On Mon,3/20/2017 10:32 AM, k7wxw wrote:
I am building my own antennas and have a couple of questions about using
antenna analyzers properly. Here's the setup:
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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