Posted by
ik8tng on
Sep 21, 2011; 7:40am
URL: http://elecraft.85.s1.nabble.com/K3-test-w-o-w-I7SWX-2T-FSA3157-H-Mode-Mixer-tp6812860p6815176.html
Hi Wayne,
Thanks very much for the prompt comments, very much appreciated. I have discussed your points with Gian, I7SWX.Hi Sergio,
Thanks for reporting these interesting results.
A few K3 users in extremely high-signal environments might benefit
from a few extra dB of dynamic range, at the cost of a mixer add-on
module like you described.
This is one of the reasons why we tried the mod and also to see how much a good K3 could be improved, we are homebrewers… hiHowever, I'd be concerned about the possibility of additional mixer
spurs. Switching mixers put out a large number of VHF/UHF spurs that
can mix with harmonics of other signal sources (primarily the VFO) to
produce HF-6 meter spurs. This is an inherent issue with high-level
superhet receiver designs.
Our first mixer design trades about 1 dB of dynamic range and
conversion loss for excellent rejection of mixer products above 60 MHz
by integrating a balanced low-pass filter into the commutating path.
Without this, there would be a "picket fence" of additional VHF/UHF
products and thus many more spurs.
This is a very interesting note. We have not thought about VHF-UHF additional products and spurs. The H-Mode Mixer has the mixing function done by the transformers and the FST/FSA Switches are not involved in the signal path. The 2T H-MM has an RF-LO isolation of >50dB, average 60/70dB, while the RF-IF isolation is >60dB. We believe that the Band Pass Filters in the K3 are good enough to attenuate strong signals outside their bandwidth. Please let me know if you do a comparison test of the two mixers in
this regard. The best way to do it is to slowly sweep through each ham
band in CW mode using a narrow crystal filter.
We will see to manage some comparison with the two mixers. we have to see about the filter.
For some infos on the 2T H-Mode Mixer you may visit http://martein.home.xs4all.nl/pa3ake/hmode/2t-hmode.html but probably you do know the site.
Thanks again for the comments.
Best 73
Sergio, IK8TNG73,
Wayne
N6KR