On Fri, 01 May 2009 15:47:41 -0700, Richard Clark
wrote:

When challenged as to how we might do that,
we got a URL pointing us to a simple standing wave meter -

Not really. It is a simple current meter - the page literally shouts
that out.

it
certainly can't discriminate Forward and Reverse.

That is correct, but I mentioned such discrimination is possible from
the Bruene SWR bridge. As I wrote previously, no one measures forward
and reverse currents on antenna elements. Construction examples would
be rare.

With care and practice as offered at the link, which attends the
issues of error (largely dismissed from the greater consideration of
"measurement" proofs offered), the Bruene style could similarly be
achieved. It is neither a difficult concept, nor a technical hurdle.

Hi Steve,

I hope you are still following the thread, because as bad as the
theory gets, there is always room for instruction - just not in phase.

I will expand on my comment of both the meter pointed to, its
construction practices, and the topic of accuracy (something everyone
offers, but can never prove).

First, as to its standing wave meter capacity (in terms of
conventional SWR meter usage). The last word, capacity, arises in
Tom's (W8JI's linked to) page:
The lack of large metallic components minimizes stray capacitance
and
I did not add a Faraday shield because the shield would increase the capacitance
I am now leveraging the word capacity to mean ability in contrast to
Tom's literal engineering application - and yet there is something to
be said about such a meter having the "capacity" to measure forward or
reverse products (as would a conventional SWR meter).

Capacitance is required to give the meter the capacity (ability) to
measure these currents. The Bruene SWR bridge has one side that is
driven by an inductive coupling, and the other side driven by a
capactive coupling. Through the combination of the two, the PHASES
contribute to either a reverse or forward energy product
(conventionally expressed as power). Clearly the link at Tom's page
illustrates half of the Bruene SWR bridge, and if that Faraday shield
had been tapped (instead of discarded), the meter could have revealed
the separate currents.

But nobody is interested - it offers nothing new. You will find 0 to
no construction examples of this more than rare application. Futher,
given its absence of discussion here in all these years, no one is
actually interested in "measuring" what they have proven through their
measurements.... Sorry Steve, another in-bred joke.

Moving beyond the hillarity that ensues from these obvious shortfalls
of academic navel gazing; there is still the accuracy to consider.

On the face of what is offered at Tom's page, there is an immediate
and irrevocable error of 5% built into the instrument as described
sitting in its calibration fixture. Under other circumstances, that
error could easily eclipse 100%. Suffice it to say it will never
achieve better without a small book of charts.

As I offered, accuracy is often claimed, but rarely (never) proven.

This is a simple counter-proof. Tom expresses it without being aware
of the implications:
T1 is a current transformer. ...
When the single turn primary (a whip or mast) has 1 ampere,
the secondary will have .05 amperes (inverse of the turns ratio).
all very standard stuff as you may well note. Going on:
This type of meter is much more reliable and linear
than thermocouple RF ammeters, and perturbs systems much less.
This, of course, is related to the "stated but not proven" class of
statements that litter the WWW (much less this thread).

Here is the literal error:
I've applied 50 watts to a precision 50 ohm load,
making wire current 1-ampere.

Let's assemble these statements. We have a current transformer. It
is loaded with 100 Ohms with a lightly coupled linear indicator. It
has 50 Watts applied through it to a load. That load is 50 Ohms.

What the meter should indicate is a current of 0.9535A if we are to
believe that the 50W is absolutely accurate (it is not, but we will
skip that for another discussion). The author, Tom, offers to trim
the potentiometer for a 1.000A reading - WRONG!

How can this be? It is all in the statements offered above. The
current transformer is also a RESISTANCE TRANSFORMER. That 100 Ohm
load to its secondary is cast into the primary as an in-series 5 Ohm
resistor adding to the 50 Ohm nominal load. The instrument is
injecting itself into the measurement and this presents the statement:
perturbs systems much less.
in a new light as it is quite easily demonstrated exactly how much (if
we ignore other sources of error) this construction example will
perturb the system and nothing is said in comparison to the technology
being replaced (thermocouples). Such is poor reporting.

What becomes of that error in a short monopole whose radiation
resistance is equal to that 5 Ohm insertion loss?
FS accuracy is not required in comparison measurements,
True enough, but it then ignores what I've offered above:
since the meter references against itself.
a 5 Ohm instrument load in series with a 5 Ohm radiator (irrespective
of phase contributions due to size) will seriously change the fabric
of the system. Such is the compounding of poor reporting.

If one were to claim to have made ANY current measurements, and then
wholly ignore the contribution of errors, then the discussion of phase
in a system such as a 5 Ohm radiator with a 5 Ohm instrument loss is
going to be absurd. Such are the fruits of poor reporting.

73's
Richard Clark, KB7QHC