GM Ed. Certainly a better choice when it comes to conversion loss. I've
built a half dozen SD5000 mixers and although at least one of them managed a
measured +50 dBm Ip3, (G3SBI measured it not me!) I never managed to get the
conversion loss below 9 dB and more often 10. Conversely, the 3125/ family
readily does 4.8 dB conversion loss thanks to the very respectable Rds on.
REALLY simplifies things in the front end department, to at least 30 MHz,
with attention paid to the front end filters, you can get away without an RF
amplifier.

Regards
W4ZCB

Hi all,

Harold, W4ZCB, has given some "comments" on the H-Mode Mixer that are
REAL and TRUE.
G3SBI has removed the mixer from the stages that are critical on a
receiver and in the CDG2000 project it was demonstrated the IMD due to
passive components like core of coils. The FST3125 fast bus switch has
lowered the conversion loss of the H-Mode Mixer and made the RX front
end "hot", although not reaching the IP3 of +50dBm it still has plenty
of +dBm to give ...around +40dBm!You can permit yourself to add a xtal
filter behind the h-mode mixer and still getting high numbers on IP3.

If you are looking for a low consumption and simple mixer you may go OK
with the classic NE/SA602 and similar ones. BUT ... if you are looking
for high performance you need the H-Mode Mixer in the 3 transformer
G3SBI or the 2 transformer I7SWX configurations.
The H-Mode Mixer has been tested on downconversion (CDG2000, STAR
projects) and also on upconversion projects (I7SWX). For upconversion I
have devised a new squarer using LVDS and test it at IF of 35 to 70 MHz
(and 100MHz) with conversion loss around -5dbm and IP3 between +35 to
+40dBm (3.3V FST3125).
The H-Mode Mixer has been tested for RF input up to 50MHz in RX and
converter to 27-28MHz IF.
At 144MHz it performs like a standard diode db mixer having a conv loss
around -8dB. The input limit is due to the internal gates timing and
unbalancing as the FST3125 may have a bandwidth between 300 to 400MHz.
For those interested I may suggest a visit to JA9TTT web page where he
has reported measurement on both G3SBI and I7SWX versions using the
74AC86 squarer with balance adjustment. The comments are in japanese
but a translator is making the reading understandable :
ja9ttt.homedns.org/. I have posted a copy in my web page
www.qsl.net/i7swx in the subdirectory homebrewing. JA9TTT page permits
to enlarge the spectrum analyzer screen pictures.
I have also developed a 1 transformer double balance
mixer/demodulator/modulator using the FST3125 and 74AC/HC86 squarer
with an IP3 of around +25dBm.
Notes on the H-Mode Mixers and 1T DBM have been reported in RadCom,
G3VA's Technical Topics column.
For those interested on more detailed information I can make available
notes in English and Italian. Please write to my e-mail address:.

73

Gian
I7SWX
F5VGU
W1-I7SWX
G-QRP #10241
I QRP #571