[NLRS] Curiosity question

[Dr. Gerald N. Johnson]

Except for line loss, good couplers should couple the same no matter the 
position. Its crappy couplers like the monomatch adopted for typical CB 
couplers that get sensitive to position with respect to the position of 
standing wave voltage or current peaks.

73, Jerry, K0CQ

On 9/27/2010 9:39 AM, Donn - WA2VOI/0 wrote:
>
>
> '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
>
>