Thanks a bunch for that link Bill, I hadn't seen that report. Very nice.
yeah, I'm using 4nec2x. I'm new to modeling but have climbed the curve
in the last couple months.
I've sim'ed a bunch of antennas with close coupling, like the N6LF
folded+dipole wide band 80m, and closely coupled parallel 80m dipoles,
so I think the nec-2 is handling this moxon okay, but maybe not as you
say. I have to pay attention to segments and do enough checking to see
if the results seem odd. (I have the N6LF close coupled folded + dipole
up in real life, so I have that sim to reality comparison).
The longer 23' boom seems to help the XM-240 conversion over my shorter
19-1/2' boom, as well as the longer elements (but I can make longer
elements too..I have a turning radius constraint though: trees)
When I do a low pass LC match, to the desired min frequency for the
W6NL, the results are very nice and shifted to where I want,, and not
much L or C is needed. So this got me thinking that maybe Leeson
modelled something extra I'm not? (balun? boom??)
Rather than stressing too much about it, I'm thinking I'm going to
optimize my 40M2L conversion for a center min SWR frequency that's 100
to 200 khz lower than I want..kind of like what I see on the W6NL
results. Then put it up and see what I get.
To shift higher or lower optimally, it seems like I want to adjust both
tips (not just de and not just reflector)
What I'm thinking, is that I can produce a table of DE and reflector
tip position for SWR min frequencies at 100 khz steps (just allowing the
final tips to vary), and then use that to adjust based on what I see
after I put it up.
I don't want to just play with the tips blindly, because it seems easy
to lose the gain & f/b unwittingly.
I'm scratching my head a bit though, because W6NL seemed to imply close
correlation between sim and reality.
I also am surprised that W6NL didn't connect the tips with light
fiberglass..it seems with any wind that you get a lot of variation in
tip spacing, which isn't good..I just bought some small diameter
fiberglass tubes from some kite supplier, that seem really nice.
(stiffness vs weight/diameter)
It seems to me, that comparing a moxon built of similar diameter
elements, and boom width and element length, that the W6NL variant's
main advantage is in 1.5 SWR bandwidth. But that a more normal moxon is
very close. I'm using 4nec2x optimizer to pick the lengths of things,
with all the diameters/lengths in there from my existing elements. (just
varying the new aluminum).
I was tempted to add boom length to get more than my 19-1/2' but it
seems good enough.
I also played with adding some tips to my moxon design like W6NL, but
couldn't find a result I liked.
For my design, centered at 7.1Mhz, at 70' over real ground/avg, I'm
seeing 1.6 SWR at 7Mhz, 1.1 at 7.1Mhz, 1.8 at 7.3 Mhz.
Forward gain goes from 10.7 dbi to 10 dbi over same range.
F/B peaks at 7.1 (27 db) but ranges from 15 db to 12 db over the same
range. (I'd like to see the W6NL numbers for the full 7-7.3 Mhz range. I
think it has the same peakiness for gain f/b ??? doesn't it? or ??)
I don't get overly stressed about the F/B number..I look at the 3D
pattern a bunch, rather than looking a single f/b comparison point.
The W6NL approach adds a bunch of aluminum, but I'm wondering if the
payback isn't there, compared to a more standard moxon approach. I'd
like to see more knowledgable heads to heads comparisons.
-kevin
AD6Z
Billy Cox wrote:
> Hi Kevin,
>
> You are on the right track with this ... and please
> give this link a close review and note their findings
> as to F/B, F/S and SWR with the W6NL Moxon design:
>
> http://www.kkn.net/dayton2008/Real%20vs%20Theoretical%20Antenna%20Mesurementsv5.pdf
>
> There are several challenges here, including which of
> the antenna software 'engines' best models the manner
> the Moxon elements are constructed. In comparing the
> same antenna model here with say EZNEC and Antenna Model,
> the results with the Moxon design are NOT the same.
>
> I hope this helps, here I am doing the same thing with
> an older Cushcraft 40-2CD, which uses different element
> construction than the XM element that W6NL used.
>
> 73 de Billy, AA4NU
>
> -----Original Message-----
>
>> From: "knormoyle@surfnetusa.com" <knormoyle@surfnetusa.com>
>> Sent: Feb 25, 2010 4:51 PM
>> To: antennaware@contesting.com
>> Subject: [Antennaware] Simulating the W6NL 40M moxon variant
>>
>> My problem: I'm working on a simulation for a M2 40M2L (shorty-forty, linear
>> loading) conversion to a moxon. I'm using the W6NL 40M moxon-like design as
>> a
>> benchmark for SWR bw, and gain/fb. (trying to get similar results, but not
>> the
>> same design)
>>
>> W6NL provided an AO .ant file so his can be easily simulated.
>>
>> here:
>> http://www.kkn.net/dayton2004/
>> (3 links there)
>>
>> I use 4nec2x, so I used it to convert the .ant to a .nec. There were some
>> minor
>> issues that I hand-corrected. (for instance, using ' in a symbol name in the
>> .ant)
>>
>> The simulation of the W6NL moxon looks good in 4nec2x. The visual is right
>> for
>> the antenna, the gain/fb and swr bandwidth is right (very wide swr
>> bandwidth).
>>
>> BUT: the swr min is centered too low I think..it's around 6.8Mhz..I would
>> have
>> expected it to be centered around 7.05 or 7.1, based on W6NL's presentation
>> curves.
>>
>> I experimented a little. I played with different grounds. The simulation is
>> at
>> 70 ft. The taper schedule is done with explicit wires of different radiuses,
>> but
>> it seems fine.
>>
>> I'd be surprised if nec-2 is simulating this wrong, compared to AO...
>>
>> So I'm assuming something is just wrong, but I can't figure out what.
>> It's like it's shifted down in frequency for some reason.
>>
>> If there was someone out there would could run the .ANT file exactly as W6NL
>> posted it above, and say what freq they see for a SWR min, that would be
>> really
>> useful for me? I also could put my converted .nec somewhere if there was
>> some
>> other simulator that could use the .nec? (or people can recommend something
>> I
>> could use without retyping in a model?)
>>
>> I'm a little worried, because I have the design for my 40M2L conversion
>> done,
>> and I think it's pretty good (got the wide bw I wanted). nNot that much
>> less
>> than the W6NL, but has just the typical moxon look (less aluminum) and on a
>> shorter boom (19-1/2') feet....But now I'm wondering if that simulation is
>> accurate..
>>
>> I don't know if there are other simulators that could use the .nec, but I
>> could
>> provide that also (both the W6NL and mine) if anyone was interested in
>> seeing
>> what they get for me.
>>
>> thoughts?
>>
>> thanks
>> kevin
>> AD6Z
>>
>>
>> _______________________________________________
>> Antennaware mailing list
>> Antennaware@contesting.com
>> http://lists.contesting.com/mailman/listinfo/antennaware
>>
>
>
>
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