Owen Duffy wrote:
"Because active SWR meters do not usually suffer from this effect, they
can normally be left in withoout causing such problems."

Ordinary meters needing only r-f to power their indicators can also be
left in the line with no visible effect because their demand for r-f is
very small.

Insertion loss is specified in the Bird Model 43 Instruction Book
between the 50-ohm line and sensing circuitry. Specification is 53 dB
down between 512 MHz and 20 MHz. Coupling decreases to 70 dB down
between 10 MHz and 2 MHz.

The 30 microamp d-c meter and its associated circuitry need negligible
r-f power from the line for nearly all ranges.

60 dB is a power ratio of one million to one.

Best regards, Richard Harrison, KB5WZI