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Jeff has a bunch of really good blog posts about directional couplers.
As I recall, he had a thorough analysis of the Tandem Match,
showing exactly how it arrived at a figure for SWR.
Unfortunately, I'm having trouble navigating his website on my Chromebook,
all I can get to is the blog post about calculating maximum flux density:


Jerry, KE7ER

Jeff,

You are correct,.
Power delivered to the load is Forward-Power minus Reflected-Power.

Unfortunately, none of the popular SWR meters actually measure power.
What they do is sample RF voltage and RF current, then add the two.
Invert one of the two before adding to switch between forward and reflected.
It applies to pretty much all the various SWR meter designs over the
last 70+ years, including the Monimatch, Bruene, and Tandem Match.
This only works if we assume the target is a 50 ohm system.

Why it works is not obvious.
The classic article on this is Bruene's "An Inside Picture of Directional Wattmeters"
from the April 1959 QST:
Clearly written, and none of it is out of date as of Sept 27, 2020.
Including the editor's snide little note in the lower left of the first page.

One minor enhancement in 2020, we now have animated GIF"s to supplement Bruene's fig 1.
GIF: /g/nanovna-users/photo/253286/0?p=Created,,,20,2,0,0
Thread: /g/nanovna-users/topic/76697419#17241
The Voltage standing wave of Bruene's fig 1 is the stationary purple trace in the GIF.

Jerry, KE7ER

You can install any version for your device at any time in any order.?
Read the various user guides that are available on the forum Wiki and file areas and watch some of the YouTube videos mentioned in various posts here.?



On Sun, 27 Sep 2020 at 8:47 AM, Richard -- N7WFK<rdykstra82@...> wrote: Do you have to do the Firmwares in order or can you just grab the most current?

Hi Richard,
Can You see more info on my website
73, Gyula HA3HZ
--
*** If you are not part of the solution, then you are the problem. ( ) ***

Yes the Nano will indicate power when used as a watt meter. More smoke means more power.

--
KT0TT
Allen Kiddoo

On Sat, Sep 26, 2020 at 04:42 PM, Jerry Gaffke wrote:

I'm not so sure any of the SWR bridges would accurately measure power
with an antenna of other than 50 ohms.

Please correct me if I'm wrong, but isn't the power delivered to a load simply Pfwd - Pref?

- Jeff, k6jca

It's firmware, not Windows updates :)
Just download the latest and flash it.

Do you have to do the Firmwares in order or can you just grab the most current?

Latest from edy555 is here:

DiSLord here:
Try to change the stimulus range ...

I just updated my firmware on my nanoVNA last night to a Feb 2020 version.... I am just wondering if there is something newer then that for the nanoVNA? Also mine seems to only goto 900 mhz... is that normal?

On Sat, Sep 26, 2020 at 12:12 PM, Jim Lux wrote:

it's not obvious from the website, but it's windows.

The program loads in WINE in Linux Mint. I (obviously) haven't confirmed that every single function works properly, but a quick glance shows that it does run in WINE.

I was mostly calling out the out of date info on personal computer power to
let people know that this stuff is more accessible than they might think
after reading the comments in the book. You can buy something for $5 (Blue
Pill, Seeeduino Xiao) that will be 10x faster than that old PC, or get a
DSP powerhouse (Teensy 4.0) for $20. You don't need any specialized
hardware; cheap commodity development boards will do. (Or use the
processors that are on those boards for a custom build.) Or run DSP on the
computer you already have for even more power, like software such as WSJT-X
or any of the SDR applications does.

Here and now may be challenging times for building RF equipment using old
analog techniques. (Just try to buy new air variable capacitors, for
example.) But it's a great time to be working in digital, as instruments
like the nanoVNA (the main topic of this group) demonstrate.

I agree that the book is worth the price. Heck, it's worth twice the price!
:)


On Sat, Sep 26, 2020 at 4:00 PM Jerry Gaffke via groups.io <jgaffke=
[email protected]> wrote:

I had a very favorable impression of the Steven Smith book.
Hit at exactly the correct level for me.
That is, not just too afraid of some math, perhaps an occasional bit of
elementary calculus,
but have long since forgotten anything I ever knew about Fourier and
Laplace transforms.

Kind of jarring to see all the examples in Basic, but then I find that the
exercise
of moving them to Python reinforces the concepts.
At least he didn't use Knuth's MIX assembly language.

The Smith book was last updated in 1997 or so, adding a few chapters on
what was
then available in DSP chips.
All I'm looking for is basic concepts presented in a comprehensible
fashion,
this fits the bill. And can't complain about the price.

Jerry, KE7ER



On Sat, Sep 26, 2020 at 09:20 AM, Shirley Dulcey KE1L wrote:

The Steven Smith book was originally published in 1987, so some things in
it are out of date. The mathematical theory of DSP is still sound;

Actually, a diode RF probe and a DVM would tell you the RF voltage at the antenna.
You will also need to know the input impedance of the antenna, but a nanovna can tell you this.
Given the RF voltage and the impedance, the power can be easily computed.
With care, this could be quite accurate.
Failing that, at least educational.

I'm not so sure any of the SWR bridges would accurately measure power
with an antenna of other than 50 ohms.

Jerry

I agree, the nanovna is not a good base from which to build a wattmeter for use on a transmitter.

A better choice would be a Bird or Telewave Wattmeter, or an Eagle return loss bridge.

While they may be better they are also way spendier, figure $400 to $1000 if buying new.
I doubt few amateurs need the accuracy they offer.

Not sure what frequencies you are interested in, but if 30mhz and down I'd
give Diz $12 for this Tandem Match Bridge kit:
Then buy a used SWR meter for CB rigs at a flea market, and replace the guts with Diz's kit.
Or, if you are lucky, you can get the flea market SWR meter to work well enough as is
to show forward power.

If you just want to buy something but not on a Bird budget, perhaps one the many
possible products from MFJ such as this:
(plus a BNC to SO239 adapters)
(bigger, has SO239's)
Note that that both can show forward watts.
Build quality of MFJ stuff does not always measure up to Bird standards, but a ham can
usually tear it apart and clean up the cold solder joints to make it work well enough.

Jerry, KE7ER


On Sat, Sep 26, 2020 at 03:13 PM, ERNEST AEC-RADIO wrote:

The Nano series is unable to be used as a wattmeter, or current source.
A better choice would be a Bird or Telewave Wattmeter, or an Eagle return loss
bridge. ...

On Sat, Sep 26, 2020 at 09:36 AM, S Johnson wrote:

If not, what is a good highly portable wattmeter for taking a power reading at
the antenna connection point (SO-239)?

The Nano series is unable to be used as a wattmeter, or current source.
A better choice would be a Bird or Telewave Wattmeter, or an Eagle return loss bridge.
Even the output of the Nano, is not enough to properly measure SWR/Return loss.
Rudimentary measurement might be possible, but you might suffer from distortion or coupling from external sources.
Best cure, is to try it for yourself.

Dry humour?


On Sat, 26 Sep 2020 at 3:58 PM, Carey Fisher<careyfisher@...> wrote: *** If you are not part of the solution, then you are part of the
precipitate.

--
Carey Fisher
careyfisher@...

I had a very favorable impression of the Steven Smith book.
Hit at exactly the correct level for me.
That is, not just too afraid of some math, perhaps an occasional bit of elementary calculus,
but have long since forgotten anything I ever knew about Fourier and Laplace transforms.

Kind of jarring to see all the examples in Basic, but then I find that the exercise
of moving them to Python reinforces the concepts.
At least he didn't use Knuth's MIX assembly language.

The Smith book was last updated in 1997 or so, adding a few chapters on what was
then available in DSP chips.
All I'm looking for is basic concepts presented in a comprehensible fashion,
this fits the bill. And can't complain about the price.

Jerry, KE7ER

*** If you are not part of the solution, then you are part of the
precipitate.

--
Carey Fisher
careyfisher@...

On 9/26/20 11:31 AM, Fred Moore wrote:

So what OS does this run on?
On Sat, Sep 26, 2020 at 1:50 PM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:

I used to use LTSpice. There is an very extensive Spice simulation
program that has more features than LTSpice and a better user interface.
Until recently MicroCap 12 had a licence fee that was in the thousands of
dollars. The fellow that developed it over 35 years has recently retired
and he made a gift of the program to the engineering community. It is now
free to download and use. I am very impressed with how this program can
simulate digital logic and analog circuits. A huge library (even older
parts) and lots of example circuits. Even has S parameter support

It can be downloaded here>

it's not obvious from the website, but it's windows.

So what OS does this run on?

On Sat, Sep 26, 2020 at 1:50 PM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:

I used to use LTSpice. There is an very extensive Spice simulation
program that has more features than LTSpice and a better user interface.
Until recently MicroCap 12 had a licence fee that was in the thousands of
dollars. The fellow that developed it over 35 years has recently retired
and he made a gift of the program to the engineering community. It is now
free to download and use. I am very impressed with how this program can
simulate digital logic and analog circuits. A huge library (even older
parts) and lots of example circuits. Even has S parameter support

It can be downloaded here>

Roger