Hi Jim,
It’s funny that you brought up this topic as yesterday when I was doing
comparisons of the signal I could hear on my 160 meter vertical TX antenna
versus my portable flag, I increased the averaging value on my portable SDR
receiver connected to my portable flag and the signal that was barely
visible on the RF spectrum display when using my portable flag suddenly
stuck out like a sore thumb when I increased the averaging value from 2 to
10 (the peaks of the noise floor dropped way down and smoothed right out).
This was a signal that was only 0.6 S units above my noise floor on my
TS-180s using my TX vertical and 1.0 S units above my noise floor when
using my half size pennant. I’m indeed able to see signals using my
portable flag with the DX engineering preamp that are not much above my
main stations noise floor (but I don’t know what my main stations noise
floor really measures, nevertheless I don’t consider it abnormally high).
I will try and determine my main stations noise floor as time permits.
Just FYI, and 73.
Don (wd8dsb)
On Thu, Feb 25, 2021 at 10:40 PM Jim Brown <jim@audiosystemsgroup.com>
wrote:
> On 2/25/2021 5:16 PM, John Kaufmann via Topband wrote:
> > The P3 averages power, not amplitude, so using longer averaging times
> just
> > smooths the display and doesn't reduce random noise.
>
> It has nothing to do with power. Last I looked, the P3 is reading and
> displaying the instantaneous voltage in the IF, and can be calibrated to
> voltage at the input.
>
> I've been doing swept measurements of complex quantities for nearly 40
> years, first at audio frequencies and now at RF. Averaging DOES cause
> random contents of a bin to approach zero (or the noise floor), making
> correlated signals stand out. This has long been well understood.
>
> I the principle to measure the dynamic response of broadcast signal
> processing in a peer-reviewed paper to the Audio Engineering Society in
> 1986. The test signal was a swept sine embedded deep in musical program
> material to the point that it was barely audible to a trained listener,
> and detected by a synchronized swept narrowband detector. Because the
> swept excitation and swept detector are synchronized, the measurement
> produces the complex response of the system, and program material, being
> non-coherent, averages out.
>
> http://k9yc.com/AESPaper-TDS.pdf
>
> 73, Jim K9YC
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