[HCDX]: Re: MW DF Antenna

[WA1ION@xxxxxxxxxxxxx]

Cardioid Antenna Array Discussion message re-try: 

I sent this out six hours ago, but it got bounced from
Zacharias's E-mail address and never showed up on hard-
core, so here it goes again ...


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.

7. Two sloping antennas oriented in opposite
directions can be phased to produce a one-sided null.
Bruce Conti, Al Merriman, and I have used this approach
at various times.  Two longwires at a right angle can
also be used as phasing unit signal inputs: the peak-
null axis would be along the bisector of the angle
between the two wires of the horizontal "V" formed.

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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