make even RF detection difficult. The results – this antenna performed better than the external antenna, probably because it was slightly higher up and perhaps the bending of the legs towards the West on the external antenna will produce some nulls and gains which might have been unhelpful. I was again easily able to communicate with North and South America on 25w before dropping the power to 5w and again repeating the test successfully.
