The *Elecraft K3 *is one of the best performance commercial transceivers
available to amateur radio operators.
While discussing with some friends it's receiver performances we decided to
see if there were chances to improve it. When a receiver has a dynamic
range over 90dB it is not so easy to pull-out additional dBs.
One easier mod to experiment was the replacement of the 1st mixer.
This stage is located in a plugged PCB unit, avoiding the usual cut and
solder when implementing mods in commercial equipment.
A volunteer K3 owner was found and we implemented the 1st mixer replacement
using the *I7SWX 2T H-Mode Mixer with FSA3157.*A test was made with the
original K3 configuration and with the I7SWX H-Mode Mixer replacement.
K3 original configuration: preRF (OFF) preIF (OFF) BW (2,4kHz)
Rx Eq Flat
PRE-AMP OFF
MDS (Sensitivity) -126 dBm
IMD MEASUREMENT WITH PRE-AMP OFF.
Two Tones Spacing 5 kHz
DR (2 tone Dynamic Range) 98.0 dB
Third Order Intercept (IP3) 21.0 dBm
K3 with I7SWX 2T H-Mode Mixer as 1st Mixer
PRE-AMP OFF
MDS (Sensitivity) -128 dBm
IMD MEASUREMENT WITH PRE-AMP OFF.
Two Tones Spacing 5 kHz
DR (2 tone Dynamic Range) 101.0 dB
Third Order Intercept (IP3) 23.5 dBm
The Audio Noise at loudspeaker output dropped of circa 6dB
*It is important to consider these numbers as relative and not absolute,
although the equipment used for the test were not well calibrated, the mod
presents a benefit of around 3dB on dynamic range, from 98 to 101dB at 5 kHz
spacing, giving also a sensitivity increase of circa 2dB and an appreciable
drop in audio noise.*
Another interesting test was done with a Panoramic unit connected to the K3.
The antenna was connected to input 1 and the selection switched to input 2.
A screen copy of this test is reported in Files “K3 test w/o & w I7SWX 2T
FSA3157 H-Mode Mixer”.
The bottom part is with K3 original configuration. No signals are visible
and mainly front-end noise is seen.
The top part is with the I7SWX 2T H-Mode Mixer. You can see signals leaking
through the antenna switch capacity and some noise reduction.
A limited number of K3 H-Mode Mixer kit is being made available to
experiment this change.
For information you may contact Gian, I7SWX, at i7swxATyahoo.com.
The PCB view is reported in Files with the Panoramic file.
I hope you find this information interesting.
73
Sergio, IK8TNG
http://elecraft.365791.n2.nabble.com/file/n6812860/K3_test_wo_%26_w_I7SWX_2T_FSA3157_H-Mode_Mixer.rar
K3_test_wo_%26_w_I7SWX_2T_FSA3157_H-Mode_Mixer.rar
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