Topband: FW: The WD8DSB mini-flag antenna (LONG!)

[Don Kirk]

Hi Jim and gang,

I would like to make one minor correction and then add some more info.  On
my SDR receiver I should have said I increased averaging from 1 to 10 in my
previous post (not 2 to 10) and this really made the noise floor drop and
smooth out and this really helped expose the signal of interest on what I
call the RF Spectrum Display.

I just ran another simple test to understand how my SDR receiver responds
to changes in the averaging value.  Averaging does indeed improve the
signal to noise ratio when looking at what I call the RF Spectrum Display,
but it does not change what I see in the waterfall display.  What's amazing
with averaging is a signal that I can't see in the RF spectrum Display when
average is set at 1 suddenly is 5 dB over the noise floor when I set
averaging to 10.  The peaks of the noise floor drops by at least 5 dB (and
really smooths out) which exposes the CW signal I am generating locally for
this test of the averaging function.

Sorry to take up so much bandwidth on the topband reflector, but it really
is an interesting discussion.

Just FYI,
Don (wd8dsb)



On Thu, Feb 25, 2021 at 11:24 PM Don Kirk <wd8dsb at gmail.com> wrote:

> 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 at 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
>> _________________
>> Searchable Archives: http://www.contesting.com/_topband - Topband
>> Reflector
>>
>