The circuit diagram published in the last QRPp for the Rainbow
Tuner shows R5 to be 51 ohms. The Parts List in the article
lists this as 10K, which is probably the correct value, since the
circuit shows C2+R5+C4 as being in parallel across R2 in the
comparison leg of the bridge. Since R5 is shown as 51 ohms, the
series combination of C2+R5+C4 would be around 51 ohms (at, say,
10MHz) and the impedance against which the antenna would be
compared would be more like 26 ohms, rather than 51 ohms. If
working from the article, please note the disagreement between
the diagram and the Parts List.
72, Chuck, K1CL
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