The latest ARRL test of ICOM 756 PRO II shows reasonable HF RX sensitivity
figures.
Also notice significant PLL noise reduction. IMD3 leaves about 10 dB room
for improvement.
Most of the previous tests showed oversensitive RX intended for inefficient
antennas.
AGC action must be delayed on weak signals in order to preserve signal to
noise ratio.
Preamp might help during 10/15 m band openings with only weak signals
present.
NEVER increase audio gain as there are too many hams with impaired
hearing...
Contest later becomes the game of picking the weak ones among many strong
signals.
EU is the nice place to learn the game with all the BCI...
73 de Mario, S56A, N1YU
P.S. There was no need to correct my statement that antenna with more gain
picks more noise!
----- Original Message -----
From: "Scott Ellington" <sdelling@facstaff.wisc.edu>
To: <cq-contest@contesting.com>
Sent: Tuesday, January 08, 2002 8:15 PM
Subject: [CQ-Contest] Receiver Gain (Was TOP BAND RECEIVING ANTENNAS)
>
> Most HF receivers do not have enough gain for decent AGC action on weak CW
> signals. (The insertion loss of the CW filters can reduce IF gain
> considerably.) This is particularly so on 10M, even with a beam in an
urban
> location. These receivers are sensitive enough, but for any signal that
doesn't
> move the S-meter, you have to crank up the audio gain. We all know what
happens
> next, when a loud signal appears.
>
> I prefer that the overall gain be high enough that the noise just moves
the
> S-meter, so any signal will result in AGC action. The proper way to
achieve
> this is to have sufficient IF gain, which most receivers lack. If there's
an IF
> gain adjustment, one can turn it all the way up. This will change the
S-meter
> calibration, but probably not have any other adverse effects. It's
usually not
> enough, though. Unless you want to modify the receiver, a preamp is the
only
> alternative, but you'll have to switch it out when there are extremely
strong
> signals around. (I sense the purists cringing.) The front end of most
> receivers provides adequate sensitivity and excellent dynamic range, and a
> preamp will almost certainly compromise the dynamic range. Still, I find
I use
> the preamp almost all the time on 10 and 15M with either the FT-1000D or
TS-930.
> I probably don't hear any better, but it's a lot more comfortable, and
maybe
> I'll still be able to hear 30 years from now.
>
> Needless to say, the preamp is often required with lossy receiving
antennas.
>
> I agree with Tom that your receiver is sensitive enough if you can hear a
> significant increase in noise when the antenna is connected. Adequate
> senstivity, however, does not guarantee sufficient gain for good AGC on
weak
> signals. The AGC threshold could still be 20 dB above that noise level.
On the
> other hand, if your noise level moves the S-meter even slightly, you're
better
> off without the preamp.
>
>
> 73,
>
> Scott K9MA
>
>
> --
> Scott Ellington
> Madison, Wisconsin USA
>
> sdelling@facstaff.wisc.edu
>
>
> --
> CQ-Contest on WWW: http://lists.contesting.com/_cq-contest/
> Administrative requests: cq-contest-REQUEST@contesting.com
>
>
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