At 07:29 AM 2/4/01 -0500, you wrote:
>At 04:56 AM 2/4/01 -0500, Tom Rauch wrote:
>>My three element 40 meter antenna has a F/R of over 50 dB.
>>
>>It has one reflector, one driven element, and one director.
>>
>>It is limited in null depth, in direct actual measurements, by the
>>ability to physically hold the elements steady and by scattering
>>from the surroundings rather than the any lack of additional
>>elements.
>>
>>It is actually quite easy to get values that high in 3 element
Exactly Peter, tho the original question was related to
physical length of reflectors
Peter
Personaly the idea of one null at one specific frequency
is not really the 'true' measure of any antenna. When is one actualy
using only a 'spot' frequency and QRM comes from exact rear?
Not very often !
First importance is FRONT TO REAR then the spread of frequency
desired to be used, a single null is not a 'free lunch'!
May I suggest the idea for one to mull over of 'interlacing' three
antennas designed for the particular band spread in question which is
basically the antenna described by me.
This way you obtain the desirable characteristics across the band with
excellent F/R and gain without having to rely on a single null at a single
frequency.i.e constant gain ,front to rear. Isn't that what we are looking
for?
Not only that, you will get an antenna with practical drive inpedances
without having to compromise on feeding methods.
With respect to the term 'gain' I prefer to think of that as a measure of
hearing,If one obtains all around rear rejection that allows for the
lowering of the noise floor and the emergence of a low level station, then
it is achieving a bench mark that "gain" was trying to define.
I am not trying to define any antenna of any magic or any confrontation
with gottchas as this thread meanders away from the number of reflectors and
length question originaly posed.
But if it becomes a forum to rethink what one is really trying to achieve
and what the real goals are, then I am all for it.
Best Regards
Art Unwin KB9MZ
>>antennas, since they can be made to have nearly perfect current
>>ratios in the elements (1,2,1 ratio).
>
>What are the gain bandwidth and SWR bandwidth characteristics that go with
>that very high F/B? I bet there's no free lunch.
>
>73, Pete N4ZR
>Contesting is!
>
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