SVXO – Pulling & Bending Crystals

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One of the 2017 winter projects was to take a little closer look, and have a bit of fun, pulling crystals to get a wider range of frequency use.  It turns out to be fairly easy to do – with the right techniques.

View the Paper here: CrystalPullArticle

Thanks Dan, AB7SQ, for writing up, guidance, and putting the final touches on this article!



*** HC49s Crystals are available in the store ***



Below is extra data, O-scope and other screen shots used in building the article.

Click on pictures for larger view.

After building the basic oscillator (no buffer or regulator at this point) some tests were performed with various inductance ranges similar to the article. Below is the full schematic, build, and initial o-scope capture of the waveform.  See table at bottom for various values and their results.

Initially I used JT-65 hooking into my IC-725 as a visual aid for stability.  In most cases the output was stable near the crystal while frequency and stability is worst farthest away.  Same is true with the Theremin effect of our hands being near the circuit changing frequencies.  Below are a few JT65 examples showing stability at the “far end”.  Note you may see strange duplicate images of the waveform, please ignore them and only focus on the main red line.  The interference is not from the oscillator but rather my ViewSonic 22″ monitor spits out tons of RF hash which is then mixing back into the receiver!  You can even hear the tonal quality improve when disconnecting the monitor from A/C.  Time for a new monitor!!

Stability with 27uH and 15uH Chokes

JT-65 27uH JT-65 2x27uH
JT-65 2x15uH JT-65 3x15uH

 

Next up was the toroid  55t on a T68-2 is about 17.24uH and ~46″ of 26ga wire.  Note the difference in waveform with and without the extra 20pF capacitor.  In a few cases the “blip” in the waveform was severe enough to cause the frequency counter to double.  The 20pF value is critical, the type of capacitor will also greatly affect performance.  I only had cheap computer grade disc and mono (MLCC) capacitors available and found the MLCC to be slightly more stable than disc.  Just by changing 1-2pF can make the difference between stability and insanity.

During tests we tried several different toroids (of T50/68 2/6 mix) just to show to try what you have on hand.  The table of toroids is at the bottom of this page.  FT37-43 and FT23-43 was also tried using the same inductance ranges and DO NOT WORK.

For stability we found an even better program than JT-65 as a visual aid.  From this point we used Spectrum Lab from DL4YHF.  The link can be found here: http://www.qsl.net/dl4yhf/spectra1.html

Toroid with No cShunt capacitor

* The “Blip” can get pretty large*

Toroid with a 22pF cShunt added

*No Blip *

Signal stability at 7050 with 22pf cShunt

Same 22pf Cshunt now at 7000

Stability becomes worse farther away from the crystal

Stability at 7050 with 15pF cShunt

Stability at 7030 with 15pF cShunt

Just a few pF lower made a huge difference

A few more screen shots of various combinations

Drifting on 30M with 17.25uH Toroid More Stable 30M with 15uH and 3.3uH choke
20M 4-xtal 7.2uH Toroid

Wild Shifting occured when a 4.7uH chokse was used on 15M

A 4uH toroid gave a much more stable result

A quick look at the oscillator from a spectrum analyzer

4×7050 crystals, Cshunt=15pF L=18.24uH (T68-6)

7050KHz

 

7030KHz

Slight attenuation on the harmonnics

Phase Noise

 

 

Last but not least we applied some of these techniques to a few of the Chinese QRP kits out on the market by replacing the crystal with a 4xcrystal/inductor/polycap combination.

Pixie – switch replaced with pulling parts

Closeup of Pixie Pulling board

Although we did provide more frequency range with these kits a few problems with RIT and chirping was noticed.

The RIT control was not consistent anymore and the amount of RIT was dependent on the amount of pulling applied to the crystal.  I found placing the RIT control a hair above fully CCW would give an approximate 800-1000hz Rx/Tx difference across the pull range.  BUT once adjusted leave the RIT pot alone!  The Rx/Tx shift could be as much as 9KHZ with the RIT fully clockwise!

Chirping was noticed.  The 49er had no real observable chirp.  The Pixie has a chirp on the receive side – which would not be an issue to the receiving station. The Super RM Rockmite had a TERRIBLE chirp.  At the time I have not looked at the schematics and determine if modifications would enhance operation.

Tx/Rx offset frequencies with various Chinese QRP radios

RIT Fully CCW      RIT Fully CW
Radio Cx Rx Tx Shift Rx Tx Shift
Pixie Max 7041.90 7041.30 600 7050.70 7041.40 9300

Pixie

Min 7052.50 7052.40 100 7054.70 7052.40 2300
49er Max 7047.40 7047.20 200 7055.50 7053.70 1800
49er Min 7053.70 7053.60 100 7052.90 7047.50 5400
Rockmite Max 7045.70 7045.70 0 7053.80 7053.30 500
Rockmite Min 7053.10 7053.10 0 7049.20 7046.50 2700

 

Pixie Keying

Rx side chirping

49er Keying

 

Super RM Rockmite Keying

This is with just a crystal

Super RM Rockmite Keying

Significant Chirping with a VXO

Poly-tuner knob attachment examples

Using 1/2″ compression insert
This works but had a wobble to it

 

Replaced the flared end with a 1/4″ dowel and a drop of glue.

 

Parts List

1 Kbob of your choice – Standard 1/4″ shaft style with set screw
1 1/4″ compression insert
1 Fuse Bead 5mmx5mm (Craft Store)
2 Alternative to Fuse Bead:  Plastic Washer .2523″ODx.139″IDx.07″Thick
1 Cheap Ball point pen cut to width and a 1/16″ hole drilled at the end
1 2.6mmdia x .46mm pitch x 6mm long screw
1 1/4″ Dowell ~1-1/8″ long
1 PolyTuner

Toroids used in testing

uH Core Turns Length(in) Gauge
4.0 T37-6 (Yellow) 37 21 30
7.2 T37-6(Yellow) 48 26 30
12.0 T50-6 (yellow) 55 39 30
14.25 T68-2 (Red) 50 42 26
17.25 T68-2(Red) 55 46 26
18.24 T68-6 (Yellow) 60 50 30

Table of results

Device XTAL #Xtals Coil1 Coil2 Coil3 Cshunt Cp Low Khz High Khz Delta Khz Stability Hz Notes
Oscillator 3560 4 100uH Choke 27uH Choke 27uH Choke 470pF 3,552.32 3,560.65 8.33 18
Oscillator 3560 4 100uH Choke 27uH Choke 27uH Choke 470pF 3,533.22 3,560.50 27.28 117
Oscillator 3560 4 100uH Choke 470pF 3,556.39 3,560.75 4.36 2
Oscillator 3560 4 None 470pF 3,559.79 3,560.19 0.4 1
Oscillator 7050 1 17.25uH Toroid 15pF 270pF 7,046.97 7,049.53 2.56 1
Oscillator 7050 1 17.25uH Toroid 22pF 270pF 7,039.46 7,049.47 10.01 50 Cheap Disc Cap
Oscillator 7050 1 27uH Choke 270pF 7,047.15 7,050.30 3.15 20
Oscillator 7050 1 none 270pF 7,049.14 7,050.75 1.61 1 Rock Solid
Oscillator 7050 2 17.25uH Toroid 15pF 270pF 7,044.27 7,050.16 5.89 3
Oscillator 7050 2 17.25uH Toroid 22pF 270pF 7,003.12 7,050.04 46.92 300
Oscillator 7050 2 27uH Choke 270pF 7,044.37 7,051.25 6.88 20
Oscillator 7050 2 none 270pF 7,049.50 7,052.22 2.72 1 Rock Solid
Oscillator 7050 3 17.25uH Toroid 15pF 270pF 7,040.42 7,050.73 10.31 3
Oscillator 7050 3 17.25uH Toroid 22pF 270pF 6,906.92 7,050.57 143.65 332
Oscillator 7050 3 27uH Choke 270pF 7,040.68 7,052.11 11.43 20
Oscillator 7050 3 none 270pF 7,049.78 7,053.34 3.56 1 Rock Solid
Oscillator 7050 4 15uH Choke 15uH Choke 15uH Choke 270pF 7,001.09 7,052.18 51.09 60 Theremin effect within 3”, but stable
Oscillator 7050 4 15uH Choke 15uH Choke 270pF 7,038.82 7,053.94 15.12 40
Oscillator 7050 4 15uH Choke 270pF 7,047.19 7,053.64 6.45 20
Oscillator 7050 4 17.25uH Toroid 15pF 270pF 7,034.19 7,051.27 17.08 3
Oscillator 7050 4 17.25uH Toroid 17pF 270pF 7,025.02 7,051.21 26.19 10 15pF+2pF Gimmick – Be careful of gimick placement
Oscillator 7050 4 17.25uH Toroid 22pF 270pF 6,795.75 7,051.07 255.32 >500
Oscillator 7050 4 17.25uH Toroid 270pF 7,046.29 7,053.52 7.23 1 T68-2 (Red) 55t 28ga
Oscillator 7050 4 18.24uH Toroid 15pF 270pF 7,029.23 7,051.66 22.43 3 T68-6 (Yellow) 60t 30ga
Oscillator 7050 4 18.2uH Toroid 15pF 270pF 7,030.65 7,051.68 21.03 5 T50-2 (Red) 55t 30ga
Oscillator 7050 4 27uH Choke 15uH Choke 270pF 6,897.52 7,051.65 154.13 450 Theremin effect within 2”, highly unstable
Oscillator 7050 4 27uH Choke 27uH Choke 270pF 6,277.15 7,050.16 773.01 >500 Theremin effect > 6”, highly unstable
Oscillator 7050 4 27uH Choke 6.8uH Choke 270pF 7,016.75 7,052.24 35.49 60
Oscillator 7050 4 27uH Choke 270pF 7,034.72 7,052.80 18.08 20
Oscillator 7050 4 7.2uH Toroid 15pF 270pF 7,048.91 7,051.80 2.89 1 T37-6 (Yellow) 48t 30ga
Oscillator 7050 4 none 270pF 7,050.17 7,054.70 4.53 1 Rock Solid
Oscillator 10120 2 12uH Toroid 3.3uH Choke 33-68pF 10,106.23 10,121.66 15.43 3
Oscillator 10120 2 12uH Toroid 33-68pF 10,111.95 10,122.13 10.18 3
Oscillator 10120 3 12uH Toroid 3.3uH Choke 33-68pF 10,091.78 10,122.99 31.21 8
Oscillator 10140 1 12uH Toroid 33-68pF 10,135.04 10,140.41 5.37 3
Oscillator 10140 2 12uH Toroid 33-68pF 10,131.60 10,142.30 10.7 2
Oscillator 10140 3 12uH Toroid 33-68pF 10,127.01 10,143.74 16.73 3
Oscillator 10140 4 15uH Choke 3.3uH Choke 33-68pF 10,063.12 10,144.35 81.23 35
Oscillator 10140 4 15uH Choke 33-68pF 10,118.22 10,144.91 26.69 3
Oscillator 10140 4 17.25uH Toroid 33-68pF 9,956.86 10,143.79 186.93 140 T68-6 Severe drifting
Oscillator 10140 4 7.2uH Toroid 33-68pF 10,136.65 10,145.79 9.14 1
Oscillator 14060 1 7.2uH Toroid 33pF 14,051.31 14,060.49 9.18 2 T37-6 (Yellow) Cp=33-68pF
Oscillator 14060 2 10uH Choke 33pF 14,014.02 14,062.58 48.56 30
Oscillator 14060 2 4.7uH Choke 3.3uH Choke 33pF 14,041.42 14,063.49 22.07 11
Oscillator 14060 2 7.2uH Toroid 33pF 14,043.70 14,063.58 19.88 10
Oscillator 14060 3 4.7uH Choke 3.3uH Choke 33pF 14,039.85 14,065.82 25.97 11
Oscillator 14060 3 7.2uH Toroid 33pF 14,031.58 14,065.92 34.34 3
Oscillator 14060 4 4.7uH Choke 3.3uH Choke 33pF 14,030.26 14,068.68 38.42 4
Oscillator 14060 4 7.2uH Toroid 33pF 14,006.34 14,067.77 61.43 13 “warbly”
Oscillator 14140 4 12uH Toroid 33-68pF 10,120.02 10,144.91 24.89 15 T50-6 (Yellow)55t 30ga
Oscillator 21060 1 3.3uH Choke 22-33pF 21,052.26 21,061.55 9.29 14 6.5Vpp Cp=22-33pF
Oscillator 21060 1 4uH Toroid 22-33pF 21,047.39 21,060.59 13.2 9 T37-6 (Yellow) 37t 30ga
Oscillator 21060 2 3.3uH Choke 22-33pF 21,047.39 21,065.25 17.86 9
Oscillator 21060 2 4uH Toroid 22-33pF 21,033.33 21,064.24 30.91 17
Oscillator 21060 3 3.3uH Choke 22-33pF 21,041.28 21,068.58 27.3 15
Oscillator 21060 3 4uH Toroid 22-33pF 21,006.05 21,067.29 61.24 26
Oscillator 21060 4 4.7uH Choke 22-33pF 20,994.28 21,067.12 72.84 74 “Wild Random Shifting”
Oscillator N/A 0 27uH Choke 270pF 3,975.00 8,974.00 4,999.00 1400000 Free Running – Theremin effect within 2”, highly unstable
Pixie 7050 1 18.24uH Toroid 1uh Choke 17pF 7,048.50 7,050.00 1.5 5 Chinese Pixie – Good RxTx Offset with rit fully CCW
Pixie 7050 4 18.24uH Toroid 1uh Choke 15pF 7,044.20 7,052.30 8.1 10 Chinese Pixie – See RxTx Offset Notes
Pixie 7050 4 18.24uH Toroid 1uh Choke 17pF 7,042.00 7,052.30 10.3 11 Chinese Pixie – See RxTx Offset Notes
Pixie 7050 4 18.24uH Toroid 1uh Choke 20pF 7,032.90 7,052.20 19.3 11 Chinese Pixie – See RxTx Offset Notes
Pixie 7050 4 18.24uH Toroid 20pF 7,040.00 7,052.40 12.4 13 Chinese Pixie – See RxTx Offset Notes
Rockmite 7050 4 18.24uH Toroid 1uh Choke 17pF 7,045.80 7,053.10 7.3 22 Chinese Super RM Rockmite – Chirps bad on Tx
49er 7050 4 18.24uH Toroid 1uh Choke 17pF 7,047.10 7,053.50 6.4 6 Chinese 49er – See RxTx Offset Notes

 

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