Re: Newbie material on HF+(more)

Leif Asbrink
 

Hi Joanne,

3) Of course SDRs have the potential for extremely
accurate S-Meters. It rather falls out of the concept.
You write "It rather falls out of the concept." and
I can not understand what you mean.

You wrote "2) There are rather few radios in the hands
of hams that are accurate with their S-Meter readings."
and I disagree. There are many SDRs in the hands of
hams today - and most of them have extremely accurate
S-meters.

That makes sense. I think I'd go with signal peak
power less 3 dB to approximate the 1 RF cycle average
power. (Correct for peak to RMS on a sine wave
carrier.)
Well, I wrote peak power, but of course the meter
gives the peak RMS power since the detector is a
true rms detector. there should be no subtraction
of 3 dB.

Regardless of what units one presents the data in
amplitude and power have the same meaning for an
RF signal. What I wanted to say is that amplitude
might implicate a peak detector. Particularly
if we talk about a CW signal. Amplitude is likely
to be inthuitively interpreted as the amplitude
during keydown while power is more likely to be
understood as the average power. None of the
interpretations is formally more correct than its
opposite, when specifying "dB" or "dBm" for an RF
signal one has to specify the detector used.
Ah, but is it "instantaneous" power (peak voltage
of the sine wave squared divided by the impedance)
or an average power over either precisely one RF
cycle or a large enough number of cycles that the
error becomes small? Instantaneous less 3 dB is a
simple way with really fast modulation compared
to carrier frequency.
Sorry I did not express myself clearer. When I mention
peak power of an RF signal I ALWAYS mean peak envelope
power. "peak envelope power (of a radio transmitter):
The average power supplied to the antenna transmission
line by a transmitter during one radio frequency cycle
at the crest of the modulation envelope taken under normal operating conditions." I have always thought that this
is a common practise when talking about radio;-)

73

Leif

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