The stability of the frequency of the local oscillators Amateur receiving and transmitting the hardware has always been an important issue. Increased particularly of the requirements for this the option with the advent of digital means of communication. Amateur digital development the frequency synthesizer, completely solving the problem of frequency stability, not yet received the wide distribution due to their relative complexity. Together however, there are more options available for addressing this problem. One of them says the author of the following article.
The device is a digital locked loop (CAPC) is intended DPJ use in conjunction with the universal digital scale (TSSH), the description of which it was shown in [1]. The use of CAPC can significantly improve the stability of the tuning frequency of the transceiver.
Diagram of CAPC shown ia figure. Frequency tuning of the GPA, which completed the device will be selectable in increments of 50 or 100 Hz depending on its connect to pre-divider on DD2, DD3 digital scale.
The operation of the circuit, with a step adjustment of 100 Hz, in a simplified form can be represented so. If the value is low (Hertz) measured frequency lies in the interval 0...49 Hz, then after time accounts on the preliminary output of the divider (conclusion 8 DD3.2) will the level of the log. 0. With further increase in frequency at the output the divider appears log. 1. This property is used in the system of CAPC. This principle is not new. It was previously used in other structures, for example, in [2].
Consider the case where the frequency of "floats up". At higher frequencies the local oscillator of the transceiver, when the younger level frequencies fall into range 50...99 Hz, after time accounts on the pre-output divider TSSH appears the level of the log. 1. The trigger DD1.2 schematic of CAPC will fix this the level and output 1 will also appear in the log. 1. High voltage open transistor switch VT1, which will lead to a gradual discharge the integrating capacitor C2. The voltage on the varicap tuning of the lo frequency will decrease, and the frequency of the GPA starts to decrease until, until the level of the log. 0 at pin 1 of flip-flop DD1.2 site CAPC. Log.0 on this pin closes transistor switch, and the voltage on the integrating capacitance and a variable capacitor will gradually increase. The frequency of the GPA will also begin to rise.
From the description of the operating principle of the system shows that it works at a constant the change of frequency "ripple" that will be the smaller, the smaller the speed frequency changes under the influence of the system of CAPC (at the speed limit, and CAPC private nursing GPA frequency equal). In this case, decrease the speed changes in the frequency, or by increasing the capacitance of the integrating capacitor C2, any increase in the value of the resistor R4. Thus it is necessary to ensure that it always exceeded the speed of the frequency drift of the GPA, otherwise the system will be CAPC unhealthy (not capture and hold frequency).
The voltage on the integrating capacitance G2 can take values from 0 to (0,7...0,9)u pit (upper and lower limits depend on the ratio of the values of resistors R4-R6). Depending on what "floats an hour of Thoth", the voltage will gradually decrease or increase in the specified range, hold the frequency of the GPA. The range of frequency tuning GPA when the voltage on the capacitor C2 (in these early limits) there is a strip of retention of CAPC.
If you analyze the work of CAPC in the case where the frequency of "floats down", make sure that it works similarly.
For the introduction of CAPC GPA in the transceiver, you must fulfill several conditions.
1. The frequency of the local oscillator must be supplied to the input f1 (pin 1 DD1) TSSH.
2. Frequency detuning of the GPA should not be less than ±3.5 kHz.
3. Own frequency drift GPA should not exceed 200...300 Hz 5...10 min.
Since the processes are very slow, CAPC does not increase the level the noise of the GPA and does not affect the electrical parameters of the transceiver.
Detuning GPA decreases with the introduction of CAPC about 1.5...2 times. If it saving fundamentally, before connecting CAPC need to increase "pulling" capacity in the circuit varicap.
When the detuning of the "incident" is an error in setting the initial frequency that an inevitable consequence of the simplicity of this system. Therefore, in the mode included the detuning is necessary to control the frequency on TSSH. The frequency shift occurs sporadically without any control, but is unlikely to occur if a small detuning of 200...300 Hz. Achievable "ripple" frequency GPA - 3...5 Hz, which in most cases is acceptable.
Resistor R4 choose the time constant of the integrating circuit at a minimum "ripple" frequency running CAPC (controlled by the frequency counter mode display units of Hz). From the values of the resistors R4, R5 and R6 depend stripe the detuning and bandwidth hold CAPC. They choose (within 1...3 MW) the required bandwidth of detuning, on the one hand, and reliable retention frequencies GPA for a long time - on the other hand (controlled after warm-up of the transceiver). During normal operation, CAPC HL1 led (operation indicator system) should be blinking with a period of about 4...15 s (depending on the speed of care the frequency of the GPA). and the frequency of the GPA must not change by more than ±5 Hz.
The author's variant of the system of CAPC GPA has the following characteristics: the number used inputs digital scale - 2; band of detuning GPA after installation ±2 kHz (before installing CAPC - ±3.5 kHz); the original freewheel lo frequency ± 1 kHz (depending on range): frequency stabilized within 5...10 MIM warm-up transceiver; a step of tuning the frequency of GPD - 50 Hz (input D of the trigger DD1.2 system CAPC connected to the output 5 DD3.1 scale).
System CAPC runs continuously (without disconnecting). Error when you install the original frequency when the detuning of about 100 Hz in increments of 5 - 10 inclusions "the handover". When the detuning of 200...300 Hz error b setting the frequency unlikely.
Amendment. Upper circuit on the output resistor R6 (see figure) must be connected to the circuit of detuning of the GPA, and the lower to the varicap tuning GPA.
Literature
Author: G. Lavrent'ev (UR4QDF)