RadioBanter - View Single Post

February 5th 04, 05:35 PM

In article ,
(gudmundur) writes:

My current I.F. bandwidth is 8mhz at the 6db points. I am looking at pulses
of .8microseconds length, or about 1.25mhz. If all else remains the same,
and I change the swamping resistors, and tweak the slugs for a 1.5mhz I.F.
bandwidth at the 6db points, what increase in signal to noise ratio should
I see?

Signal to noise ratio changes as the _square_root_ of bandwidth
change. Wouldn't be much of an effect going from 1.25 to 1.5 MHz.

With 0.8 uSec pulses and a 1.25 to 1.5 MHz bandwidth (I presume
Mega Hertz, not milli Hertz), the output envelope will be very
rounded, almost Guassian or "cosine-quared" in shape. Rounding
happens because of the limitation of passing the harmonics of the
pulsed RF; all you have left is the carrier frequency.

The relatively narrow bandpass and pulse rounding MAY be okay
in your application. It wasn't stated. I spent some years on a
program that deliberately used 1 MHz bandwidth filters for 1 uSec
wide pulses on carriers 1 MHz apart. Interesting to see the effect
of "matched filters" on adjacent frequencies...those immediately
on each side came through with a reduced amplitude "bow tie"
envelope shape, the "knot" in the middle.

Len Anderson
retired (from regular hours) electronic engineer person