Hi Bob
I put up a brief description of the Uzi yesterday onto the reflector, which
should be help.
When I am better, I will try to take some photos and perhaps ask Nick VK1AA
if I can put them on his 'Who's Who on 160' site.
The general idea is that the two linear/capacitively base-loaded delta
loops are slung off the top of my tower, with their apexes (voltage points)
only about a foot apart. This helps the loops to couple very tightly.
Bases of the loops are spaced about 32 metres apart. Each loop has 40m
sides (slightly smaller, in my case) and each loop is corner fed, via choke
baluns.
Each loop is fed with a half wave of 50 ohm coax (a quarter wave of 75 ohm,
followed by a quarter wave of 50 ohm coax would be better, as each loop has
an 80 - 90 ohm impedance, which increases to 120 to 130 ohms when they are
used as the driven element of the critically coupled beam). The difference
between critical coupling and conventional parasitic coupling is that
instead of the feed impedance dropping when you add another element, it
actually increases - a very useful phenomenon.
For details of critical coupling, see Les Moxon's (G6XN) 'HF Antennas for
All Locations' book (published by the RSGB. The commercially available Hex
Beam is a critically coupled antenna, as is Les's classic Moxon Rectangle
2-element HF beam design.
The reflector tuning is achieved with a simple series tuned circuit, which
is switched between the two elements to change (cardioid) direction. The
figure 8 pattern is achieved by feeding both elements, with one's feedpoint
connected 180 degrees out of phase with the other (i.e. the coax connection
to the loop is reversed on one element). The omni pattern is achieved by
feeding one loop and open circuiting the feed connection to the other in
the shack.
My tower is located towards the middle of my lot. If you can have a 90'
support roughly in the middle of your lot, the antenna will fit into a
rectangular space 40m long by 32m wide - very small, as you can see. As
the elements run along the two 40m sides, the space has to be suitably
sited for the directions you need the antenna to fire in - i.e. my two 40m
sides are on the northern and southern sides of the block, so the array can
fire north/south.
Vy 73,
Steve, VK6VZ
At 10:04 AM 8/06/2003 -0700, you wrote:
>Hi Steve
>Enjoyed your short note about the biggest 160m delta loop array.
>Not having access to the magazine article it is based on,
>could you give us a little verbal sketch of the beast. It sounds
>interesting.
>73, Bob N6WG
>
>
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