Not transistor saturation but mixer saturation where the RF input is
sufficiently that for a given LO level the IF output level is saturated
(ie doesnt increase (or increases very slowly) with increasing RF signal
level).
Bruce
li...@lazygranch.com wrote:
What am I missing here? Vce = Vbe, so the diode connected transistor isn't
saturated.
-----Original Message-----
From: Bob Camp<li...@rtty.us>
Sender: time-nuts-boun...@febo.com
Date: Sun, 9 Sep 2012 19:16:22
To: Discussion of precise time and frequency measurement<time-nuts@febo.com>
Reply-To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: Re: [time-nuts] HP10514B Mixer Terminations
Hi
….. and of course, once you go into saturation the mixer doesn't look much like
50 ohms any more. Sort of gets us back to terminations again.
Bob
On Sep 9, 2012, at 6:21 PM, Bruce Griffiths<bruce.griffi...@xtra.co.nz> wrote:
NIST have indicated that mixer PN noise measurements with a non dissipative
terminations (even RF) are intended to be made.
Using a discrete mixer using diode connected transistors may also be useful at
least for 5MHz and 10MHz input frequencies in that their flicker noise can be
significantly lower than for mixers using diodes. NIST used a simple diplexer
arrangement that terminates the RF sum frequency in 50 ohms whilst using a
reactive termination for the difference frequency.
With such a termination the minicircuits phase detectors had lower measured PN
noise than the 10514.
Another issue to consider is saturated or unsaturated (linear) operation of the
mixer.
Saturated operation, for most mixers, produces lower noise (flicker and floor)
however linear operation can have for some mixers lower phase shift tempco
which can be important depending on the environment and required phase shift
stability.
Bruce
Bob Camp wrote:
Hi
In general, you terminate the mixer in 50 ohms at the RF frequencies (say 10 and 20 MHz).
Termination at the "IF" (in this case audio) frequencies is what turns out to be tricky.
Any time you terminate a source in a high impedance, you get a higher output voltage. Reactance
rarely adds noise to a termination. With a DMTD, slew rate is the issue, generally mixer noise goes
up less than the slew rate increases with a "non-50 ohm" termination.
Bob
On Sep 9, 2012, at 4:41 PM, Bruce Griffiths<bruce.griffi...@xtra.co.nz> wrote:
David Kirkby wrote:
On 9 September 2012 18:28, Pascual Arbona<p.arb...@securimar.com> wrote:
Hello Brian,
I am a radio amateur and and also in the Time nuts list, At the
moment I am planning to bild a DMTD for experimentation. and as you have a nice
experience in this field , for me will be very wellcame your help. My ask is
¿whitch is te best temination for the mixer? (FI 10Hz or 100Hz) ¿what about
the amp, limiters and zero crosing detec.)
Mixers should be terminated in 50 Ohms - at least at all frequencies
where there is an output. Someone mentioned minicircuits. They sell
constant impedance filters, where the impedance in the both the
passband and stopband are 50 Ohms. Most filters have a impedance far
away from 50 Ohms in the stopband.
This is an often repeated fallacy.
For low IF frequencies such as in a DMTD, a reactive IF termination can have
the advantage of lower noise and larger IF signal slew rate.
The resultant reduction in RF and LO port VSWR is easily corrected (at least
for low RF and LO frequencies) with a series resistor and/or resistive pad.
There are a number of NIST papers on the effect of mixer termination for DMTDs
and phase noise measurements.
The minicircuits phase detectors (actually specialised mixers) are specified
for use with 500 ohm IF terminations.
I don't know the details of what you are trying to do, but keep in
mind what I said.
Dave
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Bruce
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
