[Elecraft] K2 KX1 K1 More advice sought on Elecraft radios

[Daniel Paul Perez]

Happy New Year 2009 everyone!

Thanks for your answers so far.  Yes, I was aware that Wayne N6KR 
designed both the 40A and K2.  I was simply amazed to receive an offline 
email from him, given the demands on his time!  I asked Wayne if I could 
share the following:

Wayne wrote that he “optimized the NorCal 40A for best noise figure by 
using ideal coupling to a gilbert-cell multiplier (NE602). Normally the 
exceptionally low MDS of the '40A (around -143 dBm) would be wasted on 
40 m, but with short, low-gain, tuned whips, it could make a difference 
because the antenna is very lossy.”

“Contrast that to the average 40-m station, which uses a full-length 
40-m dipole, or -- noisier still -- a 40 m ground plane. In this case 
the noise floor is probably 15-20 dB higher than the short whip, so the 
MDS of the receiver won't matter. At least on 40 m.”

“While the low NF of the NC40A is nice, the NE602 is a very weak mixer, 
so it can't be used in the front end of a high-performance rig like the 
K2 or K3. Thus these rigs use switching mixers. The K2 uses a 
conventional diode mixer and preamp, resulting in an MDS of about 6 dB 
worse than the 40A, but about 20 dB better dynamic range. The K3 uses a 
custom, low-loss switching mixer and an extremely low-noise preamp and 
synthesizer, so its MDS is only a few dB worse than the 40A's. But its 
dynamic range is 10-20 dB better than the K2, and thus 30-40 dB better 
than the 40A! “

What I am trying to grasp now is -- what is the relationship between the 
MDS and the blocking dynamic range and third-order IMD dynamic range in 
terms of listening experience?  Also, how does the absolute IMD level, 
and the difference between IMD level and blocking level translate into 
the listening experience?  Is a lower relative IMD level a quieter 
radio?  I have the sense that the depth of the IMD level and the delta 
between IMD level and blocking level create a quieter experience?  I’m 
looking at “QST Product Reviews: A Look Behind The Scenes”  QST October 
1994, pp. 35 figure 2 found on the Elecraft site.  If two radios with 
the same absolute BDR and IMD dynamic range but different MDS levels 
would one want the lower MDS?

If the 703+ has an IMD level of -50? this is between the 40A -68? and 
the K2(-41?)/K3(-34?) both higher, what does this indicate?

Wayne also explained:  “Once you have full-size antennas up, MDS will no 
longer be the limitation. You'll need better dynamic range “

Can someone help me understand these receiver comparison concepts?

Are these right?

NC40A
-143 mds
? bdr
75 imd
Imd level -68
Blocking level

K2
-136 mds
126 bdr
95 imd
Imd level -41
Blocking level -10

K3
-138 mds	
140 bdr
104 imd
Imd level -34
Blocking level -2

703
-141  mds
122 bdr
91 imd
Imd level -50
Blocking level -19

K1
Mds >40A and <K2
?

KX1
Mds >40A and <K2

	Best,

Dan Perez
AD1P