On 20 April 2013 20:52, Tom Van Baak <[email protected]> wrote: > For the rest of you: > > http://www.leapsecond.com/images/gps-pinwheel-1.jpg > http://www.leapsecond.com/images/gps-pinwheel-2.jpg > > It's a thing of mysterious beauty. And the GPS World photo saves me from the > temptation to break open my own pinwheel antenna just to see what's hidden > inside. > > /tvb
Does the antenna work better than other types? As someone who used to design antennas for a living, I'm well aware there are a lot of antenna "designs" which are either badly understood by their "designers" or are just put together to look impressive. One company I used to work for based their specifications on that of their competitors. This seems to be pretty common practise in the antennae industry. I once offered my boss at a company I worked for a bet. I would pay to get one of our antennas tested at NPL, and if it met the specification we claimed, then he owed me nothing. But if it failed, he had to pay the cost of the testing. I could possibly not win any money with this bet - the best I could hope for was to break even, but I was sufficiently convinced it did not meet the specification that I could take that chance. Needless to say he would not accept the bet!!! There are lies, damn lies, and antenna specifications. This particular antenna design http://www.rason.org/Projects/collant/collant.htm has a claimed gain of 9 dB. We don't know if that is 9 dBi, dBd, or dB_wet_string. Both myself and someone else have modelled this based on the use of perfect conductors and we get a gain of about 7 dBi. I used the dimensions given in that article, him a rescaled version for 2.4 GHz. We used different software - me the exceedingly expensive HFSS 3D electromagnetic simulator and him another very expensive EM simulator. These both solve Maxwell's equations, although one uses the integral form and the other the differential form. I've contacted the author and got no response. One obviously way to convince yourself that antenna can't work as described, is what would happen if the coaxial cable had a very high permittivity lossless dielectric - say Er=10^6. All dimensions would scale down by 10^3 from free space, and you end up with a very high gain antenna 1.4 mm long. Hence I tend to take antenna specifications with a pinch of salt. Dave. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
