[HCDX]: Cardioid Arrays

[WA1ION@xxxxxxxxxxxxx]

Hello Zacharias.  Your request for information on 
cardioid array antennas is one of several E-mails
I've recently received on the subject.  Because of this,
I'm posting this reply to the hard-core list.  I think 
that several DXers will find the information useful.

You asked -

"I remember that, in a message of yours 2 years ago you 
wrote on a design of a cardioid (DF) MW antenna, one of 
them coming from QST ('95 issue).

I'm interested in making such an antenna.  Do you know if 
there is a ready drawing for this for MW (0.5-1.7 MHz )
absolutely ?  I know that the QST design could be mostly
for 1.8 MHz so that modifications must be made on the L and 
C components.  Is there a web address for this ?" 

There are several ways to generate a cardioid pattern.
Among the methods are the following:

1. Two passive or active vertical antennas (e.g. two
MFJ-1024 whips) spaced at about 50 m on the axis of the 
desired peak-null line.  The outputs of the two verticals 
are transferred via coaxial cable to the inputs of a 
phasing unit such as a Wellbrook APU 100 or a modified 
MFJ-1026.

2. An active whip can be phased against a broadband loop.
The antennas may be closely spaced: these can even be on 
top of a vehicle (this is what I use on beach DXpeditions).
The broadband loop I use is square and about 1.8 m per
side.  The two ends of the single turn go through a 1:1
balun transformer (Mini-Circuits T1-6-X65) to go from 
balanced to unbalanced.  At that point it can be fed via 
50 ohm coaxial cable to a low-noise amplifier of about 
20 dB gain or, unamplified, straight to one of the phasing 
unit's inputs.  The loop head is positioned for maximum
pick-up from the desired-DX direction (such as the east).  
The MFJ-1024, or similar, whip antenna output goes to the
other phasing unit input.  The phasing unit is adjusted
to null stations in the direction opposite desired DX.
Wellbrook Communications offer a couple of ready-made
broadband loop designs for DXers in Europe.  Contact Andy 
Ikin (e-mail = " andrew.ikin@xxxxxxxxxxxx "). A workable 
broadband loop, especially one that is stationary, is not 
that difficult to build.  If you have room for something 
more than 3 m per side, especially in a high-signal area 
such as Europe, you won't need to amplify it.  If you 
can't get the balun transformer from Mini-Circuits, you 
can probably wind your own on a toroidal ferrite core or 
get something like the DX One balun.  Experiment with
different turns ratios to get maximum signal transfer
to a 50 ohm line.

3. In a case similar to paragraph 1, two broadband
loops can be set out at an approximate spacing of 50 m
on the desired peak-null axis.  Each loop should be
positioned for maximum desired-signal pick-up.

4. Two closely-spaced broadband loops can be fed to
the phasing unit.  In this case (spacing less than
30 m), one loop should be oriented for pick-up 45
clockwise of the peak-null axis and the loop should
be positioned 45 degrees anticlockwise of this axis.
    
5. A single properly-terminated Beverage can produce
something close to a cardioid pattern.  Even better
results can be had from phasing two parallel Beverages, 
spaced at about 50 to 100 m (for MW use).  The feed
end of each Beverage can be presented to the phasing 
unit via 4:1 or 9:1 transformers to coaxial lines.
It may help if one of the Beverages is terminated 
and if the other is not.  Two oppositely-oriented
Beverages have also been used with some success,
especially if both have terminations of at least
moderate effectiveness.  Needless to say, Beverages
take up a lot of space, 300 m of length minimum
for decent medium-wave performance.  Few people have
the kind of room at their home locations for a
proper Beverage installation.  That's why serious
DXers go to far-flung locales such as Cappahayden,
Sheigra, Valhalla Beach, the Coorong, and Lemmenjoki
for those legendary loggings not possible with
ordinary antenna systems.

6. The K9AY loop is a single-antenna cardioid
pattern producer that has been used with great
success by Al Merriman, Werner Funkenhauser, Andy
Ikin, and others.  It was developed by Gary Breed,
K9AY.  Gary's E-mail is " editor@xxxxxxxxxxxx ".
For a better description, see Al Merriman's 
write-up on Werner Funkenhauser's Web site 
(" http://home.inforamp.net/~funk/termloop.html ").  
Al's article refers the reader to the original 
SEP 1997 and MAY 1998 QST articles (which might be 
available in the periodical sections of big-city 
libraries or in the hands of local ham clubs).  
Gary's QST articles refer to earlier articles 
on the "Ewe" antenna, a cardioid array predecessor 
to the K9AY loop.  The Ewe data may also be of use 
to you if you can locate the QST's in which they 
were published.

I hope this information has been of value to you
and that you get a suitable cardioid array antenna
system into operation.

73 / good DX ... Mark Connelly, WA1ION

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