"Richard Harrison" wrote in message
...
Art, KB9MZ wrote:
"O.K. Reg, I`ll take you up on the 50 dB F/B."

It requires good balance for such cancellation.

Yes, it will not come by accident but Reg has said that 50 db F/B is
"silly"!
Why would he say that without back up evidence? He also did not offer
a max F/B that was obtainable in theory. I have seen computor results
that offer 50 db F/B based on NEC, Can I trust gain if F/B cannot
be trusted? Obviously 50 db is hard to get but is it beyond the realms
of possibility?
The F/B that you offered is a bit unfair but then it is an antenna and
Reg did not qualify his statement.
I personaly modelled a antenna that comprised of a driven element
with the remaining elements acting as reflectors only. And we all know
that extra reflectors are a waste of time for H.F.( grin ) but they do give
very high F/B figures.
I wonder what a corner reflector antenna would provide

Regards
Art KB9MZ......XG


Kraus gives the gain for a 100-meter dish near Bonn, Germany on page 676
of the 3rd edition of "Antennas". Gain is a function of frequency and
varies from about 48 dB at 300 MHz to about 98 dB at 150 GHz. I don`t
know if shielding has been added to make this a "high-performance" dish
but I would wager that this enormous radio ear and mouth has an
excellent front-to-back ratio. Probably exceeds forward gain at some
azimuths and elevation angles.

Arnold B. Bailey has a lot to say anout a "connected" (driven) element
and a parasitic reflector, starting about on 447 of "TV and Other
Receiving Antennas", Bailey says:
"The optimum spacing for highest gain of a parasitic reflector is S=0.15
wavelength plus or minus 0.025. Here the relleector is operated at Q=+1
(longer than resonant) and the gain in direction 1 is approximately 5.5
dB. Reasonable compromise for a less critical system is to use a spacing
of 0.2 wavelength and a parasitic element longer than resonant (at
Q=+1). This case gives a gain in direction 1 of 5 dB."

On page 440 Bailey says: The front-to-back ratio ---is 17.5 dB in this
case, and the Y/X ratio only about 9 dB, where +X represents the optimum
direction.---" A picture is worth 1000 words.

Best regards, Richard Harrison, KB5WZI