[Elecraft] KX3 Field Ant. for 80/40/30

[Bob McGraw K4TAX]

A relatively new ham asked for a copy or diagram of my portable antenna 
design.   Here's my response.

********************

Welcome on being a new ham.  As to the antenna design..........well 
there is no such thing in existence.

We usually camp in National parks and State parks.  There's usually a 
few to a lot of trees around.  I carry a 100 ft spool of #22 insulated 
hookup wire wound on a plastic spool.  That was the way I purchased 
it.   Once the travel trailer is in position, I will scout out a nice 
tree limb some 15 to 30 ft off of the ground.  I then unroll about 50 to 
75 ft or so of the wire from the spool, drop a half hitch around the 
spool to prevent the remainder of the wire from rolling off of the 
spool.  Using a method similar to that of "David when he slew the 
Giant", I hurl the spool over a limb.  Of course sometimes my estimated 
distance or height is in error and I find it necessary to make another 
attempt or two.  The spool and wire simply keep the wire taught over the 
limb and to the trailer.  On the trailer, I have a feed through which 
was originally for a TV antenna, no longer used for that purpose.  To 
this I attach the end of the wire to the F connector.  Inside I have a 
length of RG 58 coax that runs to the F connector and terminates into a 
BNC connectro.  This attaches to my home made L network for the tuner.  
The L network is comprised of a single variable C of about 500 pF and an 
air wound inductor which is  1 1/2" in diameter and about 6" long.  I 
have a 20 position tap switch that is configured so I can use individual 
tap or select turns of the inductor.  This is mounted in a4" x 4" x 8" 
aluminum  box with a BNC on each end.    I recall having about every 2 
turns tapped to the switch.  Using this L network I can find a point of 
C and L values which produce suitable SWR, less than 2:1 for my 
operation.   After all my RG-58 is only 6 ft long so there is little 
loss on HF in the "feed line".   If this doesn't find a match, I just 
reverse the IN and OUT to provide a different impedance range.     
Should I then have difficulty in obtaining a match, I will loosen the 
wire, allow more to spool off and then try again.   Usually a length of 
some 50 to 75 feet will work about any band except 160 M.   I need more 
wire for that. When we are finished camping, I turn the end of the wire 
loose at the trailer allowing the spool and wire to fall to the ground, 
wind it up and stow it for the next adventure.    All of this is best 
described as an end fed long wire with a L matching network.    There is 
nothing exotic about it, no baluns, no specific lengths, just use the 
wire length and space available.

In reading the various posts and opinions on the topic, I'm amazed at 
the lengths, expense and trouble many hams go to in order to put up an 
antenna.

Hope this helps

***************************

73

Bob, K4TAX


On 11/21/2017 6:06 PM, Ignacy wrote:
> Antenna performance does not depend on how it is fed (if feeder losses are
> low) but on height and ground type. For KX3 with AT, any special length
> makes little sense, especially in portable conditions. KX3 matches most
> random wires, and KX3 with 4:1 balun matches any wires. Lack of balance is
> not too important with battery operation. I try to make random wire +
> counterpoise at least 1/4 wave on the lowest frequency for reasonable
> efficiency.
>
> For 1.5 KW, an endfed with a 49:1 or so transformer makes lots of sense as
> wideband tuners for QRO are rare, expensive and heavy. "Myantennas.com"
> perfected a  transformer that has very small losses and does not
> self-destroy at high power. But in inv V configuration, it is way down from
> a flattop.
>
> Ignacy, NO9E
>
>
>
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to rmcgraw at blomand.net
>