I use my '150 with the high impedance input, using a Radio Shack air core
loop antenna. My reason for this is so the input circuit doesn't load down
the loop............this way, I can take advantage of the unloaded Q of the
antenna. This provides a sharper tuning characteristic.
The preamp is good for very short antennas. Since it is a broadband preamp,
it sees many tones (signals). It has a relatively low dynamic range; its
multitone response is not very good. The result is that signals far removed
from your desired receive frequency can drive the preamp into gain
compression if their level is high enough.
There is another complication here........it doesn't have to be just one
strong signal. Several medium level signals, if their integrated (combined)
power is high enough, can also drive the preamp stage into gain compression.
There are two results that I know of that can happen. First of all, the
amplifier can appear to not have any gain at the desired frequency, and
second, since the distortion of the amplifier rises at the 1dB compression
point, signals can appear at different points on the tuning dial where they
are not supposed to be.
An example of this is with my AOR-7030. In the Chicago area, if I have a
long wire connected and the whip amplifier is engaged, I can hear MW
stations in the 15MHz range.
If you thing of the absence of bandwidth limiting in the same manner that
you think of the aperture of an optical system, things become clearer. If
you were to connect a sensitive RF power meter to a long wire antenna and
compare the power levels of broadband response vs bandwidth limited response
(preselector), you would see a lower level of integrated RF power with the
bandwidth limited response. This is the reason that receivers with input
filtering ahead of the 1st stage perform better than receivers with a wide
open front end. There are exceptions such as the Racal 6790, the WJ
receivers, the AOR7030, and other receivers in the "premium" catagory, but
even these units would perform better with some sort of preselection.
My definition of preselection can be either a tunable form or fixed tuned
lowpass, highpass or bandpass circuits.

Pete

"Lucky" wrote in message
...

"RHF" wrote in message
oups.com...
Lucky,
.
If the Whip Antenna's SO-239 Jack and Pre-Amp 'position'
work together; then you could use a Shielded Coax Cable
Loop Antenna instead of the Whip Antenna connected to
the SO-239 Jack and switch-on the Pre-Amp. Consider
to possibility . . .
.
iane ~ RHF
. . . . .


But, if you put the antenna switch to "Norm", you can use the 239 jack
without the preamp according to the manual. This is what I used to use
when I first got it. I rarely used the long wire spring antenna terminal.
So again why a loop with the preamp??

I wonder what antennas most people use on their 150's? The wire spring
terminal or the coax socket and why??

Lucky