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[TenTec] My last words on tuners/antennas- (maybe?)

To: <tentec@contesting.com>
Subject: [TenTec] My last words on tuners/antennas- (maybe?)
From: kr4wm@sccoast.net (Webster D. Williams)
Date: Sat, 27 Sep 1997 10:21:41 -0400
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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