Roger Beep

*** NEWS *** PCB  now available, kits now available.

Roger Beep tones have been used to signal more clearly the end of a transmission with SSB transmitters. The Roger Beep tone in its simplest form is a short tone burst (a beep) that is transmitted when the user releases the PTT button. Hams often use a variant where the letter K is transmitted in Morse code instead of the simple beep.

• Design
• Implementation
• Testing and performance
• Operation
• Sourcing parts
• Links

Design

The Roger Beep (RB) is  based on an 8 pin microcontroller chip which performs the logic and timing functions and synthesises a low distortion sine wave for injection into the transmitter audio path.

Features

The design features include:

• low distortion sine wave audio injection;
• no additional controls or indicators required for operation or configuration;
• low power consumption to allow powering from existing mic socket auxiliary power;
• low parts count;
• sleep when inactive to reduce risk of RFI (clock stops);
• inexpensive microcontroller with internal EEPROM for configuration storage;
• four modes:
  • do nothing (except to repeat PTT);
  • send Morse T (or beep) at user PTT release;
  • send Morse K (or dah-di-dah) at user PTT release;
  • send repeated Morse V as a test signal;
  • send continuous tone (for alignment or test);
• adaptable to a wide range of transceivers, microphones, and sequencers;
• PTTOUT is released after a short period of silence following the tone.

The audio output is a low distortion sine wave. The output waveform has a frequency of close to 1kHz and is synthesised using three IO pins of the PIC chip in a simple digital to analogue converter (DAC). 

Fig 1:

Fig 1 shows the design unfiltered DAC output. There are five different voltage levels and two key time intervals in constructing the waveform. These are chosen to have low level low order harmonics so that a simple filter can be used to recover the fundamental with low distortion.

The DA converter output, driven by the firmware logic, is a waveform that has no even harmonics and very low level third, fifth and seventh harmonics. A very simple filter reduces the level of all harmonics to give a total harmonic distortion (THD) af about 2%.

For a deeper discussion of the waveform design, see Roger Beep - tone waveform development.

Fig 2: Circuit diagram

Fig 2 shows the RB circuit diagram.

Table 1 shows the usage of pins on JP1.

The RB is designed to suit the common transceiver PTT interface of the PTT switch sinking current from a positive source to ground. The circuit requires a PTT switch input that is s/c for transmitter on, and o/c for transmitter off. The PTT OUT is an open collector output to sink current to ground. The 2N7000 is rated for 60V and 200mA. Note that relays switched by the output should have back EMF quenched by a parallel diode.

Rs is selected to suit the V+ supply voltage. The source of V+ if often of quite limited current, so the zener diode must be operated below the preferred minimum current. Select Rs=(V−5.1)/6kΩ. The 12F629 must not be operated at more than 5.5V.

Ra is selected to provide adequate microphone injection level. Use as high a value as possible. Start with a value of 10k; and make it larger or smaller as appropriate to obtain a correct level of tone injection with the pot adjusted in the top half of the range. Open circuit output is about 100mV RMS with the pot adjusted for maximum output, output will be of the order of millivolts when loaded by a typical microphone circuit.

The resistors connected directly to pins 2, 3 and 5 are preferably 1% resistors for lowest distortion. Adequate results will be obtained with single 5% resistors of  3k9, 5k6 and 10k resistors, good results with single 1% resistors of  3k9, 6k2 and 10k resistors (see below for prototype test results).

The potentiometer could be up to 2k, but the parallel resistor should be adjusted so that the combination is between 300R and 500R.

The 12F629 is loaded with custom firmware. Neither binary nor source code is available, but programmed chips are available, see below.

An alternative to the 2N7000 output switch is to use an NPN bipolar (eg BC337, BC548) with 3k3 resistor in series with the base (R6).

Pin 4 of the 12F629 is a RESET pin, grounding the pin will cause the MCU to restart when the ground is removed. It will not normally be used but is provided for ICSP (in circuit serial programming).

Implementation

The microcontroller uses an internal RC clock at 4MHz to reduce parts count. The output tone is designed to be close to 1000Hz which is the frequency of maximum signal to noise ratio of most transceivers. The timing results in an audio output tone of about 977Hz ±1%. The microcontroller is sent to sleep when the PTT output is release so as to reduce the risk of RFI from clock harmonics. The microcontroller will awaken on a change in the PTT line.

RB configuration requires no additional controls of indicators, it is performed using the PTT button and observing the transmitter busy indication on the transceiver.

Fig 3: Component side of PCB

Fig 3 is a view of the component side of the board.

Fig 4:

Fig 4 shows the RB encapsulated in clear heatshrink for fitting to the radio.

Fig 5:

Fig 5 shows the RB tucked in under the cables under a TS2000 in the centre of the picture. The module is connected at the back of the microphone socket. The tab in the lower part of the picture is the central lower tab of the front panel.

Fig 6:

The PCB is designed to drop into the slots on a 54x83x30 Jiffy box (eg Jaycar  HB6005) which may be convenient to construct an outboard RB device.

The PCB may fit into larger microphones, the base of some desk microphones, or inside some transceivers with spare space.

Connections can be direct wired to the holes for the 6 pin header, or headers, either 90° or standard installed.

Testing and performance

Distortion

Fig 7: Filtered DAC output

Fig 7 shows the measured filtered DAC waveform with a simple RC filter. The R component is actually the equivalent resistance of the DAC. The lowest line of the graticule is zero volts and the scale is 100mV/cm. The small DC offset (~350mV) of the lowest point of the waveform is due to the saturation voltage of the PIC output drivers. The output of the RB is capacitively coupled so DC offset is not an issue.

Measured total harmonic distortion (THD) at the Tx Monitor output of the TS2000 is 0.7%. Note this prototype used single 1% resistors of  3k9, 6k2 and 10k resistors for the DAC.

Fig 8: Measured spectral distribution of filtered DA output

Fig 8 shows a spectrum analysis of the filtered DAC output of a prototype, vertical scale is 20dB per grid line. Note that the harmonics below the ninth are each more than 50dB down, and the ninth is 38dB down. The measured THD is 2%.

Note that most of the distortion component is well above an SSB transmitter's pass band, so even less of those distortion products will appear in the transmitter output.

Comparison to a whistled K

An experiment was performed to compare the effectiveness of the Roger Beep K compared to a whistled K. On-air subjective tests suggest that the Roger Beep K is substantially 'louder' than a whistled K.

The experiment compared the level of the tone of a transmission of the 'dah' of a whistled K with the Roger Beep. The transmitter was a TS-2000 and the TX MONI output was examined using a spectrum analyser to determine the the relative level of the tone. The best of five whistled Ks is reported in Table 1.

The results in Table 2 show that in both cases, the Roger Beep tone was substantially higher than a whistled tone which accounts for the perceived loudness of the Roger Beep. In the case of the 100W PEP transmitter without speech processing, the Roger Beep achieved the rated 100W PEP output and the tone in the whistled K was a mere 2W PEP.

Factors that appear to contribute to the lower effectiveness of the whistle include:

1. much of the power in the whistled K is distributed as noise and would not assist in recognition at a distant receiver; and
2. peaks in the complex wave shape of the whistle cause ALC action, reducing the relative power in fundamental tone component of the whistle.

Use of speech processing reduces the effect of factor 2.

Results will vary with the spectral content of an individual's whistle, and whistles vary from one to the next.

Operation

Normal

The RB wakes up on PTT change and echoes the PTT status to the PTT-OUT to the transceiver. The RB will perform the configured end-of-over action when PTT is released by the user. The end-of-over action is configurable to be one of:

• do nothing;
• send Morse T (or beep) at user PTT release;
• send Morse K (or dah-di-dah) at user PTT release; or
• send Morse E (or shorter beep) at user PTT release.r

Additionally, two test modes are provided:

• send repeated Morse V as a test signal; or
• send continuous tone (for alignment or test).

The RB will hold the PTT-OUT active whilst a tone is being sent, and release it after a short silence period following cessation of the tone.

In the case of the test modes, the transmission can be started and stopped by pressing PTT momentarily.

TAPnYAP

The TAPnYAP feature provides a latching PTT when the PTT is tapped quickly (contact closure less than 250ms). The next closure of PTT resumes normal PPT operation and the normal beep / transmitter release occurs when the PTT is released. TAPnYAP is subject to a timeout which can be set from 1 to 10 minutes, or 0 to disable TAPnYAP.

TAPnYAP is in firmware V1.06 and later.

Configuration

The RB is prepared for configuration change by holding the PTT button down for at least two seconds when power is applied then releasing it.

PTT is again operated and the RB will pulse the transceivers PTT-OUT to the transceiver and a mode is selected by releasing the PTT switch during the appropriate pulse. After releasing PTT, wait for two seconds before pressing PTT again.

Chips shipped after 10 May 2008 are V1.06 or later. For information on configuration of older firmware versions, see Roger Beep - older firmware versions.

Menu option 7 activates a sub menu for setting the Morse code speed. The speed can be set from 5WPM to 40WPM in increments of 5WPM, factory default is 20WPM. Close the PTT again and release it after one to eight pulses to set the Morse code speed. After releasing PTT, wait for two seconds before pressing PTT again.

Menu option 8 activates a sub menu for setting the TAPnYAP timout. The TAPnYAP timeout can be set from 0 to 10 increments of 2 minutes by selecting 1 to 11 pulses respectively. If the TAPnYAP timeout is set to 0 (1 pulse), TAPnYAP is disabled.

It is not envisaged that the configuration would be changed frequently. Typically, a beep mode (T,K) will be chosen and configured at installation, and not changed again (though it can be).

When a mode is successfully selected, the RB starts operating in that mode immediately.

The configuration is stored in non-volatile memory (EEPROM) on the microcontroller chip for the persistent modes, it does not need power to preserve the configuration. The non-persistent modes will not survive power-off, and the RB will revert to the previously stored mode.

Sourcing parts

Parts are available from the author. Preferred method of payment is Paypal, and is the ONLY option accepted for international payers.

Item	Price (A$)
	Item	P&P (Australia, New Zealand, UK, and USA)
Kit of parts including programmed MCU and PCB	$15 each	$5
Programmed MCU	$5 each	$5
PCB only	$6 each	$2

Neither the binary nor the microcontroller source code are available to end users.

Links

Roger Beep - kit contents and construction notes

Changes

Last update: 14 June 2008 15:58

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