A recent ZOOM presentation was made to members of the Amateur Radio Emergency Service to introduce the NanoVNA.
It's about 105 minutes long (I haven't watched it all yet) but it seems to be very well presented.
The audio in the beginning is choppy, but gets fixed at about 6 minutes.

Topic: NanoVNA (Vector Network Analyzer)
Speaker: Alan Wolke, W2AEW

Viewing: https://vimeo.com/481077181
Download: https://vimeo.com/user107547861/download/481077181/271487d76c
Documents: https://www.dropbox.com/sh/rx5f81jw29232gr/AACimwxlG5cISvRCj6Yf_Psya?dl=0

I'd be interested in reply comments.

-Neil W0NRP

W2AEW Alan knows the material and is an exellent instructor. His videos are exsquisite .

The Nano VNA is quite the tool. Be sure to do an adequate calibration.
I found it much easier to use once I loaded Nano VNA SAVER (Win10).
It allows many more calibration points, and shows up 6 graphs on one monitor screen.
For those of us a bit color blind, small screens in four colors on the VNA are awful.

I also then learned a whole lot about Smith Charts, and PHASE measurements on an antenna.

I still am struggling with RETURN LOSS (dB) but I see its value to describe a mismatch.

If I think of the center or Bull's Eye of a Smith Chart as the ideal location (SWR 1:1) then the farther your antenna lands from the Bull's Eye on a Smith chart, the worse the match.
So think of a Smith Chart like a DART BOARD.

Question: on a single band 80m dipole, 130 ft long, center-fed
At typical heights above ground, the minimum SWR is not necessarily at "resonance" or where the reactance is zero. My 80m dipole, when mounted 20 ft above ground, showed an impedance of only 20 ohms, so the minimum SWR was not so good ... until I added a matching coil across the input (haripin match).

This is one great teaching tool.

Barry k3eui
Philly

Thanks Neil,
Very well worth watching Alan's presentation.
For those not familiar, Alan's entire channel on YouTube (W2AEW) is outstanding.

73 de k1jbd
bammi

Return loss - I could be wrong, but I see 'return loss' as an indication of how well the antenna is radiating instead of reflecting.

O db return loss indicates that all of the energy is being bounced back at the source and none is leaving the antenna.

The greater the return loss (deeper the notch), the more energy is leaving the antenna by radiation (of some form) and less being reflected back to the input at the notch frequency.

20 dB return loss indicates that 1/100 of the energy is being reflected, and 99% is being radiated.

I'm sure that can be converted to an SWR, but the NanoVNA does that for you.

On 11/23/20 11:26 AM, Neil Preston W0NRP via groups.io wrote:

Return loss - I could be wrong, but I see 'return loss' as an indication of how well the antenna is radiating instead of reflecting.

How much power is being absorbed by the load (whether it is radiated is another story entirely).

10dB return loss means 10% of power is reflected back *if the source is 50 ohms*, which it might not be - you can easily have something with a RL of 3 dB on both ends which has very low loss (for instance, both the source and load are 300 ohms, and you're measuring with a 50 ohm instrument).

O db return loss indicates that all of the energy is being bounced back at the source and none is leaving the antenna.

The greater the return loss (deeper the notch), the more energy is leaving the antenna by radiation (of some form) and less being reflected back to the input at the notch frequency.

In *a 50 ohm system*

20 dB return loss indicates that 1/100 of the energy is being reflected, and 99% is being radiated.

Radiated or absorbed. (a 50 ohm load has infinite RL)

I'm sure that can be converted to an SWR, but the NanoVNA does that for you.

RL = 20 * log10( (VSWR-1)/(VSWR+1)) (using the convention that RL has positive sign -> loss)

or
VSWR = (10^(-RL/20)+1/(10^(-RL/20)-1) (using same sign convention)

My sincere thanks to RATPAC for arranging this presentation and of course
to Alan-W2AEW, who I've been following on Youtube since I first stumbled on
one of his NanoVNA videos last week. He is truly a fantastic presenter!
I've got the Ham Radio "Itch" again after being away from the hobby for too
many years. My NanoVNA SAA-2N should ship from R&L today!


On Mon, Nov 23, 2020 at 10:29 AM bammi via groups.io <jbammi=
mac.com@groups.io> wrote:

Thanks Neil,
Very well worth watching Alan's presentation.
For those not familiar, Alan's entire channel on YouTube (W2AEW) is
outstanding.

73 de k1jbd
bammi

Return loss has nothing to do with antenna radiation or efficiency. It is
a measure of the impedance match between a source and a load. An antenna
with high ground losses could look wonderful from a return loss point of
view, but would make a poor radiator.. Return loss is nothing more than
another way of expressing the VSWR, and has nothing to do with antenna
efficiency.

A 50 ohm resistor looks great for return loss, but is a rotten antenna in
terms of radiating RF.

My inverted L for 160 with no radials shows a perfect 1:1 swr, because it
has 13 ohms of ground loss to compliment the inherent 37 ohms of radiation
resistance of the antenna itself. Adding radials increases the swr, yet
increases efficiency because ground losses have been reduced. When I added
20 radials 50 feet long the swr stopped increasing, indicating little more
could be gained, even though from a return loss point of view, things had
been made worse.

Don't conflate low swr with radiating efficiency, they are two completely
different things.

73, N0AN
Hasan

On Mon, Nov 23, 2020, 1:26 PM Neil Preston W0NRP via groups.io <w0nrp=
yahoo.com@groups.io> wrote:

Return loss - I could be wrong, but I see 'return loss' as an indication
of how well the antenna is radiating instead of reflecting.

O db return loss indicates that all of the energy is being bounced back at
the source and none is leaving the antenna.

The greater the return loss (deeper the notch), the more energy is leaving
the antenna by radiation (of some form) and less being reflected back to
the input at the notch frequency.

20 dB return loss indicates that 1/100 of the energy is being reflected,
and 99% is being radiated.

I'm sure that can be converted to an SWR, but the NanoVNA does that for
you.