The AM Forum
December 04, 2024, 07:42:26 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Base Loading For 43' Vertical  (Read 16849 times)
0 Members and 1 Guest are viewing this topic.
DMOD
AC0OB - A Place where Thermionic Emitters Rule!
Contributing
Member
*
Offline Offline

Posts: 1806


« on: June 07, 2014, 10:21:59 PM »

Every antenna is a compromise and the 43 foot vertical is no exception. But if you have limited space, a 43 foot vertical with 25 ground radials out to the limit of your property can provide you with all band capability.

For 60 through 10 meters, one can tune the vertical with preferably a manual tuner through a 1:4 Unun at the base.

For 80 through 160 meters, it is more of a challenge since the capacitive reactance on 160 meters is more like 600 ohms and the radiation resistance is very low.

Capt. Paul Lee was one of the early pioneers to address the tuning of practical Amateur Radio verticals in his book, The Amateur Radio Vertical Antenna Handbook, CQ Communications, 1984. Rudy Severns, Phil Salas, Jerry Sevick, Shef Robotham, Al Christman, Barry Boothe, and others both modeled and experimented with short verticals.

The simplest approach to tuning the short vertical and the one I used was adapted from Phil Salas, AD5X.

This loading design uses an autotransformer to transform impedances.

Specifically, the lower taps of the coil’s total inductance are presented to a 1:4 Unun, via the switching of those taps using a two relay system.

Phil Salas presented a number of designs both using toroids and open air coils. Of course, 12 guage and larger open air coils have the least heating and power loss.

My first switched base loading coil implementation for feeding my 43 foot S9 antenna used the T400A-2 toroid material, but power loss and heating was more than anticipated.

I had acquired two large edge wound coils at Hamfests over the years and decided to use these coils in the latest design.

One coil, L2 was 10.5 uH and the other, L1 was 40 uH, giving me a total of 50.5 uH, producing an inductive reactance of 603 ohms at 1.9 Mhz. I used a 12X12X6” plastic weatherproof box to hold the components. Calculated power level is 3kW continuous (conservative rating).

Included is a pdf of the “Large Coil” implementation I used, Phil Salas’ amended article, and some photos.

Your vertical implementation may require slightly different taps on the L1 coil, depending on your configuration.

Note: Updated 1/8/2015: Updated Photos to include the more efficient 1:4 Unun which uses 12 guage insulated wire.


Phil - AC0OB

* 43 foot Matcher RevA by Salas.pdf (738.08 KB - downloaded 3714 times.)
* 160 m 80 Loading Coil Relay Circuit.pdf (572.62 KB - downloaded 2549 times.)
Logged

Charlie Eppes: Dad would be so happy if we married a doctor.
Don Eppes: Yeah, well, Dad would be happy if I married someone with a pulse.NUMB3RS   Smiley
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.052 seconds with 19 queries.