Penning Down a Crystal

My previous post dealt with the fact that I needed a crystal which is non standard, but close enough to a mass produced crystal frequency, very close actually.

Years ago, I came across an old technique in which material is applied to a crystal in order to lower its' resonant frequency. When I remember correctly, that was done by attaching small patches of Scotch tape.
In more recent tests, done by a couple of radio experimenters, permanent ink was used to paint dots on the crystal to achieve the drop in resonance.

When I severely experimented with surplus crystals earlier in my life, the crystals' housings were soldered and could be opened by a medium powered iron. Today, housings seem to be welded and much harder to open. Well, it is not that hard after all.

This is what I do:
Using a high speed electric cutting tool, a groove is formed along the lower end of the housing. I do not recommend to use the tool to cut through the material however. The tool leaves a nicely roughened surface, at which a metal saw finds good grip. It is tempting, but do not hold the xtal at its' main housing, hold it at its' leads. Now carefully and slowly cut through the sheet metal by means of a manual saw.
This is how it looks just before the housing comes off:

Moments later:

It is clear that this procedure does not create an all in all precise cut, but, that is not too bad. Having some edge features helps the later reassembly. In order to place the same rough edge in the same rough corner, I mark base and housing.

Now that the crystal is open, some oscillation device could be of use. Not really spectacular, this is what I came up with:

The photograph shows an additional 78L05...

What you see is the usual Pierce type gate oscillator. This is a relatively stable oscillator. However, it oscillates above the XTAL's series resonance. Sure, one could compensate with an inductor, but, for penning, grinding or matching crystals, relative measurement are usually acceptable.
Example: a crystal having a nominal series resonance frequency of 4.9152MHz should be penned down to 4.908MHz is a 7.2kHz drop. Assume the oscillator generates a 4.9170MHz signal, a 7.2kHz drop would read 4.9098MHz.
An additional consideration was, that many of my projects involve Pierce oscillators of exact that kind, hence, it would be reasonable to pull the crystal to the exact frequency it will operate later in the application.
 
I spare you photographs of a crystal wearing black paint...

And no, I did not start directly with my 4.908MHz project, I did some color burst tests first.

With the drop being not too far, i.e. not that much paint applied, one can actually observe the changes in frequency in the process of applying the paint. With a lot more paint applied, oscillation stops. When that happens, a funny effect could be observed: the oscillation starts again at higher harmonics and slowly drops to the fundamental frequency.
Example: the color burst crystal (3.579545MHz) with some paint applied stopped oscillating. When the counter came back to life it first showed (about) 28.48MHz, then 17.8, 14.24, 10.68, 7.12 and finally 3.56. This corresponds to the 7th, 4th, 3rd, 2nd and 1st overtones. The more paint needed to cure, the longer the oscillator remained at the individual frequencies...

OK, that was more like a fun side remark. The interesting bit is, I was able to obtain stable oscillation of a color burst crystal at 3.530MHz, which is a remarkable drop of 50kHz.

Finally, even a painted crystal deserves a proper housing:

The penned down color burst crystal now ready for A1A action on the 80m band.

LSB for the IC-M700D

As I wrote before, the Icom IC-M700D, the German version of the famous IC-M700 marine radio, did not come with LSB. What I was reading on the internet lately, there is a French version, the IC-M700F, which also lacks LSB. There is hope, maybe something could be done...

Luckily, my IC-M700D came with a circuit diagram. The schematics of the IC-M700 can be found on the internet.
Studying both circuits, the following can be said (corrections made, due to an error in the Service Manual):

1. the MAIN UNIT pcb of the IC-M700D is the same as the one of the IC-M700
2. both sidebands are using the same oscillator
3. two crystals are switched by means of 1SS53 switching diodes (a 1N4148 will probably do)
4. the LSB crystal's traces are present on the D's pcb, so is the LSB control lead from the MATRIX (ending at Q334's base)
5. the D's LSB crystal and surrounding bits'n pieces (a switching transistor(2SC3402), a varactor (FC51M), an inductor and some resistors) are not populated
6. for LSB a 4.908MHz 4.920MHz crystal is required
7. the mode switch needs to be wired up correctly, there may be a further transistor (Q1210) missing on the MATRIX pcb, further, there could be a jumper somewhere...

Have a look at the IC-M700D PCB

and the corresponding IC-M700 circuit diagram

 The question now would be, if there is any cheap option for the crystal. Well, I figure, we are lucky on that one... there is a cheap crystal for 4.9152MHz. I intend to open one up and pen it down to 4.908MHz grind it up to 4.920MHz. A drop of 7kHz  raise of 4.9kHz should easily be doable, although, this is a little harder than it sounds.

The plan now is to pen down grind up a crystal first and think of the rest of the modification later.

Remark: Never trust a Service Manual!
Reasons: The filter center frequency is 9.0113MHz. The (USB) beat frequency is a mix of 10.24MHz and 4.908MHz divided by four, i.e. 10.24-1.227=9.013.
To get to the other side of the filter, the resulting beat frequency should be higher, i.e. 10.24-(4.92/4)=10.24-1.23=9.010MHz.
I should have seen that before going into penning down crystals, which was a good exercise however.
Now, I need to do both, grinding up, and pen down, when ground away too much crystal material....

30m - 10m Diplexer for QRSS use

Just an idea....

Diplexers are very popular for running VHF and UHF transceivers into the same (simple) antenna. This works since 435 is three times 145. A 1/4-wave radiator for the 2m-band is a 3/4-wave radiator for the 70cm-band.

Could this trick work on shortwave too? The 10m band is about a third of the 30m band ... well... sort of. I figure, I suitable diplexer would separate frequencies below and above about 20MHz, maybe 19MHz for good measures.
The hope is that a vertical of about 7m length would form a 1/4-wave radiator for the 30m-band and a 3/4-wave radiator for the 10m-band.
The numbers tell the following story:

wavelength for 30m: 300/10.14=29.6
wavelength for 10m: 300/28.32=10.6

30m radiator length (assuming a velocity factor of 0.95): 29.6*0.95/4=7.03
10m radiator length (assuming a velocity factor of 0.90): 10.6*0.90*0.75=7.15

A compromise could therefore be a radiator length of 7.1m to suit the 30m grabber and the 10m MEPT at the same time.

Next step, think of a 19MHz diplexer design.

Off Topic: Acer Aspire One 110L HDD mod

I went out in order to buy stuff... what I came back with was a 30GB USB-HDD called LaCie Little Disk. When I connected it to a PC, the hardware recognition reported a Samsung HU030HA disk. Ah! That calls for google ... this and this came up. I am actually able to read both, Italian and Dutch.
It all comes down to pulling the ZIF cable from the drive and insert it (same end) the other way around.

Here's what the drive looks alike, the ZIF cable is already turned.

Now lets have a look at the open Aspire One 110L. The SSD is still in place. In order to remove it, the right hand side I/O PCB need to be removed, since the SSD's second holding screw is hidden below this PCB.

Now, with the HU030HA installed, just before the I/O PCB was reinserted.

This is what you have been waiting for:
$ sudo hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads:   56 MB in  3.02 seconds =  18.53 MB/sec

$

BTW, my Aspire One is running Jolicloud. Was it worth building in the HDD? I don't know yet. The netbook feels somewhat more responsive, mass-storage is increased from 8GB to 30GB and there is no need to be afraid of too many write cycles...

IBP Beacon Superhet-RX XTALs

IBP beacons are nice and easy propagation indicators. With dedicated single frequency receivers, a nice propagation alert system could be built. Basic idea here, detect Morse-code and signal strength by means of micro-controllers, transfer this information to a PC and upload it to a web-page (e.g. grabber).

For coverage of all bands, 5 receivers would be required. Again I was thinking of the N3ZI boards, which would need pairs of crystals. Some back and forth thinking and looking at numbers, I was able to find pairs of well available crystal pairs. The suggested IF would be represented by the lower frequency (better ladder-filter) or cheaper crystal.
This is what I came up with: (suggested IF / suggested LO)

20m (14.100MHz)

• 4.096MHz + 10.000MHz
• 2.097MHz + 12.000MHz

17m (18.110MHz)

• 8.000MHz + 10.106MHz

15m (21.150MHz)

• 6.144MHz + 15.000MHz
• 8.867MHz + 12.288MHz

12m (24.930MHz)

• 14.746MHz + 10.180MHz (*)

10m (28.200MHz)

• 4.194MHz + 24.000MHz

(*) 10.180MHz is a crystal found in 22 channel CB-radios.

Now, lets hope that the PCBs are a success, and a fully automatic propagation alert system will welcome the upcoming solar cycle.

Ceramic Resonators for VFO use

Not only crystals make suitable LOs, VXOs or super-VXOs, there are also VFOs designed with ceramic resonators. VFOs with ceramic resonators are not stable enough for QRSS or WSPR, however, CW or SSB do not require the same VFO stability as the digital mode.

Some resonator frequencies (MHz) I know about:

• 2.00
• 3.58
• 4.00, 4.03, 4.16, 4.19, 4.50, 4.91
• 5.00, 5.50, 5.74
• 6.00, 6.50
• 8.00, 8.64
• 10.00, 10.70
• 12.00
• 16.00

In combination with some crystals, those resonators would make some awesome VFOs.

Universal NE612 PCB

N3ZI offers nice little PCBs (click here) for superhet receivers.
It appears that those little receivers can easily be turned into transmitters. I got some ideas in my mind, which I will successively add to this post, so, stay tuned.

For a 10MHz I.F. and a crystal controlled LO, please see my earlier post. For QRSS I would favor 7000800Hz, 14000800Hz, 21000800Hz and 28000800Hz, since crystals (oscillators) are available for 3MHz, 4MHz, 11MHz and 18MHz.
More cheap crystal combinations could be found on my web-page. Note that only pairs with M=1 are "drop in" compatible with N3ZI's PCBs.
One nice option appears to be a dedicated 17m WSPR receiver, or maybe even a transceiver. This design would make use of a 8.000MHz I.F. and a 10.106MHz crystal (30m QRP). A tiny bit of pull and the carrier frequency should be 18.1046MHz.

600m is easily available with the following crystals: 5.000MHz - 4.5000MHz - 4.000MHz - 3.500MHz - 3.000MHz - 2.500MHz - 2.000MHz.
Remember, the subtractive mixing product compensates for thermal drift of the oscillators.

Transmit?? you may ask yourself... Yes, I believe that Douglas' PCBs are equally suitable for generating a single side band signal. Please have a look to the schematics on N3ZI's webpage.
A modification to a transmitter, in my view, could be the following:

1. feeding an AF signal to pin 1 of U1, the input filter and transformer make place for an AF network
2. X6 should have the same frequency as the filter-crystals
3. U2 is now a converter, thus, X5 serves the LO
4. Q2 a buffer, C17 should therefore be replaced by a some means for linearizing Q2
5. C22's capacitance should definitely be reduced

I figure that this PCB, modified for transmit, together with a simple MP3-player, makes an excellent base for a MEPT in combination.

Two PCBs will provide a nice and easy transceiver. One PCB just like intended, the other modified for transmit as shown above. Here, some additional considerations seem appropriate:

1. feed the BFO from the RX board to U1 of the TX board, alternatively use an external BFO
2. feed the LO from the RX board to U2 of the TX board, alternatively use an external LO or VFO

As soon as I got the first results, I will write an update on this site. Stay tuned....

10.000MHz I.F. Superhet Crystal Combinations

Employing a 10MHz I.F., some options for a cheap and simple crystal controlled LO could be:

QRSS

• 3.599900 = 10.000 - 6.400
• 7.000800 = 10.000 - 3.000
• 14.000800 = 10.000 + 4.000
• 21.000800 = 10.000 + 11.000
• 28.000800 = 10.000 + 18.000
  

WSPR

• 14.0956 = 10.000 + 4.096

HiFer

• 13.560 = 10.000 + 3.560

 Others

• 5.000 = 10.000 - 15.000 (WWV)
  
• 14.194 = 10.000 + 4.194 (SSB)
  
• 15.000 = 10.000 + 5.000 (WWV)
• 21.060 = 10.000 + 11.059 (QRP)
  
• 28.432 = 10.000 + 18.432 (SSB)
  

Doubtful

• 20.100 = 10.000 + 10.106 (Radio Jove) 

Ceramic resonators
Ceramic resonators can be pulled further and more easily. This results in less stable VFOs which will be good for CW and SSB. They could be stable enough for some digital modes such as PSK. They will certainly not be suitable for QRSS, WSPR, etc.

• 10.000 - 6.50 = 3.500
• 10.000 + 4.00 = 14.000
• 10.000 + 4.03 = 14.030
• 10.000 + 4.16 = 14.160
• 10.000 + 4.19 = 14.190

Maybe there are more combinations available. Please let me know. I will update this list as soon as there is more...

Ten Tec SCOUT/ARGO Modules for 600m?

Having both radios, the Ten Tec SCOUT 555, for more than 10 yrs by now, and the ARGO 556 ( = SCOUT w/o the P.A.) which I was lucky to obtain some months ago, a thought came to me if the transceivers modules could be modified for 500kHz or even 136kHz.

In principle nothing should speak against this. The SCOUT uses an I.F. of 6.144, the L.O. is generated by a 2.2MHz PTO signal, mixed to and by a NE612 XO/mixer in the band modules.
For 80m that means: 7.444 (XO) + 2.2 (PTO) - 6.144 (I.F.) = 3.500 (QRG)
This would mean for 500kHz: 4.444 (XO) + 2.2 (PTO) - 6.144 (I.F.) = 0.500 (QRG)
It would be necessary not only to replace the crystal but also the LO filter network.
The 160m module can be tuned to about 1.5MHz, however, the PTO stabilizing aka FLS (frequency lock system) does not lock in anymore, Ten-Tec mention here that the AM band rejection  in the 160m module would be causing this.

Since the modules also carry the band filter, it seems that no modification to the radio itself is required.

Now we've seen that 4.444MHz is the highest usable local oscillator frequency. So, what crystal will be available and where would the lower band edge will be?

• 4.433MHz => 489kHz
• 4.194MHz => 250kHz
• 4.096MHz => 152kHz
• 4.000MHz => 56kHz

The PTO has a range of 500kHz from the lower band edge, so all the above standart frequencies will cover the 600m band.

WARC bands - WSPR/QRSS Crystals

OK, 30m is trivial, so let's forget about that for a moment.
What about 17m and 12m?


For 17m I found a very suitable combination:

• 13.104MHz + 5MHz = 18.104MHz

Some upwards pull by 600Hz, and we are there. Personally, I would build the filter(s) from 5MHz crystals, the pulled XO would therefore be at 13.104MHz. Both crystals are available from Pollin (www.pollin.de).


12m will be somewhat more tricky:

• 16.9344MHz + 8.000MHz = 24.9344MHz

Here, a downwards pull by 9.8kHz is required to reach the WSPR band, that is a lot. However, it should be doable with the 16.9344MHz crystal, which would therefore serve as XO while the 8MHz crystals will form filters. Those crystals are also available at Pollin.


Just as a quick reminder, there is nothing wrong with operating QRSS next to WSPR.