> -=> 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 
riven,
 >  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?
A quad DE, quad reflector, yagi (dipole) directors.
My point is, why not replace the quad elements with J-poles?
 >  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 
f
 >  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 
w
 >  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...
;-)
 > How much power would need to be dissipated?  10% of the transmitter
 > output?  50%?
50%, as I recall.  Depends on the correlation between the reflector and the 
DE.  if the reflector isn't doing the job as reflecting, it's probably 
absorbing some of the power generated by the DE.  Might not be a bad idea to 
go with more.
Would probably be best to go find a ceramic block resistor at the proper 
ratings.
 > 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?
the F/B ration increases dramaticall.  any signal comming in the 'back end' 
of the antenna is attenuated several db with the 'dummy load' reflector.
There would be no change in the forward ERP gain.
 > And a stray thought: What would happen if you added
 > resistive loads to
 > the director(s)?  Probably knock the foreward signal
 > down.
similar to inserting a flow restrictor in a water hose ;-)
   73 = Best Regards
   -Jeff KA5THB
   ka5thb@bigfoot.com
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