Paul Rampelbergh wrote: >4. It seems there is'nt a problem to construct Log-periodic antenna's. > Construction data is available. > Do not require special items as ballun's, etc. > It seems more difficult to have data and to build Bi-conical or > simular antenna's. Anybody can help? > How good can avail calibrations data be used when the antenna is copied? > Who can provide this data and info?
The problem with an antenna is the unknown attenuation of the antenna itself. I used a simple approach, I bought a pair of scanner (discone type $40) antenna's and used a spectrum analyser with a tracking generator. The tracking generators signal was fed into one antenna and the spectrum analyser connected to the other antenna (using identical cables). And presto....the spectrums attenuation appeared on screen. Since the 'transmitter' and 'receiver' used identical antennas the antennuation will be (almost) identical and thus twice as much as for one antenna. So the 'real' power spectrum per antenna will be shifted over 6db. I tried with various setups and distances to determine 'worst case' situations. Results where very consistant though. Although the results might not be 100% accurate it sure beats the $3000 or more of a 'real' measurement antenna. The spectrum analyser and tracking generator can be rented (personally I borrowed one), Hameg sells one for around $1200 (12khz smallest bandwidth but I have found it very usefull for EMC 'debugging'). You do need more antenna's to cover a full 30Mhz...??Ghz spectrum, but that is not different from a 'professional' setup. For the 9khz..30Mhz I just use loop-probes. I still would like to see a cheap way of creating current probes. Any idea's ?????? Bas van Rossem
