W2EHE'S 'POOR BOY'S SteppIR*'
(a work in progress. updated to 5/29/2006)
Don't know if this qualifies as a real Moxon or not, but it does seem
to simulate well with EZNEC 4.0
It covers 20- 17- 15 -12 and 10 meters with a simple adjustment of a
tuning cap in the reflector center section. It would be fed with an open wire system to a tuner.. it is NOT a 50
ohm system. That's the price to pay for flexibility.
This is a clean - simpler version with only a single cap that need
adjusting.. pretty good performance even on 20 meters. I took the wing spread to 20 feet.. that helped.. Still #12 wire and an 8
foot boom !
Each file has been optimized for the center of the band.. (except for 10
meters where I include a file for every 500khz)
You need rather high segmentation density to get the thing to converge,
but then it gives repeatable results and
the tuning is REAL CRITICAL. A pf one way or the other will skew the
results. See attached file -- tunable.ez -- for configuration and
details (I assume you have EZNEC ??)
(cap adjusted for 17 meters) wingspread is 20 feet and boom is 8 to 15
feet depending on a 10 meter director all done with #12 bare wire (no attempt to use insulated wire and
velocity factor reductions)
14.175 33.9 pf
18.11 43.0 pf
21.225 23.5 pf
24.94 15.5 pf
28-29 mhz don't care
a director was added for 10 meters to give it a little kick.. removing
the director will shorten boom by 7 feet and reduce
10 meter gain and F/B. This will also make the configuration more akin
to a real Moxon.. There will be 3500 volts on the cap at 1500 watt's. (700 at 100 watts)
I'm just throwing this out for someone to think about when designing
Moxon's.. The added tuning section does seem to
open up some options.
ez.nec file here (tunable.ez)
73, Chuck Templeman
ALL EZNEC FILES SHOWN ABOVE IN A SINGLE ZIP FILE.
Named this beast 'POOR BOY'S
SteppIR' .... looks pretty good on 17 thru 10 meter, but just
not enough metal in the air for 20 meters to perform well..:: gain
low but F/B usable. 15 foot boom, 17 foot wing spread, 3 - #10 wire
elements in 'Moxon' configuration, passive 10 meter reflector
to help broadband 10 meters (might try a passive director
as well to see what happens) two 0-50 pf tuning caps one in refl
and one in director. 200 ohm balun and coax with a really
broadband tuner.. or open wires to a tuner (best).
freq tuning cap gain F/B
14.175 32.6 pf 5.40 15.85
18.11 43.9 pf 5.88 21.49
21.225 23.4 pf 5.83 14.37
24.94 15.2 pf 5.58 11.37
28 11.2 pf 4.89 21.79 * aux refl optimized for
lo-end of 10 meters..
28.5 10.4 pf 5.63 29.07 could have been 12
meters or hi end of 10
29 9.9 pf 5.60 12.96 --designers choice--
29.5 9.5 pf 5.30 9.45
Anyway, it keeps me off the streets..
BTW, still trying to figure out
how to set caps with the beast up in the sky.. This is gonna kill
the project if I can't figure out how to adjust the two tuning caps..
( I know, just listen to a station and null F/B.. but I want something
a little more subjective)
How does SteppIR do it?
73, Chuck Templeman
(*SteppIR is a trademark of