Re: [IRCA] ALA 100

["Chris Knight" <chris@xxxxxxxxxxxxxxx>]

Guy,

Thank you for the info! I'll read it over. Spacing is definitely important
when antennas are side by side. What about flags in the same plane? For
example, Flag #1 is oriented N/S, but is terminated on the north such that
the lobe is to the south. Not too far away (but north of Flag #1) is Flag #2
also pointed N/S with its termination on the south end making its receive
lobe to the north. Two cardioids, 2 opposite directions in the same plane.
If these antennas are phased/mixed together "appropriately", is the
resulting pattern a narrow figure-8?

Just a thought :-)

73, Chris

-----Original Message-----
From: irca-bounces@xxxxxxxxxxxxxxxx
[mailto:irca-bounces@xxxxxxxxxxxxxxxx]On Behalf Of Guy Atkins
Sent: Wednesday, January 28, 2009 4:10 PM
To: irca@xxxxxxxxxxxxxxxx
Subject: Re: [IRCA] ALA 100


Hi Chris,

It wouldn't quite fit in your back yard, but an intriguing design is the
Phased Flag Array as designed and described by Dallas Lankford (see the
Kongsfjord.no DX site and look in the "Dallas Files" section). He and I have
been discussing this antenna quite a bit recently. If the EZNEC plots are
close to real-world performance it should outperform my Wellbrook Phased
Array in terms of rearward nulling. I'm considering building Dallas' design
for use on coastal DXpeditions.

This antenna, with its broad forward lobe but also relatively broad null on
the backside would be well suited for unattended use with a recording SDR
like Perseus or the RFSpace units. This single antenna could receive
stations from a range of azimuth bearings in the desired direction while
reducing the level of many stations "behind" the receiver, and not need any
knob twiddling once set up correctly. The Wellbrook Phased Array is similar
but the phased flags definitely show a better pattern for nulling stations
in what Dallas calls the "null aperature".

Dallas believes that the 100 ft. spacing between the flags is the minimum
that will successfully cover the entire band, so unfortunately it can't fit
into a 60 ft. backyard without low band attenuation of signals. I wonder if
a longer length of delay line could compensate for a < 100 ft. spacing?

Dallas has also done computer modeling on a 4-flag array, with of course
greater complexity in parts, cost, and required real estate. The details are
shown at the end of his phased flags article.

Regarding the ALA100, someone asked about a photo of the control box
(interface). There is a picture of the box (white, with black label) on my
blog posting here:
http://perseus-sdr.blogspot.com/2006/09/in-shadow-of-mt-rainier-dxing-with.h
tml
The ALA100 box is just to the left of the smaller black box (PA0RDT
mini-whip interface) and the two gell cell batteries in the second picture.

73,

Guy Atkins
Puyallup, WA
www.perseus-sdr.blogspot.com
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