[time-nuts] HP10514B Mixer Terminations
Brian Kirby
kilodelta4foxmike at gmail.com
Tue Mar 30 10:36:06 UTC 2010
Wavetek/Rockland 5120A Synthesizer.
EWKehren at aol.com wrote:
> Good morning Brian.
>
> What do you use as an OFF SET oscillator?
>
> Thank you
>
> Bert Kehren Miami
>
>
>
> In a message dated 3/29/2010 11:31:15 P.M. Eastern Daylight Time,
> kilodelta4foxmike at gmail.com writes:
>
> Your correct - your also keeping me up past my bedtime !- I got to
> be 90
> miles from home tomorrow morning by 7:30 AM....
> It looks like I got the squarest wave at 150 pF. Lesser
> capacitance,
> give a peaked sinewave, like maybe a second harmonic. Past 200 pF,
> it
> starts rounding. 150pf= XC of 53 ohms....
> This DMTD system, will only go to 100 hertz maximum beat for my
> design...
> The scope is set to 100 mV per div, 1ms per division, I
> intentionally
> mis-triggered it to show rise and fall times. 100 hz beat signal.
> ANd
> Bruce told me how to calculate slew rate, but it has to be beated in
> my
> thick tough head.....
> And Bruce, I'll try some coax tomorrow, if I get back home early
> enough
> - my work project may keep me late. And I plan to only use this
> system
> to 100 hertz beat, I was just playing around at 1K.....I like
> learning.
> Good night.....Brian....KD4FM
> Bob Camp wrote:
> > Hi
> >
> > You can get a *much* more squared output from the mixer than the
> photos you show on the scope. The waveform looks a lit like a
> triangle wave with the tips chopped off. Normally the fastest edge
> happens into a capacitive load at RF that's below about 0.5 J ohms
> for a "50 ohm" mixer.
> >
> > Bob
> >
> > On Mar 29, 2010, at 10:06 PM, Brian Kirby wrote:
> >
> >
> >> I have been working on a Dual-Mixer Time Difference system. In
> the first "design type/experiment", I was using HP10514B mixers and
> a LT1037 preamp and a OP27 zero crossing amplifier/limiter - all a
> very basic setup. I obtained some fair measurements;
> >>
> >> Using 10 MHz sources, a 9.9999 MHz offset for a 100 hertz beat,
> the "floor" of the system looked like this:
> >> 0.01 second = 1x10-10
> >> 0.1 second = 1x10-11
> >> 1 second = 1x10-12
> >> 10 second = 1x10-13
> >> 100 second = 1x10-14
> >> 1000 second = 1x10-15
> >> 10,000 second = 1x10-16
> >> this was three days of data
> >>
> >> Running it again, with a 10 hertz beat; it looked like this;
> >> 0.1 second = 4x10-12
> >> 1 second = 4x10-13
> >> 10 second = 4x10-14
> >> 100 second = 4x10-15
> >> 1000 second = 4x10-16
> >>
> >> I also had a lot of good suggestions From Ulrich Bangert, Bob
> Camp and Bruce Griffins, who I will call my mentors and thank for
> all the help.
> >>
> >> I went back and did some basic experiments this evening. Looking
> at mixer terminations. I have attached two photos - low res.
> >>
> >> The first photo named mixer_10db, is the mixer driven with +10
> dbm on both ports. The o'scope is looking thru a basic RC filter of
> 1 kilo-ohm resistor in series with the mixer output, and on the
> output of the resistor is a 0.1 uF capacitor to ground. This is a
> mixer that is intentionally over driven to use as a phase detector.
> The mixer is rated +13 dbm maximum, and about everybody I have
> talked with (NIST and BIPM) about these mixers ran them at +10 dbm
> on both LO and RF ports. As these mixers are hard to find, and they
> are not made anymore, I would not over-drive them any further.
> These mixers also have some of the lowest phase noise measurements
> on record.
> >>
> >> The second photo named mixer_330 pF, is the same setup, except I
> have put a 330 pF capacitor across the mixer output. By capacitive
> terminating the mixer, it squares up the output of the mixer - which
> makes it easier to be converted to a high slew rate signal.
> >>
> >> What I found, is you want to run the minimum capacitance value
> for the highest beat frequency you plan to run. That way the signal
> stays "squared up" from the highest to the lowest beat frequency.
> >>
> >> I got this value by playing around by looking at the mixer
> filtered (RC) output at 1 hz, 10 hz, and 100 hz. When I was using
> 0.1 and 1 uF terminations, The 1 and 10 hertz beat was OK, but the
> 100 hertz beat was still a sine wave. That may be why the results
> above shows a difference.
> >>
> >> For a test, at 330 pF, I did try it at 1 KHz, it was back to a
> sine wave. So 330 pF looks good for trying to get a "squared" wave
> out of the mixer for 1, 10 and 100 hertz beats.....I tried 36 pF for
> 1 KHz, it did not present enough capacitance to give the "squared"
> wave at 1, 10 and 100 hertz beat.
> >>
> >> We have been running email outside of Time-Nuts group as I am not
> sure if any of you wanted to see the project I am working on. I did
> not want to clutter up the forum......but if there is an interest, I
> can bring it back. My next plans are to start over building a new
> system using a much lower noise op amp, the LT1028. If the mixer
> terminations are OK with my mentors, I will use a LT1028 preamp set
> for about x15 gain and it will dump into the first set of limiter
> diodes. And I believe that will call for 1.6 KHz low pass filtering
> on the first limiter diodes.
> >>
> >> Comments ?
> >>
> >> Brian - KD4FM
> >>
> >>
> <mixer_330pf.jpg><mixer_10dbm.jpg>__________________________________
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