[NLRS] Curiosity question

[Donn - WA2VOI/0]

'Morning, Tod.
I think the definitive answer is "maybe."

It depends on what you're trying to measure, and the frequency at which you're 
doing the measurement.  The idea behind the dual coupler is to measure FWD and 
REV at the SAME POINT on the transmission line.  With two couplers, you're 
making the measurement at two different points.  If the wavelength is very large 
relative to the distance between the couplers, it doesn't matter (as is the case 
in the QEX article -- i.e., HF).  BUT at VHF and up (say, starting at 50MHz), 
the distance becomes significant, and you'll get errors that may make the whole 
exercise not worth doing.  At HF, I suspect the errors are minimal and two 
couplers stacked next to each other would be just fine.  It would be worth doing 
TWO measurements:  one with the two couplers and a second with a single coupler 
which is reveresed in place to get the two values (FWD and REV).  If the answers 
are close, there is little error from the difference between the two seperate 
couplers.

Also, run the test with the position of the two "identical" couplers swapped: 
i.e., coupler A measuring FWD, coupler B measuring REV; and then with coupler A 
measuring REV and coupler B measuring FWD.  The point is, the couplers aren't 
necessarily "identical."  Depends on how much accuracy you're after.

73 Donn
WA2VOI/0



----- Original Message ----- 
From: "Tod - ID" <tod at k0to.us>
To: <nlrs at mailman.qth.net>
Sent: Monday, September 27, 2010 2:08 PM
Subject: [NLRS] Curiosity question


>
>
> In the Sept/Oct issue of QEX the cover shows a bi-directional coupler used
> as a part of the measurements made in the article.
>
> I am curious to know if one could simply use two identical directional
> couplers and use one with reversed input and output to provide the reflected
> signal. Anyone know if this will work --- or not work?
>
> Tod, K0TO
>
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