[Elecraft] FW: Sherwood Engineering

[Edward R Cole]

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: k3ndm at comcast.net
To: "Burdick, Wayne" <n6kr at elecraft.com>
Cc: elecraft <Elecraft at mailman.qth.net>
Subject: Re: [Elecraft] FW:  Sherwood Engineering Tests
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         <1691035197.17114594.1424829382558.JavaMail.zimbra at comcast.net>
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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
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