-=> On 09-29-97  13:14, Jeff Edmonson said to Ivy Iverson,<=-
-=>"About High Gain Antennas for 2M...,"<=-
 
 JE> You see my message to Stan on Quagi's?  Why not 4 J-poles (two driven,
 JE> opposite of each other) two reflectors (same configuration) and yagi
 JE> directors?  Put the whole thing on a 20' wooden boom...
 
 II> Nope, missed that one.  Sounds interesting.
 
 JE> It's been pointed out, it might be a bit cumbersome...  but a pair of
 JE> 5/8  elements as DEs and yagi directors does sound reminiscent of a
 JE> Quagi.
 II> Hmmm... Not quite what I had in mind, but it might be quite workable.
 
But a quagi is a quad loop, (possibly with 1 or more quad-type
reflectors), and one or more dipole-type directors, isn't it?  Or does it
use dipole-type reflectors?
 
 II> I am more interested in something new that isn't in all the books,
 II> which hopefully will have advantages, (like gain and/or directivity),
 II> over the standard designs.  IOW, just experimenting with something
 II> different to see how it compares.  If it works, great!  If it
 II> doesn't, try somethng else.   :-}
 JE> True.  However, doesn't a 5/8 wave posses some gain over a quad
 JE> element? 
 
Not sure, but I think a quad element has aproximately the same gain as a
dipole element, doesn't it?  a 5/8 element has aproximately 3 dB gain over
a dipole, so the answer would probably be "Yes."
 
 JE> for better front-to-back, it's been suggested (and even commercially
 JE> sold) to  add a reflector at the end of the boom, with a 50ohm resistor
 JE> across the  elements.  A 'dummy-load' to signals from the back side of
 JE> the beam, and at  power levels on 2m such as most commonly 50w, it
 JE> shouldn't be too hard to find  or build a 50ohm load out of several 1w
 JE> resistors in series/parallel for that  power level.
 
Hmmm... so howcome I don't see it on beams or in advertising?  Don't
bother answering that... just like cars and every other consumer product,
they save every penny they can in manufacturing.  In Detroit, if they can
save ONE screw, (cost: 1c), it adds up to thousands of dollars per model
year!  I'm sure it isn't much different with antennas.  Or 2-way radios.
 
How much power would need to be dissipated?  10% of the transmitter
output?  50%?  Assuming 50% of a 50 watt transmitter, (I doubt it would
need to be anywhere near that much), would be 25W.  5- 10 Ohm, 5 watt
composition, (not wirewound) resitors in series would be plenty.  Or
28 100 Ohm composition resistors in 4 series groups of 8 parallel, or
8 400 Ohm resistors in parallel.  Of course, there are hundreds of other
possible combinations...  They could be put inside a hollow insulating
tube with the ends sealed against the weather with silicone sealer.
 
My next question is, How much would this increase the F/B ratio, and how
would it effect the foreward ERP compared to conventional reflectors?
 
And a stray thought: What would happen if you added resistive loads to
the director(s)?  Probably knock the foreward signal down.
 
73 DE KB9QPM
   Ivy
 
 
 
... When the band is open you can work the world on a piece of wet string!
 
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