John (Smith), all you have is a circuit which might light up a couple
of light-emitting diodes from an RF source via a current transformer.
What purpose is served by the 100K resistor is anybody's guess. But it
has nothing to do with SWR.

As Cecil implies, you should go right back to square one and think
about it.

Actually, you are in good company. Most people don't know how their
SWR meter works or what it does. Most people and Tx manufacturers
don't connect it in the correct place for it read SWR on the
transmission line. Consequently it doesn't even indicate SWR and its
name is a very misleading misnomer.

All it indicates is the magnitude of the reflection coefficient of the
load on the transmitter relative to the impedance the transmitter is
designed to see. And it only does THAT provided the meter has itself
been designed to cater for the same impedance. It is fortunate there
exists a standard impedance of 50 ohms.

But don't allow me to put you off. Just obtain a circuit diagram of a
so-called SWR meter (an HF version) from a handbook and, with little
more than Ohm's Law, you can see and work it out for yourself.

Reg, G4FGQ.

The resistance in the anode circuits of the LEDS only serves as an attempt
at limiting the current through the FWD LED to full brightness (and a
constant current source would best replace this)--and to keep it from
"burning out."

My goals are this:
1) CHEAP!!
2) Cheap!
3) Fewest possible parts...
4) Marginal functionality...

I want to be able to cover the world with these devices (put one on every
single antenna project of mine (even the EH Antenna!!! grin)

I will continue to toy with the design as my time permits....

I am quite willing to suffer the slings and arrows of others, education is
expensive yanno!!! And, I do see most, if not ALL, are saying there is much
more to SWR than at first it seems...

Thanks Reg...

Warmest regards,
John

"Reg Edwards" wrote in message
...
|
| John (Smith), all you have is a circuit which might light up a couple
| of light-emitting diodes from an RF source via a current transformer.
| What purpose is served by the 100K resistor is anybody's guess. But it
| has nothing to do with SWR.
|
| As Cecil implies, you should go right back to square one and think
| about it.
|
| Actually, you are in good company. Most people don't know how their
| SWR meter works or what it does. Most people and Tx manufacturers
| don't connect it in the correct place for it read SWR on the
| transmission line. Consequently it doesn't even indicate SWR and its
| name is a very misleading misnomer.
|
| All it indicates is the magnitude of the reflection coefficient of the
| load on the transmitter relative to the impedance the transmitter is
| designed to see. And it only does THAT provided the meter has itself
| been designed to cater for the same impedance. It is fortunate there
| exists a standard impedance of 50 ohms.
|
| But don't allow me to put you off. Just obtain a circuit diagram of a
| so-called SWR meter (an HF version) from a handbook and, with little
| more than Ohm's Law, you can see and work it out for yourself.
|
| Reg, G4FGQ.
|
|

John Smith wrote:
Well, If there is a voltage, there is a current (albeit, at times very
small)--the opposite is also true, ohms law is standing proof...

Yes, but the amplitude and phase relationship of current to
voltage can have any possible value and there are an infinite
number of possibilities. In the equation, Z = V/I, you cannot
determine Z unless you know BOTH V and I.

Why can't I measure the standing wave ratio as a ratio of power, ...

You need both voltage and current to determine power. Your design
senses only current.
--
73, Cecil http://www.qsl.net/w5dxp

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OK. Perhaps here the problem lies....

I am looking at it like this:
I don't care what value is V, nor what value is I...
I care only how much power the antenna is radiating, and how much is
"reflected" back and sits on the plates, collectors, or drains and is wasted
as heat--develops itself on the feedline--radiates from other antenna
components--etc....

I am thinking the "directional coupler" is doing that action, and forcing
the amount of "forward" power to one LED (amount of power actually leaving
the antenna (allowing for losses)) and giving indication--and the
"reflected" to the other LED (the amount of power "wasted") and giving
indication...
I take for granted that when 'Z' of "output of xmtr" = coax = antenna input,
I see the "REF LED" at dark condition....

There WELL may be an error in my thinking and, the "thing" (frankenstein?) I
have constructed only "seems" to work... (kinda like time yanno grin)

Thanks for your patience Cecil....

Warmest regards,
John

"Cecil Moore" wrote in message
...
| John Smith wrote:
| Well, If there is a voltage, there is a current (albeit, at times very
| small)--the opposite is also true, ohms law is standing proof...
|
| Yes, but the amplitude and phase relationship of current to
| voltage can have any possible value and there are an infinite
| number of possibilities. In the equation, Z = V/I, you cannot
| determine Z unless you know BOTH V and I.
|
| Why can't I measure the standing wave ratio as a ratio of power, ...
|
| You need both voltage and current to determine power. Your design
| senses only current.
| --
| 73, Cecil http://www.qsl.net/w5dxp
|
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On Wed, 4 May 2005 11:23:39 -0700, "John Smith"
wrote:

The resistance in the anode circuits of the LEDS only serves as an attempt
at limiting the current through the FWD LED to full brightness

It, in fact, serves to reverse bias the other LED, turning it OFF
(until the first LED depletes the capacitor which then reverses the
situation - the original RDL flip-flop running asynchronously). Which
one lights up is a matter of an indeterminate logic race, not some
proportionality of powers.

(and a constant current source would best replace this)--

If you think about this statement, you would recognize that
either/both LEDs would always be ON and equally bright. [the word
"constant" should be a dead give-away]

and to keep it from "burning out."

Then you put a current limiter (not constant current device) in EACH
LED lead (not sharing). To select a 1KOhm limiter presumes a 20V drop
across it for a 20mA LED excitation current (a typical current
specification). You may achieve the 20mA limit, but it will come at
the cost of more than 40V across 100 Ohms backing through the current
transformer (it is NOT a directional coupler) which can only be
supplied by a transmitter excitation of several KW to a matched load.
If you did nothing other than simply connect an LED across the current
transformer's terminals and adjust the transmitter for 20mA through
the LED, you would need 8W into a matched load.

To put it simply, you are fixated on a problem so remote from your
goal, that solving it basically accomplishes nothing towards measuring
(or even indicating) SWR. As several suggestions have been offered to
research a real topology, you might want to pursue that first.

73's
Richard Clark, KB7QHC

John Smith wrote:
I wish an indication of SWR which is cheap, uses fewest parts possible, and
has the possibility of "automatic operation" and one can be placed on each
and every antenna I am playing with (or anything else, maybe one on the bird
fountain! grin)...

Got just the device for you on page 520 of "The radio amateur's
handbook", 1957 by the ARRL. It's called the "twin-lamp" and
consists of a piece of 300 ohm twinlead and two flashlight bulbs.
I used one in 1957 on my all-band off-center-fed dipole. I ran
40 watts on 11m in those days. :-)

You might want to take a look at another type of design for SWR
meters. There is one that uses a short piece of slotted line
with two parallel conductors that separate the forward and
reflected components without phasor addition/subtraction.
Here's a schematic of the Heathkit HM-11 SWR meter.

http://www.qsl.net/kb7rgg/heath/sche...chema_hm11.gif

Note the low component count. The only tricky part is the slotted
line but that is a mechanical problem, not an electronics problem.
Resistors R1 and R2 attenuate one wave in one direction leaving the
other wave in the other direction to be rectified by d1 and d2.
--
73, Cecil http://www.qsl.net/w5dxp

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John Smith wrote:
I want to be able to cover the world with these devices (put one on every
single antenna project of mine (even the EH Antenna!!! grin)

http://www.qsl.net/kb7rgg/heath/sche...chema_hm11.gif
--
73, Cecil http://www.qsl.net/w5dxp

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John Smith wrote:
There WELL may be an error in my thinking ...

No, there *IS* an error in your thinking. Blood from
a turnip comes to mind. The current in your feedline
is one amp. What is the power? See the problem?
--
73, Cecil http://www.qsl.net/w5dxp

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Well, that is how my "meter SWR" which I constructed looks all right--but I
wished to get away having to construct a directional coupler from tubing and
pickup loops...
Only, my (metered) SWR meter uses just ONE pickup loop, I switch terminating
50 ohm resisistor and take-off ends and use the single loop for BOTH "FWD"
and "REF", with a physical switch--my thinking was it would keep the device
more "balanced" using the same pickup...

Warmest regards,
John

"Cecil Moore" wrote in message
...
| John Smith wrote:
| I want to be able to cover the world with these devices (put one on
every
| single antenna project of mine (even the EH Antenna!!! grin)
|
| http://www.qsl.net/kb7rgg/heath/sche...chema_hm11.gif
| --
| 73, Cecil http://www.qsl.net/w5dxp
|
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For anyone interested, here is the datasheet on the siemens LED,
unfortuantly, mostly in german frown
This opens a "prohosting page", a link is given you there to view the
..pdf... sorry Richard H.
http://blake.prohosting.com/mailguy2...-LO5436-TO.pdf

Regards,
John

"John Smith" wrote in message
...
| This is a SWR bridge I built using leds and a homemade "directional
| coupler."
|
| ALL critiques on it, and ideas for improvements are welcomed!!!
|
| Please excuse my rough drawing, I am NOT a draftsperson!
|
| Hopefully, the attachment of the .jpg was successful....
|
| Warmest regards,
| John
|
|