Some months ago I decided that the time had come to replace the station antenna with something hopefully more efficient.  The old antenna had started life off as a 40 meter centre fed dipole which also operated reasonably well on 15 meters.  During some bad weather the dipole had snapped near the centre and as a temporary measure I had left one end still fixed to a telephone pole and bought the centre point through the window and into the shack.  This was now effectively a quarter wave on 40 meters and was resonated against earth using a home brewed matcher.  Looking back it's surprising just how well this piece of wire actually worked, I normally use cw so perhaps that helped...

The two most convenient points for anchoring an antenna at this qth are the chimney on the front of the house and  convenient poles at the bottom of the back garden.  The distance between these two points is approximately 68 feet.  The shack is on the ground floor, at the back of the house roughly two thirds the distance from the chimney to the back garden antenna support(s).  A 40 meter off-centre fed antenna is the obvious choice, the feeder literally falling into the shack window...

There are various books and articles on OFCD antennas (off-center fed dipoles).  My first port of call was Les Moxon's "HF Antennas For All Locations" who appears not to think much of the Windom.  The original Windom antenna was fed with single wire whilst nowadays it is more commonplace to feed a Windom with coaxial cable for convenience.  An article in QST by John Belrose VE2CV and Peter Bouliane VE3KLO provided some interesting reading as did Pat Hawker's Technical Topics in RadComm.  By now I had 'discovered' Jim Thompson's excellent web pages at RadioWorks.  Jim manufacturers the well known Carolina Windom and his site is well worth visiting.  The Carolina Windom is basically a co-ax fed OFCD antenna but has a fixed length of coaxial cable forming an integral part of the antenna.  This fixed length of cable hangs vertically from the feedpoint balun and is said to radiate vertically polarised signals in addition to the antenna's usual horizontally radiated signals.  This could conceivably give lower angle radiation and be beneficial for dx work.  Having being introduced to controlled feeder radiation (CFR) it was back to the textbooks again.  An article by G2HCG in RadComm May 1990 is recommended.

Having looked at the price of the various 'bits' I would require to make up a Windom I decided that there was some merit in purchasing a ready-made antenna and I subsequently emailed Jim to see whether he was willing to deal directly with UK customers.  His reply was that whilst he would prefer UK sales to be channeled through the UK agents he would be willing to despatch direct from the USA.  I soon realised however that the carriage costs would be prohibitive so this idea was shelved.  Some weeks later I purchased a Carolina Windom 80 Special for a 'special' price at one of the local Ham Radio Rallys.  I was not aware of the existence of the CW 80 Special but seeing as it was the exact same size as the CW 40 which I had been examining and appeared to operate on 80 meters as well I felt that this might be a bonus....

First impressions. The antenna comes packed in a strong plastic bag with a 'manual' which also doubles as a catalogue and a large source of general antenna information - very handy.  The quality of all the components supplied appears to be good, a nice touch is the sealing compound.  It is very important that this is used as per the instructions, certain antenna components are not weatherproof and I have heard of instances of antenna failure where this sealing compound has not been used properly.  You have been warned!

The antenna consists of the dipole itself, total length 66 feet, with a balun placed 41 feet from one end.  This balun has a 10 foot length of coaxial cable trailing from the bottom and terminating in a choke. This cable is the vertical 'radiator'.  The choke has an SO239 socket from where the coaxial feeder is led to the shack, certain suggestions are made regarding the length of this cable.  The balun and choke as supplied are very large and heavy and possibly over engineered for the United Kingdom's 400 watt allocation.  An immediate problem is that they tend to pull down the centre part of the antenna, this is unfortunate as the vertical 'radiator' is also pulled down and it's obviously important that this should be as high as possible and in the clear.  A third insulator has been provided, already threaded onto the horizontal portion of the antenna and this can be used to 'hang' the antenna from a tower or suitable support.  It is stressed that the vertical 'radiator' should be kept as far away from any metal work as possible.

Erecting the antenna.  Every location will present different problems and call for different solutions.  At the front of the house I simply lashed a small tv mast to the chimney.  (in the event it turned out to be too small and will require changing for a larger diameter pipe as it is already bending...).  I wanted the antenna to run over and parallel to the roof ridge to the back garden support.  This took a bit of engineering.  I had an aluminium pole at one corner of the back garden and the Telephone Company had a pole at the other corner...so I ran a length of stout nylon rope between the two poles, having previously threaded this rope through the end insulator of the antenna.  Tightening everything up and the antenna rose majestically into the air.  Except for the middle bit which drooped dramatically.

I had some strong brackets bolted to the back gable-end of the house right up at almost ridge height.  The solution was some sort of nonmetallic pole which would have the balun strapped to it's top, the pole would then be pushed up as high as possible before being secured to the brackets.  Having spoken to a fellow amateur locally it became obvious that the ideal centre support would be a wooden stairway handrail and I subsequently obtained a 15 foot length from the local timber yard.  The balun is laid parallel against the top of the pole and held in place using strong cable-ties (rat's tails).  These handrails have a small 'flat' machined along their length where the wall brackets attach and the coaxial cable (the vertical 'radiator') from the balun to the choke is laid down this 'flat', again secured every 12 inches by cable-ties.  The choke is mounted in a similar fashion 10 feet down the pole.  The coaxial feedline was also secured to the pole for the first 5 feet again using cable-ties before dropping down to the shack.  This ensured that there was no strain on the PL259 plug at the bottom of the choke.  Incidentally the third 'free' insulator provided to hang the antenna from a tower or similar structure was removed as it was not required.

Initial results.

Jim recommends using RG8X for the feeder because of it's low loss and cheap availability.  He also recommends a feeder length of 86 feet for the Carolina Windom 80 Special.  This should ideally present an 'acceptable' swr on all bands 80 to 10.  In answer to one of my emails, Jim suggests an swr of 5:1 as being acceptable.   Initial results are reasonably promising.  The built in automatic antenna tuner on my Icom IC 761 tunes the antenna to resonance on all bands, including 80 meters.  I normally work cw on the higher bands and of course propagation has generally been good so results need to be analysed carefully.  In the next few weeks I need to raise the centre of the antenna by about 3 feet and shorten the feeder, this should reduce cable losses slightly and increase overall efficiency.  Watch this space for the final results...