[RFI] Re: Why we badly need "party line" materials for all hams

Ward Silver hwardsil at centurytel.net
Mon Jul 19 23:05:12 EDT 2004

> Almost any ham has the ability to provide useful data. All he has to do
> 1.) Use a step attenuator to calibrate the dB change in his particular S

Here's an alternative that is less accurate, but still better than raw

Have a nearby friend with a power meter transmit a signal that is capable of
reaching S9.
1) Increase the transmitted signal to a received signal strength (RSS) of S9
and note the transmitted power.
2) Halve the transmitted power and note RSS in S-units.  This is a change of
three dB.
3) Repeat step 2 until the transmitted power measurement is unreliable (say
less than 10% of full-scale on a Bird meter).
4) Change the antenna system - either point the antenna somewhere else,
change antennas, or switch to a load.
5) Adjust transmitted power until RSS matches the smallest reading of step
6) Halve transmitted power, note RSS, and repeat until no further power
reduction or antenna changes are possible.

This gives a sequence of 3 dB steps starting at S9.  The transmitting
station needs to be close by and the RSS stable during the measurement
period.  You could also start at a weak signal and increase signal strength.

It might also be possible to calibrate this way over a narrower range and
use the adjustable attenuator on the radio to measure wider ranges.  That's
a more difficult measurement and prone to error if you haven't done it

73, Ward N0AX

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