[Amps] article in Nature, modified Aurora via HF
Gary Schafer
garyschafer at comcast.net
Mon Apr 18 11:59:24 EDT 2005
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
>
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
More information about the Amps
mailing list