generatore subtoni by iz5tyy


IZ5TYY personal description

My name is Marcello Bazzotti.I was born in Chiusure, a small village close to Siena, Italy on April 12TH 1938

I felt passion for radio since my teenager hood and then this passion extended to the whole electronic field.

My job was and is in the Oil & Gas field as Senior Process Engineer.

My first serious approach to the radio was in the sixties for the 11 meter band (27 MHz). Then, in 1971 after the OM examination, I got the licence as IW2AXO, when I was living in San Donato Milanese (Milan).

In the nineties, I had to interrupt my radio activity for job reasons. Then, in 2011, after getting back to my hometown , I restarted the activity, with the new label IZ5TYY.

Today I live in Asciano (Siena, Italy) even if I often travel to Fano (PU, Italy) because of my job.

Address: Via A: Grandi N.19 53041 Asciano (si) Italy

Tel. 0039 0577 719493, cell +393316149413

At the moment I only have VHF/UHF apparatus as FDK Multi2000, Kenwood TR7200 and the just bought Yaesu FT 8900, for mobile contact.

I hope in the next future to arrange for HF band too, after installing an appropriate aerial.

On my own I built several electronic apparatus mainly for lab instrumentation and in order to automatize pumps running (for my garden and to collect rainy water).

At the present time, I am working on a sub tone generator in order to let my Multi2000 to access to the repeaters equipped with sub tones. See below where the generator is detailed.


Sub Tone Generator details

The generator works in the range 50 - 200 Hz, useful to unlock radio repeater when a sub-tone is required.

See the block diagram of Fig. N1.

Tone Generator is made using 3 IC and a module volt-meter 3 ½ digit powered by a 9 Volt battery.

The electrical wiring diagram is shown in FIG. N.2.

CD4047 is used to generate the primary frequency of 800 to 3200 Hz through the resistors and capacitor between the pins 1 and 3.

According to the CD4047 data sheet, the astable mode pulse width is calculated using the following formula:


Where the unit are: TA, seconds, R Ohm and C Farad.

In my system, C is a capacitor of 7.1 nano-Farad, R is a series of 10 kΩplus a variable resistor of 30 kΩ. The resulting frequency is:

f = 1/ T= 800 to 3200 Hz

Note: to get the exact frequency a parallel resistor of 150 kΩis added to R, and two parallel capacitors of 300 pF and 6810 pF are used. For the variable resistor, a ten turns 50 kΩ with 75 kΩ parallel resistors is used.

The generated primary frequency, at pin 10 of CD4047, gets the input of LM331 through a 5 nano-Farad capacitor and is directly connected to CD4040 frequency divider (pin 10).

The resistors at pin2 of LM331 are selected in order to have the required output voltage (at pin 1) and the best linearity: they require a series of 10 kΩ and 27 kΩ. With this arrangement, the LM331 output voltage is in the range of 0.45 to 1.8 volt. The appropriate voltage divider at the LM331 output drops the tension to 50 - 200 mV, shown as frequency in the DVM module.

To set up the system, a measure of pulse width is performed using a stop watch, reading the pulse at pin 1 of CD4040. At this pin the frequency is divided by 212, however the pulse width is 5.12 seconds. The measure has to be done reading at least 10 pulses to minimize the error.

At the pin 5 of CD4047, the primary frequency is divided by 24 getting just 50 to 200 Hz with almost 5 volt peak.

The voltage divider at pin 5 of CD4047 allows to drop the sub-tone signal to a suitable value, then a double RC filter, 2 x (15 kΩ and 0.22 micro-Farad), smoothes the wave to approach a sinusoidal shape.

FIG. N.3 shows the wave shape, after the double filter.

The system is powered by a 9 Volt battery and stabilized to 5 Volt with the IC 78L05.

FIG. N.3: Wave shape seen at the oscilloscpope.

The components are disposed on a 1000 holes card, as shown on the following sketch.

FIG. N.4: Components lay-out

FIG. N.5 shows the 1000 holes card with the components and the ten turns potentiometer.

FIG. N.5 Final Card


The Card has to be arranged in a plastic box with mike connection and a microphone cable to connect the transmitter input, as shown on FIG. N.6


FIG. N.6 Mike Connections


Orario e data di accesso

Sono le ore 10 e 54 minuti
del giorno 11 - 12 - 2018


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