Hi-Gain Vertical Half Wave Antenna

[Barry06]

Has anyone successfully made a working replica of this antenna?

I’d like to buy one if anyone can build one to sell.

[Gigahertz]

Really surprised with the details available someone is selling them on ebay by now.

[RF-Head]

link ?

[mixfm]

used one back in the day [ better then a dipole ] our tech guy built it the man, offcock have it now lol

[Gigahertz]

link ?

Sorry I meant to say considering the details are available on here someone hasn't got them made up and flogging them by now.

Teach me to read what I write

[Gigahertz]

More for giving it a try and as this thread had seemed to go quite. I can assume no one has built one from the details provided by Lee???

I started the 50watt version out of bits I have from an old CB antenna, some metals enclosure that I cut for the plates. Just waiting on some nylon bolts and will put it together.

Just wondering if anyone can point me in the right direction. I can't see anything mentioned in the documentation about the coil winding on the cold/earth side for the 50watt version (unless I missed it). Pictures shows 7 turns of enameled wire on the higher power versions but I think I can see 3-4 turns of brown insulated wire on the low power version? Just read bottom coil is 7turns on all versions

Also where there any details of the distance between plates. As this forms a capacitor was any values given or is this trial and error.

[Gigahertz]

Just a start on it.

[Frequent Lee]

The size of the plates is critical and as you rightly assumed the air space between them is to tune it, start of with them being approximately 1cm apart and that won't be far off.
The 50 watt coil is just solid copper core from twin and earth mains power cable hence why some were blue sheath and some brown.

The bandwidth is about 5mhz either side of the tuned length of the radiator.

Claimed gain is 4.6dbi with a narrow angle of radiation, get them high up and mounted in free space and they hands down out perform a twin stack or a J pole.

I used to get them for £25 each built as I had known Stephen for over 20 years and put a lot of business his way.

[shuffy]

Just a start on it.

I already love it.

[Albert H]

The big problem with a ½-wave aerial is that the feedpoint impedance is (theoretically) infinite. In reality - because of materials losses - the impedance is just very high (Stephen estimated it at 5 - 6 kΩ). The big trick is getting an efficient impedance transformation, so that the antenna matches 50Ω.

Practical experience showed that the SWR was virtually flat over about 2½ MHz either side of the designed frequency, and rapidly rose to about 2 : 1 by 4 MHz away. The gain - at frequency - is around 2.8 dBd (gain over a dipole) and is truly omni-directional. We measured the real gain on an antenna range. It needs to be mounted in free space at least a wavelength (~3m) above anything else. The radiation pattern is flattened, with very little energy going upwards - it radiates in the direction you really want!

Practical experience showed that it was a very effective (and cheap to construct) aerial, and would withstand the rigours of the worst of European weather. I never liked the inverted plastic funnel over the capacitor, and made up some proper covers that had (effectively) a funnel-shaped top, with a tin-can sized lower section that screwed into threads in the upper section. The entire cover was made out of a kind of PVC plastic material that could be (quite coarsely) threaded, and provided complete water-proofing for the matching system.

Friends of mine experimented with various means of matching this aerial - mostly in an effort to eliminate the home-made capacitor - and also tried to construct a "general" version of the aerial that could be quickly tuned to anywhere in Band II with a variable length radiator. They had some success, but found that Stephen's version was probably about as good as possible.

The "Flowerpot" aerial is a relative of this design, and can also be cheaply made, and has the advantage of easier matching, but has less gain. One interesting version of the Flowerpot is the 0.64-wavelength type. This can have gain comparable to Stephen's half-wave job, but has narrower bandwidth and is more critical to tune.

[Gigahertz]

Just a small updated!

Fitted the bottom coil, decided on 3 - 1/2 turns as the of the tube is larger and if that doesn't work will change it to the 7 turns (coil).

Also fitted the plates. Nothing has been set up yet just wanted to get it built and will add coax and start checking with analyzer and see where I'm at.

Everything could do with tidying up but this is only testing stages.

[Gigahertz]

The size of the plates is critical and as you rightly assumed the air space between them is to tune it, start of with them being approximately 1cm apart and that won't be far off.
The 50 watt coil is just solid copper core from twin and earth mains power cable hence why some were blue sheath and some brown.

The bandwidth is about 5mhz either side of the tuned length of the radiator.

Claimed gain is 4.6dbi with a narrow angle of radiation, get them high up and mounted in free space and they hands down out perform a twin stack or a J pole.

I used to get them for £25 each built as I had known Stephen for over 20 years and put a lot of business his way.

Cheers Lee for info!

You were getting them cheap back then