Re: [Discuss-gnuradio] BER over air

[Iain Young, G7III]

On 28/12/14 16:41, Marcus Müller wrote:

> I have to stress this: SNR is *signal* to noise ratio. Signal is what your
> application defines to be signal!

_THIS_

The Signal is what you want to hear. Whether that be a nice square wave
from MSF, DCF, WWV, or where ever at a nice 1bps, or 802.11 PSK, or
1200 baud AFSK, or whatever, *everything else* is noise.

That noise *will* be coming from the earth, the sun, the universe,
pickup from your downlink cable, any mast head preamps or anything else
that happens to be around.

It will also include your next door neighbour doing experiments not
far from your chosen frequency, or anyone else local using an adjacent
channel.

Even if there is an intended signal, it can still be noise.
Take for example, a "ham" station working a remote station quite
nicely.

Then 2.5kHz away, some other local ham station keys up with 1500W. No
longer can the remote station be heard, due to the noise floor rising.

It's nothing to do with the receiving station becoming less sensitive,
or the transmitting station dropping power, but simply that the
receiving station's noise floor has risen, thus his SNR has dropped
significantly (more likely massively)

The fact that the 1500 Watt station was working a station the other
side of the globe *does not matter* to the original station's ability
to receive the station he was working.


A further example. TDF is an AM station that transmits a time signal
(like MSF, DCF, WWV). But due to this being an AM station they can't
modulated the AM carrier, so they twiddle its phase.

In trying to decode (And yes, for those following my posts over the
months and years I've now managed it!) the time data, all the AM
modulation, music, and speech is all noise. I have to filter it
out.


73s

Iain