Re: Microwave Noise


Andy G4JNT
 

And to add to that, multicarrier systems like OFDM obey all (I think; certainly 'very nearly all') the tests for a Gaussian noise waveform.    Even a comb of a large number pure sinusoids does.

The question really came about after reading an article in the latest QEX about noise monitoring and WSPR, where they use two methods of measuring noise, both of which I've adopted in the past.   The RMS of the time domain signal, measured during the quiet period of no WSPR transmissions.  And the FFT techniques where the bins are put into order of power and noise deemed to be the level in the bin at the 30% point ( I use the lower quartile plus 5dB - thoughts on this differ but the delta is minimal)

In that article they mention that often the two measurement methods give significantly different results, and at other times are very close.   This is put-down to the non-Gaussian nature of noise at HF.    Hence my thoughts at higher frequencies.



On Wed, 16 Sep 2020 at 12:20, Chris Bartram G4DGU <chris@...> wrote:

An interesting question, Andy, and quite complex to answer. What do we mean by 'noise'?

Gaussian noise is the effect of random (stochastic) processes. The 'noise' generated by radio systems tends to be cyclic, albeit sometimes in a rather complex manner, but is still non-stochastic, particularly after filtering, and is thus not strictly Gaussian!

Professional transmitters - and that includes mobile phone systems - are designed to very high standards with regard to noise outputs, and usually have extensive filtering to allow co-siting of transmitters and receivers. A lot of the 'noise' from other services detected in amateur systems seems to me to be a function of reciprocal mixing, and even-order intermod taking place in our receivers. IMD2 ... is rarely considered in amateur receiver design.

73

Chris G4DGU



Andy G4JNT wrote:
Until recent years we can safely say all received noise on the uWave bands was purely Gaussian, unlike at HF where its can be moe spiky in nature.

With some of our QRN now coming from Cell Phones and other transmissions, is it still the case the noise can be considered Gaussian?  

What about VHF / UHF ?

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