[AMRadio] Antenna Tuner Wonderings


Donald Chester k4kyv at hotmail.com
Wed Dec 22 19:03:21 EST 2004


>What kind of "crappy" antennas are you using, i.e., doublets fed with coax,
>open wire lines, etc., or end-fed wires?   Or, some combination of types 
>maybe?
>
>
>Rather that building up a bunch of tuners you might consider putting your
>efforts into erecting a set of antennas that all worked directly off a 50 
>or 75
>ohm coax feedlines.   Half-wave dipoles, one for each band, for example, or 
>one
>or more of the multi-band arrangements (G5RV, fan and trap dipole, etc.).

I think the best solution would be to erect one good dipole, as high as you 
can get it, for the lowest frequency band you operate.  If you don't have 
that much space, consider a  shortened dipole for the lowest band.  Feed it 
with open wire  line and a balanced tuner (not one of those bogus jobs with 
unbalanced T or L network coupled to the balanced line via a balun).  I 
prefer to make my multi-band tuners using plug in coils and split stator air 
variables.  You should be able to transform the driving impedance of that 
antenna to 50 ohms nonreactive on about any amateur frequency, without a 
forest of separate dipoles growing out of the shack.  Then couple whichever 
transmitter you are using to the tuner.

At present I use a system a little more complicated.  I still use one dipole 
for all bands, but a separate tuner for each band.  That way the tuner is 
pre-tuned to frequency and all I have to do is load the appropriate 
transmitter into it and switch the feedline to it.

The dipole is cut for 80m, but I can load it up on 160 as a quarterwave 
dipole with fairly good results.  It is about 110 ft. high, so the height 
somewhat compensates for the shortness of it on 160.

I use a separate L-network to match the the quarterwave base-insulated 
vertical on 160, which is  my main topband antenna.

73, Don K4KYV





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