[TowerTalk] 40m Moxon over or under 4-el Steppir?

[Grant Saviers]

An oops correction: I misread the swr plot and the modeled resonance 
plot is at 26.4 MHz.  So interaction on 12m might not be a problem.

Grant KZ1W



On 8/28/2020 20:08, Grant Saviers wrote:
> David,
> 
> One question is which W6NL Moxon as there are three - original scratch 
> build, Cushcraft mod, and high strength Cushcraft mod??? I've built two 
> of the original and own a third from another builder.?? Mine when up was 
> at 91ft with an 86ft 80m L loaded rotatable dipole above at 102ft.?? No 
> interactions noticed.?? SWR plots as expected.?? Performance as predicted.
> 
> My Moxon shows a measured resonance at 23-24Mhz (the only dip), I think 
> the loading tips are the cause, so would expect some interactions on 12m 
> with the 4L pattern/swr.?? I don't think which is the top Yagi will 
> matter for this.?? Beyond that, some modeling is appropriate, AC6LA has 
> all of the SteppIR models built for AutoEZ.?? With that software you 
> might find a 4L setting to minimize the pattern/swr issues.?? My bet is 
> any triband+17/12 antenna will behave the pretty much the same on 12m 
> but you wouldn't have the ease of tuning with the SteppIR.
> 
> I have the SteppIR 4L on another tower and am quite pleased with its 
> performance and reliability the last 8 years.?? A DB36 replaced the Moxon 
> to gain 30m, with 40m and the rest and it is a different story 
> altogether for high DB36 swr with the 80m dipole on 30 & 40, even with 
> the 80m boom parallel.?? I think this is due to interaction with the 
> effectively linear loading of the trombones to cover those frequencies. 
> Higher bands act like my 4L since the tape isn't looped in the trombones.
> 
> If I didn't want 30m, I wouldn't hesitate to put the Moxon and 4L on the 
> same mast.?? I think a pair of very good antennas.
> 
> have fun, stay safe, 73
> 
> Grant KZ1W
> 
> 
> On 8/28/2020 15:32, David Aslin G3WGN wrote:
>> Consulting the TT hive mind.?? I'm sure someone has faced/modelled this 
>> question:
>>
>> I have a 100ft tower with 16ft stub mast.?? The two antennas I plan to 
>> mount are a W6NL 40m Moxon and a 4-el Ultrabeam (which is electrically 
>> identical to the 4-el Steppir).?? Both antennas have similar weights 
>> and similar wind areas and will mount around 12ft apart on the mast.
>>
>> My logic to date is that I'd want the Moxon to be the higher of the 
>> two, as 115ft is lower than ideal for the 40m band, but the best I can 
>> do.?? And that the similar weights/areas suggest that there is no 
>> mechanical reason why one particular antenna should be on top of the 
>> stack
>>
>> But, I had not previously understood the possibility that the Moxon 
>> may screen the 4-el and thereby reduce the performance of the 4-el 
>> (maybe the Moxon too?)?? That might suggest the 4-el should be above 
>> the Moxon.
>>
>> What does the hive mind say??? Am I overthinking this or is there 
>> indeed a preferred configuration dictated by experience and/or modelling?
>> 73, David G3WGN?? M6O?? WJ6O
>>
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