NEC-LIST: Fano Criteria and Optimization

Dear George, et al.:

Let me pass to you some of my own experience on *MW Broadcasting*
optimization:

1) The larger the broadband of the antenna (or array) in use, the best
will be the final optimization characteristics (seems obvious but hard
enough to get it). That's why I've been trying all these years an
"antenna type" that could have a good initial response for the
purpose. In some aspects, I succeeded to reach this goal by adopting
the "self-resonant folded unipole antenna" (see article published on
Oct.99 issue of BE Radio magazine, or www.beradio.com) on main
installations;

2) The following process describes the optimization through its
matching network :
 - measure the antenna side-band impedance values, say at +-5 and +-10
kHz and central frequency, feeding it by its own transmitter (with
reduced power in most cases), through a RF-PLL type of generator in
place of the transmitter's oscillator. If the measurement are not
possible by any reason, try to figure out these impedance values
through a suitable method, such as NEC evaluation.
 - avoiding a time consuming calculation, I developed along these
years an Excel Spreadsheet to do it by "trial and cut" method of
calculation. The idea is to slowly modify the phase shift of a T or
PI network in order to get at its input the 50 ohms at center
frequency *and* equal conjugate impedances values at +-5 and +-10 kHz.
 - to illustrate this subject, the result that follows was measured at
the self-resonant folded monopole antenna's input tunning unit:

        frequency(kHz) impedance(ohms)
        1450 49.7 + j2.66
        1455 49.9 + j1.35
        1460 50.0 + j0
        1465 49.9 - j1.30
        1470 49.7 - j2.57

Such an installation is able to transmit an audio signal up to 20 kHz
at least, with an incredible fidelity for an MW-AM transmission (if
the studio, link and transmitter's response would allow it of course),
without any intermodulation between side-band tones that local
generates (at the transmitter site) non-existent audio contents,
distorting and masking the original music.

Hope this can contribute in some aspect for the optmization of antennas
subject.

Best regards to you all,

Sylvio M. Damiani

P.S.: I was very pleased when you mentioned Dr. Chen To Tai's name. I
was one of his students here in Brazil, back in 1960. At that time he
was teaching Electromagnetic Theory and Antennas in my College. Dr
Chen To Tai spent 3 years in our country through an interchange
teaching program existing back in late 50's.
Received on Sun Feb 13 2000 - 03:59:40 EST