RaDAR – Equipment check

For some time now, I have been evaluating what equipment best suits the RaDAR operator, the on foot operator in particular. Many configurations have been tried during the past few months. There is not always one same solution for every kind of deployment and improvements can always be made. Often, when doing re-deployments, new ideas for improvements are realized. Certainly the faster you can pack up and move without leaving any kit behind is the ultimate goal, even in the dark! Taking everything with you to the first deployment site without leaving anything at home precedes that!

EddieRaDARBigBackpack

Backpacks – Certainly the space required to carry a full RaDAR kit becomes an issue. There is the ultralight option where only a rig and antenna are carried mostly used for short term QRP contesting or a slightly heavier solution where all options need to be catered for, even digital. The general size of backpack for most deployments are in the region of 20 to 30 litres. Anything larger than that is geared more to deployments lasting longer than a day. Anything smaller, well that’s for an afternoon sitting under a tree. A pack that has a waist belt and sternum strap is an added advantage.

Masts – The telescopic kind that is not so heavy. The “Klaus mast”, “Eskom pole” or paint roller mast. They are all quick to deploy using simple nylon guy ropes and tent pegs. If need be they can be strapped to a tree stump or any man made structure – whatever is available. Certainly the “Eskom pole” is the strongest option and more than one wire antenna or even a small yagi can be accommodated! It is also the heaviest!

Antennas – Certainly the most effective wire antenna is the simple centre fed dipole mounted as high as possible. The coax can be a little heavy though. For really fast antenna deployments that work is certainly the End Fed Half Wave antenna. It requires a tuner to match the rather large impedance difference.  A open wire fed delta loop is also a good option but requires a 4:1 and tuner. The LDG auto tuners are a good option.

Power supply – I have experimented with Lipo batteries of the type used in radio controlled model aircraft, rechargeable batteries and gel cells. Lipos are too sensitive to discharge, once they go below a certain voltage they are damaged forever and that happens way too easily. A costly experience no doubt! Rechargeable penlights are quite effective but they should be measured individually with a voltmeter for abnormally low voltages and removed permanently if low. They will cause failure! A 7 A/Hr gel cell appears to be the most effective but can take up a lot of room and heavy. A good stress test is a good idea after charging. If it fails the stress test it will fail you in the field!

Digital modes – Much has been said in the past about smartphone technology and the digital modes. It is my experience, after many tests, that this is only a solution for an ad hoc digital contact. Smarthphones are difficult to use in the field with their touch screens and very difficult to use in the sunlight. Smarthphones are also very heavy on batteries while the screen is active. Simple interfacing to a transceiver is difficult to achieve. A netbook running your choice of operating system software that can interface to a Signalink sound card interface is a far better option. Try to get a larger battery that can last a few hours under continuous operation. These little computers generally have good and robust keyboards. I am presently looking at the little 5 volt powered Raspberry Pi Linux computer. More about this little wonder in the future.

Other equipment – These are GPS’s, a compass, maps, signal instructions. GPS’s are rather heavy on batteries and it’s a good idea to use a GPS that works off penlight batteries. It’s easy and lightweight to carry spare penlights. In order to determine direction you need to move while holding the GPS in your hand which can be rather time consuming. In this case a simple compass can make all the difference. Know the magnetic deviation for the area to be able to determine true north. Batteries can and will go flat. Having maps on hand can save your life if you ever get lost. Up to date signal instructions listing known frequencies for example can be an enormous help. Why not carry your ham license and other documentation too. Don’t forget a logbook / notepad and pen / pencil!

Logistics – Food, water and protective clothing can not be over emphasized. These can be rather bulky and often determines the size of the backpack which ideally shouldn’t be too big unless you’re going on a five day trip! Of course the duration of the trip is relative to the amount of food and water that needs to be carried. It’s a good idea to identify refill areas before taking on the journey. RaDAR South Africa has not gone that far yet but I have discussed ideas with other enthusiasts regarding hiking trips through the Drakensburg for example. It’s rather difficult keeping a station running for a few days. It would be rather embarrassing being well fed and hydrated but unable to communicate!

Most important – Have fun!

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RaDAR – End Fed Half Wave Antennas

From numerous experiments done during the last year or two while practicing RaDAR, Ihave come to believe that the best HF antenna for rapid deployment and re-deployment is the End Fed Half Wave Antenna or EFHWA. Various designs have been tried with excellent results. The latest experiment was building and testing the well known Fuchs end fed antenna tuner. This is a very versatile tuner and by using a 21 meter length of antenna wire, any bands from 40m through to 10m, including all the WARC bands, can be tuned very effectively. With a longer wire, around 41 to 42 meters, 80m can also be catered for. Antenna deployment time – FAST!

So what is the Fuchs tuner? The following diagram sums it up quite nicely.

FuchsCCT

Winding the toroids may look difficult but really are quite simple to do. L3 should take the following form when complete.

L3

Various combinations of control settings have been tried and tested. The authors results were as follows:

21m long wire (No radials or earth)
40m Coupling 3/4 L3 3, Cap 60% SWR Good
30m Coupling 2, L3 2, Cap 100% SWR Good
20m Coupling 3/4 L3 2, Cap 33% SWR Good
17m Coupling 2 L3 1, Cap 90% SWR Good
15m Coupling 3/4 L3 2, Cap 25% SWR Good
12m Coupling 3 L3 1, Cap 50% SWR Good
10m Coupling 1 L3 1, Cap 25% SWR Good

41m long wire (No radials or earth)
80m Coupling 6 L3 4, Cap 90% SWR Fair