Optimize EWE F/B (details of wideband JBTerminator)

1. a variable R and a variable L (or variable C) connected in series (see photo below)

2. an accurate R / L / C meter

3. a curvebestfit calculating program like Octave or Matlab


This variable R and L was used for doing the measurements


The DIP switches shortcut the SMD inductors 5, 10, 10, 10, 47, 47uH

That covers a range of 5130 uH

·  Pick 8 ..10 channels across the MW band that have a tx sitting on the EWE rear. Make sure they are a bit strong, best time is short before the greyzone when levels are good, but don't yet suffer fading from skywave propagation.

·  For each channel find the best F/B by varying the R and L (or C) of the termination

·  Write down the found R/L/C values per frequency, convert L or C to its respective reactive resistance for that frequency (column "XL" in table below)

·  Repeat it the following days to rule out errors or propagation oddities.

·  Enter the found values into a curvebestfit calculator and let it find a network that fits best all your measured values.

This task was done by Christoph Mayer ( Thanks ! ) using Octave. I ended up with the result seen below.



Measured on 15. April 2011 kHz Ohm L/C XL 540 1718 4,3nF 70 630 1500 34uH 135 756 1364 85uH 403 801 1294 74uH 377 972 903 27uH 164 1134 873 94uH 670 1431 536 58uH 521 1458 562 59uH 540 1521 493 58uH 554 Some of these frequencies were entered in Octave to find a RLC network that best represents the measured R and XL of each channel (solid line) Since F/B is more sensitive to resistor changes than L variations, we forced the blue line to deviate only slightly, and gave the red line more freedom. Resulting circuit: 
Result of bestfit aproximation (created by Christoph Mayer)
P1 = 2,2 k P2 = 77 pF P3 = 192 uH (I use 2x 100uH fixed inductors in series) 