On Dec 11, 11:06 pm, "AI4QJ" wrote:


I think you were right, it is a front end overload issue. But I think adding
an attenuator that simply reduces all input signal strength in a linear
manner does not act the same as de-tuning.

My vote is that they act the same. I've never seen any indication
that reducing the length of wire, or applying a mismatch, or even
using a step attenuator act any differently than one another.
All decrease the level in a "linear" manner. IE: all three
treat noise no differently than any other desired signal.
RF is RF is RF...

Comments from others on their
experiences would be interesting. It is easy enough to try out out; just
find a strong 75m station and using a tuner, tune out the noise and see if
you can still receive (and more pleasureably). Is this the same as
attenuating all input signals 20dB? I lack a technical explanation and we
haven't agreed that the effect is real so I will drop out of this discussion
unless someone else wants to pick it up.

Due to receiver quirks, it's possible the radio might not sound quite
the same using the two methods, but still, a 20 db decrease in
level is 20 db no matter how it is done. It will decrease noise
and desired signals in an equal manner as far as the
fundamental frequency is concerned. So my vote is yes.
They do the same at the end of the day.
Most radios have way more level than they need.
I've never seen *any* antenna that could magically weed noise
from desired RF without making use of a directive pattern.
As an example, many claim full size loops are quieter than
dipoles on the lower HF bands.
But I've never seen it myself. The only way an antenna can receive
less noise, and not reduce the level of the desired signal is
with directive gain/nulls. And if a certain noise signal say to the
south is reduced on a loop vs dipole, you can bet a desired signal
in the same direction and polarity will be reduced also.
There is no free lunch.
Of course, if you were in the high mountains and had corona
buildup ala HCJB, a loop may well be quieter than a dipole, but I
consider that a rare case, and not applicable to most average
hams.
In most all cases, the receiver just sees a 20 db drop in level.
It has no idea how it came about, and the end result should
be the same as long as directive gain or nulls don't come into
play.
MK