RadioBanter - View Single Post

March 9th 05, 05:39 PM

In article ,
says...

gudmundur wrote:
This is on a 10 gig receive setup. There is no LNFE, just antenna
to mixer direct couple in a balanced waveguide mixer assembly.
The question is, if I remove the 1N23E/1N23ER pair, and go with a
balanced set of schottkey microwave diodes, this would allow me to
drop my local oscillator injection perhaps 6db. Will I see any
increased sensativity, or should I just keep the 1N23 setup?

wow, those 1N21/23 diodes are stone age! They are Germanium diodes
and usually have to be biased for lowest noise, best conversion
figure. Also when used in cavities, the diode itself forms part
of the coupling network. The letter in the diode part is a measure
of noise figure, the higher up in the alphabet you go, the lower
the rated noise figure. BTW those diodes a dated from the
1940's!

Yes, they were used in WWII radars with 2K25 klystron locals,
and we call that generation 1, in the late 70's they quit using
ATR/TR tubes on the lower power stuff, and went with circulators
and diode limiters, but the 1N23E/R remained firmly rooted in these
gen 2 radars until the late eighties. Gen 3 brought about the LNFE/MMIC
front end with a double balanced mixer featuring I/Q phase rejection
in the mixer stage producing I.F. output only when the local osc is
above the incoming signal. These front ends have about 6db gain over
the broadband 1N23 setup, and are much quieter, giving about a 10db
better SNR overall. So now the little Gen3 2.2kw units see targets that
the old 4kw units never could!

Yes this is some older stuff I have, a mid eighties radar front end
with a 10gig hamband gunn local, now back to our regularly scheduled
question, Should I buy $70 worth of matched schottkey, or $40 worth
of 1N23EMR. I have to buy something, my old crystals are way shot!!