Re: K3 output buffer modification

Posted by N8LP on
URL: http://elecraft.85.s1.nabble.com/K3-output-buffer-modification-tp4262685p4269725.html

Because of the gain distribution, when the K3 preamp is on the improvement in overall noise figure due to the buffer mod is less obvious than when the preamp is off. The preamp dominates the noise figure when it's on, but the buffer loss dominates the noise figure when the preamp is off. Since it's generally smart to run with the preamp off on the lower bands, therefore, the mod is quite helpful for low band use.  

Larry N8LP

Bill W4ZV wrote

Jack Smith-6 wrote

The main reason one might wish to apply the buffer modification to the
K3 instead of cranking up the LP-Pan gain or purchasing one of my Z10000
buffer amplifiers is that a somewhat improved noise figure will result
if the K3's IF output follower loss is reduced. In practice, the
improvement in noise figure is not huge as the overall NF is set mostly
by the early gain stages in the K3.

Another reason to reduce transfer loss inside the K3 is that you're not forced to use the internal PREamplifier to compensate for the loss at IF OUT.  If you enable PRE to get more output to LP-PAN, you potentially risk degrading the dynamic range of the K3 itself by applying more gain than needed to its internal IF chain.

73,  Bill