Posted by: GW7AAV | July 23, 2010

The Pidgon Perch and the Patio Heater

I have very little time for magical antennas that purport to do the impossible. Miracle Whips, Wonder Wand, Buddipoles and the rest are in my humble opinion at best dummy loads for dummies with loads of money and no sense. There is no alternative YET for metal in the air and there is no such thing as a small effective antenna for HF. Antennas can be small or effective but not both at the same time.

In this months RadCom the Bilal Isotron for 80/40m is reviewed and the reviewer Steve Nichols G0KYA has his say but some of his comments made me laugh. Far from being objective it sounded like he was making excuses for the manufacturer. Surely we should be able to rely on the magazine produced by the UK’s national radio society to tell the truth as it is and not try to avoid saying things that might upset the supplier of the reviewed antenna who also happens to supply pages and pages of advertising.

One thing the article mentioned is that it is a space saver, suitable for people unable to get up an antenna for 80/40m. What is missing is the fact that this antenna looks like something that fell off H.G. Wells’ Time Machine and that if you put it up outside firstly the neighbours would object to the eyesore and then they would probably send in the men in little white coats and have you committed.

Later on Steve mentions that the noise level on 80 metres was down three S-points on his off-centre dipole. What that means to anyone with half a brain that it is a deaf antenna. He goes on to say that received signal strengths were down 1-2 S-points. Which seems to indicate a one S point improvement in the signal to noise ratio, but which I believe is due to the attenuation, as I often use an attenuator to work marginal stations when noise is high. Transmitted reports were down 10-20 dB. So in other words only those hearing signals that would be S9 + from a dipole would be heard. As someone who gets a lot of enjoyment out of weak signal working I just cannot see the point. Where is all that lost RF going? It is heating the antenna of course and in my opinion that is all the thing is good for, it is a patio heater.

The worst thing about these joke antennas is the amount of money they cost and always the hook is because you have not got the room for a real dipole. Sorry but tell it to the birds, I have loads of friends with gardens the size of postage stamps and where there is a will there is a way. Wire in the loft, inverted vees and wire hidden around the eaves of the house, to name a few. The usual reason people don’t put up proper antennas is the Mrs factor. Blokes are to scared to stand up to the wrath of their wives. “You can take that down” she says and like the pussies they are down it comes. One guy I know put up a new washing line for his wife and she still does not realise it is an antenna five years done the line (so to speak). So even pussies can get an decent wire antenna up for HF if they try.
Further on in this months RadComic there is an item by Peter Dodd G3LDO on the Windom Off-Centre Dipole, which although there have been some ridiculous claims for it over the years is a pretty effective antenna (not magic at all). It is just a pity that it is a review of a commercial antenna, which I find a bit sad when it is so simple to build your own for next to nothing. One thing I picked up on was that Peter said “It was not possible to determine if the balun was a current (as claimed) or voltage transformer because the unit was sealed.” Another good reason why you should build your own rather than rely on some plastic enclosed blob with who knows what rubbish inside. One thing that concerns me in the article is the inclusion of a drawing entitled Figure 5: The feed system of a multiband OCFD, showing a method for eliminating antenna (I3) currents. It shows the suspended 4:1 balun connected to a 1:1 balun fed with some 50 ohm coax which drops down to a second 1:1 balun just above ground level. The coax to the shack has an earth wire connected to the braid which then runs to an earth spike in the ground. As drawn there are eight PL-259 connections and assuming a tuner and SWR bridge in the shack that is twelve PL plugs and sockets in the feeder. I can only think that the losses due to these connectors must go somewhere to producing the stated elimination of unwanted currents. It seems to me over complex and likely to be prone to many failures as damp could get in any of these connections and as shown in the drawing without some form of strain relief the connections are most likely to fail as the suspended feeder and multiple baluns swing about in the wind. Not a good design and from my experience keep it simple works best. I would suggest that a better solution is to replace the two 1:1 baluns with simple coaxial choke baluns made from winding the feeder around a plastic formers such as lengths of drain pipe. That would eliminate the need for four PL connectors to start with, but the buy it rather than make it brigade would probably find that too much like hard work. Like any antenna used for multiband it is a compromise but a better compromise than most, however it seems a bit dumb to go overboard trying to make it better only to find you are constantly servicing it or that because of the losses in the multiple connections you are loosing both signal strength and output power.
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