Several versions of the synthesizers with one PLL (phase-locked loop) described on site were followed by the synthesizer mentioned herein. The synthesizer controlled by Atmel 89C52 microcontroller This synthesizer was re-reproduced by many radio amateurs, the computer-operated programme was written for it. As compared to other designs - this is a simple and inexpensive synthesizer with rather good performances for home-made transceiver with the 1-st intermediate frequency (IF) up to 12 MHz. The “direct synthesizing” variant highly advertised in Internet was also tested – they used DDS from Analog Devices - AD9850, AD9851 – The conclusion – unfortunately still low noise characteristics of these microcircuits do not allow to use such synthesizer in high-class transceiver.

The search for the most suitable and inexpensive version of the synthesizer for HF transceiver was continued and in the long run the variant described below was obtained.

                   Synthesizer Structure Chart


CLK – frequency standard crystal oscillator for 20 MHz.

DDS – AD9832 microcircuit producing the signal with frequencies 80-350 kHz.

FD – phase comparator.

VCO – voltage-controlled oscillators Upll i.e. the voltage with comes to varicaps.


Dividers 1/256 and 1/4 – dividers of frequency by 256 and 4

The chart should be re-writed for all abbreviations to de in Russian language, though it can be left as in – since there is an explanation.

DDS microcircuit generates the frequencies from 80 to 350 kHz depending upon the band, which come through LPF to the one of FFD input.

The frequencies from VCO output in 20-84 MHz are divided (by a divider) by 256 and come to the second FFD input. The voltage from FD output having come through LPF, goes to VCO agility varicaps. The voltage is changing until the frequencies in both FD inputs, coincide with each other, accordingly when frequencies coincide PLL ring (FD-LPF-VCO 1/256) will be locked and will keep the frequency. The frequency hopping will occur when the frequency starts to change i.e. the frequency generated by DDS microcircuit. DDS frequency control is actuated from the processor under the set programme. For VCO frequency to match with “standard” TRX with IF in 0-12 MHz band, it should additionally divided by 4.

Synthesizer Performances / specifications

Happing pith: 1,10,20,30,50,100,1000,5000 Hz. Transceiver IF can be from 0 MHz to 100 MHz. Actually such synthesizer’s structure allows to use it for obtaining various output frequencies – to do it, it’s enough to change the 1/256 divider factor between VCO and FD just to receive the required frequency on the second FD input which should coincide with the frequency from DDS. All frequencies layout in the “basic model” of the transceiver is given in the Table No1. It gives the calculations for IF = 8,862 MHz, site  – here this Table is given in Microsoft Excel, that’s why it can be recorded from there and one can put the value of his IF, dividers factors and the programme will automatically calculate all frequencies.

Table No 1









Put the required values:







Divider on device output







Divider in PLL circuit







Divider after DDS

Band, m

Frequency band, kHz

sign IF






DDS , Hz




























































































The table column “IF sign” shows how the frequency is calculated i.e. if the sign is 1 then VFO frequency = frequency received by transceiver +IF. If the sign is –1 then VFO frequency = difference of received frequency and IF frequency. This is so-called “standard” of frequencies layout accepted in the majority of home-made transceiver with fixed 1-st IF. VFO frequency – is a frequency that comes directly to transceiver mixer. The Table No2 gives the frequencies layout when local frequency = received frequency +IF – this variant is suitable for any IF including that one for the transceiver with the “conversion to the top”. The Table gives the calculation for IF 90 MHz. If one will use such VFO frequencies with low IF then it is easier to press side receiving channels in 20m bands and higher.


Table No 2

IF,  kHz – 90000  Divider  PLL  256


Band, ì

Frequency band ,kHz

  VCO hopping  ,kHz

DDS band, Hz

































































What can be said about noise parameters of this synthesis? My spectrum analyzer CK4-59 does not allow to measure noise characteristics. The resolution of this device is limited by the manufacturer-plant, it is guaranteed up to 115 dB and can be estimated up to 135 dB. Below there pictures of CK4-59 display which are shown while various synthesizers measuring.


                        Band pattern ÑÊ4-59 500 kHz                                                           Band pattern ÑÊ4-59 200kHz





                              Band pattern ÑÊ4-59 50 kHz                                          The picture (united in one) with synthesizer on AD9851




  Because of it is enough big volume of this page of the picture of the screen CK4-59 with miscellaneous synthesizer look here >>>>>


There using the synthesizer with the transceiver which specifications were 0.3 uV/50 Ohm and DB3 = 95dB, here were no any degradation of receiver’s performances. It is worth to mention that the measuring of DB3 parameter was performed with feeding 2 signals with 22 kHz diversity – it is rather mode for receiver testing. Usually this measuring is carried out when signals big diversity.


Synthesizer’s Control Buttons. Total – 18 pcs. The buttons united in field of 12 – are designed for synthesis frequency control and 6 buttons (not united) located on transceiver’s front panel-they are designed for switching the modes in TRX. The buttons for transceiver operation mode control are functioning in quasi-sensor mode i.e. the buttons without fixation – to activate the mode it is necessary to press the button, to press it once again – the mode is off. In order to understand whether the mode is on or off – there is a light diode near each button, it is lighting – the is on. The synthesizer’s frequency control buttons have several functions. The main functions is determined by the inscription (message) near the button, additionally each button has a figure, 9 buttons indicate bands and some buttons have subfunction in “Menu” mentioned below.

The front panel of the transceiver with such synthesizer  >>>>>

Synthesizer’s frequency control buttons



































Synthesizer control buttons description.

In buttons description their main function is mentioned first i.e. what will happen when it is pressed for the 1-st time, then there is an assigned figure, assigned band when enter the “Band” function, assigned designation on principal diagram.


STEK, “0”, K10 – frequency extraction from stek. There are 5 cells of stek, they can be looked through by pressing the button consequently. Before frequencies extraction from stek cells there is a STEK message with cell number coming shortly on indicators. Stek entering is done automatically when the band changes, while extraction from memory cell and while scanning.


RIT, “1”, 1, 9, K11 – detuning activation. The frequency being at the moment on indicator, is remembered when pressing the button and it will be used for transmission. The detuning value is set by changing the frequency with vocoder or any other means. In spite of the fact whether you remain on the same band where detuning was activated or transfer to another band, when coming to transmission the synthesizer will return to the frequency which was on the indicator at the moment of detuning activation. Thus modes SPLIT and CROSSBAND are provided. When the detuning is on, the dot will light up additionally after tens MHz (when use of indication board on LED). The detuning is off by repeat pressing this button. When use of LCD indicator – message “RIT” comes on it (the pictures of LCD display in various modes will be given in the description below).


FREQ, “2”, 3, 5, K12 – encoder pulses programm multiplication on/off for frequency hopping. When this button is pressed, there is a message “2n” for a short time on indicator – encoder pulses are not multiplied i.e. for example having 60 spurs of encoder disk and hopping pattern 10 Hz we shall receive 1 hopping on frequency 600 Hz at on rotation of encoder handle. When next button, on indicator will light “4n” message and encoder pulses will be multiplied with 4 i.e. 2400 Hz on handle rotation (not 600 Hz).


BAND, “3”, 7, K13 – bands switch. When pressing the button “-Band-” comes on indicator and after the relevant button is pressed the mid of selected band is set. The bands are assigned to buttons K11 – K1, accordingly K1 – 1.9 MHz, K12 – 3.6 MHz, K13 – 7 MHz etc. i.e. all 9 SW bands, the last K1 – 28 MHz. The extra bands can be introduced. For selection press the button ¹3, next button ¹0 and then buttons ¹1,2,3,4. The bands are stipulated for buttons 1-4 50 MHz, 144 MHz, 430 MHz, 136 kHz. When 50 MHz is on, logical zero appears on output ¹11 of DD1 microcircuit, VCO board, and this signal can be controlled by any of VCOs most suitable on the frequency to be generated. When bands 144 MHz and 430 MHz are on, the transceiver is transferred to 28 MHz band VHF band converter can be used. To switch on the required converter  DD5 microcircuit outputs are used – logical zero on output ¹12 when 144 MHz is on, on output ¹11 when 430 MHz is on, and on outputs ¹8 when 136 kHz is on. When 136 kHz is on, the transceiver is transferred to 1.9 MHz band.


IN, “4”, 10, K14 – keeps the current frequency and status of 6 buttons of transceiver control in one of memory cells. When is pressed, “-PUSH-” appears on display and then the button with the relevant cell number should be pressed, to set the numbers from 10 to 15 it is necessary to press the second figure from 0 to 5 for one (1) second after the figure 1 is pressed. After the number is set, the cell number will appear on indicator. In cell “0” there is information used for synthesizer’s initial state setting when the power is on, i.e. the desired values can be set into this cell, for example hopping pattern value, any mode switching in TRX, the frequency which will be in synthesizer when the transceiver power is on. For instance – it is agreed with the ham to meet on  21.225  MHz frequency. We  transfer TRX (by any way) to this frequency, for good sound – we switch UHF, select the hopping pattern and then press the button “IN” and cell “0” the setting are entered cell “0”. Now we can switch off the transceiver, then the power is on, the processor shall set all that modes which we saved in cell “0” – it will activate UHF, 21.225 MHz frequency and hopping pattern.


A-B, “5”, 14, K5 – exchange with additional receiving frequency. This is so called the mode of second “local oscillator”. To memory the frequencies in “virtual” cells “A” and “B” it is necessary  to adjust the required frequency and press this button – the memory is on and the frequency is kept in cell “A”, accordingly the frequency on indicators will “jump” to cell “B”, virtually we switched to the second local oscillator. Here we can make any changes of frequency – the preservation in cell “B” will occur only when button “A-B” is pressed once again and that frequency will be kept which was on digital scale at the moment when button “A-B” was pressed. Now we can change the frequency by any ways – we work on “local oscillator” A, but preservation “A” will have the frequency which was on indicator when the next pressing A-B. This in cells “A” and “B” two frequencies are kept i.e. the frequencies which were on digital scale at the moments of pressing A-B button. This mode can described in the other way – let’s imagine that inside of transceiver there are two VFO and this button can switch the tuning handle to VFO “A” or to VFO “B” – may be such explanation in easier. For us to be clear, with which “local oscillator” we are working – in mode “A” dot near LED (MHz scale) appears on indicator, in mode “B” the dot near MHz lights off and three dots light up near LED values of Hz scale (dorens, hundreds etc.)


SCAN, “6”, 18, K16 – scanning. When pressed, “-SCAN-” appears on indicator. There are three scanning sub functions (after the button ¹6 SCAN is pressed).

a)    When button ¹8 OUT is pressed -> scanning on memory cells 1-15 with 3 sec. Stops on each cell.

b)    When button ¹2 FREQ is pressed -> scanning from less frequency recorded in cell 1 up to bigger frequency recorded in cell 2. If frequency in cell 1 is bigger than in cell 2, when SCAN is pressed the message “ERROR” appears. The scanning is available only within one band.

c)     When button ¹3 BAND is pressed -> hopping in current band from lower band limit up to the upper one and back.

The scanning is interrupted when any button is pressed, encoder is rotated or transmission button. The scanning can be continued in any moment from the stopping point by pressing SCAN button twice.


R-T, “7”, 21, K17 – this mode is activated when detuning is on (button ¹3) – transmission frequency makes an exchange with receiving frequency i.e. the button was pressed – the frequency which was a transmission one, will be the receiving frequency; the receiving frequency will be the transmission frequency, the button was pressed once again – all will come to initial state. If the detuning is off when button ¹7 is pressed, “SELECT” message appears – menu from basic setting .

1.     IF correction – the relevant frequency from USB, LSB, CW is selected i.e. we can programme three IF values – when TRX local oscillator is switched on in lower part and upper part of pilfer and when CW mode is activated. What is the benefit? The benefit is: the correct values of frequency on indicator while switching to inverse side bandage, when standard oscillator frequency shift in telegraph mode (if it is stipulated in the transceiver). The required IF value is switched automatically when the relevant modes U/L and CW are activated. For correct frequencies input – we shall warm up the transceiver, frequency-meter and measure the frequencies of transceiver standard oscillator in these modes with the last symbol up to Hz values. Enter menu of IF programming – button ¹6 – “SELECT” massage appears on the scale, then press button ¹1 (IF input) – the value already available in memory will appear on the scale, input IF value in the same activated mode where we measured the frequency of standard oscillator. For example, the main “basic” IF can be set in non-activated modes USB/LSB and CW, then we shall activate inversion of side bandage – in author’s transceiver this button is called U/L, and input IF value measured by the frequency-meter while inversed side bandage – as a rule in transceivers with one crystal filter, the inversion occurs because of standard oscillator frequency movement from lower part of crystal filter to its upper part. In case in the transceiver the separate filter for CW receiving is stipulated – more often it is a little shifted in frequency as compared to SSB filter – accordingly to activate this mode, in author’s TRX there is a CW button which activates the CW mode and “reads” IF set for this mode. If  no IF shift is needed when transferring into side bandage inversion mode and telegraph mode, for example if the separate filters are used in the transceiver for lower, upper side bandages as will as if the telegraph filter is also used which does not require the shift of standard oscillator frequency – than input one IF value in all three these cells. Record the value of each frequency from frequency-meter in Hz and dial these figures by encoder rotation, on scale indicators. The set values will be kept by any button pressing. It’s worth to mention that the encoder hopping pattern will be saved when IF input i.e. in case it is necessary to input the value before Hz values – the hopping pattern of synthesizer should be 1 Hz. But in case you require the significant IF hopping, more big hopping pattern should be selected beforehand.

2.     Frequency direct input mode – i.e. frequency keyboard input. Enter menu SELECT i.e. press button ¹7 and then button ¹2 – “FREG” message for a short time appears on the scale, then all indicators will light off and “lower line” will light up in the high-order digit – that is “invitation” to frequency input – “print” the required frequency value using the keyboard buttons. In case the wrong frequency input, the programme will enter the standby mode again to input the frequency.

3.     Calibration of all clock inner constants depending upon frequency dividing factor between VCO and mixer.

a)    without dividing the frequency goes from VCO to mixer;

b)    the frequency is divided by 2;

c)     the frequency is divided by 4;

        The calibration is made in any band. Enter menu “SELECT” – press button ¹7 then button ¹3 – “GEN” message appears on the scale, rotating the encoder “dial” the required frequency value on VCO board output. To receive the exact values we require the frequency-meter and some calculations. At first we will calculate the frequency value which should be on the transceiver mixer. Connect frequency-meter input in any point between VCO board output and the mixer where the frequency has already suffered the required number of divisions. We look at frequency-meter scale and “adjust” the frequency (using the encoder) on VCO output up to the required value. The value will be saved by pressing any button.

4.     Divider’s selection – 1,2 or 4 “one pressing – one divider”. Depending what dividing value the frequency will supper from VCO while it goes to the mixer – there can be no division at all (for example in the variant of up-conversion), there can be division by 2 (also up-conversion, but not high IF = 20-24 MHz), “usual” variant -  when the frequency is divided by 4. Select the mode – press button ¹7 – “SELECT” message comes on indicator, then press button ¹4 i.e. select the required value. The value is selected by subsequent pressing button ¹7 and ¹4. The scale will indicate messages DEL - 1, DEL - 2, DEL - 4 – it’s necessary to stop when the required division value appears.

5.     Selection of structural arrangement of local oscillator frequencies. If it is powered odd, on indicators – PLUS 0 – this is a selection mode for “standard conversion” – when the local oscillator frequency on bands lower than 20m is represented as Frx + Fif, and on bands 20m and higher  - Frx + Fif. The second mode PLUS 1 – for the variant when in all bands the local oscillator frequency is calculated as sum of Frx and i.e. this variant is required when up-conversion and when there are problems with side receiving channels with low IF. Press button ¹7 and then button ¹5 – on the scale the messages “PLUS 1” and ”PLUS 0” will come one by one for a short time. We shall stop when the required mode appears.

6.     Selection of additional division of VCO frequency on band 20m – this mode is required when use of one united VCO for 20m and 160m, when additional division by 2 is required for local oscillator frequency on 20m band. The button operations logic is the same – press button ¹7 and then button ¹6. On the scale the messages “20 bd-1”, “20 bd-0” will appears for a short time. We shall stop when the required mode appears. The division is on, when “20 bd-1” appears.


OUT, “8”, K18 – restoration of frequency and status of 6 buttons (transceiver control) from one 16 memory cells. When it is pressed, on display comes “-POP-” and then the button with relevant cell number pressing is expected, to input numbers from 10 to 15 it is necessary to press the second figure from 0 to 5 within 1 second after figure 1 is pressed. After the number input, the memory cell number will appear for some second on the indicator.

T=R, “9”, 28, K19 – this mode operates when the detuning is activated (button ¹1), the transmission frequency becomes equal to receiving frequency, but when the detuning is off while button ¹9 is pressed, on indicator comes “-STEP-” and the required synthesizer pattern is selected by buttons LEFT and RIGHT. It can accept 8 values: 1, 10, 20, 30, 50, 100, 1000 and 5000 Hz. The select pattern saving occurs when this button is pressed once again.


LEFT – frequency operational reducing. Press the button – the frequency down hopping.


RIGHT – frequency operational increasing. Press the button – the frequency up-hopping.


These two buttons are very convenient for quick frequency moving – the button is pressed, hold -> and the frequency is changed to the required level. When operation with transceivers TS-870S, FT-100D, FT-817 there were no such buttons. In those transceivers for quick movement within a band it is necessary to enter the menu or select the more large hopping pattern, then rotate encoder, then again enter menu and return to usual pattern. On enter other menu and there input the required frequency – it is clear that the synthesizers control programmes are creative not by real radio amateur who would work with his transceiver. And for so popular mode i.e. to quickly move the frequency within a band – it is necessary to several times press various buttons.

Circuit diagram

The synthesizer comprises three elements and three PCBs respectively. These are a controller board, a generators board and an indication board.

Controller board. Fig. 1. >>>>>               Preparing charge >>>>>

The synthesizer is controlled by chip DD1 PIC16F628. It was selected due to its low cost and the required operation quality. There is point to describe the operation of the microcontroller here – full description of this chip can be found on the manufacturer’s site – or Let us confine ourselves to such description: PIC 16F628 is a chip containing various “units and elements” that are controlled by the program embedded in it. When power supply is switched on, the program sets the frequency and the transceiver modes – i.e. the status of 6 transceiver control buttons – from memory cell No 0. Thus it is possible to write the parameters that we want to have immediately when the transceiver is on into cell No 0 and the program will initiate them. On the outputs from the processor to the periphery there are RC-filters – these are R17-19; C20-22. Filtering ceramic and electrolytic capacitors are installed on all power supply pins.

The microcontroller controls the operation of DDS (Direct Digital Synthesis) chip DD7 AD9832 on lines RA2, RA3, RA4, which generates a sine 80-350 kHz HF signal (from line No 14). Detailed description of this chip is available at the manufacturer’s site at In brief, this chip may be describer as follows: it generates a high-frequency signal with digital means. The company produces a number of DDS chips with different characteristics. For our purpose we chose the one with the lowest frequency and – which is of importance too – not so expensive as the analogues with higher frequencies. According to the manufacturer, the quality of the output signal of the DDS chip is within the declared parameters if its frequency does not exceed ? of the reference generator frequency. To enjoy the highest-quality signal, it is required to work with the maximum frequency of the reference generator; for AD9832 this is 25 MHz. For our variant this is 20 MHz – frequency is limited due to cutoff clock frequency for the microcontroller PIC16F628. As the reference frequencies received from DDS range from 1/60 to 1/250 of the basic frequency it might be assumed that when output frequency of DDS is this low, the drop of reference generator frequency by 25% (from 25 MHz to 20 MHz) will not affect its quality. Here are the figures of the DDS output signal at 1.1 MHz and 2.1 MHz frequencies – from the manufacturer’s site at


 The figures show how the density of stray radiation grows with the increase of the output frequency. Generally speaking, this is not really important for us, as the LPF at the DDS output will reject their greater part and, in addition, the loop of the phase lock itself will filter the control signal Upll from the generator board varicaps. Experiment-lovers will find enough freedom of action here, unfortunately, as usual, for extra money. What I mean is that AD9832 can be substituted by its follow-on modification AD9835 with higher frequency. These chips completely coincide in respect of pins as well as program control logic. Thus it is possible to use AD9835 instead of AD9832 and everything will work. However, to feel the difference of the supposed quality improvement with the use of AD9835 it is necessary to raise the reference generator frequency, which will require separate reference generators for PIC16F628 and DDS, but one more generator in the synthesizer of a sensitive receiver will by no means lead to the improvement of all its characteristics. There is no guarantee that additional derived frequencies will not appear somewhere in the receiver’s frequencies. Making such complicated assembly as a short-wave transceiver frequency synthesizer, our chief restriction was to remain within the minimum cost and to reach the required quality characteristics of the synthesizer that should not affect the parameters of the transceiver we have. Its manufacturer – Analog Devices – recommends using a reference generator with the highest-quality signal as this signal determines the DDS output signal quality. Measurement of the different reference generators noise characteristics with the ÑÊ4-59 spectrum analyzer did not give any remarkable results. Evidently, generator noise characteristics are beyond the resolution of this device. No difference was discovered either with the ÑÊ4-59 spectrum analyzer nor with any other means between different types of generators used as a reference generator for DDS. Probably, when the ratio between the reference generator frequency and the DDS output frequency is so big [as we have], noise parameters of generators do not influence the DDS signal quality so seriously.


  The DDS output signal is filtered by elements C10, 11, 12; L3, 4. This LPF cutoff frequency is around 700 kHz. Here is the figure representing the gain-frequency ratio (a photo from the screen of X1-38).


Frequency/phase detector is represented by DD8 chip – but it can be also HEF4046 (Philips Semiconductors), CD4046, its Russian analogue K1561GG1. Input No 14 SIGNin has the maximum sensitivity (according to the chip description – 150 mV) that is why it is fed with the signal from DDS – after the LPF the signal it not more than 0.5 V. The second input of phase detector No 3 should be supplied with a TTL level – that is why it is fed with the signal from the divider by 256.


Indication of the PLL lock-in is output to an indication board – LOCK LED controlled via VT1. Chain of elements C19, R12, R13 determines the time response of the LED glow. When the PLL is locked – the LED is off, if the loop is open – the LED either flashes or glows constantly. Control voltage Upll for varicaps of voltage-controlled oscillators is formed by elements R5, R6, R7, C14, C15, C16 at the DD8 output. Operational amplifier DA1A boosts this voltage up to the required level. It should be noted that the voltage on the varicap should be maximum possible – as the varicap Q-factor decreases at low voltages. That is why stable supply voltage of CA1A formed by DA2 chip should also be maximum possible – 78L08 is set for 9V voltage. It is more preferable to use 10V regulator but I could not buy such regulator in a small-size case. To supply all +13.8V transceiver power directly to DA1A without additional stabilization is a gamble as the transceiver exploits 100W push-pull linear amplifier and at the maximum output power the voltage may vary by 0.5V. Although the PLL will respond tothis supply voltage changes as the operating speed of the whole system allows this, this is by no means accepted in an up-to-date transceiver. If the supply voltage in the transceiver is stable or the synthesizer is supplied from a separate stabilized power supply source – i.e. a transceiver with internal power supply unit for different voltages – then we can definitely apply to DA1A power supply up to 15V. Thus the upper limit of Upll will be raised and due to the increase of this voltage we can extend the limits of the generators frequency tuning without affecting the varicaps Q-factor or to make such an adjustment that the voltage on the varicaps was not lower than 3V.

Transistor VT2 forms IRQ_TX voltage that controls the processor when RIT is switched on. This voltage increases the speed of processor response at RX-TX switch-over, which respectively enhances the general speed of the synthesizer operating with VOX and digital communication means in SPLIT mode. TX_IN voltage applied to VT2 gate is the voltage of TX transceiver that may be between +5-14V.

For control of different modes the transceiver exploits chips DD2, DD3 and DD4. Supplementary chip DD5 (not used in the transceiver) is provided and has connection layout on the board – it may be used for additional switching of transceiver modes. Bus D – outputs D0, D1, D2 and D3 is used for switch over of bandwidth filters and generators. Filters R26-29 and C24-27 were introduced to reduce possible interference form the digital part of the synthesizer. DD4 chip works as a buffer increasing the power of the switches – the domestic analogue is K155LN3, LN5. Inside, these chips contain six powerful inverters with an open collector. Output current of one inverter may reach 40mA, its voltage – up to 15V. Foreign chips have slightly different parameters – 74F06,07 – current 64mA at 12V; 74F06A,07A – current up to 48mA at 30V. Besides these, there are plenty of analogues with similar parameters. E.g. recommended parameter of Texas Instruments SN7406 chip are 40mA, 30V.

DD9 K561LA7 (CD4011) chip was used for negative voltage driver that is required for reliable cutoff of the diodes connecting supplementary capacitors to the generators circuit. This is a typical several hundred kHz generator having voltage doubler on VD4, VD5 and filtering capacitors C37, C38 at the output. It has dedicated outpins on the controller board to send no pickups to the generators. At C40, R14 values indicated on schematic circuit, oscillation frequency being 500 kHz, IF in the transceiver – 8.3-8.9 MHz – no pickups were detected. 


Generators board. Fig. 2. >>>>>           Preparing charge >>>>>

Generators are made in Hartley oscillator circuit on transistors VT8, VT9, VT10. As the required frequencies for some bands coincide, it was possible to cover all 9 bands with three generators (voltage-controlled oscillators) and four supplementary capacitors. Generator on VT8 provides frequencies for 3.5;21MHz, when C12 is connected – 1.9MHz, when C11 is connected – 18 MHz. Generator on VT9 provides frequency for 28MHz, when C15 is connected – 10MHz, when C14 is connected – 7;24MHz. Generator on VT10 operates at 14MHz. For the highest-frequency VCO, a unipolar transistor with the maximum gain slope should be used – this is KP307G; for the low-frequency one – KP303G,D, KP302B,G will do; for intermediate values – KP307W,D,E; KP303E. In this case three separate generators can produce approximately the same HF signal amplitude. The supply voltage is additionally stabilized with 9V DA1 stabilizer. The required generator and capacitor are switched with transistor switches VT1-VT7 controlled by decoder DD1. Codes entering the decoder inputs via bus D0-D3 from processor 16F628 are decoded by DD1 and, depending on the active band, open the decoder outputs. The DD1 output correspondences are: No 1 – 1.9 MHz, No 2 – 3.5 MHz, No 3 – 7 MHz and so on up to No 9 – 24 MHz, No 10 – 28 MHz. For example, when 160m band is initiated, VT1 opens, voltage from the collector via R19 opens diode VD5, aligning capacitor C12 switches on and the supply voltage via VD1 diode goes to the VT8 generator transistor. As the ac voltage in the circuit may transform and open diodes VD5-VD8, they are supplied via resistors R21, R22, R24, R25 and filtering chain R23, C36 with cutoff negative voltage generated by chip DD9 located on the controlled board. Transistors VT11, VT12 gain the HF output signal up to the necessary level required for operation of dividers DD2, DD3 – 74AC161. Resistors R44, R45 provide additional shift of the DD2 output – that is why just 1V HF voltage is sufficient for its stable operation. From output No4 the signal comes divided by 2, from output No 13 – divided by 4, from output No11 – divided by 16. Chip DD3 divide the frequency by 16 once again, which results in the required value of VCO frequency division 16x16=256. 

Spectrum all VCO frequencies is given in Table No1 above.

Tuning of VCOs involves setting of the required limits of each band change at 0.8-8V voltage supplied to varicaps from a separate variable resistor, Upll circuit broken in advance. If the HF signal amplitude at the VCOs outputs will significantly differ for VT8, VT9, it is required to apply the transistors with lesser gain slope. Formless coils L1. L2 are wound on 7mm and 5.5 mm arbors respectively with 0.8mm varnished enameled wire. L1 has 8 winds with a lead from the 3.5 wind; L2 has 6 winds with a lead from the 2.5 wind. After the final tuning and alignment, the insides of the coils are filled with pieces of foam-rubber and paraffin. Coil L3 is wound on a 10mm form, it has 16 winds of 0.6-0.7mm varnished enameled wire. Chokes L4, L5, L6 may be wound on 5-10mm ferrite rings, permittivity 600-2000, 11-7 winds of 0.15-0.22mm wire is enough.

Why this variant of VCOs was chosen for generation of all-band frequencies? Reduction of VCOs quantity to less than three will lead to the extension of their frequency change limits; it may sharply impair the synthesizer noise parameters. Reference literature on synthesizers reads: “For frequency control with varicaps their capacity shall comprise only a small part (<20%) of the total circuit capacity, otherwise, with the varicaps Q-factor being relatively low, phase noise significantly increases”. V.Manassewitsch writes: “In a VCO with a wide band of electronic tuning, frequency noises appearing due to the presence of electronically tuned reactive element (in our case this is a varicap) not only prevail but may increase the generator noise level by 20-40 dB as compare to the noises of the same generator without a electronically tuned reactivity”. What does the number of VCOs have to do with this? The reason is that to get the frequencies for all the bands from one generator we have to extend its tuning limits and it can be done only through the increase of varicaps capacity with respect to the total circuit capacity. I.e. to get the highest-quality signal from the generator tuned by a varicap it has to be connected to the circuit so weakly that the varicap capacity change limits were sufficient only for the generator tuning within one band. Of course, to make a separate VCO for each band is rather expensive. That is why I had to adhere to this tradeoff variant – three VCOs + addition connection of capacitors helping to retune the generator to other bands. Number of VCOs depend on the IF used in the transceiver. At happy choice, when the frequencies from the synthesizer for some bands coincide, quantity of VCOs may be reduced. My conclusions about direct link between varicap quality, VCO quantity, tuning limits and varicap-circuit connection alone should not be considered as “fundamental” – that only this influences a synthesizer noise parameters in general. Scientific and technological progress goes on – probably there are varicaps with very good characteristics, which will not affect a generator noise properties so significantly – the author just could not find and use them. Besides varicaps there is number of factors influencing the noise characteristics of a synthesizer. To describe all this nuances is beyond my task – those who are interested can find this in specific literature…


Indication board and encoder. Fig. 3. >>>>>    Preparing charge  >>>>>

The same as in the previous synthesizer on 89C52, indication is static “noiseless” no matter how much it consumes. Current frequency data are sent to the indicators as a serial code at control button push, which enabled to reduce the number of conductors between the boards. For information storage 8-bit shift registers are used. This connection design has a number of advantages: 1) no noise from the indication board; 2) signal line number is reduced; 3) it is possible to display not only digits but also some symbols. Both foreign 4015 and domestic K561IR2 chips may be used as registers DD1-DD7 on the indication board. LED seven-segment matrixes DD8-DD14 with a common cathode are offered in great quantities in the market, different in size and in colour. Chip DD16 generates control pulses from keyboard buttons – this may be 4017 chips or domestic R561ÈÅ8. Buttons A1-A6 serve for activation of different transceiver operating modes. Their operation is quasi-sensor based – that is why to know if the mode is on or off, there is a LED at each button respectively indicating the active mode with its light. LED VD11 indicate the frequency lock and holding with the PLL system. Its light indicates the PLL break. Transistor switch VT2 serves for RIT mode – its input is fed with TX transceiver voltage (TX_IN) which may be within +5-14V limits. Element DD15C invert, gain and decouple the VT1 transistor input from the BLINK PIC16F628 output. Elements F, B, E, D of chip DD15 serve for pulse generation from the encoder. Optoelectronic couple VD8, VD9 may be presented by combined in one case emitter and receiver AOT137. These optoelectronic couples operate on reflection – that is why it is enough to rotate a disc with black and white sectors or cuts in from of two such optoelectronic couples – and the encoder is ready. The value of current-limiting resistors R2, R3 connected serially with the emitters should not be reduced less than 510-4700Ohm, otherwise emitting diodes can fail. On +5V pin DD15 there is an additional filter R5, C4, as the total sensitivity of triggers is high, and noise sometimes appearing in +5V bus interrupts the encoder stable operation. In addition, resistor R5 may be used for encoder tuning adjustment changing the chip supply voltage and, respectively, the trigger sensitivity.

In the second variant of indication board Fig. 4 >>>>> instead of seven-segment LED matrix one LCD indicator is used.


Standard mode

Heterodyne inversion

Band selection

Tuning spacing selection

Input of frequency into memory cell

Scan initiation

 This may be any two-row matrix indicator of 1602 series both from foreign  companies like Powertip, Sunlike, Wintek, Bolymin and Russian MT-16S2. The board has connection layout for 1602J – outputs down to the left, though the use of other types is not excluded, as the connection of the plated holes with LCD pins may be realized with the help of wire pieces.

 According to the LDC used, the desired contrast should be adjusted by resistor R8 – it exploits  connection layout on the board for standard 0.125W. Backlighting intensity is adjusted by resistor R10.

 Sealled charge, type frontal >>>>> type behind >>>>>


 Recommendations on installation and tuning

 The synthesizer does not have any tuning peculiarities. If all the elements of the digital part are operable it starts functioning immediately and there is nothing to adjust in it. It should be noted that the LPF capacitors used on the DDS output should be with the minimum TCC (temperature coefficient of capacitance) – it will prevent the filter pattern from smearing during the transceiver warm-up – these are C10, C11, C12. Any silicon diodes may be used. In case it is required to get the maximum voltage in the negative voltage generator then any germanium diodes should be used. Quality requirements to capacitor C40 in respect of TCC are the same as to LPF capacitors – although it is unlikely that the frequency will change significantly and it will somehow influence the synthesizer operating quality. We can only

 assume that if this generator frequency tuning is too great then derived frequencies may appear somewhere in the receiver. Layout connection for PIC16F628 is made in such a way to enable its ISP. Based on the previous experience of noise control, this variant has additional RC filters in the board lines from the synthesizers as well. Although to hear no noise from the digital part of the synthesizer in the telephones it is enough (using modern processes) just to make a correct arrangement of the supply wires in the transceiver. Increase of capacitor capacity on buses CLK, DAT, BLINK may cause errors in the periphery controller control.

 Values of these elements will be determined by installation of the synthesizer in the transceiver. From the very start it is possible to use jumpers instead of resistors and not to use capacitors (what I do usually do) and only in case of noise exactly from the digital part – to introduce these filters later. There are two types of noise from the synthesizer. The first – during the encoder rotation on some frequencies appear very short “pip-pip-pip” which are impossible to be tuned for – they disappear when the encoder stops. These are serial codes entering the indication board registers. The way to counter them – to install a separate +5V stabilizer on the indication board supply, to install an RC filter on input 8705 – this is 1-2W,10-15 Ohm resistor and an electrolytic high-capacity capacitor (my “default” variant is 10000mF) from the point of this resistor connection to input pin 7805 for GND. The capacitor capacity may be chosen based on audible noise suppression. If such short noise appear only in AMP mode (or any other mode in transceiver) – then the AMP switch wire should be decoupled with an additional LC or RC filter or the AMP point should be grounded on the band-pass filter board with an electrolytic capacitor selected according to the maximum noise suppression (1-100mF). The second type is derived points – “short” carriers that are most numerous at 20m. They appear as the result of transformations in the mixer and get into the transceiver IF pass band. The basic fundamental method to counter this noise is screening of the controller board where the generator is located. Screening of the generator only does not give any results – the pick-up spreads from the board lines feeding 20MHz to 16F628 and DDS. The screening method should be chosen depending on the location of the controller and generators boards in the transceiver. The best one is to completely cover the board with a screening box made of tin plate of fiber-glass plastic covered with copper foil. On the controller board from the side of element installation the case foil is next to solid so it acts as a screen. At the board corners there are 4 mounting holes and there is no foil under them – this was done on purpose. During installation of the boards into the transceiver - if a derived point from the 20MHz generator is found – the plating foil at the board corners should be grounded to metal racks on which the controller board is mounted (the   13mm racks are made of steel) for the maximum suppression of this noise. As a rule, I had to ground the foil at the corners next to Ê155LN3. The foil on the board is split in two parts – one piece where DDS chip is located, another one - at DD1 and the reference generator – that is why grounding different corners of the foil it is possible to provide the required screening of this or that elements. Arranging the wires between the boards it is not necessary to bind them into tight assembly, moreover – to unite digital and analogue wires. Each board is supplied via a twisted-pair strand cable. One cable is case, another – supply power. The Upll wire should be screened, as any puck-up to the Upll circuit will result in changes of the varicap capacity and, respectively, of frequency manifested as undesired “chatter”, background, etc. Upll may also be fed via a tightly twisted pair of thin wires. For more details on board tuning see

Drawings of the printed charges look here >>>>>



1. Author’s site

2. V.Manassewitsch “Frequency Synthesizers. Theory and Design”. 1976 byJohn Wiley and Sons, Inc.

3.  Eric Tart Red “Arbeitsbuch fiir den HF-Techniker”. Franzis-Verlag GmbH, Miinchen, 1986

Back to main page