This is my last posting to the Ten Tec reflector about
antennas/feedline- and is concerning putting the tuner
at the antenna vs. putting the tuner at the rig end of
the feedline.
When you put the tuner at the antenna end, what you are
doing, in fact, is NOT tuning the antenna to resonance,
rather, you're either inductively or capacitively "loading"
the antenna. Of course, this resonates the "system", but
your "antenna" is not "necessarily" brought to resonance
by placing the tuner at the antenna. Remember, conjugate
impedance matches are a function of XC cancelling XL to
equal Z0 (where Z0 is desired impedance, which in our case,
is most likely 50 ohms). It's possible that the antenna
still "could" not be resonant, even though your feedline
sees a 50 ohm load and source at the ends. What happens
with the tuner at the antenna is that you simply don't
lose any (read- "as much", all coax has some inherent loss)
RF as heat in the feedline. What will happen (as in mobile
HF antennas) is that the inductor of your tuner you placed
at the antenna end will radiate a portion of the RF you're
sending to the antenna. If you don't believe this, try
resonating a 5 foot piece of wire on 75 meters with a tuner-
the inductor will get HOT! There's NO WAY the 5 foot piece
of wire is resonant on 75 meters, rather, the combination of
the tuner AND the 5 foot piece of wire is resonant. If the
tuner was enclosed in a metal box, then none of the radiated
RF would add to your signal. It would just heat up the inside
of the box. Now if you enclose the tuner (remember, we're
now talking about placing it OUTDOORS, at the antenna!) in a
plastic box, it would contribute "some" to your signal. The
same principle applies to larger (read- "more closely resonant",
remember, we're talking 75 meters and comparing to a 5 foot
piece of wire) antennas, although to a lesser degree (less
inductive loading equals less RF lost as heat). Now watch
someone "correct" me and say the capacitor radiates too!
No argument from me! WHO CARES?
Thanks to all for the insight into tuner construction....73, Web
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