[Elecraft] KX3 - Does It need Preamp for 6M?

[Edward R Cole]

Using my eme path link program I compared using Jim's 1-dB cable loss 
to 100-foot of RG-58 (3.2 dB loss/100 at 50-MHz).
http://www.kl7uw.com/emelink.xls  (this downloads an excel file)

The limiting factor on 50-MHz is sky noise (from the Milky Way 
Galaxy).  That is approximately Tsky=2000 Kelvin
Using a K3 as reference with 500-KHz bw it shows 8-dB Noise Figure 
which translates to MDS = -136 dBm
1-dB coax loss:  0.5 dBNF preamp with 25-dB gain at antenna, MDS= 
-138.4 dBm, at radio MDS= -138.2 dBm
3.2-dB coax loss: preamp at antenna, MDS= -138.3 dBm, at radio, MDS = 
-137.7 dBm
(in the program MDS is given by Pn)

that is only 0.6 dB loss in sensitivity if you are using RG-58 on 6m 
(and who would do that?)
good old RG-8 loss at 50-MHz is 1.3 dB;  then the difference would be 
about 0.3 or 0.2 dB

If you are working 6m moonbounce, you might be concerned.  For 
everything else - it is insignificant
Hint* running 1000w thru RG-58 with 500w dissipated in the coax is 
probably not good, so doubtful one would use it on eme.

73, Ed - KL7UW
http://www.kl7uw.com
dubususa at gmail.com
"Kits made by KL7UW"