[TowerTalk] parasitic 4-square for 40 meters

[Paul Playford]

per W1XT:

Use 8 elevated radials for each vertical element, and the whole system has
got to be isolated from ground.

The drive points of the vertical elements are 1/4 wavelength apart, on a
square.

Install the element support structures.

Install two radials in the form of a dipole and trim to length at desired
operating frequency.  Resonance is 0 ohms reactance on the MFJ.

Cut the rest of the radials to this length and install.

Install the identical vertical elements (slightly long to allow trimming to
length)

Install feed lines to each element, consisting of 3/8 wavelength
(electrical) of RG-213 (or equal) - measure this with your MFJ 259B as the
real velocity factor is not always as published.  Once you determine the VF
of a roll of coax it will be the same for the whole roll.

Fabricate a relay box: one DPST relay for each element.  Wire the relays
such that when one relay is operated it will connect the center conductor
and the shield of the transmission line (from the transmitter) to the center
conductor and shield of the feed line to one element - the center conductors
and shields of the other 3 feed lines will remain open from each other and
the transmission line.  The fed element is the driven element and the other
3 will be reflectors.

Observe the resonant frequency of each driven element by switching the
direction relays.

Allow a little 'Kentucky windage' (the resonant frequencies will probably
not be the same) and trim each vertical element the same amount to your
desired operating frequency.

When completed all radials will be of equal length and all vertical elements
will be identical.  The vertical elements will be a little bit longer than
the radials.

Have fun!

FWIW, the handbook parasitic sloping dipole array was installed on W1XT's
tower - his old call, can't remember what it was.

Bob had an array installed about 1 mile from my QTH.  We are both weak
signal Dxers and if I could hear/work a station with my 4 square phased
array he could also, and vice versa.  So we rated the arrays as equal.

I modeled both arrays with EZNEC 3.0, which really cannot handle that many
segments, but my conclusion is that the parasitic array is narrower in
bandwidth than the phased array.  EZNEC 3.0 shows 40m as not a problem but
75m and 80m cannot be done parasitically.

de Paul, W8AEF

 

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Ron Feutz
Sent: Monday, February 21, 2005 4:29 AM
To: towertalk at contesting.com
Subject: [TowerTalk] parasitic 4-square for 40 meters


>
>TT'ers
>
>I have everything I need for a parasitic 40 meter 4-square but can't 
>find design info.
>
>I want to try this antenna as my marginal cost will be zero.  I have 4 33'
>verticals, an Ameritron RSC 8-V switch and plenty of radial wire and 
>coax on hand.
>
>Any info on design and tuning will be appreciated.  I believe the 
>design has 3 "reflectors" that use the inductive reactance of the open 
>feedline to make them "reflectors,"  right.  How long should the 
>feedlines be?  I can tune with the MFJ 259B.
>
>Any models out there to tell me what to expect?
>
>Archive and google search turned up nothing.
>
>73,
>
>Ron KK9K

-- 
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.300 / Virus Database: 266.1.0 - Release Date: 2/18/2005