In article dSYVf.14404$6a1.2034@fed1read04,
"Caveat Lector" wrote:

"Tom Holden" wrote in message
...
"Caveat Lector" wrote in message
news:Y5WVf.14396$6a1.13272@fed1read04...
I refer you to the Elecraft page
http://www.elecraft.com/K2_perf.htm

Sez MDS = Minimum Discernible Signal (3db increase above noise
floor). Larger negative numbers are generally better, but too much
sensitivity can reduce strong signal dynamic range and Ip3.
Pre-Amp On MDS numbers of -130 dBm or more are more than adequate
for most HF band operating, since band noise is typically above
this number. (Lower frequencies need less MDS (more +number) due
to an increase in atmospheric noise.)


-- CL -- I doubt, therefore I might be !

I have no dispute with that. Rather with your first comment:

Just FYI: I see a lot of these mods to increase sensitivity --
resulting in trashing the dynamic range


Which of these mods do you think increase sensitivity at the
expense of dynamic range?

You did not answer the question. The answer may well be 'none'. I'm
not aware of any aimed at increased sensitivity, unless adding an
amplified preselector counts as a mod. And that could arguably be
for improved dynamic range and sensitivity by improving front-end
selectivity and noise figure. Most regard the DX-394 as a very
sensitive receiver that is outperformed in that spec by few others.
But itcould do with improved overload threshold and IP3.

Methinks you might be trashing imagined mods rather than the ones
well-documented in the user group.

I don't want to join this group as I don't own this radio. So I
didn't read any of the mods My FYI was a general info to be careful
of mods having to do with sensitivity. Perhaps there are none for
this radio as you pointed out.

I would feel much more comfortable if a modder would measure and
present all the receiver specs after the mod, one seldom sees that

So be careful, the mod you make - may or may not have been
thoroughly thought out and properly implemented

I double checked my statements with a friend who has designed
receivers of all types for many years and he concurs.

So be aware of what you are doing to the entire receiver
specifications when you make mod.

Case closed

I have not been into radio receiver design but it seems to me that the
radio as designed has a certain dynamic range and the mod Tom mentioned
would cause some loss. In this case some amplification would bring the
sensitivity back to what it was. This bandpass amplification example
should be able to improve the receiver front end as opposed to
broadband amplification. I have not looked at these modifications but
an additional preselection circuit with an amount of amplification to
make up for the preselection circuit loss should result in an overall
improvement. This certainly sounds like a good idea for a radio that
does not have a preselector circuit to begin with.

A more simplistic case of just providing more broadband amplification
where the receiver is already sensitive enough will plainly reduce the
"useful" dynamic range. Another example of merely providing this
broadband amplification to a receiver of poor sensitivity but good
dynamic range could result in an improvement.

Conclusion... it depends on other factors and what you are trying to
accomplish. The modifications would have to be judged on their design
and the state of the radio to begin with.

So... mods should be judged on a case by case basis.

--
Telamon
Ventura, California