> it's single conversion. The thing that has really surprized me is
> that, at least for me, I don't find all this hash or whatever one
> might call it on the 756 PRO - I have used the PRO for hours and do
> not get the listener's fatigue I hear people talk about.
One problem with comparing things is many of the effects are
subjective, like "fatigue". One person might be bothered by
something that won't bother another person at all.
The other major problem is our locations and operating habits vary.
If we live in a quiet location, use narrow filters, have directional
receiving antennas, and work weak signal DX receivers that might
make someone else very happy can "fall apart" and be useless.
For example, I can't (and MANY others can't) use receivers with
low gain much of the year when working weak-signal CW on my
receiving antennas, even with a 10dB gain distribution system
ahead of the receivers. A low-gain receiver, like an Omni-6 or an
Elecraft, can not get down into the external noise floor. The AGC
won't do anything, and I have to crank the volume wide open.
On wider bandwidth, like 2 kHz or wider, most receivers are OK
because the noise power is 10dB more than with 200Hz selectivity.
On my TX antennas, even so-called "quiet antennas", lower gain
receivers are OK because the noise power summed from all
directions is higher and the antennas provide a bit more signal
level.
Bottom line for gain is you should be able to hear the noise
increase a noticeable and clear amount when you connect the
antenna on the quietest day using the narrowest filter. If you can
not do that, then your system is gain limited under those
conditions.
As for ringing and other flaws, the number of conversions is not the
problem. The problem is how well everything is designed and how
well the system actually works.
Most receivers seem to be planned for SSB bandwidths, urban or
suburban locations with modest or high local noise, and TX
antenna noise levels. Most important, few of them are better than
around 80dB for close-spaced blocking and dynamic range...and
many are worse. 80dB DR is very marginal in quiet locations on
low bands.
I'd bet most receiver filters are never tested for group delay errors,
or ringing.
If the filters ring (for whatever reason) sharp rough noise pulses are
stretched into longer pulses that are more destructive to
readability. Some similar filtering systems are better, some are
worse. The IC751A's 250Hz crystal filters are useless with any
sharp noise, because they ring. The "Drake" 250 Hz crystal filters
in my solid-state modified R4C's are useful under almost any
condition, even though the stock R4C receiver is a VERY poor
performer.
73, Tom W8JI
W8JI@contesting.com
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