[Elecraft] Less Than Perfect Antennas [was Flumoxed]

[Fred Jensen]

The center-fed dipole fed with open wire balanced line may be the second 
oldest antenna design, the first being the Marconi-T.  Its only real 
disadvantage is that today's solid state transceivers are all 50 ohm, 
coax oriented and some form of balanced to unbalanced and possibly 
impedance conversion is necessary.  Solid state gear is also very 
unforgiving of mis-matches, unlike an 807 PA with a link coupled tank 
circuit. [Note how deftly I avoided using the dreaded word, "balun". 
[:-)] Fan dipoles, where one coax transmission line feeds multiple 
dipoles on different bands work very well ... if you can get them cut 
correctly.  There is a lot of interaction between them since all the 
dipoles are directly fed.

The lesser known Coupled Resonator antenna is much more forgiving in the 
tuning department.  It consists of a center-fed dipole for the lowest 
frequency normally fed with coax through an unbalanced-to-balanced 
network.  Close to it [like 1 - 1.5 inches max] are conductors cut for 
each of the desired higher frequencies, but which are *not* connected to 
the feed point. Trim the lowest frequency to desired resonance first, 
then move up to the next in sequence.  There is little if any 
interaction with the previously trimmed conductors.

A convenient construction method is to use open wire or "window line" 
for the conductors with the lowest frequency one also suspending the 
assembly.  Trim the other one for the next higher frequency.  For 3 
bands, bond another length to the longest conductor and trim the other 
side for the the 3rd band.

I once saw a 5-band C-R with 5 conductors strung through the holes in 
the crossed spreaders normally used to create "cage" antenna elements.  
The fed conductor was larger wire through the center hole and used for 
suspension, with the other four bands at the ends of the spreaders.  You 
can also feed the C-R with balanced line terminating at a transformer to 
get to unbalanced, 50 ohm coax to keep your TX happy.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 12/7/2018 8:39 AM, Don Sanders wrote:
> As Don has said, a good dipole as high as possible, even in an attic, fed
> with balanced line will out perform most other compromise multiband
> antennas.
> While being retired in Ecuador I had the advantage to try several antennas.
> The best over all was a fan dipole for 40, 30, 20,and 17 fed with RG6 up 80
> feet AGL mounted on 30 foot bamboo poles at the top of a hill.