Barry,
Yes, remembering the pentode front end of my AN-ARC1 (modified for 2m
AM) had a horrible Noise Figure (which impacted receive
sensitivity). One could probably have a better NF with today's
double balance mixers (which are commonly now the front end of HF receivers).
This is done for best Blocking Dynamic performance. HF bands may
often have -115 dBm noise levels (or higher) so sensitivity is not
the main thing driving the design. Lower sideband noise of the new
synthesizer will directly improve operating in a crowded band.
For what I mainly do in ham radio, low noise figure is mandatory and
sensitivity levels like -170 to -180 dBm are strived for. I am
talking about eme (moonbounce). As frequency gets higher, sky noise
drops rapidly so that receiver internally generated noise becomes the
limiting factor. But low phase noise from the LO is also important.
It is still somewhat controversial whether that is only in presence
of strong adjacent frequency signals or even important for other
reasons. I will update my K3 because its possible, so if that has
potential of improving my weak-signal ability, my station will
benefit. Synthesized PLL LO's are beginning to replace xtal LO's in
microwave equipment and particular attention is given to low phase noise.
I see the new synth as only good stuff, and spending a couple hundred
bucks to keep my 5-year old radio up to current technology is pretty
cheap, vs having to buy a brand new radio to get it.
73, Ed - KL7UW
--------------------------------------------
From: [email protected]
To: "Burdick, Wayne" <[email protected]>
Cc: elecraft <[email protected]>
Subject: Re: [Elecraft] FW: Sherwood Engineering Tests
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=utf-8
I'm old enough to remember that the most important characteristic of
a receiver was sensitivity. Nothing else seemed to matter. Some
receivers of the time had 2 RF amplifiers to make sure that they won
the sensitivity battle. And, what would happened when a strong
signal, not necessarily S9, would appear, bad things happened to your
radio. At this point I won't define the date.
This lunacy was being looked at by a number engineers, to include Dr.
Ulrich Rhode, W2 something. I forget his call. He said in a series of
papers in professional journals and Ham Radio Magazine that
sensitivity was not the most important parameter at the time. It
would turn out to be LO noise sidebands and dynamic range. That still
holds today, and now, IMHO, ultimate rejection should be added. All
of this is shown in Sherwood's data. What this all means is that all
of the receiver parameters must be looked at to decide what makes a
great radio. I suggest a review of some of Rhode's papers. His
writings make extremely interesting reading as it addresses this
discussion directly.
73,
Barry
K3NDM
73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[email protected]
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