NC-300 Xtal Marker Too High in Freq

[W1KSZ]

I have a HB Xtal Oscillator that someone built using the National circuit as a guide.
At Max C on the Trimmer Cap it is still about 44 CPS too high. I tried adding another
12 pf to the 20 pf Trimmer Cap, but that killed the oscillation.

Any ideas on what I might try next ?

Thanks, Dick, W1KSZ

[KB2WIG]

Parall or series.?

KLC

[W1KSZ]

If you mean the location of the Trimmer, it's parallel to the Xtal.
If you mean resonance, I think it's also parallel.

73, Dick, W1KSZ

[W4AMV]

Dick, can you post the circuit? Do you know the crystal specification? The required load capacitance? Assuming it is 32 pF implies the crystal at resonance requires 32 pF total load C and the crystal looks like 32 pf of equivalent inductive reactance at 100 kHz. I can't recall what 100 kHz xtal typical look like. I have a few and I'll take a measure and see. If it is a Colpitt oscillator arrangement, then the total C around the xtal including device loading and C feedback etc... should amount to 32 pF. Need to identify the circuit configuration. Alan 

[W1KSZ]

Attached is the schematic of the National Calibrator.

73, Dick, W1KSZ

[KA2DZT]

Your 100Khz oscillator is off by 44hz.  That error is less than 5/100%  What are you using to read the frequency??

[W1KSZ]

I have an HP 5334B Counter whose Reference Oscillator is a Trimble Thunderbolt GPSDO.

44 CPS @ 100 Kc = 13.2 Kc @ 30 Mc. Not exactly accurate.

73, Dick, W1KSZ

[KA2DZT]

I'm still using a HP-5245.  I calibrated the time base oscillator against WWV (IIRC).  Don't remember how I did it.  Don't think back in the 1950s, when most of this stuff was made, they had anything that could read frequency that close.  In the late 1960s I worked for Westinghouse Electric.  We had one of those giant 200lb HP counters, 500 something.  Don't remember the exact number.  We used it to check and calibrate the lesser HP counters that were used around the plant.  The monster counter was suppose to be 10 times more accurate than the lesser ones.

[WBear2GCR]

I have an HP 5334B Counter whose Reference Oscillator is a Trimble Thunderbolt GPSDO.

44 CPS @ 100 Kc = 13.2 Kc @ 30 Mc. Not exactly accurate.

73, Dick, W1KSZ

Is that correct??
It's not being multiplied by mixing.
It's just the harmonic due to the rise time of the leading edge, no?

I'd check that theory with a solid state rig of known calibration, like vs. WWV and look
at the calibrator signal at 5mHz and 10mHz, etc and see if it is actually off many kHz or not.

[W1KSZ]

Back in "the day" I used to borrow the lab's 5245L to check my Xtals at home.
At the time, it was the best we had at the time.

Today, we have the GPS system and can use that to discipline a 10 MHz Oscillator
such that we now have Frequency measurement capabilities that far exceed those
available in the 60's. Look at the articles written by N1JEZ, you can build a simple
one for less than $100. A few years ago, the Trimble Thunderbolt was available from
Chinese Breakers for around $20, but that supply has dried up.

I use a Trimble with an SRS FS710 Splitter to supply 10 MHz to all my counters and
as a bench reference. With an HP 5345A and a 1,000 Second Gate Time, I can measure
Frequency, accurately,  down to the milliHertz range. Pretty awesome when I can look
at the difference between a GPSDO and a Rubidium.

73, Dick, W1KSZ

[KA2DZT]

OK FB,  sounds like your freq measurements are accurate.  Getting back to the problem,  most likely the 100Khz crystal is off.  Can you open the crystal case??  I think there are some things you can do to bring the freq down.  I think some pencil lines is one of them.  Someone here may know more.

Fred

[KU8L]

It doesn't take a cal lab setup to get to 44 Hz on a calibrator.  Measuring beats against an OTA signal like WWV can get to a Hz or 2.   Now, it isn't gonna stay there for long, but you can surely measure it.

All the frequency measurement folks did it that way prior to having access to GPS locked references.  It is how the ovenized ref oscillators were typically adjusted.

You can do it now using soundcard software and a laptop.

FWIW
Curt
KU8L

[W4AMV]

Hi Dick. Thanks for the schematic. The 6AK6 is ~ 3.6 pF and the circuit C looks like the max is 23 pF. So at 27 pF it would appear that the 100 kHz crystal is not designed for a 32 pF load C. I believe the crystal package is a HC13/u and not sure if the holder C would account for an additional 5 pF. I have a few of these 100 kHz crystals in the old style HC13/u package and I'll make a measurement and see what the crystal looks like. If it is 32 pF equivalent at 100 kHz that is a clue. As a prior post implied, if the crystal has aged, it may not be possible to load it sufficiently to bring it down to 100 kHz. In doing so lowers the reactance of the parallel circuit to the point that the oscillator will not start. Again, measuring a good xtal of this style will provide some clues as to what can be done with this circuit to pull the xtal. Alan

[W1KSZ]

The Xtal is an old Petersen Radio Type Z6-A. Older than dirt. Could be it never
worked right and I am just pushing that old boulder up a hill.

I think I should junk this thing and look for a real Xtal Calibrator. The Nationals
are a tad pricey, but the Heathkit HRA-10-1 looks like it will do, just need to re-wire
the octal plug.

73, Dick, W1KSZ

[Carl WA1KPD]

Hi Dick,

44 CPS?
If this for use on a boat anchor rcvr bother? You are never going to hear the difference.
Carl

[W4AMV]

Yes, I agree 44 Hz. Quite fine. In any case after effort, my analyzer stops at 100 kHz! However, I have a vector Z meter and with care and patience, I was able to set it to 100 kHz spot on. Viola, 32 pF inductive. So, for what it is worth, the 100 kHz xtal as used for example in the Drake 2B calibrator and others, correlates to 32 pF. Alan

[Tom WA3KLR]

Look for some more 100 kHz xtals at the next hamfest or your local buddies junk boxes.

[W1KSZ]

I agree, 44 cps @ 100 Kc may not seem like much but when you multiply it by 300
to get a marker at 30 Mc, it can be substantial.

For example: It reads 100.044 Kc, multiply that by 300 and you get 30, 013.2 Kc.

So you can see my A/R need to get it closer !!

73, Dick, W1KSZ

[Carl WA1KPD]

Got it.
 I "assumed" you were talking about compared to 10 MCS WWV. My standard.
My bad
Carl

[W1KSZ]

WWV is OK as a first approximation, but ever since I got hooked on the GPSDO,
my bar has been raised to astronomical heights. 

I actually bought an HP 5345 Counter so I could use the 1000 second gate time to
measure the Frequency difference between my GPSDO and a couple of Rubidium
Standards I acquired.

There's a Reflector called "Time-Nuts" that makes me and my obsession look
positively primitive !!

73, Dick, W1KSZ

[Jim, W5JO]

You can measure the crystal with a signal generator, a scope, a 56 K resistor and a 3 Pf. cap.  Put the resistor in series with the output of the generator then attach to the crystal.  Put the other side of the crystal to the ground side of the signal generator, then attach the 3 Pf. cap to the high side and put your scope probe on that output.

Sweep the generator and look for the null.  Parallel resonance is just a bit above the series resonant point.  If the crystal won't come on at 100 Kc. you have a bad one, replace it.

[N8ETQ]

   Hey Dick,,

       Wonder what your AC Mains are at?
Those filaments running hotter than a
downtown hooker could be the problem.

       Not just with the calibrator, but
also the rest of the rig.

GL

Please keep us in the loop as u progress.

/Dan

[W1KSZ]

I'll put a Variac on the line and see. My line runs anywhere from 120 to 125 VAC.

So far, not much progress, I posted a want for 100 Kc Xtals, but no response yet.

There was a Heath HRA-10-1 Calibrator over on the evil empire, but the last bid
was $41+8 for shipping. My Yankee heritage recoils at spending that much or
more, especially considering how little I paid for the NC-300 !!

73, Dick, W1KSZ

[Jim, W5JO]

Check AF4K for the crystal in the HC series holder.  He is quite reasonable.  ICM sold them for about 25 dollars, but that was before they closed.

[N8ETQ]

  Hey Dick,


      Is your addy gud in QRZ?
I'll send u a HB 100khz Cal.

uses a 2180(?) xtal. runs off
9 V dc. I got one in my 300.
use a 33K 2 W "R" in the dc line.

  Works FB.

/Dan