I have the PRO/NEC4 license (which cost me some change) and need the
heavyweight often enough (mostly for buried wires). Though it might
be my advancing age (and a few other things my wife might tell
you...), I find it necessary to get back into the extensive doc often
enough to make sure memory is not fuzzing things, which it does far
too often. Having run many thousands of models does not seem to be an
adequate hedge against getting back into the documentation to return
to true north.
Personally I find the half life of enlightenment from a spell in the
help screens to range from an hour to three weeks depending on the
froth level of family life and the severity of the latest virus
brought around by the grandchildren. It is true that others may have
far greater retention than I, but an hour in the helps can sometimes
prevent weeks of frustration out on the antenna farm.
To the question, if you feed from two sources in a model, you can
either specify that the voltage and phase will be forced to a given
level (V source) or that the current and phase will be forced to a
given level (I source). Both devices are used properly in various
situations. Or, one can specify feedlines to the connection devices
and only feed the common point, leaving EZNEC to figure the
interaction.
Not all antenna systems can be developed to use multiple sources in
the model, or those that can may just be somewhere the modeler doesn't
want to go for sake of complexity or construction cost. In the latter
specifically modeling feedlines and their combining devices and
adjusting them to satisfactory results has been easier for me than
insuring an equal current or equal voltage source. Some designs do not
respond well to commonly found variations in coax impedance and
velocity factor, where a few degrees in some current phase has an
unexpectedly large effect.
SI and SV should be used with connected pairs of wire ends.
73, Guy.
On Tue, Mar 2, 2010 at 1:15 PM, Paul Decker <kg7hf@comcast.net> wrote:
> Hi Guy,
>
>
>
> Thanks for the reply. Yes, that makes sense, often I had not made models
> with multiple feedpoints so I didn't notice a difference between I/V. In
> many cases I was using SI/SV at non wire junctions, but that didn't seem to
> make a difference either. I do see a difference when switching between
> I/SI and V/SV at a wire junction.
>
>
>
> I won't take your rtfm as a blow off, although i did read the manual some
> years ago. I have either forgetten what I knew, or didn't think I
> understood it enough. I'll check again and see if it makes sense. When
> you say "two feedlines connected in parallel, do you mean for example a
> slitter which acts as a phasing array?"
>
>
>
> thanks,
>
> Paul
>
> ----- Original Message -----
> From: "Guy Olinger K2AV" <olinger@bellsouth.net>
> To: "Paul Decker" <kg7hf@comcast.net>
> Cc: antennaware@contesting.com
> Sent: Tuesday, March 2, 2010 12:46:04 PM GMT -05:00 US/Canada Eastern
> Subject: Re: [Antennaware] model sources
>
> If you have a single feed point, I or V is immaterial. SI or SV is
> used put a feedpoint at a wire junction, as in a Vee antenna. Mark the
> two connected points as SI or SV.
>
> When you have more than two feedpoints in a model you now have to
> decide whether you will drive them with forced voltage (two feedlines
> connected in parallel) or forced current (various devices) and set
> their phases. That's where the I and the V come in. By far the most
> concise discussion around on these is to be found in the EZNEC help
> screens. This is not a put-off of any kind as in RTFM, it is a
> sincere recommendation to probably the very best first reference
> source. And it is indexed and searchable.
>
> 73, Guy.
>
> On Tue, Mar 2, 2010 at 8:11 AM, Paul Decker <kg7hf@comcast.net> wrote:
>>
>>
>> Hi group,
>>
>>
>>
>> I use EZ-NEC 5.0, but I'm wondering what the different sources mean and
>> when they should be used. For example there is a selection for I, V, SI and
>> SV . Over the past few years I have been using them mostly interchangeably
>> without seeing any differences in the the results. Now I have built a
>> model where I see dramatic difference between using I sources vs. using V
>> sources, so I'm interested in what the different sources mean.
>>
>>
>>
>> thanks and 73,
>> Paul (KG7HF)
>> _______________________________________________
>> Antennaware mailing list
>> Antennaware@contesting.com
>> http://lists.contesting.com/mailman/listinfo/antennaware
>>
>
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