Vertical for 40 & 80 - follow-up

[Darwin, Keith]

Hey Elecrafters, Elecraftonites & Elecraftonians!
 
Several months ago I posted a question about using a Hustler 80 meter
resonator on the top of my simple stick vertical antenna to turn it into
a 2 band antenna.  I have this 1/4-wave-on-30-meters vert that I feed
with a tuner.  It is fine on 40, 30, 20 but is lousy on 80.
 
Anyway, I picked up a Hustler 80 meter resonator.  Hustler says it is
just a big coil, not a resonator.  Hmmm.
 
I mounted it to the top of my vertical and it works perfectly.  The
impedance of the vertical with and without the resonator on it is very
nearly the same (measures slightly taller with it on) except there is a
narrow dip in the SWR curve on 80 meters with the resonator in place.
 
So, my vertical continues to resonate on 30 meters but now also
resonates on 80.  The impedance on 40 & 20 is essentially unchanged so
my tuner settings very similar to what they were.
 
- Keith KD1E -
- K2 5411 -
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Ron D'Eau Claire-2]

Keith KD1DE wrote:

Anyway, I picked up a Hustler 80 meter resonator.  Hustler says it is just a
big coil, not a resonator.  Hmmm.

----------------------------------

A short antenna is capacitive. It requires inductance to make it resonate,
i.e. show zero reactance at the operating frequency. So a coil for a short
whip to bring the reactance down to zero is often called a "resonator".

The antenna tuner does the same thing. It provides "base loading" or
inductance at the base to achieve resonance, since it's at the feed point.
Moving the coil out on the antenna improves the current distribution.  The
trade-off is that the less antenna there is between the coil and the far
end, the more coil you need to achieve resonance. Coils introduce their own
ohmic losses, especially at RF, so the coil losses go up as it gets bigger.
The general rule of thumb is that center loading is more effective than base
loading. It provides better current distribution without introducing
excessive ohmic losses. If the system is naturally resonant, your antenna
tuner only needs to provide the impedance transformation required to match
the feed point impedance of the antenna to the 50 ohm impedance load needed
by your rig.  

Good going on your 80, 40, 30, 20, meter short vertical combination. It's
effectiveness is highly dependent upon the ground on the lower frequencies.

Ron AC7AC

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com