Preparing for setup
Before setting up the oscillatory circuits, you need to make sure that the rotors of the KPI unit are not skewed or knocked down relative to each other. When the rotor is fully inserted, the air gaps between the plates must be the same, and the cut of the rotor plates of all sections must be in the same plane (this is verified by applying a ruler). Such defects are not very common, but if you overlook them and try to eliminate the mismatch by adjusting the coils and trimming capacitors to the faulty KPI unit, you can completely upset the receiver. If there are mechanical defects in the KPI unit, it is necessary to either eliminate them or replace the unit with a new one.
Leveling the capacitance of individual sections of a capacitor bank is possible using capacitance meter and a special device that provides alternate connection of different sections of the block to the meter with rigid conductors that do not change their position. When leveling containers, it is necessary to ensure that the capacities of all sections differ by no more than 1 pF at any angle of rotation of the rotor.
Then you need to check the connection of the scale pointer with the drive mechanism so that at its extreme position it coincides with the extreme mark marked on the scale, or if there is no such mark at both extreme positions of the capacitor rotor, it deviates symmetrically from the ends of the scale. The receiver volume control should be set to approximately 4/5 full volume, and the tone control should be set to the position of greatest transmission of high tones, if this control does not simultaneously adjust the passband of the intermediate frequency amplifier.
If the receiver has a device for adjusting the bandwidth of the transmitted frequencies, then it should be set to the narrowest band. In receivers with AGC, the latter should be temporary turned off. To do this, the regulating voltage line must be interrupted and negative voltage must be applied to the grids of regulated lamps in addition to it.
Of course, you also need to make sure that the circuits being adjusted are mechanically serviceable (no short circuits between the stator and rotor plates of the control unit, integrity of the coils and serviceability of the range switch). The receiver itself must be located on the table so that access to all adjustment elements and to the grid circuits of the tuned cascades is sufficiently free. Some receivers have to be removed from the box for this purpose.
Connecting a signal generator and output meter
The receiver being adjusted is always connected to the generator through a capacitor or antenna equivalent, which recreates the real operating mode of the receiver input circuits. In addition, a capacitor or antenna equivalent separates the receiver and oscillator DC and prevents short circuits or leakage in the power supply circuits of the electrodes of the receiver lamps.
The shielding sheath of the cable from the SG must be connected to the housings or grounding terminals of both the receiver and the generator. Before each adjustment, the generator must be set to the frequency to which the given receiver circuit is being adjusted. The RF voltage supplied to the adjustable circuits should always be as low as possible, so that, on the one hand, the lamps are not overloaded, and on the other, so that the increase in sensitivity can be monitored using the output meter. If the sensitivity increases during adjustment, then the supplied high-frequency voltage should be immediately reduced.
With a modulated oscillator, you can adjust the receiver by ear, but the adjustment is more accurate if you use an output meter. To connect it, the additional speaker jacks available in the receiver are convenient. To increase the deflection of the output meter needle, it can be connected to the primary winding of the output transformer, and not to the secondary. In order not to load the output meter with constant anode current of the output lamp, it must be turned on through a capacitor with a capacitance 0.2-2 µF.
You can also adjust the contours with an unmodulated signal. Then, a DC lamp voltmeter connected in parallel with the load resistance of the diode detector is used as a setting indicator. You can also judge the tuning using the optical tuning indicator included in the receiver, but in this case the tuning is less accurate.
Tuning intermediate frequency circuits
If the detuning is not very strong, you can try to tune all the IF circuits in one step, for which the signal from the generator is supplied to the control grid of the mixing lamp. Oscillations of the local oscillator must be disrupted during the adjustment of the amplifier. To do this, it is enough to connect the control grid of the heterodyne lamp through a capacitor with a capacity 0.05-0.1 µF with the ground.
The oscillatory circuits are tuned by sequential rotation of their adjustment elements until the maximum output voltage is obtained. After adjusting both circuits of the two-circuit filter, you must again return to the first of the circuits being tuned and refine its setting. Through a series of such successive approximations, it is possible to achieve precise tuning of all circuits to resonance, and the gain of the intermediate frequency amplifier will become maximum.
To speed up the tuning of bandpass filter circuits, you can weaken the influence of the second circuit on the one being tuned by temporarily shunting the second circuit with a resistance of 10-20 kOhm ( rice. 1 ).
Rice. 1. Setting up a bandpass filter
1 - customizable circuit.
It is useful to connect a capacitor in series with this resistance with a capacitance 0.01-0.02 µF, blocking the path of direct current. The second end of the shunt chain can then be connected directly to the metal chassis of the receiver in all cases. The use of such a chain is absolutely necessary when tuning to the maximum if the bandpass filter has a strong coupling that creates a double-humped resonance curve.
When one circuit is shunted, the resonant curve even in this case turns into a single-hump curve with one maximum corresponding to the resonant frequency of the unshunted circuit. If the circuits are severely detuned or the circuits of a newly mounted receiver are being initially adjusted, then the signal generator should first be connected to the control grid of the last IF lamp and, first of all, the circuits included in its anode circuit should be adjusted. Then the generator is reconnected to the control grid of the previous lamp and the circuits included in its anode circuit are adjusted, etc. up to the circuit included in the anode circuit of the mixing lamp.
Immediately after setting up all the IF circuits, without changing the generator frequency, adjust the IF blocking circuit at the receiver input. The cable from the generator is connected to the antenna socket through an equivalent antenna and the voltage of the generator is increased to the extent necessary for a signal to appear at the output of the receiver. The barrier circuit is adjusted to the minimum output voltage of the receiver.
Since adjacent channel selectivity, frequency bandwidth and frequency distortion within it mainly depend on the resulting selectivity curve of the amplifier, after tuning its circuits it is useful to remove and plot the resulting selectivity curve. To do this, you need to have a signal generator that allows controlled frequency changes within small limits 20-30 kHz in the region of the intermediate frequency of the receiver. When using a generator type GSS-6 For this purpose, they use a scale on the vernier handle, and the value of the scale division is determined by dividing the change in frequency on the main scale with 1-2 full turns of the vernier handle by the corresponding number of its divisions.
In amplifiers equipped with filters with adjustable bandwidth, after adjusting the circuits at the weakest connection, you should remove the selectivity curve for the two extreme settings of the bandwidth regulator (the technique for removing selectivity curves is described in section " Basic tests of AM receivers".
Local oscillator adjustment
After the tuning of the IF circuits is fixed, the calibration of the receiver tuning scale will be determined only by the tuning of the local oscillating circuit. The quality of its coupling with the input circuits, and therefore the effectiveness of preliminary selectivity, which determines real sensitivity and other important characteristics of a superheterodyne receiver. Therefore, setting up the heterodyne circuit requires special care. Before you start, you need to carefully study schematic diagram local oscillator and find out:
- Location in the installation of all adjustment elements of the heterodyne circuit on each subband.
- The presence of tuning elements that influence tuning on several subranges.
So, for example, with the range switching circuit shown in rice. 2a , adjusting the inductance of coil L1 will affect both ranges and its tuning core should be considered as a tuning element in the range of shorter waves. The tuning core of coil L2 will only affect the tuning of the longer wavelength range (when the switch is open).
Rice. 2a, b
Having analyzed the action of the local oscillator adjustment organs, it is possible to outline the correct sequence for adjusting the various AM ranges, which will allow each range to be adjusted only once. Modern multi-band receivers, as a rule, use a band switching circuit that ensures independent adjustment of each of them ( rice. 2b ). In this case, the order of adjustment of the ranges does not play a significant role.
Tuning the heterodyne circuit is usually carried out by an indirect method - by receiving a frequency corresponding to the receiver tuning scale, i.e. differing from the local oscillator frequency by an amount intermediate frequency. In this case, the frequency corresponding to one or another mark on the receiver scale is set on the signal generator, the output of the signal generator is connected to the control grid of the mixing lamp, and by adjusting the corresponding organ of the heterodyne circuit, the maximum signal at the receiver output is achieved. With this tuning method, you must always have firm confidence that the signal is not being received according to mirror channel.
In broadcasting receivers, the local oscillator frequency when receiving on the main channel is usually higher than the received one by an amount intermediate frequency. Thus, comparing two signal generator settings that differ by twice the intermediate frequency f1 And f2, at which reception occurs, it is always possible to determine the true frequency of the local oscillator
fg = (f1 + f2) / 2
and which of these two frequencies corresponds to the main channel, and which to the mirror one. To avoid errors due to the reception of harmonics of the signal generator frequency, the output signal level must be taken into account when various settings generator (harmonics give a significantly lower output signal level).
Local oscillator adjustment using the one-point method
Local oscillator tuning using the one-point method is found in extended HF ranges. In this case, the tuning knob is set so that the arrow is on the tuning scale mark corresponding to the exact pairing frequency. This frequency is set on the signal generator and the heterodyne circuit is adjusted with a tuning core or capacitor of this range according to the maximum output signal.
To make it easier to adjust the local oscillator before making the adjustment using the corresponding organ, you can determine the deviation of the local oscillator setting by achieving signal reception by rotating the receiver tuning knob. If reception occurs when the needle deflects towards higher frequencies on the tuning scale, this means that the natural frequency of the local oscillator is lower than the required one and tuning will be achieved by reducing the capacitance of the tuning capacitor or unscrewing the ferromagnetic core from the local oscillator coil.
If the signal is received when the needle on the receiver scale deviates towards lower frequencies, this means that the natural frequency of the local oscillator is higher than required and reverse measures are needed for adjustment. If the exact conjugation frequency is unknown, then when conjugating at one point, select a frequency corresponding to approximately the middle of the scale.
Construction of a local oscillator using the two-point method
The construction of a local oscillator using the two-point method (using a parallel trimming capacitor and inductance adjustment) begins with adjusting the initial capacitance near the highest frequency of the tuned range, and then adjusts the inductance near the lowest frequency of the range ( rice. 3 ).
Rice. 3. Scheme for adjusting local oscillator circuits when paired at two points
After adjusting the inductance, they return again to the highest frequency of the exact coupling and restore the tuning at this frequency with a tuning capacitor, etc. until both points match the scale. If, during two-element tuning, the exact pairing points are unknown, then they are taken at frequencies that differ from the highest and lowest frequencies of a given range by 10-15%.
Local oscillator adjustment using the three-point method
Tuning a local oscillator using the three-point method requires the presence of three trimming elements in the local oscillator circuit: two trimming capacitors (parallel and series) and a trimming core at the loop coil. The capacitance of the series (mating) capacitor is usually quite large, and a constant capacitor is often used in installation. Then the adjustment of the required capacitance is carried out by replacing this capacitor or selecting a small additional capacitor connected in parallel. The first adjustment in this case is also carried out near the highest frequency of the range using a parallel tuning capacitor. Then they proceed to adjusting the local oscillator near the lowest frequency of the range using a series trimming capacitor.
The third in order is to adjust the setting at the midpoint of the range by adjusting the inductance of the heterodyne circuit coils. In which direction should the capacitances and inductances be changed in case of a particular deviation from the scale calibration, explains rice. 4 .
Rice. 4. Scheme for adjusting local oscillator circuits when paired at three points
After a single adjustment at all three points, they return again to the first point (near the highest frequency of the range), and if it turns out to be knocked down, then repeat the described operation until a stable coincidence of the settings with the scale graduation is achieved at all three points. If the exact values of the frequencies at the three junction points are unknown, then the frequency can be taken as the midpoint of the junction 250 kHz in the range of Far East and 1000 kHz in the CB range, and as extreme frequencies - frequencies that differ from the highest and lowest frequencies of this range by 5-7%.
High Frequency Circuit Tuning
High-frequency circuits are usually adjusted at two points coinciding with the extreme points of local oscillator coupling. The output of the signal generator is connected through an equivalent antenna to the antenna-ground terminals. The receiver is tuned according to its scale to the lowest precise coupling frequency, and the signal generator is adjusted to the maximum signal at the receiver output. Then, by adjusting the coil core of the input circuit, the maximum increase in the output signal of the receiver is achieved. If the high-frequency part of the receiver contains more than one oscillating circuit, then you can first try to tune them simultaneously.
After the tuning at this point is completed, you need to make sure that the generator frequency exactly matches the received frequency. To do this, you need to remember the position of the signal generator tuning knob and, while monitoring the output signal of the receiver, slightly change the generator frequency in one direction or the other. If the deviation of the generator frequency in any direction from the initially set one causes a monotonous decrease in the output signal of the receiver, then this is a sign correct settings. If the maximum of the output signal has shifted away from the initially set frequency of the generator, then the adjustment of the input circuits should be refined by adjusting the signal generator to the new position of the maximum.
If in the input circuit of the receiver there are two tuning circuits that form a bandpass filter, then each circuit must be tuned separately, shunting the other circuit with a resistance 10-20 kOhm, as described for setting up IF filters. If the receiver has an amplifier high frequency(UHF) with an oscillatory circuit in the anode circuit, then if there are complications in simultaneous adjustment of all HF circuits, you should first adjust this circuit by applying the signal from the generator directly to the control grid of the UHF lamp.
After the high-frequency circuits have been adjusted at the lower precise coupling frequency, the receiver is tuned according to its scale to the highest precise coupling frequency. The generator frequency is again set to the maximum output signal of the receiver, and the circuits are adjusted using tuning capacitors, achieving highest magnification this maximum. Then they return again to the first point and refine the adjustment of the coil cores, etc., until the next transition to another point in the range, its additional adjustment turns out to be unnecessary.
In conclusion, to check the quality of the pairing, you need to check the operation of the receiver at the middle frequency of the range. To do this, compare the values of the input signals supplied from the generator, necessary to obtain the same output voltage when tuning to the average frequency and at the frequencies at which the input circuits were adjusted. They should differ by no more than 2-3 times.
Features of tuning in the shortwave ranges
In many receivers, there is a certain mutual influence of the settings of the local oscillator and input circuits in the HF range. Therefore, the initial coupling of the heterodyne circuit with the tuning scale should be considered a preliminary operation. The final adjustment of the heterodyne and input circuits may require simultaneous additional adjustment of them already when the signal is supplied from the generator to the antenna input of the receiver.
The second feature is that most modern receivers are equipped with “stretched” short-wave ranges, and additional capacitors are introduced into the oscillatory circuit circuits, reducing the range overlap coefficient ( rice. 5 ). When adjusting such circuits, first of all, you need to make sure that the overlap coefficient of the heterodyne circuit is not affected.
Rice. 5. Circuit diagram with stretched tuning on range 2 (regular tuning on range 1)
To do this, you need to take the ratio of the extreme frequencies indicated on the receiver scale and compare it with the actual ratio of the extreme frequencies received by the receiver. If these relationships coincide, then it is enough to adjust according to the method of one or two interface points provided by the adjustment bodies. If the overlap coefficient is off, then this indicates a deviation in the capacitances of the “stretching” capacitors ( Wed1 And Ср2 on rice. 5 ) from their calculated values.
Then the local oscillator adjustment should be carried out according to three point method, and it may be necessary to replace the stretch capacitors. A damaged overlap coefficient in the input circuit is reflected in a sharp unevenness of sensitivity across the range after adjusting the circuit contour at one point (usually only one adjustment element is provided here). In this case, it is also necessary to clarify the overlap coefficient of the input circuit by appropriately replacing the stretching capacitors. If the input circuit is configured correctly, then at any point in the range after adjusting the signal generator to the maximum output signal of the receiver, deviation of the adjustment element in any direction from the set position should be accompanied by a decrease in the signal at the receiver output.
It is necessary to note here once again the special danger of reception via the mirror channel precisely in the short wavelength range. Therefore, when tuning a receiver in the HF band, you must especially carefully follow the above instructions on this issue.
Malfunctions detected when setting up circuits
When adjusting oscillatory circuits, you can encounter a number of specific malfunctions.
- The circuit has high attenuation. This malfunction is expressed in the fact that the resonance turns out to be very dull, a cascade with such a circuit does not provide noticeable amplification, and a strong restructuring of the circuit changes the readings of the output meter little. The reason for this is the deterioration of the quality of any of the parts included in the circuit (capacitor, core, coil), and it can sometimes be eliminated only by sequentially replacing each of the parts of the faulty circuit.
- The circuit does not adjust to the specified frequency elements provided for adjustment. For example, when rotating the core in the coil of the intermediate frequency circuit, it is not possible to obtain the maximum reading of the output meter. This indicates that the circuit is too detuned. The reason for this may be mechanical damage to the coil or circuit installation, or sometimes to a mismatch in the capacitance of the capacitor in the circuit. If major malfunctions are not noticeable, then to adjust the circuit, you can replace the constant capacitor. They also tune highly detuned heterodyne circuits, selecting parallel capacitance at the beginning of the range and series capacitance at the end.
- False high. Trimmer capacitors typically rotate 360 degrees, with their capacitance reaching maximum and minimum values at certain positions. If the maximum output voltage of the receiver coincides with one of these positions of the trimming capacitor, then, without paying attention to this, you might think that resonance has been achieved. A similar false maximum may appear when the trimmer core passes the center of the coil winding.
To prevent errors in tuning circuits caused by false maximums, after any adjustment it is necessary to inspect the adjustment element to make sure that it is not in the position of minimum or maximum capacitance (inductance). If during tuning only one maximum is detected and it is false, then this means that the control limits of the tuning element are not enough to achieve resonance, and this circuit must be recognized as not being adjusted to the given frequency.
- In certain parts of the range, reception of stations disappears. Complete cessation of use in certain areas of the scale may be a consequence of:
- short circuit of the rotor and stator plates of a variable capacitor, then reception stops at this section of the scale, regardless of the range
- failure of local oscillator generation due to the low quality factor of its circuit or a drop in the slope of the heterodyne lamp characteristic, then the cessation of reception on different ranges generally occurs at different points of the scale. Type 2 faults most often occur at the end of the HF band. It can also be caused by a decrease in operating voltages on the electrodes of the local oscillator lamp (including a decrease in filament voltage, for example, due to a voltage drop in long and insufficiently thick connecting wires of the filament circuit).
Along with other means of eliminating “dips” in the local oscillator, it is possible, as an exception, to increase the feedback (bring the coil closer feedback with a loop coil or increase the number of turns in the first coil).
VC. Labutin."The Radio Master's Book". 1964
Narrowing the FOS bandwidth
Microphone amplifier with AGC
Resonant amplifier circuit on K174PS1
The frequency range 0.2...200 MHz is determined by the choice of circuit L. The transmission coefficient is not less than
20 dB. AGC depth is at least 40 dB.
LED S-meter
Connect the S-meter to the ULF input, before the volume control. The setting consists of replacing resistors R9 and R10 with one tuning resistor to clarify the values of this divider.
Low-pass filter for transistor power amplifier of HF radio station
The proposed low-pass filter works in conjunction with transistor amplifier power in the frequency range from 1.8 to 30 MHz with an output power of no more than 200 watts.
The low-pass filter inductors are frameless and wound turn-to-turn with PEV-2 wire with a diameter of 1.2 mm for ranges 14; 18; 21; 24.5; 28 MHz and PEV-2 wire with a diameter of 1.0 mm for the rest. The values of capacitors C1, C2, C3, which do not fall into the standard series, must be selected from several capacitors in parallel or series connection.
Structurally, the low-pass filter is made on a three-section ceramic biscuit switch 1 type 11P3N in the form of a single one, enclosed in a shielding housing made of non-magnetic material. Copper bus 2 is the common wire of the low-pass filter and is connected
electrically with housing 3, radio chassis and ground bus. The middle biscuit of the switch is a support one - for mounting the filter elements. Coaxial connectors of the SR-50 type are installed at the input and output of the low-pass filter.
I. Milovanov UY0YI
Band switch
The emitters of the transistors are loaded onto the range switching relay
Q-multiplier for a simple receiver
An attachment that allows you to increase the sensitivity and selectivity of the receiver due to positive feedback without modifying it.
A Q-multiplier is an underexcited generator of electrical oscillations with positive feedback, the value of which can be changed. If the operating mode of the generator is selected such that the compensation of active losses in the oscillatory circuit is incomplete, then self-excitation of oscillations will not occur, but the quality factor of the circuit will be very high. When such a circuit is included in the resonant amplifier of the receiver, selectivity and sensitivity can increase tenfold. Most often, a Q-multiplier can be included in an intermediate frequency amplifier. The Q-multiplier itself is made in the form of a separate structure, which has leads for connecting it to the receiver.
The emitter current of the taranistor, which determines its amplifying properties, can be smoothly adjusted by variable resistor R2. When the emitter current is low, the effect of the PIC is weak. With a gradual increase in the emitter current, the influence of the PIC increases due to an increase in the amplifying properties of the transistor and, finally, at a certain feedback value, the generator is excited. If the Q-multiplier is brought to self-excitation, then it will work like a second local oscillator; in this case, the mixer bandwidth can reach 500 Hz or less. In this mode, the receiver can receive telegraph radio stations. Circuits LC and L1C1 must be tuned to intermediate frequency.
Crystal oscillator 500 kHz
Sports equipment uses quartz oscillators with a frequency of 500 kHz. But it happens that a radio amateur does not have the necessary quartz. In this case, a quartz oscillator comes to the rescue, followed by division to the desired frequency. We present to your attention a diagram of such a device on the IC 4060 chip (generator and 14-bit counter)
The generator operates at a quartz frequency (widely available) of 8 MHz. The output signal has a frequency of 500 kHz. The output low-pass filter has a cutoff frequency of approximately 630 kHz and removes the first harmonic, resulting in a pure sine wave. The buffer amplifier is implemented on bipolar transistor according to the "common collector" scheme
Mixing type GPA
V.Sazhin
A mixing-type VFO is designed for a transceiver with an intermediate frequency of 9 MHz. The tuning range of the master oscillator on transistor VT1 is 5.0…5.5 MHz. The RF voltage at the output of the source followers is about 2 volts. Equality of output voltages in different ranges is achieved by selecting the resistances of resistors Rv connected in series with L2. Filters L2-L3 are adjusted to the middle of the GPA operating range. Filters, like T1, are wound on HF3 ferrite rings with a diameter of 10 mm.
Frequency converter
The mixer shown in the diagram provides a wider dynamic range(compared to active mixers) and very low level noise, which allows you to obtain high sensitivity of the receiver even without preliminary AMP. The mixer output uses a circuit tuned to the IF frequency.
The circuit differs from the one proposed in [L.1] in the way it applies a negative bias voltage, relative to the sources, to the gates of the transistors, which is necessary to obtain maximum sensitivity. The gates are galvanically connected through the T1 winding to the common power supply negative. And the sources are supplied with a positive bias voltage from trimming resistor R1. Thus, the gates are at a negative potential with respect to the sources. This method of supplying bias is beneficial for designs with a common negative, since it does not require an additional negative power source.
The HF transformer is wound on a ferrite ring with a diameter of 7 mm and a permeability of 100NN or 50HF. Winding is carried out in three wires, 12 turns. One winding is used as “3”, and “1” and “2” are connected in series (the end of one winding to the beginning of the other). For the transistors indicated in the diagram, the optimal bias voltage is 2.5 V (set to maximum sensitivity) and the local oscillator voltage level is 1.5 V. Transistors are applicable KP302,303,307 with the lowest cutoff current. Several better parameters can be achieved with KP305 transistors.
The mixer is reversible and can be successfully used in a transceiver.
A variant of the circuit using EMF is shown in Fig. 2.
Literature
1. V. Polyakov B. Stepanov
heterodyne receiver mixer
Radio No. 4 1983
Receive/transmit mode switch
heterodyne receiver mixer
V. Besedin UA9LAQ
An article with this title was published in. It described the mixeron field-effect transistors used as controlled resistances.The mixer diagram shown in is made using a matched pair
n-channel FETs and receives bias from the sourcenegative voltage of a bipolar power supply. This kind of foodquite cumbersome for a receiver, especially a portable one. Currentlyequipment with a unipolar source has become widespreadsupply with “grounded minus”.
To adapt the mixer to modern realities, I propose replacing transistors V1 and V2 with a transistor assembly of the K504 series. In this case, we have an identical pair of transistors with a p-channel, the gates of which are supplied with a positive voltage through the tuning resistor R1.
Research conducted by the author has shown that this assembly works satisfactorily even at frequencies in the 2-meter range (144–146 MHz), but a VHF receiver with such a mixer is somewhat “dumb.” However, the author used this mixer in the VHF FM version of a superheterodyne receiver at 145.5 MHz for the local VHF TRAN network. The frequency of the quartz local oscillator is 67.4 MHz, the intermediate frequency of the receiver is 10.7 MHz. The high-frequency amplifier on the KT399A transistor helped achieve a sensitivity of the receiver in units of microvolts.
Because the field effect transistors assemblies require bias to “close” them, then, using the data from, you can select an instance of the assembly for the receiver’s supply voltage. In addition, the field-effect transistors in the K504NTZ and K504NT4 assemblies are quite powerful, which can have a positive effect on the dynamic characteristics of the receiver.
This circuit has simple range switching (switching coils), has enhanced stabilization of the generation mode and shows very decent stability. It was planned as a GFO at IF = 5 MHz, but the stability at 24 MHz was very decent (about 200 Hz per hour). In general, with the indicated ratings, it continuously covers the range from 6.7 to 35 MHz with amplitude unevenness of no more than 6 dB
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More and more attention is being paid to filtering the signals emitted by transmitting devices. The emission of signals at frequencies different from the operating one can be regarded, by analogy with road traffic, as driving into the oncoming lane due to the oversized vehicle.
On the one hand, both radio amateurs and professionals use low-pass filters (LPF) at the output of transmitters to suppress only harmonic components. On the other hand, in pursuit of reduction in size, and therefore savings in structural materials, manufacturers of transmitting equipment are creating more and more “masterpieces” of transceivers, which either have the simplest filters at the output of the transmitters, or do not have them at all. In the latter case, the calculation is made for connecting external filtering matching devices - various kinds of tuners, which are either produced separately as an option, or are not produced for a particular transceiver at all.
If you want to increase the power of the output signal of the transmitter, the radio amateur makes or purchases a power amplifier, which contains only a low-pass filter (for example, in the form of an output P-circuit). Such a filter to a certain extent suppresses the harmonics of the main signal, and the amplifier itself amplifies the entire spectrum of the signal that comes to it from the transceiver. Consequently, the suppression of harmonic components, which are caused by the nonlinearity of the stages in both the transceiver and the power amplifier, is reduced. Other components, the frequencies of which are below the low-pass filter cutoff frequency of the power amplifier, entering it, are amplified and pass into the antenna. A resonant antenna, well matched at the operating frequency, partially suppresses unwanted spectral components, which, however, become the cause of interference in the near field.
Currently, in addition to local oscillator interference and their harmonics “creeping through” to the transceiver output, the output signal of the transceiver also contains “digital” fluctuations from various kinds of digital “gadgets” (scales, shapers, dividers, DSP, from those introduced into the transceiver at sharing with computer noise components).
Thus, to protect the airwaves from “preparatory” auxiliary signals, it is necessary to have at the output of the transmitting equipment not only a low-pass filter, but also a high-pass filter with a total transparency band, ideally equal to the band of the emitted signal: for SSB - 2.4 kHz, for CW - for AM - 6 kHz, for FM - 10...15 kHz. Since it is not possible to provide such bandwidths at the output of transmitting devices in practice (and even taking into account the restructuring of such a bandwidth across ranges), it is necessary to install a bandpass filter at the output of, for example, a transceiver, which will ensure not only suppression of harmful signal components, but also output matching transceiver transmitter with antenna or power amplifier input. In this case, the main signal will be cleared of both harmonics and noise components that are lower in frequency than the useful output signal. Since a bandpass filter has, depending on the quality factor of the reactive elements of its components, a certain passband, then either in the entire frequency subrange or in the required part of it, the filter settings and matching do not need to be changed.
The bandpass filter can be made either according to a circuit with inductive coupling, which is more desirable, or according to a circuit with autotransformer coupling.
Figure 1 shows a circuit of a filter with inductive coupling for use on VHF, and Figure 2 - with autotransformer coupling for use on VHF. On VHF, to improve filter parameters, resonators should be used instead of coils (for more low frequencies- spiral, at higher levels - coaxial).
By analogy with VHF, KB can use both spiral resonators and conventional coils.
Figure 3 shows a diagram of a bandpass filter with coupling coils, and Figure 4 - with autotransformer coupling. Filters with coupling coils make it possible to ensure matching without opening the resonators, and filters with autotransformer coupling, when matching, require moving the input and output taps along the turns of coil L1 (Fig. 4), or along the central conductor of the coaxial resonator (Fig. 2).
Filter settings and input and output matching can be done simple method using a GSS and an HF voltmeter, but it is most obvious to carry it out using a meter frequency characteristics(for example, X1-48). A bandpass filter is a symmetrical device, so the input and output can be swapped.
Capacitor C1 is designed to tune the half-wave resonator (ideally) to the operating frequency emitted by the transmitter, in reality - to the average frequency of the filter passband, the width of which depends on the L1/C1 ratio and the degree of load of this circuit through the inductive (using serial circuits L2- C2 and L3-C3 - Fig. 1 and 3) or an autotransformer connection with it, through taps from L1 (Fig. 2 and 4).
On the CRT X1-48 screen you can see the PF characteristic, the influence of trimming elements (C1-SZ) and load on it.
The resonator, of course, has a greater physical length, but there is a silver lining - this circumstance allows the PA to be taken away from the transceiver, which reduces the electromagnetic field strength at the operator’s location, near the transceiver. Thanks to this, the environmental situation in the workplace is improved and the resistance of the entire radio transmission system to interference, self-excitation, etc. is increased.
The use of such filters at the input and output of a power amplifier will make it possible to emit a narrow spectrum into the air, reduce the likelihood of TVI and BCI, and also use the resources of the power amplifier more efficiently. In fact, if you apply a signal from a transceiver, especially one that does not have a tuner at the output, then output power the amplifier connected to it will be larger without a bandpass filter, even if we take into account the attenuation in the filter and add drive power from the transceiver to compensate for the attenuation. This happens because part of the output power comes from “extraneous” components of the transmitter spectrum, which, in the absence of a bandpass filter, easily pass to the amplifier input and are amplified. Having cleared the transmitter spectrum using the PF, the freed “reserve” can be used for its intended purpose, i.e. to increase the transmitter output power at the operating frequency.
If a bandpass filter is used not only at the input of the power amplifier, but also at the output (which is highly desirable), then special attention should be paid to the filter parts, or more precisely, their suitability for use in such a filter. So, for example, a variable capacitor C1, installed at the point of maximum voltage on the circuit, depending on the output power of the amplifier and the quality factor of the resonator (coil), should have a gap between the plates of 3-10 mm. Reliable contact with the common wire at coil L1 is very important, because at this point in the circuit there is a maximum current, so the diameter of the wire of the coil L1 must be large enough.
The optimal setting of the bandpass filter can be determined by the maximum deviation of the anode current meter needle tube amplifier power, or an antenna current indicator, or by the maximum brightness of a neon light bulb located directly at the antenna output of the filter or power amplifier.
More and more attention is being paid to filtering the signals emitted by transmitting devices. The emission of signals at frequencies different from the operating one can be regarded, by analogy with road traffic, as driving into the oncoming lane due to the oversized vehicle.
On the one hand, both radio amateurs and professionals use low-pass filters (LPF) at the output of transmitters to suppress only harmonic components. On the other hand, in pursuit of reduction in size, and therefore savings in structural materials, manufacturers of transmitting equipment are creating more and more “masterpieces” of transceivers, which either have the simplest filters at the output of the transmitters, or do not have them at all. In the latter case, the calculation is made for connecting external filtering matching devices - various kinds of tuners, which are either produced separately as an option, or are not produced for a particular transceiver at all.
If you want to increase the power of the output signal of the transmitter, the radio amateur makes or purchases a power amplifier, which contains only a low-pass filter (for example, in the form of an output P-circuit). Such a filter to a certain extent suppresses the harmonics of the main signal, and the amplifier itself amplifies the entire spectrum of the signal that comes to it from the transceiver. Consequently, the suppression of harmonic components, which are caused by the nonlinearity of the stages in both the transceiver and the power amplifier, is reduced. Other components, the frequencies of which are below the low-pass filter cutoff frequency of the power amplifier, entering it, are amplified and pass into the antenna. A resonant antenna, well matched at the operating frequency, partially suppresses unwanted spectral components, which, however, become the cause of interference in the near field.
Currently, in addition to local oscillator interference and their harmonics “creeping through” to the transceiver output, the output signal of the transceiver also contains “digital” fluctuations from various kinds of digital “gadgets” (scales, shapers, dividers, DSP, from those introduced into the transceiver at sharing noise components with a computer).
Thus, to protect the airwaves from “preparatory” auxiliary signals, it is necessary to have at the output of the transmitting equipment not only a low-pass filter, but also a high-pass filter with a total transparency band, ideally equal to the band of the emitted signal: for SSB - 2.4 kHz, for CW - for AM - 6 kHz, for FM - 10...15 kHz. Since it is not possible to provide such bandwidths at the output of transmitting devices in practice (and even taking into account the restructuring of such a bandwidth across ranges), it is necessary to install a bandpass filter at the output of, for example, a transceiver, which will ensure not only suppression of harmful signal components, but also output matching transceiver transmitter with antenna or power amplifier input. In this case, the main signal will be cleared of both harmonics and noise components that are lower in frequency than the useful output signal. Since a bandpass filter has, depending on the quality factor of the reactive elements of its components, a certain passband, then either in the entire frequency subrange or in the required part of it, the filter settings and matching do not need to be changed.
The bandpass filter can be made either according to a circuit with inductive coupling, which is more desirable, or according to a circuit with autotransformer coupling.
Figure 1 shows a circuit of a filter with inductive coupling for use on VHF, and Figure 2 - with autotransformer coupling for use on VHF. On VHF, to improve filter parameters, resonators should be used instead of coils (at lower frequencies - spiral, at higher frequencies - coaxial).
By analogy with VHF, KB can use both spiral resonators and conventional coils.
Figure 3 shows a diagram of a bandpass filter with coupling coils, and Figure 4 - with autotransformer coupling. Filters with coupling coils make it possible to ensure matching without opening the resonators, and filters with autotransformer coupling, when matching, require moving the input and output taps along the turns of coil L1 (Fig. 4), or along the central conductor of the coaxial resonator (Fig. 2).
Setting up the filter and matching the input and output can be done in a simple way using a GSS and an RF voltmeter, but the most obvious way to do it is using a frequency response meter (for example, X1-48). A bandpass filter is a symmetrical device, so the input and output can be swapped.
Capacitor C1 is designed to tune the half-wave resonator (ideally) to the operating frequency emitted by the transmitter, in reality - to the average frequency of the filter passband, the width of which depends on the L1/C1 ratio and the degree of load of this circuit through the inductive (using serial circuits L2- C2 and L3-C3 - Fig. 1 and 3) or an autotransformer connection with it, through taps from L1 (Fig. 2 and 4).
On the CRT X1-48 screen you can see the PF characteristic, the influence of the trimming elements (C1-C3) and the load on it.
The resonator, of course, has a greater physical length, but there is a silver lining - this circumstance makes it possible to place the PA away from the transceiver, which reduces the electromagnetic field strength at the operator’s location, near the transceiver. Thanks to this, the environmental situation in the workplace is improved and the resistance of the entire radio transmission system to interference, self-excitation, etc. is increased.
The use of such filters at the input and output of a power amplifier will make it possible to emit a narrow spectrum into the air, reduce the likelihood of TVI and BCI, and also use the resources of the power amplifier more efficiently. In fact, if we apply a signal from a transceiver, especially one that does not have a tuner at the output, then the output power of the amplifier connected to it will be greater without a bandpass filter, even if we take into account the attenuation in the filter and add drive power from the transceiver to compensate for the attenuation. This happens because part of the output power comes from “extraneous” components of the transmitter spectrum, which, in the absence of a bandpass filter, easily pass to the amplifier input and are amplified. Having cleared the transmitter spectrum using the PF, the freed “reserve” can be used for its intended purpose, i.e. to increase the transmitter output power at the operating frequency.
If a bandpass filter is used not only at the input of the power amplifier, but also at the output (which is highly desirable), then special attention should be paid to the filter parts, or more precisely, their suitability for use in such a filter. So, for example, a variable capacitor C1, installed at the point of maximum voltage on the circuit, depending on the output power of the amplifier and the quality factor of the resonator (coil), should have a gap between the plates of 3-10 mm. Reliable contact with the common wire at coil L1 is very important, because at this point in the circuit there is a maximum current, so the diameter of the wire of the coil L1 must be large enough.
The optimal setting of the bandpass filter can be determined by the maximum deviation of the needle of the anode current meter of a tube power amplifier, or the antenna current indicator, or by the maximum brightness of the neon light bulb located directly at the antenna output of the filter or power amplifier.
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