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Roger Beep

This article describes a simple device to generate Roger Beep tones. The device could be retro fitted to transceivers, microphones, or constructed as a standalone device to be inserted between microphone and transceiver.

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

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:

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:
Pin Description
1 +DC
2 Reset (NC)
3 PTT in
4 PTT out
5 Ground
6 Audio out

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 to ground 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+ is 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.

Before installing the chip, check that the zener regulator is producing 5V at the chip socket to ensure that the diode is in the correct orientation and that it is indeed a 5.1V zener.

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.

Table 2
Configuration Roger Beep tone relative to best whistled tone (dB)
Speech processor OFF, mic gain adjusted for a small amount of ALC 17
Speech processor ON and adjusted for moderate compression of 6-8dB, processor out adjusted for a small amount of ALC 5

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.

Listen to an example recorded off air under real QSO conditions. Chris, VK2DO, is mobile on 2m SSB, and on request has whistled a K at the end of his over as part of the test. Compare the loudness of the speech, the whistled K and the RB's K. Chris is using an optimally configured IC7000 with compression.

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:

Additionally, three test modes are provided:

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.

The woodpecker mode waveform is 10 cycles of ~1kHz sine wave (~10ms) repeated every 100ms, duty cycle=10%. Note that the indication on wattmeters may be as low as 10% deflection of that due to PEP, indicated power may be as little as 1% of PEP, depending on meter rectifier characteristics, and meter dynamics.

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. Operating PTT again starts the configuration menus which are signalled by pulsing the transmitter on and off.

The configuration process, step by step is:

  1. turn power off;
  2. close and hold PTT;
  3. apply power;
  4. wait at least two seconds;
  5. release PTT;
  6. wait at least one tenth of a second;
  7. close and hold PTT, the RB will pulse the transmitter on and off;
  8. count the pulses and release the PTT during the appropriate transmitter on pulse (ie while the transmitter is transmitting) per Table 2;
  9. wait at least two seconds;
  10. if the configuration option uses a second level menu (eg set Morse speed), go to Step 7;
  11. all done, RB has exited configuration mode.

If you want to change two or more configuration items, you will need to go to Step 1 after each item is configured.

If at Step 8, you do not release the PTT until after all the valid options are pulsed, the RB will exit configuration mode and no change is made.

Chips shipped after 1 Nov 2008 are V1.07 or later. For information on configuration of older firmware versions, see Roger Beep - older firmware versions.

Table 2: Mode configuration menu - V1.07
Pulse Mode Persistent Comment
1 disable YES no tone is sent, but PTT is relayed
2 T YES single beep (Morse code T)
3 K YES Morse code K
4 E YES single beep (Morse code E)
5 V... NO PTT to activate and deactivate
6 continuous NO PTT to activate and deactivate
7 woodpecker NO PTT to activate and deactivate
8 set Morse code speed YES See below for setting Morse code speed
9 set TAPnYAP timeout (min) YES See below for setting TAPnYAP timeout

Menu option 8 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 9 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. Do NOT send me a cheque under any circumstances. If you pay by Paypal, I will ship to your registered Paypal shipping address, please make sure it is correct and EXACTLY as should appear on the address label.

Item Price  
Item P&P (Australia, New Zealand, UK, and USA)
Kit of parts including programmed MCU and PCB US$14.00 each US$4.00

Conditions

Parts are supplied on a cost recovery basis, this is not a commercial enterprise. Price is denominated in US$ as most of the parts are purchased in US$.

Parts are usually posted same day for orders received by midday (local time). There may be rare occasions when I am absent for up to two weeks, so despatch may be delayed. In any event, I will send you an email confirming that goods have been or will be posted that day.

Postal service times are outside of my control and service. The above prices include ordinary post and the risk on loss or damage in the postal network is with the buyer. If you want insured post or express post, send me an email requesting a quote. If you do not agree to these terms, do not order the parts.

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

Links

Roger Beep - kit contents and construction notes

IC7000 + HM-151 installation notes

IC7000 + Traveller headset installation notes

IC910 installation notes

MC80 installation notes

SM8 installation notes

TS2000 installation notes

Changes

Version Date Description
1.01 23/12/2007 Initial.
1.02 21/04/2008 Morse speed setting update
1.03 11/05/2008 TAPnYAP update
1.04 13/06/2008 PCB update
1.05 01/11/2008 Woodpecker update


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