[TowerTalk] Modeling Ladderline as an Antenna Element

[Joe Giacobello]

Jim and Tom, many thanks for your replies.  Let me tell you what I'm up to.

I would like to put up an 80M EDZ between two towers.  However, my 
towers are only 300' apart and I need about 340'.  I have considered 
drooping the ends vertically, but I thought either a folded dipole or 
linear loading a few feet on the ends with ladderline would allow me to 
fit it inside the 300' span.  I use EZNEC 4+ for modeling.

I wonder if minimal lengths of ladderline for linear loading on each end 
would provide the shortening while making the high resistance losses 
arising from lower Q negligible?  I haven't tried modeling it yet.  I 
thought I'd first see if anyone had successfully modeled ladderline as 
an antenna element.

73, Joe

P.S. Tom, I wanted to comment on your replies regarding  tuners with 
balun inputs. I will do so in a separate post later.

Jim Lux wrote:

>At 02:32 PM 10/23/2005, Joe Giacobello wrote:
>  
>
>>I am thinking about using ladderline for a folded dipole or for linear
>>loading a wire antenna.  I wonder if anyone has successfully modeled
>>ladderline and, if so, what parameters they used for the insulation.  I
>>assume that the insulation is PVC, but what is the thickness and how are
>>the alternating windows accounted for?
>>
>>I'd appreciate any information that members of the reflector can provide
>>on this subject.
>>
>>73, Joe
>>K2XX
>>    
>>
>
>what program are you using to model it?
>If NEC, insulation models assume uniform thickness around the conductor, 
>which is not representative of ladder line, so the "fine scale" details of 
>the field in proximity to the ladder line will not be correct.
>
>
>Since the windows are very much less than a wavelength long, you can 
>probably model it as a suitably insulated pair of wires with insulation 
>properties chosen to match the actual properties of the wire.
>
>Even better, you could probably represent the ladder line as a suitably 
>built NT card for the transmission line properties, and a single insulated 
>wire to represent the "common mode" properties.
>
>If you're hoping to model the effects of things within, say, 5 times the 
>cross sectional size of the ladder line, NEC is probably not a good tool. 
>You need something like HFSS or one of the other programs that models 
>dielectrics.  Method of Moments (MoM) just isn't all that great at handling 
>dielectrics.
>
>
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