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Programmable 22 Meter Band Part 15 CW Beacon Kit

Just $35 with Free Shipping! (We ship to the USA Only)

Also available with extra oscillator tuning components for $43 (see below for details)

New and improved version of our popular 22m beacon kit. Now you can program your own CW message, and change it as needed. Programming the board is simple, and can be done repeatedly (the EEPROM is rated for 10,000 write cycles), so you can change the message whenever you wish.

It features a non volatile EEPROM which stores your message, adjustable in length from about seven seconds to three minutes via a trimmer pot. There is a built in pushbutton for entering your message, and of course you can connect your own key to use instead, which is ideal for longer messages.

The key samples the key input and stores 4096 readings, the trimmer pot sets the sample rate and therefore total message length. So it will preserve your "fist". You could of course also send a sequence of random length symbols in addition to morse code, or vary the CW WPM.

The speed pot changes the playback rate of the message as well, so you could record your message at a faster rate, then adjust the pot to slow it down to a QRSS message.

This kit is a sub-assembly, not a complete transmitter. You need to provide your own power supply, enclosure, RF connectors, coax, and antenna.

The kit includes the PCB and components, including a programmed microcontroller.

Small size - just 2.9 by 2 inches (74 by 51 mm). Easy to build, with just a few components, all through hole, no surface mount. Full assembly instructions are on this page, just keep reading!

You'll obviously need a soldering iron to assemble the board, as well as a multimeter to identify some of the components, and verify proper voltages.

An oscilloscope can be useful, but is not required. You'll also want an HF radio of course to listen to your beacon and set it up.

You can contact me via email prior to ordering with questions.

Many 22m enthusiasts log reception of beacons on this message board: https://www.hfunderground.com/board/index.php/board,35.0.html

You can also add your beacon callsign and frequency to the HFU Part 15 Beacons Wiki page

Also available for an extra $8 (at time of purchase) is a kit containing a SIP strip socket, and two each of the following components:

  • 3.3 pF capacitor
  • 6 pF capacitor
  • 10 pF capacitor
  • 22 pF capacitor
  • 47 pF capacitor
  • 10 uH inductor

These components can be used to help "pull" the 13.560 MHz crystal to a lower or higher frequency. As pulling is often a trial and error process, the SIP socket can be broken into individual pins, and soldered on the PCB into the mounting holes for the tuning components. Parts can then be inserted and tested. Once the final setup is found, they can be soldered into the sockets.

Regulations concerning operation in the 22 meter band

This beacon kit will allow you to operate in the 22 meter band. Part 15 of the FCC regulations allows for unlicensed operation in the 13553-13567 kHz band:
Section 15.225(a): The field strength of any emissions within the band 13.553-13.567 MHz shall not exceed 15,848 microvolts/ meter at 30 meters.

Full text here: https://www.gpo.gov/fdsys/pkg/CFR-2011-title47-vol1/pdf/CFR-2011-title47-vol1-sec15-225.pdf

As it is difficult for hobbyists to perform these field strength measurements, W1TAG has done some calculations on the power levels into various antennas which meet this limits. I strongly suggest reading his entire paper, so you are aware of the methods he used, and you can stay within the generous field strength limits for this band.

In a nutshell, he calculated that the limits are 4.6 mW into a half wave dipole, or 2.3 mW into a quarter wave ground plane antenna. Assuming 50 ohm loads, these are 0.48 Vrms and 0.34 Vrms respectively. An oscilloscope could be used to measure the output of your beacon, to verify compliance with the regulations.

K6STI has also calculated power levels to stay within Part 15 limits for several types of antennas and ground conditions, with somewhat different results: http://ham-radio.com/k6sti/hifer.htm

Note that these calculations are not mine, and could be incorrect for your particular setup. As always, it is up to you the operator to verify proper compliance with the field strength limits.

This beacon could also be used on the amateur bands, where these field strength limits do not exist. You would need to change the values of the coils and capacitors in the output filter (although only minor adjustments most likely for 20 meters). Note that other than on 10 meters, HF amateur beacons must be operated with a control operator, so you can not run it unattented continuously.

Circuit details

Below is the schematic. Click on it to view full sized:

Parts List:

Ref	Value	
C1	0.047 uF	(or 0.1 uF)	
C2	Select on test
C3	Select on test
C4	100 pF	
C5	Not used
C6	Select on test
C7	Select on test
C8	Select on test
C9	Not used
C10	220 pF	
C11	0.047 uF	(or 0.1 uF)		
C12	Not used
C13	Select on test
C14	Select on test
C15	Not used
C16	100 pF	
C17	0.047 uF	(or 0.1 uF)		
C18	470 pF	
C19	100 uF
C20	0.047 uF	(or 0.1 uF)	
C21	0.047 uF	(or 0.1 uF)	
D1	Orange LED	
D2	Blue LED	
L1	15 turns on T50-2 toroid	
L2	15 turns on T50-2 toroid	
R1	100K resistor	(Brown / Black / Yellow)
R2	2M resistor	(Red / Black / Green)	
R3	1K resistor	(Brown / Black / Red)	
R4	4.1K resistor	(Yellow / Brown / Red)
R5	4.1K resistor	(Yellow / Brown / Red)	
R6	10K resistor	(Brown / Black / Orange)	
R7	100K resistor	(Brown / Black / Yellow)	
RV1	1K trimmer potentiometer	
RV2	100K trimmer potentiometer	
SW1	Pushbutton switch
U1	74HC02
U2	ATTINY85-20PU	
U3	MCP1702-5002E/TO92	
Y1	HC49 crystal 13.560 MHz

(2) 22 pF capacitors for tuning the crystal
8 pin socket
16 pin socket
Wire for coils

U1 is an ATTiny85 microcontroller. It has a built in oscillator. Output PB1 (pin 6) is used to key the transmitter on and off. Inverted polarity is used, a logic 0 (low output) turns on the transmitter, a high output turns it off.

Resistor R1 pulls the output line low, should U1 not be installed. This allows the beacon to continuously transmit a carrier, for testing and measurement purposes.

Output PB0 (pin 5) turns an LED on when the output is keyed, it is the same signal as PB1 but the opposite polarity.

Digital input PB3 (pin 2) is is CW key input, and is monitored by software. It is pulled up to 5 volts by R6, and C18 provides some filtering. There is a built in pushbutton SW1 that can be used for keying, and an external key can be connected across J1. Only a key/switch should be connected to J1, never a power source, or the board will be damaged.

PB4 (pin 3) is an analog input, fed by potentiometer RV2. It is also monitored by the software, and used to set the sample rate for the CW message.

Output PB2 (pin 7) turns an LED on when the message is being programmed into the microcontroller.

U2, an 74HC02, is the oscillator and amplifier. The first gate is the oscillator, which always runs.

Most 22m beacons are operated on frequencies other than exactly 13560 kHz, as this frequency often has considerable RFI/QRM from the multitude of Part 15 devices. The supplied crystal can be pulled to another nearby frequency by use of tuning capacitors in the oscillator circuit. Please see the separate Crystal Pulling section below for details on this.

The other three gates of U2 are connected in parallel and are a low power amplifier. They are controlled by the PB1 output from U1, which allows keying the transmitter.

The output from U2 is capacitively coupled to trimmer resistor RV1, which is used to set the desired output level. RV1 can be replaced with a jumper, for full power output, for example on a ham band.

Following this is a low pass filter, to attenuate harmonics, and provide some impedance matching to the antenna. Note that all of the capacitors are not used. Extra footprints are provided, in parallel, should the user wish to adjust the filter characteristics, and need to use two or three capacitors in parallel to obtain the desired total capacitance.

The output is at pin 1 of J2.

Power Requirements:

DC power is applied to pin 1 of J3. Up to 12 volts may be applied, which is regulated to 5 volts by U3. The beacon can also be operated at a lower voltage, from roughly 3.5 to 5 volts, by installing a jumper in place of U3, from pin 2 to 3. This allows operation from a small solar panel / battery setup.

Current consumption varies with the voltage, message length, etc. With 5 volts of DC power, it generally runs around 10 mA average. Somewhat less at 3.7 volts. I have been able to continuously run the beacon powered by the solar cell / battery from a small solar powered garden light.


Assembly Instructions

Note:

It's possible that some components may not look exactly as pictured, for example a capacitor could be a different color. Please double check resistor values with a multimeter before installing them, to save grief.

While it is believed that the assembly details and schematic are correct, there is always the possibility for a typo. If you believe this is the case, or have any questions, please contact me prior to assembly, to verify the correct steps. I want to you succeed!

Here's the PCB, we'll start assembly. Below will be a series of photos with each assembly step. Solder at each step:


These are the seven resistors:


Install them first, the parts list gives the color code for each resistor. If in doubt, use a multimeter to verify you have selected the correct resistor for each component. R4 and R5 (4.1K) set the current for the LEDs. D2 is only illuminated when the microcontroller is being programmed, but D1 lights up as the CW message is sent. If your setup has limited available power, you may want to increase the value of R4, to reduce the current draw to illuminate D1, or leave it out all together. Save the cut leads, you may need them later as jumpers.


There are two potentiometers.


They look identical, but RV1 is 1K and RV2 is 100K. Use a multimeter across the two pins on the same side to verify you have selected the correct part. The 1K potentiometer / pot (RV1) is used to reduce the output power, to stay within the Part 15 field strength limits. You can install the pot, or you can install a jumper wire. You might prefer the jumper wire if you are using the beacon on the ham band, where you want to transmit at the highest possible power. One of the pins of RV1 goes to ground, install the jumper between the two other pins (use a multimeter in resistance mode to confirm which pin is ground).


Next install the 8 and 14 pin IC sockets:


I find it is easy to secure them before soldering by carefully bending the corner pins of each socket. Be sure to not bend the pin onto an adjacent track with a different signal, to avoid shorts. Then solder:


Next install the switch:


The switch footprint is rectangular, not square, so make sure you have it correctly aligned when inserting into the PCB, you should not need much force. It can be installed in "either" correct orientation as it is a double pole switch.


Install the voltage regulator if you will be powering the board from more than 5 volts (12 volts maximum):


Note the regulator must be installed in the correct orientation:


Next install the five 0.047 uF (or 0.1 uF, depending on what I have to ship) capacitors (C1, C11, C17, C20, C21)


Save the cut leads, you may need them as jumper wires in a later step:


Install the 470 pF capacitor, C18.


You know the routine... save the cut leads, you may need them as jumper wires in a later step:


Install the 100 uF electrolytic capacitor, C19.


Make sure C19 is installed in the correct orientation, as it is a polarized capacitor:


Next install the crystal (Y1).


Try to get it flush with the PCB, to avoid movement, which can affect the frequency:


There are two LEDs, the orange has longer leads, the blue shorter:


I install the orange LED as D1 and the blue as D2, but the choice is yours. Make sure to install the LEDs with the correct polarity:


Next install the three filter capacitors.


Note that there are two 100 pF capacitors (C4, C16, marked 101) and one 220 pF capacitor (C10, marked 221), install them correctly:


Next the two toroid coils (L1, L2) need to be wound for the low pass filter. Insulated hookup wire is provided. While it is common to use enameled (magnet) wire, it is tedious to sand and strip off the enamel, hookup wire works just as well for this application, and is easier to use.


Each coil has 15 turns of wire. Try to be neat, but as this is being used for a filter, it is not critial that each coil be exactly the same or perfect. Strip off some insulation at the end of each wire:


Install the two coils:


Crystal Pulling

Most 22m beacons are operated on frequencies other than exactly 13560 kHz, as this frequency often has considerable RFI/QRM from the multitude of Part 15 devices. The supplied crystal can be pulled to another nearby frequency by use of tuning capacitors in the oscillator circuit.

There are four optional sets of capacitors that may be installed in conjunction with the crystal Y1:

  • C2 and C3 on the input to the NOR gate
  • C6 in parallel with crystal Y1
  • C7 and C7 in series with crystal Y1
  • C13 and C14 on the output to the NOR gate
In general, increasing capacitor values will decrease the operating frequency (to a point, then the circuit may not oscillate).

Note that it is not necessarily required to install any capacitors (as long as the circuit does oscillate and is stable) and some may be left empty, with the exception of C7+C8 - either one or both must be installed, or one must be shorted with a small piece of wire, otherwise crystal Y1 is not connected.

The parallel arrangements are so that two capacitors can be used to obtain a particular value not possible with off the shelf values. You could use trimmer capacitors for your tests, then replace them with fixed value capacitors. I would not recommend trimmers in your final beacon as they could cause frequency drift or shifts.

Rather than repeatedly soldering and unsoldering capacitors, which is laborious and could damage the PCB, one option is to install pins liberated from machine pin IC sockets on the PCB, then plug in the capacitors as you test. Once you have finalized your component selection, solder in the capacitors into the pins.

I performed a number of experiments, measuring the oscillation frequency with different combinations of capacitor values. Below are the results. They are not in order by frequency but instead grouped by changes to certain capacitance changes, which I think better illustrates the general effects. Also because it is not possible to use this as a "cookbook" to obtain a given frequency, due to tolerance/component value variations, both the capacitors and the crystal itself. You will also need to experiment if you wish to obtain a certain frequency, but this data can be used both as a starting point as well as to see the general effects of changes to each of the four sets of capacitors.

Capacitor values in pF, frequency in kHz:

C6 C7+C8 C2+C3 C13+C14 Frequency
0 short 0 0 13564.6
0 short 3.3 0 13563.6
0 short 6 0 13563.1
0 short 10 0 13562.55
0 short 0 3.3 13563.9
0 short 0 6 13563.46
0 short 0 10 13563.0
0 short 3.3 3.3 13563.2
0 short 6 6 13562.3
0 short 10 10 13561.4
0 short 22 0 13561.5
0 short 0 22 13562.1
0 short 22 22 13559.6
22 short 22 22 13557.4
0 short 47 0 13560.4
0 short 0 47 13561.6
0 short 47 47 13558.0
22 short 47 47 13556.95
47 short 47 47 13556.45
47 short 69 47 13556.35
47 short 47 69 13556.35
0 94 0 0 13564.75
0 47 0 0 13565.1
0 22 0 0 13565.65
0 10 0 0 13566.75
0 6 0 0 13567.6
0 3.3 0 0 13568.8
0 3.3 22 22 13566.8
0 3.3 47 47 13566.25
0 6 47 47 13564.2
0 10 47 47 13562.6

Note that in a few cases, the frequency is outside the 22m Part 15 limits. I present this data for completeness, but of course all operation should only take place within the assigne band.

A small inductor can be placed in series with crystal Y1, instead of a capacitor, which will pull the frequency much lower:

C6 C7+C8 C2+C3 C13+C14 Frequency
0 short 47 47 13558.0
0 10 uH 22 47 13551.0
0 10 uH 47 47 No osc
0 10 uH 0 47 13557.4
0 10 uH 22 22 13552.95
0 10 uH 10 10 13556.7
0 10 uH 10 22 13554.95
0 10 uH 10 47 13553.2
0 10 uH 6 47 13554.35
0 10 uH 3.3 47 13555.5
When using an inverting gate as a crystal oscillator, some component combinations will not produce oscillations, as in one example above. This will also happen if the values are too high (except for C7/C8). In the case of C7/C8, there can be problems if the value is too small. The frequency will be very high, possibly outside of the band limits, as well as unstable.

You may wish to not install U1 or U2 the first time you apply power, to make sure the voltages are correct. Apply power to J3. Note that the square pin closest to the J3 text is positive, and the other pin is ground. Do not apply more than 12 volts (5 volts if you did not install the regulator IC) and observe the correct polarity!

With a voltmeter, double check that you have the corect voltage on U1, you should measure 5 volts (or less if you did not install the regulator and are using a lower voltage power supply) between pins 8 (positive) and 4 (ground). If this is not the case, stop at this point, and locate the construction error. Do not install ICs if you have move than 5 volts, or they will be destroyed.

Now, install 74HC02 IC (U2):

At this point, you are ready to power up your beacon! You can leave U1, the microcontroller, uninstalled for the first tests. With it not installed, the beacon will continuously transmit a carrier, which makes it easy to make adjustments and measurements.

With a nearby receiver, you should hear a carrier somewhere close to 13560 kHz, depending on the oscillator tuning/pulling components installed. An SDR receiver is of course very handy as you can see the entire band and spot your carrier, without the need to tune around to find it.

You may need to install a short piece of wire as an antenna at J2, the output is the square pin.

If you do not hear anything, you should double check your construction. An oscilloscope will be useful to check that the oscillator stage of U2 is correctly operating.

With an oscilloscope connected to the output pin at J2, a nice sine wave should be observed:

A 50+/- ohm resistor can be placed across the two pins of J2 to simulate an antenna, and adjustments made to RV1 to set the desired power level. I'm including a 51 ohm resistor you can use for testing purposes if you wish.

A dipole antenna can be connected directly to the two pins at J2. If you have a balun, it can be used as well.

Programming the Message:

Next, remove power, and install the microcontroller (U1). Re-apply power.

Rotate RV2 fully counter clockwise (CCW) for a minimum recording time, about 6 seconds.

Each microcontroller is programmed and tested here with a short CW message, so you should see activity on D1. If you have a receiver tuned into the frequency if your beacon, you should also hear the message.

Press the pushbutton, and the recording LED D2 will turn on, D1 will also be on.

Release the button, the recording LED D2 will remain on, D1 will turn off.

You can press the button a few more times, each time it is pushed, D1 will turn on.

After about 6 seconds, recording LED D2 will turn off, indicating recording has finished. Then the unit will pause for a few seconds, and then it will begin playing the recorded CW message, which is probably just the random pushbutton sequences you entered.

Next you can experiment with keying some actual morse code. You can of course connect a real key at J1, which will make it easier to send good CW vs the pushbutton. You can also increase the recording time by rotating RV2 clockwise. When you rotate it in playback mode, it will also adjust the playback rate, making it slower or faster than when it was recorded. This is a handy way to record and send in QRSS (slow CW) mode. Record at the shorter message length setting, then adjust the pot to increase the message length and slow down the CW speed as desired.

Notes and Troubleshooting

Sometimes the 74HC02 oscillator will not start without a reasonable load capacitance.

RV1 sets the output to the antenna, full clockwise is maximum power. Be sure to dial it down to stay within Part 15 limits!

Because the oscillator is always running, you can locally hear it, even when the beacon is not keying on. This is especially noticable if no antenna is connected to the beacon board. The output of the oscillator is much weaker than the final output, and will not be heard remotely (unless reception conditions are exceptional!)

The oscillator frequency is voltage sensitive. It's normal for it to vary slightly as the output gates switch on and off. The onboard voltage regulator helps to reduce the power supply voltage shift when keying. If you are not using the regulator, be sure your power supply is fairly well regulated. Usually a battery, such as those in solar lights, is stable enough so the frequency shift when keying is minimal.


Email your comments and questions to info@blackcatsystems.com

Last updated July 5, 2021