Multi-band (Fan) Dipoles

[Edward R Cole]

I am always amazed how some have so much difficulty making dipole antennas.

With multi-band dipoles (or Fans as it is being called here), tuning
of one dipole interacts with the tuning of other ones.  It is not too
bad with harmonically related bands as the non-resonant reactance
isolates the others pretty well.  I made a 4125 KHz/5167 KHz dual
dipole (Fan) for work and the two are so close in frequency that
serious interaction took place.  The lower frequency dipole (4125
KHz, Marine HF chan-4A) tuned pretty easily but 5167 (AK Emergency
Chan) was extremely narrow in bw (10 KHz).  That made 5167 not usable
in some kinds of wx.

But I have had a 80/40/20m dipole (now it is 80/40m) up for years and
they are not that hard to tune.  You start with the lower freq
dipoles slightly long and tune the highest freq. dipole first.  Then
the next, and so on.  You should re-check tuning on the highest
freq.after tuning the nest highest to see if it is affected and make
adjustment.  I said not hard, but it does take longer to get all resonant.

Using one of the portable antenna analyzers it the ONLY way to go
(much simpler and convenient).


73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 144-1.4kw, 432-100w, 1296-testing*, 3400-winter?
DUBUS Magazine USA Rep [hidden email]
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[Niel Skousen-2]

On a similar vein...   I've seen in the past an antenna that used to be a common 'emergency' antenna.  I cant remember the name or dimensions, so hopefully someone can understand my description and point me to additional information.

The mult-band antenna is similar to a 3 wire fan dipole, but the elements are generally paralleled (not 'fanned out).
A dumb ascii art diagram follows with the feedpoint (a), only half of the symmetrical antenna is shown
- The middle element is approximately the length of the dipole,  
- one of the outside elements is only about 70% of the full length,
- the last and longest element is  folded around the end of the middle wire
  with a gap (b) between the end of the short wire and the long wire.
  (generally the guy wire is attached at the fold point (c)

dumb ascii art ....
         ---------------------.  (b)  ------
       /                                               \
      /                                                  \
(a) -------------------------------------   |--(c) ---- (guy)
      \                                                 /
        \___________________/
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