[hpsdr] VNA calibration loads

[Jim Barber]

John,

You may be building your loads as a hobby/educational project, and if so
please ignore the rest. :-)

You can buy a set of loads very inexpensively right off Amazon. Choices of
connector are pretty much limited to SMA,
but if you're using a Hermes board and not going past 60 mHz, a SMA->BNC
adapter wouldn't hurt much.

Complete load kits, search "SMA Calibration Kit"
If you want to replace the imported 50-ohm load with an Amphenol, search
"Amphenol SMA Load"

I have several sets of these loads, and have replaced the 50-ohm parts with
Amphenols. Using the loads, both my "amateur grade" VNAs agree with each
other down to very small variances, and S21 results match my calibrated
spectrum analyzer quite well. I don't have a calibrated lab grade VNA any
longer to use as a standard, but for HF and even VHF use I've been very
pleased with the results.

73,
Jim N7CXI


On Thu, May 14, 2020 at 9:25 AM <radio at netins.net> wrote:

> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Larry,
>
> First, I really enjoy watching your SimSmith videos on Utube.  My wife
> bought a "Smart TV" which makes them much easier to follow than on my
> computer screen.
>
> My "VNA" is a Hermes SDR radio and a circuit from an old ARRL handbook
> meant to isolate two RF generators. It uses female BNC connectors.  The
> software was written by VK6PH.  The loads are made with male BNC
> bulkhead connectors.  The "50 Ohm" load was made using just a small
> leaded part that measures close to 50 Ohms on my multimeter.  It is
> mounted from the center of the connector to a small copper tube soldered
> to the BNC connector (a bit like inside a coax).
>
> After watching several of your videos and running SimSmith myself, it is
> pretty obvious my calibration loads can be improved.  One of the videos
> showed calibration loads you made with copper clad board for use with a
> dual banana to BNC adapter.  I would like to duplicate them.
>
> Did you make a layout and then etch the board material or did you cut
> the board with an Exacto blade to remove the copper?
>
> The mating surface of the copper looks as if it had been tinned.  Is
> there a reason for this?
>
> John,  W0GN
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