[Elecraft] K3 - Performance on 6M?

[Tom W8JI]

It has been said by many hams over the years that if you 
connect an antenna
to a receiver and you can hear the noise level increase, 
then you don't need
a preamp, as it will simply amplify the noise and the signal 
equally. In
general, I've found that to be true. HOWEVER...

Let's say that the noise figure of the receiver's internal 
preamp is 1.5 dB,
and the noise figure of the external preamp is 0.5 dB. Each 
preamp will give
you about 10 dB of gain. It seems clear that using the 
external preamp
instead of the internal one would give you another dB of 
signal+noise to
noise. Is my reasoning accurate on that score? If so, then 
it would be
useful to know the noise figure of the K3's internal preamp 
at 50 MHz. I
don't know what it is.>>>>


I don't know the figures of the K3, but here is how it would 
work out for some arbitrary numbers:

.5 dB NF preamp 10 dB gain to 1.5 dB amp 10 dB gain to 8 dB 
NF 8 db gain mixer. = 0.85 dB NF

1.5 dB NF 10 dB gain RF amp to 8 dB NF 8dB gain mixer = 2.89 
dB composite NF

There can be a larger NF increase than the difference in NF 
between the preamps.

I doubt any of us would actually need a 0.5 db NF with a 
terrestrial aimed antenna of normal beamwidth and gain on 
six meters. I certainly don't and I'm in a quiet rural 
location on a dirt road. A few dB NF is enough here.

What noise figure do other people **really** find they 
need?? Anyone know exact figures?

73 Tom