Newsgroups: rec.radio.amateur.antenna
From: ed@fore.com (Ed Bathgate)
Subject: modifying RS fm beam for 2METERS
Keywords: 2 METER BEAM, YAGI
Nntp-Posting-Host: baleen-atm
Organization: FORE Systems Inc.  Pittsburgh, PA.
Date: Tue, 5 Jul 1994 22:24:24 GMT


I shortened some of the details so it would not be as lengthy.  Ed N3SDO


Happy building.
	Ed  N3SDO

** I built one and discovered some length differences in the elements.
** My opinion, build it to the longer lengths N3KMJ specs, and try tweaking for
** best results, then if it doesent work try trimming to N3SDO shorter lengths.
** Post your results or email Ed@fore.com and I will compile the results.
** Perhaps a NEC expert will model this and give us some tips!
** I bet this will make a long thread for weeks to come... {:-)


	Ed  N3SDO
___________________________________________________________________________

5 ELEMENT 2 METER BEAM FOR UNDER $20?!?

** THESE PLANS WERE TYPED IN AND SHORTENED BY ED  N3SDO. **

Converting the Radio Shack FM stereo yagi cat # 15-1636) for 2 meter use.
by Eric Allison N3KMJ.  Tell your friends you got the info from N3KMJ and
 PGH HILLTOPPERS.

Materials List:

drill, 5/8" & 1/16" bits
cutters/tin snips
assorted screwdrivers & wrenches...
qty 6 5/8" long sheet metal screws
2 pieces 4" heavy stranded wire (16-18 ga)
misc wood mast or pvc (needed for vert mount only)
sealant for connections...


INSTRUCTIONS:

STEP 1:
Drill holes in boom for vertical mounting using 5/8" bit, same position
as existing holes on sides, but on top/bottom for mounting vertically.
(for ssb use skip this step)

STEP 2:
Unfold antenna, & snap elements in place.  Using cutters remove all crossing
wires from elements with plastic insulators. (cut as close to rivet as possible)

STEP 3:
Completely cut off element between director 2 & 3 (see diagram) as close to
boom as possible.  You can completely remove element & bracket by drilling 
out main rivet to boom.  (save this for scrap box future use) {:-)

STEP 4:
Drill 1/16" holes at base of each element, just below the rivets on directors
1,2 and driven element.  Install sheet metal screws 1/2 way.  These are the 
plastic mounted ones.  Be careful to make sure element will snap in place with
screw installed.  

STEP 5:
Wrap bare stranded wire around left screw on director 1, to right screw on 
director 1, tighten screws & cut off excess.
 (shorting elements together, left to right to make dipole director)
Then do the same for director 2.

STEP 6: 

(ORIGINAL PLANS,  LONG LENGTHS N3KMJ)
** NOTE ** THESE LENGTHS DID NOT WORK FOR ME, SEE BELOW.

Cut elements to length.

REFLECTOR: 57 1/2"
DRIVEN ELE: 38 1/2"
DIRECTOR 1: 37 1/4
DIRECTOR 2: 36"
DIRECTOR 3: 34 1/2"


=============================================================================



SHORTER LENGTHS BY N3SDO - DETERMINED EXPERIMENTALLY BY SWR & PATTERN TESTS

REFLECTOR:  43"    (ALSO CONSIDER TRIMMING REF TO 40")      
DRIVEN ELE: 35.5"  (SWR ABOUT 1.5:1 MIN AT 146 MHZ)
DIRECTOR 1: 34.5"
DIRECTOR 2: 34.2"
DIRECTOR 3: 33.75"

	(N3SDO PLANS TO CONTINUE EXPERIMENTING AND WILL POST RESULTS)
	
	FIELD STRENGTH TESTS SHOW FORWARD LOBE FS10 WITH BACK LOBE UNDER FS1,
	BUT STILL THERE.  NO SIDE LOBES DETECTABLE.


	.    < FS 10
      .   .
     .     .
     .     .	
      .   .
       . .
        | <VERTICAL MOUNTING 	
      .   .
        .    < FS .75


FOR FS REFERENCE:END FED 1/2 WAVE DIPOLE APPROX FS 1.75 - 2

N3SDO CRUDE FIELD TESTS:
 ANTENNA ON WOODEN POLE, CENTER OF ELEMENTS ABOUT 7' FROM SOGGY GROUND.
 FIELD STRENGTH METER (HOMEBREW) COAX FED BY BEAM.
 SIGNAL SOURCE XYL WITH 1.5W HT HELD OVER HEAD @ 20' FROM BEAM.
	ED  N3SDO  {:-)



MEASUREMENTS OF A FACTORY MADE 3 ELEMENT BEAM ASSEMBLED FROM BOX OF PARTS
MFG UNKNOWN,  INCLUDED FOR ELEMENT LENGTH REFERENCES.  N3SDO

REFLECTOR: 40.25"
DRIVEN ELE: 36"     (INCLUDED MATCHING SHUNT & COAX CABLE BALUN 32" LONG)
DIRECTOR 1: 35 1/8"


ED  N3SDO  {:-)
=============================================================================

STEP 7:
Assemble antenna as per instructions for mounting hardware, end caps ...
Attach to pvc pipe if vert.  Attach coax, to driven element.  strip about 3"
of coax shield, attach center & shield to driven element screws and tighten.
Caution, don't allow shield to short to mast.
Use silicone or sim to weatherproof.

** NOTE THAT THIS DOES NOT SPEC ANY TYPE OF BALUN OR IMPEDANCE MATCHING
** NETWORK.  I HAVE FOUND THAT COAX PLACEMENT IS A BIT CRITICAL, BUT NOT
** BAD.  I TAPED THE COAX TO THE MAST AND DID NOT NOTICE SWR FLUCTUATIONS
** WHEN I MOVED THE CABLE AROUND.  PERHAPS A BALUN MIGHT IMPROVE SWR FURTHER.
	N3SDO 



Conclusion;
This antenna is mainly for repeater work 145-147.  With 3 of these antennas in use
the unscientific HILLTOPPER tests show an approx 8-10 db forward gain with about
2dbs off the back.  The radiation pattern is very sharp, with fairly weak side
lobes.  These babys aim like a rifle!, so be prepared for some rotor tweaking.
ENJOY!



DIAGRAM:  

			     DRIVEN     | <REF
		X		|	|
	|	|  |	|	|	|
	|	X  |	|	|	|
	==================O=O============
	|	X  |	|	|	|
	|	|  |	|	|	|
		X		|	|
	^	^  ^  	^		|
   DIR  3       ^  2    1
		^
		^
             REMOVE X




COMPOSED BY N3KMJ,  TRANSCRIBED & SHORTENED.
** ANYTHING UNCLEAR IN THE INSTRUCTIONS, PLEASE CONTACT ED@FORE.COM
TEXT IN UPPER CASE ADDED BY ED N3SDO - AKA ED@FORE.COM