Wireless Waffle - A whole spectrum of radio related rubbish
Spray-On Antennasignal strength
Monday 27 February, 2012, 14:13 - Radio Randomness
Posted by Administrator
Regular readers of Wireless Waffle will be familiar with our relentless drive to improve both the availability, performance and aesthetics of antennas that can be used to listen to radio signals in situations where normal aerials are not feasible.

The Wireless Waffle Super Signal Holiday HF Antenna Apparel (WWSSHHFAA), a cunning aerial designed to go almost unnoticed on the wearer (though anecdotal evidence suggests that it does cause the wearer to become highly noticeable) which we updated in 2010, is one such solution. Whilst there are many examples of the WWSSHHFAA on beaches across the beaches of the Mediterranean, we have yet to receive an offer from anyone wishing to put it into full commercial production.

spray on antenna kitWe were surprised, therefore, to recieve a tip-off about an antenna that, in principle, can surpass the performance of even the WWSSHHFAA in quality of reception, in its ease of application, and its resulting aesthetic manifestation... Go and take a look at the Spray-On Antenna!

The Spray-On Antenna is, in essence, a metallised spray which coats whatever it is sprayed on with... metal. As metal conducts electricity, it can, of course act as an antenna. Thus by spraying any everyday thing with metal paint it will become an antenna. If the resulting metallised object is connected directly to the transmitter (the tools for which appear to be provided with the spray-on antenna kit) it can be used as an antenna. If it isn't it can still be useful as a reflector. A reflector on an antenna is just like a reflector on a flashlight or car headlight, it refocuses emissions that would otherwise have been heading out in the wrong direction and points them in the right direction. Putting a reflector behind a transmitting antenna therefore focuses power in the opposite direction. How effective it is depends on a number of important factors such as:biquad antenna
  • The relationship between the size of the object that has been sprayed and the wavelength of the frequency being used - ideally the two would be harmonically related, or at least the antenna/reflector would be larger in wavelength than the frequency being used.
  • The distance between the reflector and the transmitting antenna (if used as a reflector instead of an antenna).
  • The specific shape of the antenna or reflector. For antennas, a line (like a wire) is good. For a reflector, parabols are good (as with satellite dishes), flat panels can work (see picture), otherwise a thin line will work as long as it is the same polarisation as the transmitting aerial.
pretzel antennaSo just about any object could be used to enhance reception. On the left here is a 'pretzeltennna'. The pretzeltenna, if placed at exactly the right distance behind, for example, a cell-phone could act as a reflector and boost signals in one direction. Alternatively two pretzeltennas could be used to form a 'dipretzel', centre-fed with coax cable. The advantage of a dipretzel is that, if you get hungty, you can feed yourself with it too (though the metal spray might poison you).

For those on holiday with no way of stringing up antennas (the problem that the original WWSSHHFAA was designed to overcome), the concept of using a spray-on antenna provides a new and interesting way ahead. A comparison of the two solutions is shown below. On the left, the original WWSSHHFAA, with hidden wires acting as an antenna stretched across the supporting structure. On the right, a spray-on antenna on a similar supporting structure. We have been unable to test the spray-on antenna in this configuration, though we would expect that it would significantly enhance reception given its larger conductive surface area.
wireless waffle holiday hf antenna apparel spray on antenna
Original Wireless Waffle Holiday HF Antenna Apparel Similar supporting structure with Spray-On Antenna

Post Script: We have received a message from Timothy Matthews from Polzeath, Cornwall. Timothy writes,
"I got, like, a can of spray-on antenna from, like, a local 'craft' shop and zizzed it on a few 's'pportin' structures'. I tried, like, tappin' in to the structures to extend my 'antenna' but all I 'received' was an extension to my overdraft, large, innit."

Well, Timothy, any kind of antenna of this type requires very delicate adjustment and we recommend that in the future, you 'leperately twelt them over the hish with a squench' as admirably described on the ropium web-site which is full of useless tips which make about as much sense as your e-mail.
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