80m Development
Since 80m generally offers a more accurate beam heading due to less multipath effects as compared to 2m I think there are benefits to be made by triangulating several beam headings to pinpoint the fox position. This is how most competitors hunt the fox, by using lines on a map. A small area is defined where the fox should be positioned.
The accuracy of this depends on the following.
1) The estimated position from where the beam heading is taken.
2) The accuracy of all the headings.
3) The accuracy of the line drawing.
4) The number of headings used.
5) The relative difference in the headings used to triangulate, 90 degree heading differences are the best, small angles introduce more error.
In the rush of a race it is quite usual for significant errors to be made in 2), 3) and perhaps 1).
It could be argued that it is not important to define exactly where the fox is, as long as competitor can get close enough to run it down in the active minute of transmission. My comment would be to offer two options, a very small area where we think the fox may be or a larger area. Which one would you prefer to search?
I think everyone would prefer to estimate the position as accurately as possible, there maybe a chance of seeing the flag during the inactive 4 minutes.
So, what would it take to define the position of the fox exactly?
As a minimum, two different, accurate headings from two different known locations.
In order to remove as much human error as possible a GPS can be used to determine current position and an accurate electronic compass for the heading. We can expect perhaps 1 degree accuracy in the compass and a few metres accuracy in GPS position. Of course added to this is the beamwidth of the 80m receiver antenna and any multipath effects, these however could average out if a few readings are taken.
I'm sure the mention of a GPS will disgust the purists amongst you. Personally I see it as an extra tool in the toolbox, generally those who aren't naturally good at certain tasks find that tools assist them. I am one such person, my navigation skills are perhaps average at best and I think GPS can help me. If it is deemed as too much of an advantage then the rule makers will decide accordingly. As it stands the quest for innovation and for state of the art equipment is fortunately very much alive and seemingly encouraged. And so it should be!
OK, back to technical talk!
Combining a GPS, an electronic compass, an 80m receiver and a processor should enable good long range position estimation of the fox. The photo's below show one of my 80m developments. It uses a G3ORY 80m receiver and a rather large box containing an LCD, batteries, a PIC processor and a small GPS module. A remote electronic compass sits at the other end of the plastic boom.
The accuracy of this depends on the following.
1) The estimated position from where the beam heading is taken.
2) The accuracy of all the headings.
3) The accuracy of the line drawing.
4) The number of headings used.
5) The relative difference in the headings used to triangulate, 90 degree heading differences are the best, small angles introduce more error.
In the rush of a race it is quite usual for significant errors to be made in 2), 3) and perhaps 1).
It could be argued that it is not important to define exactly where the fox is, as long as competitor can get close enough to run it down in the active minute of transmission. My comment would be to offer two options, a very small area where we think the fox may be or a larger area. Which one would you prefer to search?
I think everyone would prefer to estimate the position as accurately as possible, there maybe a chance of seeing the flag during the inactive 4 minutes.
So, what would it take to define the position of the fox exactly?
As a minimum, two different, accurate headings from two different known locations.
In order to remove as much human error as possible a GPS can be used to determine current position and an accurate electronic compass for the heading. We can expect perhaps 1 degree accuracy in the compass and a few metres accuracy in GPS position. Of course added to this is the beamwidth of the 80m receiver antenna and any multipath effects, these however could average out if a few readings are taken.
I'm sure the mention of a GPS will disgust the purists amongst you. Personally I see it as an extra tool in the toolbox, generally those who aren't naturally good at certain tasks find that tools assist them. I am one such person, my navigation skills are perhaps average at best and I think GPS can help me. If it is deemed as too much of an advantage then the rule makers will decide accordingly. As it stands the quest for innovation and for state of the art equipment is fortunately very much alive and seemingly encouraged. And so it should be!
OK, back to technical talk!
Combining a GPS, an electronic compass, an 80m receiver and a processor should enable good long range position estimation of the fox. The photo's below show one of my 80m developments. It uses a G3ORY 80m receiver and a rather large box containing an LCD, batteries, a PIC processor and a small GPS module. A remote electronic compass sits at the other end of the plastic boom.
By storing at least two beam headings from different positions the unit is able to calculate the distance and bearing from the present position to the fox. For a quick demo I took two beam headings to a fence post in my garden, indoors the first image tells me it is 19 metres away at a bearing of 222 degrees. My present heading is 324 degrees and I haven't yet got any estimations for transmitters 2 to 5.
The top line tells me my nearest transmitter which happens to be the only one I have input data for, transmitter 1. It also tells me the current transmitter period is 2. The bearing is input by pulling a small trigger switch which isn't clear on any image. It automatically knows which fox it is by the timing in a 5 minute cycle. It can be set up for a selected number of foxes in the 5 minute cycle, 1,5,7 or 8.
The second image shows a different screen function, the mapping function. A little difficult to see but it maps the position of the competitor relative to the fox. The fox is a central dot and a 'snake' type image is formed as the user approaches the fox. The snake plots the route taken by the competitor and so it is visually easy to see if we are heading for the fox or need to make slight left or right adjustments. it is autozooming.
The 'Map' information lets the user know how far the fox is away on the orienteering map to further aid positioning, the map scale is a setup parameter.
There is also a small arrow to tell the user which relative direction to run. The demo above implies the fox is behind, hopefully the arrow is pointing forward most of the time!
There is also a function to enable straight headings to be followed and if, due to obstacles, it cannot be followed information is available to get you back on the heading. This is extremely useful when close to the fox but haven't found it by the time it ceases transmission. Just prior to the end of transmission a heading is taken and you try to follow this as close as possible. The 4th line in the second image shows <23m 339. This means that the user has wandered off the ideal heading by 23 metres. To get back on heading turn left and go 23m. This will then continually update until the reading displays almost 0m and then the correct heading of 339 can be resumed. Hopefully the user will be back on track to find the fox.
The processing is not too difficult but contains there is a continual swapping between magnetic north and GPS north. Also there are algorithms to handle a number of bearings and to select the ones deemed to be more accurate. It never works out quite as simple as first expected. The icon links to the c code for the operation of the processing and display.
The top line tells me my nearest transmitter which happens to be the only one I have input data for, transmitter 1. It also tells me the current transmitter period is 2. The bearing is input by pulling a small trigger switch which isn't clear on any image. It automatically knows which fox it is by the timing in a 5 minute cycle. It can be set up for a selected number of foxes in the 5 minute cycle, 1,5,7 or 8.
The second image shows a different screen function, the mapping function. A little difficult to see but it maps the position of the competitor relative to the fox. The fox is a central dot and a 'snake' type image is formed as the user approaches the fox. The snake plots the route taken by the competitor and so it is visually easy to see if we are heading for the fox or need to make slight left or right adjustments. it is autozooming.
The 'Map' information lets the user know how far the fox is away on the orienteering map to further aid positioning, the map scale is a setup parameter.
There is also a small arrow to tell the user which relative direction to run. The demo above implies the fox is behind, hopefully the arrow is pointing forward most of the time!
There is also a function to enable straight headings to be followed and if, due to obstacles, it cannot be followed information is available to get you back on the heading. This is extremely useful when close to the fox but haven't found it by the time it ceases transmission. Just prior to the end of transmission a heading is taken and you try to follow this as close as possible. The 4th line in the second image shows <23m 339. This means that the user has wandered off the ideal heading by 23 metres. To get back on heading turn left and go 23m. This will then continually update until the reading displays almost 0m and then the correct heading of 339 can be resumed. Hopefully the user will be back on track to find the fox.
The processing is not too difficult but contains there is a continual swapping between magnetic north and GPS north. Also there are algorithms to handle a number of bearings and to select the ones deemed to be more accurate. It never works out quite as simple as first expected. The icon links to the c code for the operation of the processing and display.
Antenna experiments
You'll notice the receiver has a ferrite rod antenna, while generally OK I have noticed instances where I didn't seem to be getting good nulls or a symmetric 180 degree operation.
Initially the antenna wasn't electrostatically screened so I modified the antenna and the inside of the case. The reason for this is that the ferrite rod antenna picks up the magnetic field part of the received signal. If this was truly the case the ferrite rod would show symmetric performance as it is rotated through 180 degrees. However if there are parts of the circuitry or the antenna picking up any part of the electric field then the signal into the receiver would be some combination. Indeed this is how the receive sense antenna works, it is deliberately switched in to receive an amount of electric field. If the antenna is the correct length the received electric field signal will cancel out the received magnetic field signal when the ferrite rod is oriented in a normally maximum direction. If rotated 180 degrees the received electric field signal essentially stays the same but the received magnetic signal inverts and now adds to the electric field producing a maximum ( which is a higher maximum than the magnetic field alone) . So if the intention is to find a beam heading from a ferrite rod or loop antenna null it is a disadvantage to receive any electric field signal.
After screening my ferrite rod and the case I seemed to be getting better performance but I didn't feel I tested it under controlled conditions. I was after a tighter null and there wasn't much I could do with the ferrite rod to achieve that. I have read that different rods give different performance but it seemed all too awkward to do. I wouldn't have the patience to find similar sized rods, wind the coils, shield them, fit them etc. etc. I was rather eager to try a screened loop, so I built another receiver and changed the antenna system.
Initially the antenna wasn't electrostatically screened so I modified the antenna and the inside of the case. The reason for this is that the ferrite rod antenna picks up the magnetic field part of the received signal. If this was truly the case the ferrite rod would show symmetric performance as it is rotated through 180 degrees. However if there are parts of the circuitry or the antenna picking up any part of the electric field then the signal into the receiver would be some combination. Indeed this is how the receive sense antenna works, it is deliberately switched in to receive an amount of electric field. If the antenna is the correct length the received electric field signal will cancel out the received magnetic field signal when the ferrite rod is oriented in a normally maximum direction. If rotated 180 degrees the received electric field signal essentially stays the same but the received magnetic signal inverts and now adds to the electric field producing a maximum ( which is a higher maximum than the magnetic field alone) . So if the intention is to find a beam heading from a ferrite rod or loop antenna null it is a disadvantage to receive any electric field signal.
After screening my ferrite rod and the case I seemed to be getting better performance but I didn't feel I tested it under controlled conditions. I was after a tighter null and there wasn't much I could do with the ferrite rod to achieve that. I have read that different rods give different performance but it seemed all too awkward to do. I wouldn't have the patience to find similar sized rods, wind the coils, shield them, fit them etc. etc. I was rather eager to try a screened loop, so I built another receiver and changed the antenna system.
I have compared this loop antenna to the ferrite rod and there is a definite improvement in beamwidth and seemingly a slight sensitivity improvement but perhaps insignificant. Since I don't have the big box of electronics strapped to it it is dream to use!
I think that I could achieve null accuracies of around +/- 5 degrees which in itself would enable accuracies to +/- 85m at 1km away.
Certainly for the sprint event it is a definite winner over the other model. I don't think the processing will be able to offer an advantage in the sprint, there is just no time for it.
I really enjoy using this 80m equipment, perhaps I have gone full circle and learned to love the simpler things in life!!
My plans now are to get the compass sorted such that it'll settle quickly or even give me fairly accurate results while on the move.
Following that I would want to modify the processor based 80m receiver and fit a loop antenna. I'm quite confident that all these modifications would be a worthwhile addition that would work from a practical perspective on a long distance event and ultimately allow me to hunt the fox quicker than I can now.
I think that I could achieve null accuracies of around +/- 5 degrees which in itself would enable accuracies to +/- 85m at 1km away.
Certainly for the sprint event it is a definite winner over the other model. I don't think the processing will be able to offer an advantage in the sprint, there is just no time for it.
I really enjoy using this 80m equipment, perhaps I have gone full circle and learned to love the simpler things in life!!
My plans now are to get the compass sorted such that it'll settle quickly or even give me fairly accurate results while on the move.
Following that I would want to modify the processor based 80m receiver and fit a loop antenna. I'm quite confident that all these modifications would be a worthwhile addition that would work from a practical perspective on a long distance event and ultimately allow me to hunt the fox quicker than I can now.
For my work with electronic compasses, click the icon.
I used the same G3ORY receiver board but changed the antenna to a balanced loop built inside a length of 8mm micro-bore copper pipe.
It has a diameter of approx 24cm and there are three loops contained within the shield.
Two loops form the balanced magnetic antenna and the other one is used to induce the sense electric field signal picked up by the whip antenna.
It has a diameter of approx 24cm and there are three loops contained within the shield.
Two loops form the balanced magnetic antenna and the other one is used to induce the sense electric field signal picked up by the whip antenna.
G4KWQ
Does it work?
Yes and no is the answer I'll give at this stage.
Under conditions where the bearings are input correctly it is very accurate (removing inaccuracies due to antenna beamwidth and multipath). Why shouldn't it be accurate, it is only maths and angles. If used optically it is fine however the main item that lets the system down is the compass. It takes too long to settle to a accurate value and in the heat of a race it is too easy to trigger a bearing when the compass hasn't settled. Also it needs effort and concentration to operate it, at present it seems easier to carry on running for the fox rather than stop to take a measurement.
In the UK most events are based on 2m, 80m events are fewer and I've had limited practise time. I really need to improve the compass and I'd be prepared to give it another go. I know it can theoretically help but I need it to be practically useable also.
Over the next few months I'll have a new compass and I'll post my findings.
Yes and no is the answer I'll give at this stage.
Under conditions where the bearings are input correctly it is very accurate (removing inaccuracies due to antenna beamwidth and multipath). Why shouldn't it be accurate, it is only maths and angles. If used optically it is fine however the main item that lets the system down is the compass. It takes too long to settle to a accurate value and in the heat of a race it is too easy to trigger a bearing when the compass hasn't settled. Also it needs effort and concentration to operate it, at present it seems easier to carry on running for the fox rather than stop to take a measurement.
In the UK most events are based on 2m, 80m events are fewer and I've had limited practise time. I really need to improve the compass and I'd be prepared to give it another go. I know it can theoretically help but I need it to be practically useable also.
Over the next few months I'll have a new compass and I'll post my findings.
