W2EHE'S 'POOR BOY'S SteppIR*'
(a work in progress. updated to 5/29/2006)
Chuck wrote:
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.
download ez.nec file here (tunable.ez)
73, Chuck Templeman W2EHE Kingsland, Texas
DOWNLOAD 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/B14.175 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 W2EHE Kingsland, Texas
(*SteppIR is a trademark of Fluidmotion Corp.)