The row and column signals are combined in a summer (68) to produce the DTMF signal.ġ. Each signal segment comprises a plurality of similar voltage steps having amplitude and polarity determined by the specialized row and column clock signals (SLOPE RATE, SLOPE SIGN). Row and column integrators (64,92) integrate reference signals to produce discrete voltage steps at the rate of the row and column integration rate signals to produce row and column signals made up of a plurality of segments for each cycle of the signal. Specialized row and column clock control signals (SLOPE RATE, SLOPE SIGN, AUTO ZERO) are produced by clock generators (58,82). Row and column integration rate signals are generated by integrator counters (50,78) also derived from the reference signal. Row and column fundamental rate signals are generated by fundamental counters (48,76) from a reference signal derived from an external crystal (12). Key board scan circuits (42,44) scan a conventional push-button telephone key board to produce row and column input signals.
#Tonegenerator send frequency generator#
If you managed calculus, then it’s quite clear why.A dual-tone multi-frequency (DTMF) tone generator circuit (10) produces selected frequency row and column tones which are combined to generate a DTMF signal. Keep in mind: The power you’ll get is half of the peak output power of your transmitter! Or you use a VTVM (valve tube voltmeter) with an RF probe that gives you an RMS reading of the transmitter’s output voltage. Divide the peak-to-peak voltage by 2.81 (two times the square root of 2) to convert p.-p- voltage to effective voltage, square it and the divide the result by your 50 ohm resistive load. To measure the peak output of your transceiver you can either use the amplitude reading of your oscilloscope. Bias setting must be increased to ensure proper amplification. The bias in this case is much too low so that lower voltage areas of the amplitude are not amplified sufficiently. The following picture shows an SSB amplifier running with inadequate bias setting: Wrong bias in SSB exciter, increase of quiescent current strongly recommended! Also a high set of IM3 products will appear thus make your signal much wider than acceptable. The transmitter will sound very distorted. At least one amplifier stage in the exciter is running in saturated mode thus not being able to deliver proper amplification of the signal’s higher amplitudes.
This is a sample of the classical “flat topping”. First one is an amplifier that is overdriven: Overdriven SSB transmitter operating close to saturation Wrong adjustments of the transmitter can be easily observed like the following pictures show. Then the two audio signals are nearly 100% equal which will result in the demonstrated signal amplitude waveform. The “balance” of the tone generator circuit must be carefully adjusted to regulate the amplitudes of the two audio signals in a manner that the cross section centering the waveform is as sharp as possible. It resembles an amplitude modulated carrier and should look like this when displayed with an oscilloscope: SSB 2-tone test signal: Transmitter correctly adjusted The heart of the device are two oscillators producing 2 sine waves which generate a new waveform that is formed by superposition of the 2 single signals. I’ll refer to that in a later page, today we want to talk about the amplitude side only. If you own a spectrum analyzer with an appropriate resolution the Third Order Intermodulation products (IM3) can also be made visible. 850 Hz and 2200 Hz are a good choice, for example. Also they should have a significant spacing in the audio spectrum. The two frequencies must not be harmonically related and must both fall within the audio passband of the transmitter. The method involves 2 audio tones simultaneously applied to the microphone input of the DUT (device under test).
Just a hint before you read on… I have designed a PCB (Through-hole technology) for this circuit (50 by 30 millimeters, about 2 by 1.25 inches) that can be purchased via my new QRP online shop: Visit DK7IH QRP-Shop The 2-tone-method is a standarized test method that can be used to determine the maximum output and the amplification characteristics of a sideband transmitter. With 2 transistors and an oscilloscope it is fairly easy to test the linearity of your SSB transmitter.
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