The device in the preamp may not have the greatest noise figure to
start with. Most preamps used in those type installations are usually
more concerned with signal handling ability, so as not to produce
intermod, rather than the last ounce of signal to noise performance.
It is difficult to have a device that will give you maximum signal to
noise performance along with excellent intermod performance. Often a
preamp is used ahead of power dividers to feed several receivers and
it is there to make up for the losses in the power dividers and not
necessarily there for the sole purpose of improving signal to noise
performance.

When comparing how it is performing you need to actually measure
sinadd or quieting of the receiver to tell if it is giving you any
improvement. Just looking at stronger noise levels on the receiver and
guessing how much the signal is above the noise can be very
misleading.

73
Gary K4FMX


On 13 Apr 2006 14:49:28 -0700, "
wrote:

Im guessing at the noise figure, im running a low level 1mv fr0m a
cushman service monitor to the preamp input. Im using a uniden 898t
scanner as a receiver because it has a digital S meter. When i turn on
the preamp jumps up 3-4 bars
but the modulation tone stays the same volume level. By this im
guessing the noise level has increased, the preamp had a ceramic
filter with the 50ohm input going directly into it and its output thur
cap to the 1st amp, the seller on ebay said just remove the filter and
move the input to the filters output trace, thats what i done but
results are poor even thou this is a commercial preamp pulled from
analog cell site. It looks to be a very well made preamp so it should
work if i figure out the
input match?