Talk:SWR meter

Coupling line

How long must the coupling line be in relatio to wavelength?

I think, if the coupling line is much smaller than the wavelength, UFWD and UREF would have the same value only from different voltage value (consider the voltage induced in a conductor by a powerline running close to it)

The line that forms the directional coupler is typically much shorter than a wavelength. Also some designs are better described as bridges as they used lumped impedances. David Woolley (talk) 18:39, 13 April 2010 (UTC)

Circuit for section "Directional SWR Meter"

The diagram in section "1 Directional SWR Meter" is unclear as to the physical connections. For the FWD(x"REV") portion, it appears that the two ground connections are made to the actual coax, one connection being in the center of the coax and the other connection being at the antenna. For the REV(x"FWD") portion, it appears that neither ground connection is made to the coax, and instead two ground rods should be used, one at the transmitter and one at the antenna. Can someone clarify this? Again from the diagram, it appears that the two half-wave rectification circuits are returning a DC value of the sinusoid peak for the wave in the ground plane and the wave in the antenna feed cable, yes? The diagram label also states that the diagram labeling is in error (FWD<==>REV), so if by chance someone redraws the diagram then make sure the labeling is correct. - Peter, Los Angeles CA, 2012jan22-0110(PT)-sunday — Preceding unsigned comment added by 71.106.222.207 (talk) 09:10, 22 January 2012 (UTC)

It's a schematic, not a physical wiring diagram; this circuit is not a coaxial cable but is a directional copuler. (We need an interior picture of a physical layout - something to do this weekend, if I can find it in the garage.) I've fixed the labels. --Wtshymanski (talk) 14:47, 27 January 2012 (UTC)

Radio Operator SWR Meter section

This section is confusing at best, and possibly nonsensical.

First, the animated graphics. I understand the concept they are trying to illustrate, but I have no idea what the actual graphics depict. I am assumming that the transmitter is on the left (the "100MHz" voltage source) with load (ie: antenna) on the right, but the plot of the the driving signal is plotted on the right and reflected signal on the left. Those plots move right to left, though I assume that's to simulate a pen plotter style display over time, not to indicate direction in space.

Then we have the area depicting I guess two parallel cables each as sandwiches of... I'm not sure what. There are grid patterns and parallel line patterns, and some yellow bars and triangles that move around indicating I don't know what. There's an alternating green and red stripe in each of the sandwiches that moves left to right -- what's that motion? Individual cycles of 100MHz? Movement of a node or antinode of not-quite-standing wave?. The resistors attached to the upper sandwich both appear to be connected to the same white bar, and also lacking rectifiers, don't seem to correspond to an SWR meter per se, but perhaps are supposed to illustrate some concept.

As for the narrative, it's quite incoherent:

 With shielding compromised, a pair of coax or twinline transmission lines, placed close enough, will suffer crosstalk.

I guess that introduces the idea of how we get any signal from one conductor to another when shielding would have been in the way.

 A wave moving in the driven line will induce waves in the measurement line. 

OK, but that jumps from "two coaxes with compromised shielding" to "a driven line and measurement line", without making the correspondence explicit. And the SWR meter has two measurement lines, so how does that correspond?

 Placed in parallel (straight or loosely coiled) a driven wave will reinforce/cancel an induced wave in the same/opposite direction.

First, how do you place a wave in parallel? Maybe it means placing a wire in parallel -- to what? This sentence might be talking about standing waves in a transmission line (ie: the phenomenon we're trying to assess), but then talks about an induced wave, suggesting it's talking about the measurement line. But maybe "induced" should be "reflected"?

 If cable pair exceeds half wavelength, cancellation is complete, and power dissipated in matched termination is approximately proportional to the forward and reflected power. 

Again, is this trying to talk about standing waves in a (single) transmission line? Or does this relate to the SWR meter measurement line(s)? And does it imply that the measurement line(s) have to exceed a half wavelength? Clearly SWR meters are not generally over a half-wavelength long, so...??? And how is power in matched termination proportional to both forward and reflected power? Perhaps this is talking about the two resistors in the upper sandwich as the "matched termination(s)"?

 The approximation improves as crosstalk weakens and harmonic number increases.

Wait, what approximation? Where did harmonic number suddenly come from?

 Over decades nonlinear high gain amplifiers have replaced nonlinear electromechanical movements which replaced incandescent bulbs, to require less crosstalk and improve linear frequency range. 

Decades: 10's of years? Or frequency? High gain amps have replaced electromechanical and light bulbs to do what? I infer the sentence is trying to talk about the readout device and the linearity thereof, but there's no way for the reader to interpret this they didn't know already.

 Though called an SWR Meter, a low measured ratio indicates not only good match, but also clean A3, F3, or G3 emission without excessive harmonics nor spurious (out-of-channel) power. 

"Though [...] but" : These two clauses are not in conflict, so "but" is the wrong connective. "A3, F3, or G3" -- completely unnecessary use of technical terms, and their use is incorrect anyway because it suggests that the implied readout of emission quality doesn't apply to any other modes, such as R3, or F8 or whatever.

In short, this entire section could use some attention from someone who knows the subject, starting with the animation, or scrapping it entirely, and then rewriting the sentences so that they present concepts in order and connect coherently from one to the next.

A key concept that would be nice to explain is how the two separate measurement conductors (with resistors and diodes wired oppositely) manage to distinguish the forward and reverse waves (or the node and antinode amplitudes). Gwideman (talk) 19:03, 21 June 2019 (UTC)

Agree, this section is nonsense and has little to do with SWR, in any case. I propose to delete it. Kbk (talk) 16:42, 23 December 2021 (UTC)

Is SWR Formula correct?

The page currently says

$\Gamma ={\frac {V_{rev}}{\;V_{fwd}\;}}$

${\mathsf {SWR}}={\frac {1+|\Gamma |}{1-|\Gamma |}}~.$

When I use this formula with my power measurements, I do not get sensible SWR results.

I think it should include a square root of Gamma:

${\mathsf {SWR}}={\frac {1+{\sqrt {|\Gamma |}}}{1-{\sqrt {|\Gamma |}}}}~,$

or, alternatively, include the square root in the inital calculation of $\Gamma$. I do get reasonable SWR results with this one. See, e.g., https://24hourcb.com/cb-stuff/vswr-reflected-power/swr-refpwr-formula.htm

shtrom (talk) 07:12, 15 March 2023 (UTC)

Edit: It's correct when using voltages, and the square root is needed when using power https://en.wikipedia.org/wiki/Standing_wave_ratio#Relationship_to_the_reflection_coefficient. It might be worth unifying both article so the formula is only present once.

shtrom (talk) 02:17, 19 March 2023 (UTC)