From: mark@ve6mgs.ampr.org (Mark G. Salyzyn)
Subject: Plans for an Extended Double Zepp for 2M
Summary: Plummers Delight Extended Double Zepp for 2M
Keywords: Zepp 2M Antenna
Organization: Amateur Packet Radio E-mail Gateway  VE6MGS
Date: Mon, 11 Jan 93 04:22:43 GMT

I would like to share with you all an Antenna I designed and built this
weekend for 2M. The plans as follows:

Cut 1/2" copper pipe into the following pieces:
	2  sections 49" long
	4  sections 8 1/4" long
	3  sections 1" long
Cut 1" wood dowel into the following pieces:
	2  sections, 40 11/16" long
Obtain the following `knick knacks':
	8  1/2" copper pipe elbows
	2  1/2" copper pipe end caps
	1  10-12pF Ceramic Capacitor
	1  N or Union High Frequency Connector
	2  1" Hose clamps
	2  1/2" copper pipe hold down clamps
	6  nails, or screws, as appropriate for above clamps
	1  120" long piece of string used as cross support

1. Build folded phasing section

Do not solder yet. Assemble a ring of two 8 1/4" long, two 1" long and four
elbows. Place the ring on a flat surface that you can solder it on. Solder the
elbows to the 1" long pieces at both ends, and solder ONE pair of 8 1/4" long 
pieces to the set of elbows. Once cool, remove the unsoldered `U' consisting
of two elbows and one 1" long piece. This ensures that this `U' and the other
`U' consisting of two elbows, one 1"long piece and two 8 1/4" long pieces are
`square and `flat' and `parallel'.

Use the small `U' above to do the same to another large `U' of similar
construction. You should now have two large (8 3/4" long X 2" wide) `U's
and one small (1 1/2" X 2" wide) `U'.

This next part will require some judicious placement of support clamps, and
a `good eye'. Solder one end of each large `U' into the small `U' so that
it forms a square cage:
		      ____<- One large `U'
		     / __/_
		    / /	/ /
		   / / / /<- Other large `U'
		  / / / /
		 / / / /
		/ / / /
    small `U' ->|/   / <- This end is open, try to make this cage `square'

		Figure 1  Folded phasing section.

2. Build pair of 5/8 Wave radiators

Solder end caps to one end of each 49" long, 1/2" copper pipe. On the other
ends, solder the remaining two elbows. Lay the two radiators, end caps
outwards, on a flat soldering surface and solder to the phasing section
(note change of orientation to Figure 1 with respect to the phasing section):
				         /|  /|
				        / / / /
				       / / / /
				      / / / /
				     / / / /
				    /___/ /
_____________________________________/   /_____________________________________

		Figure 2  Extended Double Zepp Radiator

3. Build `Gamma' `hairpin' `phasing stub' (Salyzyn :-) feed system

I can't find this feed arrangement in *any* of my Antenna Handbooks, nor do
I know precisely why it works so well. If you can describe this matching
arrangement better than me, I'd be pleased to hear about it. It accomplishes
several objectives though. We need to cancel some inductive reactance at the
feed point (due to the fact we are using .64 wavelength, rather than the
typical < .625 wavelength radiators in commercial designs), we need about a
4:1 balun to take the characteristic resistive component of the Double Zepp of
200 ohms and bring it down to 50 ohms balanced feed and I require a
mechanically stable vertical Double Zepp. Basically the 10pf (I used precisely
11.2 pF measured on mine) capacitor is tied to the base of one of the 5/8 wave
radiators, the other end of the capacitor is tied to the center conductor of
the feed connector. The ground of the connector is soldered to the small `U'
to place it sort of in the center of the phasing section `cage' facing away
from the phasing section:
				     /|        /|
				    / |       / |
				   /  |      /  |
				  /   |     /   |
				 /    /    /    /
			        /    /    /    /
			       /    /    /    /
			      /    /    /    /
			     /    /    /    /
			    /    /    /    /
			   /    /    /    /
			  /_________/    /
			    |  _  |     /
	  Feed Connector -> | (_) |\<----Tied to Center conductor
			    |_____| O<----10pF Capacitor
. . . _____________________/        |/_____________________________ . . .

		Figure 3  Feed Arrangement `Blowed Up'

6. Test antenna

Attach an SWR meter to the Feed connector and to a signal source and take
SWR readings across the band. Trim the antenna (I was lucky, I didn't need
to :-) as necessary to achieve a match. I designed this antenna for 145.09,
a local packet channel, and that `happened' to be near the resonant dip
of 1.2:1 match I encountered for this antenna. I performed a couple of
tests on Simplex and repeater frequencies dotted across the 2M band and
found the antenna to be superior to my Larsen 2/70 Dual Band 5/8 Wave Mag
mounted Vertical, which may not prove that the antenna has the design
6.4dBq gain, but not bad for $15Can ($2US :-) :-) in parts. I leave it
up to the followers of this antenna to tell me what I got right, and
what I got wrong!

5. Build tower mount

Nail the two 1" hose clamps to one end of each of the 40 11/16" wood dowels
that form a 1/2" wave offset support from the tower. These hose clamps will
be used to attach to the tower or mast, so you may wish to use an alternate
mounting strategy depending on your needs. The other end will have the 1/2"
copper pipe clamps nailed (or screwed) to hold the tips of the vertical
Double Zepp structure. A single 120" string is used to provide mechanical
cross support from the top tower side to the bottom antenna side of the
offset supports:

		|
		|
		|________ <- Upper offset mount
		|. 	|
		| .	|
	Tower ->| .	|<- Antenna
		|  .	|
		|  .	|
		|   .	|___
		| .----<____| <- Folded Phasing stub/Feed
		|/Feed	|
		| Line	|
		|    .	|   <- `dotted' line a rough representation of cross
		|     .	|	support string.
		|      .|
		|_______|
		|	  <- Lower offset mount
		|
		|

		Figure 4  Tower or Mast mounting schematic

The tower support is not tested, it is -32C (-20F) outside and I will leave it
up to the imagination of the reader how much I despise this fact! I guess I
would not have built this Antenna if I had a warm beach and a hot summer sun
beckoning me out of doors ...

Enjoy, 73 de VE6MGS/Mark -sk-
-- 
-- Ciao -- Mark Salyzyn  mark@ve6mgs.ampr.org/adec23.UUCP finally has a .sig ...
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