Jim,
Thanks for the reply and the pointer to simsmith. That's the first free and
usable smith charting program I've seen. That's the good news. The bad news is
my CAA-500 is an analog analyzer, so no files to feed it. But it is a start.
I agree, what I am doing is probably "good enough" But I am trying to make the
leap from putting up antennas that work - all three of my current antennas
certainly fall into this category - to learning how to design and characterize
antennas to make them work well. I was hoping that leap wouldn't require a
$500 VNA but maybe it does.
Grateful for the help.
73 de Bill K7WXW
> I have a 133' doublet, fed with 46' of 450 ohm window line, into a Johnson
> matchbox. My rig is a FT-897D. I mostly run QRP though I venture up to 100W
> on SSB. Because my inline SWR meter is on the repair bench, I depend upon the
> rig's SWR indicator.
That's probably good enough.
> To characterize the antenna/tuner system from the radio, I've connected a
> Comet CAA-500 on the radio side of the matchbox to sweep through the bands by
> hand. Basically I set the frequency on the analyzer, and tune for lowest SWR.
> So each measurement consists of the bandswitch/tune/match settings on the
> matchbox and the SWR and ohmic readings on the analyzer.
That's also probably plenty good enough.
>
> So, three questions: does an analyzer like the CAA-500 have enough drive to
> properly drive the matchbox/feedline/antenna system?
If there are no strong signals (like nearby AM broadcast stations)
nearby, yes.
> If it doesn't, what other options do I have for characterizing the antenna
> system?
My favorite is the VNWA 3e. http://sdr-kits.net/VNWA3_Description.html ;
Depending on your technical background, you may find that you need a lot
of self-study to take full advantage of it. For your needs, what you
have is probably good enough if it will generate a Touchstone file that
you can export to SimSmith.
> And lastly, can anyone point me to a good tutorial on Smith charts? I'd like
> to see if I can convert the impedance I am seeing at the matchbox to what is
> happening up at the dipole feedpoint.
The ARRL Handbook and ARRL Antenna Book are great for this sort of
thing, and ought to be on every ham's bookshelf. For SimSmith (free,
runs in Java), there are both text-based and video tutorials, but they
assume that you know the fundamentals of transmission lines and
antennas. That's where the ARRL books come in.
73, Jim K9YC
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