Frequency Modulation Of Free Space R.F. Signals

We have modified the frequency of a propagating R.F. signal using a pulsed plasma discharge. In our experimental work, we have utilized two frequency shifting mechanisms. The first is to use the plasma as an nonphysical plunger to upshift the frequency of the signal. Theory indicates that the frequency shift for one bounce should scale as f
_r
= f
_t
(1 + 2 V
_p
/c + . . .) where f
_r
is the frequency the receiver observes, f
_t
is the transmitter frequency, and V
_p
is the velocity of the plasma stream. This also contains the higher order terms in c
^-n
but they do not significantly affect the result when V
_p
<< c. Using this method, we routinely observe frequency shifts of 0.2% from the original signal. The second method uses the phase velocity increase of a plasma growing in density to change the frequency of the incoming radiation.