I had a most interesting letter from Talbot Kirk on D/F reception in UK, complete with his local station lists and frequencies. A right smart operator is Talbot — checks his cruising area and retunes his IFT’s a little to shift images and interference, etc. Jolly good — please stand him a pint from the Naylor Noggin for smart seamanship on the airwaves!

He has made me think a little more constructively on the subject. A direct conversion receiver with an 800 c hertz low pass filter — now a lightweight possibility by using an IC op-amp and a few resistors and condensers to assemble an active filter — will separate each beacon without interference. In fact, the ability to use either side of Zero-beat on every station offers a further choice to evade interference. A point Talbot, in Australia, Marine beacons are few — hold it — aeronautical beacons, NDBs, are prolific! Dot one in about every 100 miles across the continent and nighttime is something to hear — you can with my 400 hertz crystal filter ex-Marconi D/F receiver. Look at it this way, if you can’t hear even one NDB you are lost — land, sea or air.

Back to radio-location, after 3 weeks I remembered the Robinson D/F system. This used crossed-loops and switched the receiver between them. This idea was for early aeronautical navigation so you heard the null and carrier alternatively and knew you were nulling a real signal and could read the beacons call-sign without moving your loop. It looks promising for the single handed sailor and dinghies. Forget the crossed-loops, they are heavy expensive bits for 747s and QE2s. The normal ferrite rod gives good sensitivity and an adequate null for small boats. Back it up with a short receiver mounted at right-angles to the axis of your receiver. Feed the signal through a buffer radio frequency amp — one transistor — into the mixer. A simple pressel switch allows you to periodically confirm your station’s identity. Some form of gain control would be an asset. Use a 5000 ohm potentiometer as the collector load and take the output via an ,01 mfd and an 50k resistor to the mixer should suffice. Take care to shield to avoid de-grading your null. Consumption would be an extra milliamp whilst the switch is pressed.

I like Talbot’s craft — I hired a similar one from a native in the New Hebrides. It was fun and had distinct ideas of its own on which side the AMA should be worn depending on wind, tide and preferred direction. I never did quite solve it and if progress was slow, I did a 180 deg and shifted 6 ft to the other end. It inspired me to find a copy of Multi Hulled Sail Boats by Edward F Cotter. This looks into several proa designs, double outriggers and then on to catamarans, small and large. Can a proa be recovered from the 100% inverted position by standing on the AMA? All comments welcome. As I weigh in at 15½ stone and like small craft — as Talbot points out you can find a lot of places to poke into and proas are fully reversible — stability is my first consideration.

Cheerio for now, and I hope you have fair weather and full sails on all your cruises.

Yours sincerely Bob McGregor 2 Wiltshire Drive, Somerville Vic 3912, Australia