Re: [Amps] article in Nature, modified Aurora via HF

[Gary Schafer <garyschafer@comcast.net>]

But the issue is one of gain "expansion" not of compression. Does 
expansion produce the same kind of distortion that compression does?

73
Gary  K4FMX


Bill Fuqua wrote:
>        I think the real issue is being missed there. The real test of 
> non-linearity is the production of harmonic and intermodulation distortion. 
> This means allows measurements of nonlinearity as small as a very small 
> fraction of a percent. Even to a part per  million with very specialized 
> equipment.
>        If  there were nonlinear propagation the RF spectra would be 
> unusable.  The apparent increase in signal strength could be  in 
> perception.  Which has to do with your reference.  On receive, a signal to 
> noise ratio of 0 db would be unintelligible but a 3 or 6 db increase in 
> signal would provide lots of improvement.  And are you measuring signal or 
> signal+noise?  It comes down to this. If no harmonics are produced and no 
> intermodulation products produced between the transmitting and receiving 
> sites the propagation path is linear.
>       Now, if you should be unfortunate enough to have a thermonuclear 
> blast between the transmitter and receiver you would have lots of 
> nonlinearity.  This is due to the greatly ionized region (large volume of 
> plasma) due to the blast. This scrambles signals and presents all sorts of 
> problems for those trying to use RF communications.
>       If you want to do such an experiment arrange for two stations near by 
> to transmit a KW signal and then look for the intermodulation products at 
> the far end of the path.  From that you can calculate the degree of 
> nonlinearity.  Don't use stations are close enough that there may be mutual 
> coupling between their antennas and sending a 2 tone test will not work 
> either because the degree of nonlinearity that you are looking for will be 
> very very small. But don't forget. There is also nonlinearity in your 
> receiver as well. But all of those sources of nonlinearity are  small 
> compared to the nonlinearity that would produce several db increase in 
> receive signal strength over the change transmitter output power.
> 
> 73
> Bill wa4lav
> 
> 
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