-=> On 10-03-97  09:22, Roy Witt said to Ivy Iverson,<=-
-=>"About High Gain Antennas for 2M...,"<=-
-=> 03 Oct 97 00:59, Ivy Iverson wrote to Roy Witt:
 
 RW> Hello Ivy.
 
Hi, Roy;
 
 RW>> provider who couldn't recieve a certain FM station without
 RW>> interference.  I built them a yagi designed for the  frequency
 RW>> of the station and mounted it from the rear with a
 RW>> counter-balance. A 5 element yagi for 97-100MHz...
 II>
 II> There is another way to this, as I learned when I was on the
 II> engineering staff of a University station in Iowa:
 II>
 II> Two cut-to-frequency yagis, one mounted 1/2 wave in front of the
 II> other, and connected with a 1/2 (or 3/4) wave harness.  The rear
 II> antenna feeds the receiver.  (I think I remember this
 II> correctly).  The F/B ratio is almost comeplete, as is the side
 II> rejection:      R  DE D  D
 II>                 o--o--o--o To RX-/
 II>                    |\
 II>            ========|==\==|
 II>                         \|
 II>                       o--o--o--o
 RW> 
 RW> Well, it got messed up here, but I know what your drawing meant.  An 
 RW> interesting concept.  This was for rejecting a station off to the side
 RW> of the  reciever and you needed to recieve a station in another
 RW> direction.  You say F/B ratio is almost complete.  What does this
 RW> imply? 
 
Sorry, I should have said that the F/B ratio was also very high, (almost
total rejection, if that means anything).   :-}
 
The way it's laid out, there is a 180 degree phase shift from both sides
and the rear, so the only direction that both antennas are in phase is
directly in front of it.  Thus it has much higher F/B ratio than a
similar yagi alone, or even one with several more elements.
 
I wish I had known that trick when I was in electronics tech school and
working as Chief Engineer of a small FM station at the same time.  (I had
earned my 1st Phone a couple of years before in a cram course.)  There
was a station in our fringe that was picking up some of our programming
for rebroadcast, and they had QRM from another station on the same
frequency.  After consulting with the instructors, the best I could come
up with at the time was give them the plans for a rhombic.  (They were on
the edge of some woods and had to shoot through them to get us at all, so
supports weren't any problem).  It took a lot of wire, but it gave them
our signal 5-9!  Since seeing that at the later job, I would have had
them assemble a pair of cut-channel yagis on a pole, (or even high on
their transmitting tower if possible).
 
73 DE KB9QPM
   Ivy
 
 
 
... Become hot stuff... learn to solder!   ;->
 
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