Hi Gian,
Your messages have arrived!!
Giancarlo Moda [EMAIL PROTECTED] wrote:
on Wednesday, May 09, 2007 2:48 PM
Geoff you are right. Certainly the H-Mode Mixer has
higher IMD performances then TUF-1 and NE602.
Some friends in Italy had problems with K2 (and also
K1) on 40meters during contests using good antennas.
This is how the idea of trying to improve the K2
started.
I experience the same problem here with the K2 on 40m all the time when the
BC stations above 7100 kHz are being received at S9 ++, and have to use
another receiver which uses H-Mode mixers etc.
Certainly the worst performance is in the post mixer
amplifier and this is the reason why the idea of the
simple 2 xtal roofing filter was implemented. THe
following bandpass xtal filter is protecting the IF
and demodulator stages.
Understood. Without running IMD tests on my K2/100's receiver and its IF
cascade I can only guess that this might not be enough protection when the
BC station carrier levels are up in the -10dbm region, and you are trying to
copy a signal that is in between them. This is the situation that I have
when using SSB between 7150 and 7197 kHz. The situation improves of course
if the beam is pointing away from the BC stations. There is also the
question of roofing filter linearity and Rx phase noise. There is not much
that we can do about BC station Tx phase noise!
Although you may have not "enough improvements"
because the stahge is limited by the phase noise ... I
believe it is better than having both the mixer and
the PLL limitations.
Understood!
NO. The H-Mode Squarer has a balance adjustment and
you do not need to put your hands in the PLL. Also the
HMM require 0dBm drive or less, so youmay have less
spurs. The BFO 50-50 balance is not necessary as the
LO frequency is low and the squarer gives quite a good
50/5o outputs.
I understand, but I was looking at the Squarer as part of the circuitry to
be added to the K2's LO (VCO) *output* which provides injection to the TUF-1
mixer.
--------------------------------------------
From your second message:
The H-Mode Mixer is not sensitive to impedances
terminations like a classic diodes d b mixer,
particularly to the LO. Even the IF output when loaded
with a variable load like a xtal filter does not
reduce too much the IP3 (tests give between 5 to 10dBm
changes.. i.e from +40dBm to +35 or +30dBm as second
of type of filter.)
Agree about terminations, but there is a limit!! The SD5000 FET array (now
obsolete) with three transformers yields an Input IP3 of +50dbm or better at
the worst case input levels below compression, but my test equipment is
becoming stretched. Perhaps the newer arrays will provide the same
performance.
Certainly the filter is a good filter but if IMD is
reduced in the TUF-1 or more in the 2N5109 post mixer
amplifier, the IF filter cannot do much.
Have you measured the filter's input IP3 with the varicaps' back bias at the
minimum value used?
Good luck and many thanks.
73,
Geoff
GM4ESD
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