Re: Quarter-wave whip earth plane

Tauno Voipio <tauno.voipio@notused.fi.invalid> wrote:

On 15.3.2025 11.23, Liz Tuddenham wrote:
  I need to do a crash

course in interpreting Smith Charts.

 
 
The NanoVNA will show the reflection attenuation or VSWR
if you're intimidated by the Smith chart.

Not so much 'intimidated' as 'outdated'.  I passed an exam in 1969 which
included them -  and haven't used one since.

The Smith chart shows the both the amplitude and the phase
of the measured reflection. The coordinates are the resistive
and reactive components of the reflection scaled to the system
reference impedance (here: 50 ohms). The coordinate lines are
circles for easy handling of the reflection. Traces of constant
SWR are circles centered on the 50 ohm center point.

It gives me a huge amount of information which I am sure is exactly what
I need if only I can get my brain around how it realtes to what I am
doing with the hardware.  I need to watch the trace on the screen and
see what makes it rotate, expand, contract and turn back on itself so
that I have a feel for how I can make it do what I want.

It is a bit like the description of learning to fly a helicopter: Waggle
the stick about and see what happens - if you want that to happen, that
is how you must waggle the stick.

>

The VNA has very small coaxial connectors (SMA), so you'll
need adapters to more conventional feed line connectors.
I prefer adapters with a piece of cable between the connectors,
to protect the small connectors from mechanical stresses.

It came with a set of short extension leads and I have connected a set
of BNC adaptors to the far ends of those leads so as to remove any
strain they would have imposed on the connectors on the side of the
instrument.  I have already standardised my R.F. interconnections with
adaptors on each piece of equipment to convert them to 50-ohm BNC, so my
learning curve shouldn't be complicated by intermittent connections from
botched adaptors.

This evening I've also made up a couple of BNC to croc-clip adaptors for
testing circuits on the bench.  For tuned circuits I have an Edometer
that ges up to 100 Mc/s, but the VNA will cover frequencies much higher
than that.


--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk