-=> On 10-01-97  08:22, Roy Witt said to Ivy Iverson,<=-
-=>"About High Gain Antennas for 2M...,"<=-
-=> 30 Sep 97 14:06, Ivy Iverson wrote to Roy Witt:
 
 RW> Hello Ivy.
 
Hi, Roy;
 
 RW>    o
 RW>  /          top view
 RW> o------o-------o-------o-------o------o
 RW>  \    DE
 RW>    o
 
 II> Ah yes, the good old corner reflector... Now if you were to
 II> replace the dipole elements with a 5/8 J-pole and suitably-sized
 II> elements, mount them vertically on a boom, (about 6-8 Ft long?),
 II> I wonder what ERP you would get with about 40 Watts at the
 II> antenna, (50W xmtr)? ...
 
 RW>> Build it correctly.  Mount it behind the reflector...This is
 RW>> about a 7.5dbd  antenna with a much better F/B ratio than you'll
 RW>> find in a normal Yagi.
 
        (Side view)
 
     |  |   |       |       |       |      |
     |  |   |       |       |       |      |
_____|__|___||______||______||______||_____||
  /\ R  R   DE      D/\     D       D      D
  |                  |
  Mount behind or at CG?
 
 II> I'm sure!  Are you talking 1/4 wave elements?  If it's built with 6 dB
 II> J-poles, what would the gain be?  How about adding more 5/8 elements
 II> to the J-poles?  Hey, might as well dream big, right?
 
 RW> I've never liked j-poles, so you'll never convince me that such an
 RW> animal you  discribe above should exist.  It's nice to experiment with
 RW> antennas, but this  has got to be a nightmare...
 
Heh heh... Howeverf it WOULD be, to me, an interesting experiment.
 
 II> And if you have a 6-8 Ft boom, that would be quite a strain to mount
 II> it from behind.  I think it would be more effective to mount it at
 II> the center of balance, on top of the supporting mast.
 
 RW> You still mount it from behind and use a counter-balance to compensate
 RW> for the  overhang.  I did this for a local cable provider who couldn't
 RW> recieve a certain FM station without interference.  I built them a yagi
 RW> designed for the  frequency of the station and mounted it from the rear
 RW> with a counter-balance. A 5 element yagi for 97-100MHz...
 
There is another way to this, as I learned when I was on the engineering
staff of a University station in Iowa:
 
Two cut-to-frequency yagis, one mounted 1/2 wave in front of the other,
and connected with a 1/2 (or 3/4) wave harness.  The rear antenna feeds
the receiver.  (I think I remember this correctly).  The F/B ratio is
almost comeplete, as is the side rejection:
 
     R  DE D  D
     o--o--o--o
To RX-/ |\
========|==\==|
             \|
           o--o--o--o
           R  DE D  D
 
 
 
 II>   Do you REALLY want a 2M "cannon"?
 RW> Nope. I work UHF, exclusively.
 
AH.  No HF either?
 
 II>   Have the J-poles paired, above AND below the mast!
 II> Also, what difference would it make if the corner had a screen
 II> instead of duned reflectors?
 RW> 
 RW> tuned? round? ??
 
Rectangular... a classic V-shaped "corner."
 
 RW> The screen will give you a higher F/B ratio.
 
 II>   This would require a non-metallic mast unless it were rear-
 II> mounted, but if the DE's were properly phased and everything
 II> optimized (resistors in the directors, etc?).
 RW> Why would it require a non-metallic mast?  Because of the J-pole?
 
If the J-poles were vertically arranged both above and below the boom...
 
 II> ..  That just MIGHT be hot enough for moonbounce if it were mounted
 II> on AZ-EL rotors!
 II> (It would also be about 15 Ft high and quite heavy with a lot of wind
 II> resistance!)
 
 RW> And more trouble than it's worth...:)
 
Perhaps... but fun (for me) to contimplate... and it could be scaled
for any higher frequency.
 
73 DE KB9QPM
   Ivy
 
 
 
... Double your dipoles. Double your flux.
 
            --
 
          ,-----> Ivy's WALL BBS Ä Home of Lakeshore Net <-----,
          |---------------> Ivy Iverson, KB9QPM <--------------|
          `-> Netmail me a request for info on Lakeshore Net <-'
 
___ Blue Wave/QWK v2.20 [NR]
--- TriToss (tm) 1.03 - (Unregistered)
---------------