[Elecraft] Smith Chart Software (Free)

[Jim Brown]

On 5/13/2012 8:47 AM, Brian Alsop wrote:
> Guys,
>
> Smith charts are great once one has made it up the steep learning curve.

That's true of almost everything worth learning!

>   A alternative simple approach for common needs is the TLW program.

Yes, TLW is quite nice, quite accurate, but it's quite tedious to use to 
design a broadband match for an antenna (for example, something that 
covers most or all of 80/75M).  I spent roughly two hours using TLW to 
simply plot the result for an elegantly simple design that W6NL had 
done.  I did it in SimSmith in about five minutes, including the time it 
took to get the antenna file out of EZNEC and into SimSmith.  More to 
the point, using SimSmith, I can try multiple design ideas, tweaking and 
optimizing each one, each simulation taking only a minute or so.

> The TLW program which came with the ARRL Antenna Handbook on CD

Yes. So does YW, a very nice Yagi design program, HFTA, the terrain 
analysis program, a stripped down version of EZNEC, NEC design files for 
most of the antennas in the book, and several other things. That CDROM 
alone is an excellent reason to buy the ARRL Antenna Book!

> The downside of these "end of coax" tools is that many of us have runs
> made up of mixed coax types. This can be confounding. You have to know
> the length(s)!  Also the coax parameters in the models are nominal and
> may not reflect your 10 year old coax.

Yes, that's certainly a challenge.  However -- most ham VNAs can give 
you a pretty good approximation of the electrical length of the line in 
Time Domain Reflectometer mode (distance to fault).  The approximate 
part of it is that Vp varies with frequency.  See my Coax and Stubs 
tutoriial if that's news to you.

>   VNA's generally handle the "as is" coax parameters.

VNAs measure what is connected to their terminals.  It's up to the 
analysis software, and what's between the ears of the person driving 
that sofware, to tell the software what that coax is.  From a modeling 
point of view, as long as all parts of the line are the same Zo, all 
that matters is the ELECTRICAL length, not the physical length, and the 
TDR can give you that.

> I don't have a $500+ VNA floating around.

More and more hams do, and it's an increasingly good bet that one of 
your ham buddies has one you can borrow.  AND -- what if that $500 (or 
$800 for the really neat German-designed VNWA3+) could save you the cost 
of a couple of automatic antenna tuners in your SO2R station, or bring 
an antenna with 5:1 or 10:1 at it's bandwidth limits down to 2:1 or 3:1 
where Elecraft's new tuner might be able to handle it at 1kW?

73, Jim K9YC