Seems like I recall that a lot of the "magic length" business originated
with efforts to minimize the effects of line pickup and attendant
unbalance or common-mode current in the case of coax.
72/73, George W5YR - the Yellow Rose of Texas NETXQRP 6
Fairview, TX 30 mi NE Dallas in Collin county QRP-L 1373
Amateur Radio W5YR, in the 55th year and it just keeps getting better!
Icom IC-756 PRO #02121 (9/00) Kachina #91900556 (12/99) IC-765 (6/90)
"Dr. Gerald N. Johnson, electrical engineer" wrote:
>
> I guess we think about resonance in the antenna being better for
> radiation, but there have been "magic" easily tuned lengths (and antenna
> and feed) in antenna articles and handbooks ever since the use of tuned
> feeders to arbitrary center fed antennas were created in the 1920s.
> Sometimes those lengths are proposed as the only ones that work which is
> wrong. Just those lengths are more convenient to tune but a truly
> versatile tuner (which leaves out everything from MFJ and EFJ) will tune
> any length of antenna with any length of feeder. I prefer the more
> general rule on selection of antenna and feed line being: Antenna length
> to fit BETWEEN the supports and feed line length to reach from the
> middle of that antenna and the radio. The older tuners (as chronicled by
> Cebik's web page) will tune the general rule antenna most anywhere from
> antenna length less than 1/4 wave end to end up through VHF (with
> suitable tuners for each VHF band). Sometimes the tuner settings will be
> extreme, but the antenna and tuner can be tuned.
>
> Magic lengths for convenient tuning are nice, but not when adherence to
> them would keep the amateur off the air because the magic lengths don't
> fit his particular premises.
>
> I've worked 160 through 10 with 80 feet in the flat top, and 160 through
> 2 with 326 feet in the flat top and on MARS frequencies too.
>
> I think the fundamental measure for the magic lengths is that the length
> of feed line plus one half the antenna is not far from an odd multiple
> of a quarter wave at each frequency of interest. That way the feed
> impedance is more towards low than high and not too reactive for
> convenient tuning.
>
> 73, Jerry, K0CQ
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