View from Oban Bothy

View from Oban Bothy
Showing posts with label DF. Show all posts
Showing posts with label DF. Show all posts

Monday, 19 January 2015

Sunday 11th January, Hide and Seek

Playing Radio

To recap, for those who haven’t been paying attention, this is Hide and Seek with radios. Some poor unfortunate will hide themselves away in the area covered by a particular 1:50k OS map. Said unfortunate will be armed with a radio transmitter with which he or she will transmit from time to time. The trick is to find the hidden station, ideally before anyone else does. There can be any number of ‘hunters’, there’s typically 5 – 10 out hunting on a good day.

Following the huge success of the last Radio Direction Finding contest in December (I won / came first / beat everyone else in etc), it fell to me to arrange the next event in the series. Competing in these events is great fun, hiding is just as much fun – it just takes a good bit of planning….and it helps if you have an evil, sadistic streak   ;-)

The hiding place was to the east of Poynton, Cheshire. The exact location was at the edge of Prince’s Wood – the tall trees should have given me loads of opportunity to erect a decent aerial. The bad news was that I’d gone up to the site the previous day with my able support team of Eden & Nat but the bitterly cold strong wind-driven rain, hail and sleet made aerial erection very difficult indeed.

image Where we woz hidden

We managed to sling 130ft of wire up into the trees. The earth system consisted of a 4ft metal spike driven into the wet ground and a long section of barbed-wire fence. I tuned the aerial with my new toy:

http://www.mfjenterprises.com/Downloads/MFJ-259C/MFJ-259C_R.jpg

The MFJ259C has proved it’s worth. Apart from making antenna tweeking a doddle it’s helped me learn more about aerials.

Like I said, we managed to get the aerial up but it would have been almost impossible without my eager assistants – thanks lads!


On the big day a total of eight teams took part, and along with their respective friends, relations, fans etc there was a total of 20 children of all ages in attendance. The children were mainly quite old – some were beyond retirement age.

My support team and I arrived on site in good time on the Sunday morning. Camouflage netting was set up, bacon butties were made (and eaten) and we were ready to go.

imageChris Heys at the start – photo lifted from the group’s Facebook page 

First transmission was 10am but we weren’t heard at the start. In these cases The Envelope is opened. The Envelope is only to be opened in cases of dire emergency – like when the transmitter can’t be heard at the start. This Envelope contains an approximate compass bearing to give the hunters half a clue of where to start looking. The start of the event, the place everyone meets up at to take the first compass bearing, was in Sale, Cheshire – about 10 miles from the transmitter.

image

Multiple transmissions are made, in theory to a sort of schedule. Unfortunately I screwed up the schedule….but only a bit.

My assistants, Nat & Eden, were lurking in the woods. They were armed with a walkie-talkie and were able to keep me up to date with news of approaching hunters. This kept them entertained for a good while. I’m sure they ‘assisted’ those trying to find the hidden station!

First man in was Dave Peacock, who charged up the hill in fine style – arriving around 11.10am, a good 3 minutes before the next man, Chris Plummer. The remaining hunters (apart from one team) arrived over the following half hour. The hunters approached from pretty well the same direction, all were pleasantly confused by the woodland. The DNF (Did Not Find) team managed to locate the apres-event pub. This was A Good Thing, a very pleasant lunch at the Boar’s Head in Poynton  rounded of the day quite nicely. 

Not being heard at the start was a bit of a pain – and a surprise. A huge and resonant aerial system should have been easily heard at a range of 10 miles – particularly when the transmitter was located in an elevated position. This has happened loads of times before, I reckon the transmitter’s knackered. I’ll bring my own next time – I know it works! 

Not much in the way of photographs I’m afraid. I took my camera with me but was so engrossed in remaining concealed that I didn’t get chance to use it.

Wednesday, 17 December 2014

14th December, Radio Direction Finding on Top Band

Variously described as orienteering with radios or hide and seek for grown-ups (or not very grown-up in most cases).

The general idea is that someone will hide themselves away in the area covered by a particular 1:50k OS map, around 1600sq km. They’ll have a radio transmitter with which they’ll transmit for short periods. Some transmissions are scheduled whilst others are random.

The only rules the transmit station has to adhere to, apart from the Amateur Radio Licence regulations, are that they must be located in an area of public access, not be in a building, and once established they must not change position. It’s a given that the transmitter doesn’t change frequency during the event. The fun begins when the competitors have to locate the hidden station – first one in is the winner. Obviously.

The transmitting station operates on Top Band, or 160m. The actual frequency coverage of the band is from 1.81mhz to 2mhz, just below the Medium Wave broadcast band. Because it’s fairly low in frequency (= long wavelength) the aerial needs to be quite long, ideally a quarter-wavelength wire - around 40m long.

The competitors are equipped with map and compass, and most importantly a radio receiver fitted with a highly directional aerial. The radios are home-made, commercial equipment generally isn’t sufficiently portable or affordable.  

imageTop Right: Transmitter, Centre: DF Receiver, Bottom Left: Breton Plotter 

So, on Sunday morning a group of DFers gathered in Sale, Cheshire, and strained their ears (and other bits too probably) to get a bearing on the hidden transmitter’s first transmission, scheduled for 10am. 

image At the start

Unfortunately the signal was completely inaudible. In such cases there’s a sealed envelope available at the start which contains an approximate bearing (+/- 20 degrees) and an idea of distance, usually within 10km. This can still be a huge area to search.

Not being able to hear the transmitter at the start can be a clue – it’s possible that the station is hidden in a valley so that the signal isn’t being radiated too well. It could also be that the operator decided not to bother and stayed in bed instead….or perhaps he/she fell in a river, fetid swamp, or got eaten by an alligator recently escaped from a zoo. Or more likely a private collection.

Anyroadup, the approximate bearing given was 67degrees which passed within 4km of the transmitter, and the distance given was between 10 and 20km from the start. A quick faff with maps, rulers and pencils soon had the hunting area defined on the map, and competitors jumped into their cars to find somewhere suitable to take a bearing from the second transmission.

In theory two bearings are needed to locate the transmitter…..where the lines cross is where the station SHOULD be. That’s if the laws of physics are to be believed. After all, electromagnetic radio waves travel in straight lines – everybody knows that. Except they don’t.

All manner of external influences can distort radiation patterns, the proximity to pylons and overhead power cables being prime examples. 

I’m not particularly mithered about winning, it’s always nice to do well of course, but I just like to enjoy the event. I left the start and travelled around the M60 towards Ashton-under-Lyne at a sedate 60-65mph. I’d pin-pointed a couple of spots where I’d try to take a second bearing and headed straight for the first one, arriving in good time for the second scheduled transmission….nothing heard.

At the third transmission I heard a good loud signal. I plotted the bearing, then jumped back into the car and drove half a mile up the road where I just managed to get another bearing before the station went off air.

Suspicions grew as to where the station might be…..very close to where Gayle and I had walked a few days earlier, Daisy Nook Country Park. I plotted the bearing onto my map and drove close to the point where the lines crossed – arriving just in time to hear another brief transmission.

My suspicions were confirmed, the signal was so strong that it overloaded my radio. I was obviously very close indeed.

I left the car and followed muddy footpaths towards the River Medlock. After much slipping and sliding, charging across the river (I was wearing my fell-running shoes!) and thrashing through very wet undergrowth I spotted the very well camouflaged station.

imageRoger, the station operator, now not hiding himself away. The box closest to him is the transmitter. The white-ish square(ish) piece of kit is my DF receiver.

At approximately 11.27am (exactly!) I officially found the transmitter. Surprise, surprise – I was first in.

image Posing with Roger, a slightly (very) muddied JJ….looking quite pleased with his little self

Around 10 minutes later we were alerted to the sound of someone crashing through the undergrowth on the other side of the river, looking for the hidden station. We kept perfectly still, trying hard not to snigger, as we watched with no small amount of glee as Chris splashed his way through the mud and bog. When he actually spotted us he declared he wasn’t going to cross the river, he hadn’t won so why bother?!

image

Chris, who didn’t come first, was heard to say something like ‘bugger crossing that river’

The next half hour or so saw the remaining competitors finding the transmitter – all coming in from a similar direction….and the wrong side of the river.

image

Chris and Roger, daring each other to cross the river

image

A happy Geoff, officially second in – because he crossed the river

image Determined not to be outdone, Hayley crosses the river

image An excellent lunch at The Hare & Hounds, Luzley

Results:

JJ                              11:27

Chris P                       11:40 (Located the station but didn’t cross the river)

Geoff Foster               11:42

Roger B                      11:48 (Located the station but didn’t cross the river)

Hayley                        11:57

Dave Chipp                 11:57:30 (Located the station but didn’t cross the river)

image

Plotted route shows my route in, a bit all over the place as I was trying to take multiple compass bearings on the hidden station in order to triangulate it’s position

image

The arrow points to the hidden station, the red line is the approx bearing from the start. The station was 10 miles from the start, as the crow flies.

Being as wot I came in first it’s down to me to hide on the next event, scheduled for 11th January.