Hi Jonjo
It came from the USA as you probably gathered. I was a bit worried about going down this route but it proved painless. Dave at DPD was very helpful and stayed in touch answering my queries until the package arrived. It took about three weeks in the end for it's arrival, frustrating, this was mostly down to delays after it's arrivial in GB and local postal services.
The link for further details is
http://www.dpdproductions.com/page_vhf_air.html.
I found it to be well constructed and more importantly to be effective. However i am sure others on here will have other suggestions. I'd say check out all your options and be patient.
Once you make a decision I am sure you will find a worthwhile increase in coverage. It's down to your choice of aerial, but location i.e. indoor /outdoor height mounted and any local obstructions i.e. mountains/other buildings which will effect the signal.
You should also be warned if you make the right choice the hobby becomes even more addictive. Good luck with you research and purchase, and enjoy the RB.
I have attached my polar diagram taken on a quiet earlyish Sunday morning with no network traffic showing. This polar diagram has been running for 10 days.
John
Sorry I just added a poor shot, of it mounted outside just for info.