Last Thursday’s SDARC Fox Hunt was a very enjoyable and technically interesting evening – and before I go any further, no foxes were hurt or distressed in the course of the activity!!
How do you have a “fox hunt” without foxes?
In Amateur Radio, a “Foxhunt” is a shorthand way of talking about a Direction Finding Competition. The format is alarmingly simple – one radio club member agrees to be “the fox” and, as part of a club activity night, goes out to an undisclosed location with a mobile radio transmitter and sends out signals. All the other members taking part (the “hunters”) set out to find the fox using direction finding techniques. At the end of the evening everyone meets up at a pub. Simples! – mmm, not quite, as you will shortly appreciate !!
So it was in the bright evening sunshine at the end of another gloriously sunny day on Thursday last, that the ‘fox’ set up just before 7pm. Following the club’s Foxhunt rules the fox locates somewhere on OS Landranger map 173. To reduce the fuel costs for the hunting teams – and our club’s carbon footprint – the fox actually declared in advance a reduced search area North of SU79 and East of SU10.
The fox transmits an establishing signal from just after 7.00pm using a pre-arranged frequency using a mobile transceiver and a standard roof mounted car aerial. Transmissions continue in bursts of 10 minutes each with 5 minute gaps up until 9.00pm when, for anyone who has not found the fox, the location of a Rendezvous pub is announced at higher power. To help hunting teams as they take bearings closer to the fox, power is reduced from 8.15 to ensure teams can actually find a ‘quality’ null direction.
What’s happening out on the roads during all this time?
The hunting teams – just four of them entered last week’s event, each have a receiver coupled to an aerial which exhibits some directional characteristics. During a transmission from the fox, the hunting teams leave their vehicles and sweep their aerial through 360% to find the direction that gives them the weakest signal – a null. They take a compass bearing from where they are located, transfer that bearing onto their OS map and draw a line. With one line on their map, the hunting teams now need to decide where the fox is located along their line.
By the time of the next transmission from the fox, the hunters have relocated to take their second bearing. This second line added to their map should intersect the first and they should now have a fairly good ‘fix’ on the fox. If they still have time, teams move before the next transmission from the fox and take a third bearing. This can be where the ‘fun’ starts!
IF the null in the team’s aerial was sharp enough AND the first two bearings taken were accurate AND if the team’s map skills have been good in transferring their bearings to their map, they SHOULD now have three lines that intersect at one sharp point – where the fox is located – and they can drive to that location, find the fox and have their efforts declared a success.
Needless to say, it doesn’t always go quite to plan !!!!
Sometimes, the lines on a team’s map can look more like railway lines – lots of non-intersecting, almost parallel lines !!
It can happen that the intersect is a vague area because the lines are coming from locations that were too close together.
Often, taking a bearing near tall, steel-framed buildings or at a dip in the level of the land can cause the fox’s signal to be reflected and appear to come from a wholly different direction than it really is !
Choosing to take a bearing from a ‘radio noisy’ location can result in the total loss of the weak fox signal in the presence of bursts of RF from nearby high-power commercial transmitters on the same band !
And just when you thought it was all ‘sorted’, you remember I said that the fox further reduces power from 8.15? That’s fine providing your team are fairly close to the fox, but if you are still some miles away when the power goes down, the fox may disappear totally! Ooops!!
How did last Thursday’s Fox Hunt go?
Well first things first…. Congratulations go to Geoff G3TPQ, who succeeded in finding the fox shortly after 8.10 and to Frank G3JOT & Deryck G3YKC who appeared at the fox’s lair a few minutes later.
Then there was a pause …..
Later, Marie-Ann M6UWS driven by Andy G0UWS, screamed to a halt in front of me in the dying minutes before the 9.00 ‘declaration’.
They were the last team to locate me, so well done to all concerned.
The actual location of the fox on this occasion was in a gateway on the side of Trenchard Rd between Stanton Fitzwarren and the B4019 Blunsdon to Highworth Road.
Apart from an inquisitive deer that came to see what I was up to on a couple of occasions, I saw very little passing traffic, so it proved to be a traffic ‘safe’ location.
So with the competition part of the evening over, it was time for a drink and to chew over the evening’s activity and learn a few lessons.
So, following the 9pm announcement of the RV point, a somewhat larger group, comprising Geoff G3TPQ, Deryck G3YKC, Frank G3JOT, Marie-Ann M6UWS, Andy G0UWS, Steve M0AKT, Ian 3YBY and the fox, Den M0ACM gathered the Freke Arms at Swanborough (www.frekearms.co.uk). The Freke is a great place for an RV because as well as a large car park, it is one of those unspoilt traditional pubs in the Arkell’s chain that’s full of character and can even source a tasty meal if you are peckish!
Well, so what next?
Watch the Club Programme page on the website to check the date for our next DF event.
We are having one DF Hunt evening in each of May, June, July and August, so get your kit ready!
Let’s see if we can get more teams involved – and more teams to find the fox!
Members and non-members are always welcome and since the hunters are only receiving signals, non-licensed hunters can take part too, so just join in and we’ll see you all at the RV point.
If you are interested in joining us and want to chat about DF aerials, come as a guest to one of our Thursday Club meetings at Savernake Community Hall. See the club web site for details.
Lessons learned?
Yes, we can all learn from doing and apart from various hunters repairing or altering their aerials for the next one, there will also be a couple of minor variations from the fox’s end in next event…
- Initial transmissions from the fox, prior to 7.25 will be at 10W instead of the 5W in the May event. This will allow 1st bearings to be from further away.
- The fox will reduce transmit power to 5W at 7.30 and then in two steps further from 8.15. Stepping will help get good nulls but try to prevent the fox from vanishing!
- In the last 5 minutes of these low power bursts there will be a brief 5W period. This to help those who have ‘gone the wrong way’ and have lost the fox.
All Rules and timings are published on the website linked from the event announcement in the programme so everyone will know what’s planned.
Thanks to all who took part and we are glad it was a good evening out. Hope to see many more next time.