Ocean direct conversion transceiver. Direct conversion transceiver with balanced mixer on active elements

The transceiver has separate high-frequency and low-frequency paths for receiving and transmitting, common for both modes are a mixer-modulator and a smooth range generator.

The smooth range generator (GPA) is made on two field-effect transistors VT5 and VT6 with source connection. It operates at a frequency equal to half the frequency of the received or transmitted signal. When working for reception and transmission, the output circuits of the GPA are not switched and the load on the GPA does not change. As a result, when switching from reception to transmission or vice versa, the VPA frequency does not deviate. Tuning within the range is performed using a variable capacitor with an air dielectric SU, which is part of the GPA circuit.

The transceiver is designed to transmit and receive SSB and CW in the range of 28-29.7 MHz. The device is built according to the direct conversion scheme with a common mixer-modulator for receiving and transmitting.

Specifications:

• sensitivity in the receive mode with a signal-to-noise ratio of 10 dB, not worse than ........ 1 μV;
• the dynamic range of the receiving path, measured by the two-signal method, about ...... 80 dB;
• bandwidth of the receiving path at the level of -3 dB .......... 2700 Hz;
• the width of the spectrum of single-sideband radiation during transmission ........ 2700 Hz;
• the carrier frequency and the non-working sideband are suppressed no worse than ........ 40 dB;
• output power of the transmitter in CW mode at a load of 75 Ohm ...... 7 W;
• drift of the local oscillator frequency after 30 minutes of warm-up after switching on, no more than ..... 200 Hz / h.

In the SSB transmission mode, the signal from the microphone is amplified by the operational amplifier A2 and fed to the phase shifter on the elements L10, Lll, C13, C14, R6, R7, which in the frequency range of 300-30-00 Hz provides a phase shift of 90 °.

In the L4C5 circuit, which serves as a common load for mixers on VD1-VD8 diodes, an upper sideband signal is allocated in the range of 28-29.7 MHz. The high-frequency broadband phase shifter L6R5C9 in this range provides a phase shift of 90 °.

The selected single-sideband signal through the capacitor C6 is fed to a three-stage power amplifier on transistors VT7-VT9. The cascade of pre-amplification and decoupling of the output circuit of the mixer-modulator is made on the transistor VT9. The high input impedance, combined with the low capacitance of C6, ensures that the power amplifier has minimal impact on the C5L4 circuit. In the VT9 collector circuit, a circuit is turned on, tuned to the middle of the range. The intermediate stage on the VT8 field effect transistor operates in class B mode, and the output stage operates in class C mode.

The U-shaped low-pass filter on the C25L13C26 cleans the output signal from high-frequency harmonics and ensures that the output stage impedance matches the antenna impedance. Ammeter PA1 is used to measure the drain current of the output transistor and indicates the correct setting of the P-circuit.

The telegraph mode is provided by replacing amplifier A2 with a sinusoidal signal generator with a frequency of 600 Hz (Fig. 21). Switching CW-SSB is done using switch S1. The telegraph key controls the VT11 offset of the oscillator preamplifier and, consequently, the supply of a low-frequency signal to the modulator.

In receive mode, the 42 V power supply to the transmitter stages is not supplied, and the power amplifier and microphone amplifier are turned off. At this time, a voltage of 12 V is applied to the cascades of the receiving path.

The signal from the antenna is fed to the input circuit L2C3 through the coupling coil L1; it matches the loop impedance to the antenna impedance. On the transistor VT1 is made URC. The stage gain is determined by the bias voltage at its second gate (the divider across resistors R1 and R2). The load of the cascade is the circuit L4C5, the connection of the cascade of the RF with this circuit is carried out by means of the coupling coil L3. From the coupling coil L5, the signal is fed to a diode demodulator on diodes VD1-VD8.

Coils L8, L9 and a phase shifter on L10 and L11 emit a signal 34 in the frequency band 300-3000 Hz, which is fed through the capacitor C15 to the input of the operational amplifier A1. The gain of this microcircuit determines the main sensitivity of the transceiver in the receive mode. This is followed by an amplifier 34 on transistors VT2-VT4, from the output of which the signal 34 is fed to the small-sized speaker B1. The reception volume is adjusted using a variable resistor R15. In order to eliminate loud clicks when switching the "reception-transmission" modes, power is supplied to the UMZCH on transistors VT2-VT4 both during reception and transmission.

Most of the transceiver parts are installed on three printed circuit boards, the sketches of which are shown in fig. 22-24, On the first board are the details of the input URF of the receiving path (on the transistor VT1), the details of the mixer-modulator with phase-shifting circuits, as well as the details of the local oscillator. On the second board - low-frequency cascades on microcircuits A1 and A2 and transistors VT2-VT4. The third board houses the power amplifier of the transmitting path.

The board with the mixer-modulator, URCH and GPA is shielded. The switching of the "reception-transmission" modes is carried out by a pedal, which turns the 42 V voltage off and on and controls two electromagnetic relays, one of which switches the antenna, and the second supplies a 12 V voltage to the receiving path. The relay windings are powered by 42 V, and in the de-energized state, the relay contacts turn on the receive mode.

To power the transceiver, a basic stationary power supply is used, from which a constant stabilized voltage of 12 V with a current of up to 200 mA and a constant unstabilized voltage of 42 V with a current of up to 1 A are supplied.

Winding data of transceiver coils Table 4

The transceiver uses constant MLT resistors for the power indicated in the diagrams. Adjusted resistor - SPZ-4a. Loop capacitors - necessarily ceramic, tuning - KPK-M. Electrolytic capacitors - type K50-35 or similar imported ones. Variable capacitors of the local oscillator and the output circuit - with an air dielectric.

For winding the URF loop coils, the mixer and the transmitter, ceramic frames with a diameter of 9 mm with tuning cores SCR-1 are used (plastic frames from the UPCH paths of old tube TVs are also possible, but their thermal stability is much worse than that of ceramic ones). The low-frequency coils of the mixer-modulator L8 and L9 are wound on K16x8x6 ring cores made of 100NN or higher-frequency ferrite (100VCh, 50VCh). Coils L10 and L11 are wound on OB-ZO frames made of ferrite 2000NM1. Coils of erasing and magnetizing generators of semiconductor reel-to-reel tape recorders were wound on such cores. The winding data of the transceiver coils are given in Table. four.

KPZOZG transistors can be replaced with KPZOZG with any letter index or KP302. The KP350A transistor can be replaced with KP350B, KP350V or KP306. Transistor KP325 - on KT3102. Powerful field-effect transistors KP901 and KP902 can be with any letter indices. Any silicon and germanium (respectively) transistors of the corresponding structure are suitable for UMZCH. Diodes KD503 can be replaced by KD514, and diode D9 - by D18.

Literature: A.P. Semyan. 500 schemes for radio amateurs (Radio stations and transceivers) St. Petersburg: Science and Technology, 2006. - 272 p.: ill.

With the spread of the Internet, amateur radio, no matter how sorry, gradually began to fade away. Where did the army of radio hooligans go, the legions of "fox hunters" with direction finders and their other colleagues ... They disappeared, crumbs remained. There is no mass agitation at the state level, and in general, the system of values ​​has changed - young people more often prefer to choose other entertainment for themselves. Of course, Morse code is not often used in the current digital age, and radio communication in its original form is increasingly losing its position. However, amateur radio as a hobby is a mixture of a kind of romance of wandering with a fair amount of skills and knowledge. And the opportunity to creak with your brains, and put your hands on it, and rejoice at your soul.

And yet I did not shame my brothers,
but embodied their forces of union:
I, like a sailor, furrowed the elements
and, as a player, prayed for luck.

M. K. Shcherbakov "Song of the Page"

However, to the point. So.

When choosing a design for repetition, there were several requirements arising from my initial knowledge in the field of RF design - the maximum detailed description, especially in terms of tuning, no need for special RF measuring instruments, available element base. The choice fell on Viktor Timofeevich Polyakov's direct conversion transceiver.

transceiver - communication equipment, radio station. The receiver and transmitter are in one bottle, and they have a part of the cascades in common.

SSB transceiver entry level, single band, 160m band, direct conversion, tube output stage, 5W. There is a built-in matching device for working with antennas of various wave impedances.

SSB - single-sideband modulation (Amplitude modulation with one sideband, from English Single-sideband modulation, SSB) - a type of amplitude modulation (AM), widely used in transceiver equipment for efficient use of the channel spectrum and the power of the transmitting radio equipment.

The principle of direct conversion to obtain a single-sideband signal allows, among other things, to do without specific radio elements inherent in a superheterodyne circuit - electromechanical or quartz filters. The range of 160m, for which the transceiver is designed, is easy to change to a range of 80m or 40m by reconfiguring oscillatory circuits. The output stage on a radio tube does not contain expensive and rare RF transistors, is not picky about the load and is not prone to self-excitation.

Let's take a look at circuit diagram devices.

A detailed analysis of the circuit can be found in the author's book, there is also an author's printed circuit board, transceiver layout and case sketch.
Compared to the author's design, the following changes were made to its execution. First of all - layout.

The transceiver version, designed to operate on the lowest frequency amateur band, fully allows for a “low-frequency” layout. In their own design, solutions were used that are more applicable to RF equipment, in particular, each logically complete node was located in a separate shielded module. Among other things, this makes it much easier to improve the device. Well, I was inspired by the possibility of a simple retuning to 80, or even 40m bands. There, such an arrangement would be more appropriate.

Toggle switch "Reception-transmission", replaced by several relays. Partly because of the desire to control these modes from the remote button on the sole of the microphone, partly due to the more correct wiring of the signal circuits - now they did not need to be dragged from afar to the toggle switch on the front panel (each relay was located at the switching point).

The design of the transceiver introduced a vernier with a large deceleration and, this makes it much more convenient to tune in to the desired station.

What was used.

Tools.
Soldering iron with accessories, a tool for radio installation and small metalwork. Metal scissors. A simple carpentry tool. Used a milling machine. Blind rivets with special tongs for their installation came in handy. Something for drilling, including holes on a printed circuit board (~ 0.8 mm), can be contrived with one screwdriver - the scarves are specific, there are few holes. Engraver with accessories, hot glue gun. It is good if you have a computer with a printer at hand.

Materials.
In addition to radioelements - a mounting wire, galvanized steel, a piece of organic glass, foil material and chemicals for the manufacture of printed circuit boards, related trifles. Not thick plywood for the body, small carnations, wood glue, a lot of sandpaper, paint, varnish. A bit of mounting foam, thin dense foam - "Penoplex" 20 mm thick - for thermal insulation of some cascades.

First of all, in AutoCAD, the layout of both the entire apparatus and each module was drawn.

The modules themselves were made - printed circuit boards, "mushrooms" of galvanized steel module cases. Boards are assembled, loop coils are wound and installed, boards are soldered into individual screen covers.

A variable capacitor for a local oscillator - with every second plate removed. I had to disassemble and solder the stator blocks, then put everything back in place.

The body is made of 8 mm plywood, after adjusting the openings and holes, the box is sanded and covered with two layers of gray paint. From the inside, the box is finished with the same galvanized steel, and the final installation of elements and modules has begun.

The galette switch and the variable capacitor of the matching device are located near the antenna connector, this allows you to shorten the connecting wires as much as possible. To control them from the front panel, extensions of their shafts from a 6mm threaded stud and connecting nuts with stoppers are used.

The axis of the tuning vernier is made from a shaft from a broken inkjet printer, on the same axis there was a braking unit, which also came in handy. The groove holding the vernier cable was made using an engraver.

The special pulley, the cable itself and the spring providing tension are taken from a tube radio.

The tuning knob is made from two large gears from the same printer. The space between them is filled with hot glue.

The walls of the local oscillator module are finished with a layer of mounting foam, this allows you to reduce the "frequency drift" due to heating when tuning to the station.

The module of the telephone and microphone amplifier is placed on the rear wall of the case, to protect it (the module) from mechanical damage, releases are made on the side walls of the case.

Setting the local oscillator of the transceiver. For her, a simple RF prefix was ​​made for a multimeter, which allows you to evaluate the level of RF voltage, for example.

Initially, it was decided to change the circuit of the output stage of the transmitter to a semiconductor one, powered by the same 12 V. In the photo above, it is he who is not fully assembled - a milliammeter for a higher current, an additional winding on the P-loop coil, only low-voltage power.

Scheme of changes. output power about 0.5 W.

In the future, it was decided to return to the original. I had to replace the milliammeter with a more sensitive one, add the missing elements, change the power supply.

The power amplifier module is thermally insulated from other structural elements, as it is a source of a large amount of heat. Its natural ventilation is organized - a field of holes is made in the basement of the case and on the cover above the module.

The basement of the building also contains a number of blocks and modules.

The transceiver circuit has the simplest solutions for individual nodes and does not shine with characteristics, however, there are a number of improvements and improvements aimed at both improving the performance characteristics and improving ease of use. This is the introduction of signal sideband switching, automatic gain control, the introduction of CW mode during transmission. The suppression of the non-working sideband can also be slightly increased by reducing the spread of the characteristics of the mixer diodes, for example, by using a KDS 523V diode assembly instead of the V14 ... V17 diodes. Improvement of individual nodes can be performed according to the schemes from. It is also worth paying attention to solutions. The applied arrangement allows to do it quite conveniently.

Literature.
1. V.T.POLYAKOV. DIRECT CONVERSION TRANSCEIVERS Publishing House DOSAAF USSR. 1984
2. Scheme of the attachment to the multimeter for measuring RF.
3. Dylda Sergey Grigorievich. TRX's small-signal direct conversion SSB path on the 80m band

("Friend-3")

A direct conversion receiver with a balanced mixer on a 235PS1 (174PS1, etc.) chip, loaded onto a matching transformer from an old radio receiver, showed a very decent quality of work, high sensitivity, and because the input circuit is lightly loaded, i.e. has a high quality factor, and very high selectivity.

It makes sense to assemble a direct conversion transceiver using this version of the receiving part.

It starts by no one, and by me, not my favorite work - drilling holes, “rustling” with a file, sawing with a hacksaw for metal ...

I got scratched, this happens with a “practicing” radio amateur: drills, hacksaw blades, etc. sometimes break, while .... see photo. "Design" thinking in this case is to count the number of connectors: 2 antenna and housing, 2 for a key, 2 for connecting phones and a power connector. If you have had the patience to do all this, consider that you have collected almost 50% of the QRP / p of the transceiver!

Those. Be sure to collect some device!

Put a button that can be used, if necessary, as a telegraph key. The LED, for indicating power and the local oscillator, is used in the local oscillator KT306. But, no doubt, any other suitable transistor can be used.

Screwed KT610B, a gift from friends, you need to apply. KT603, etc. quite suitable for

for this purpose, there is no need to use exactly KT610B. There are a lot of options.

Scheme of the transmitting part. Actually, some time ago, in one of the messages, I demonstrated this circuit and the assembled transmitter. For the transceiver, I assembled a similar transmitter, it took a slight refinement:

1. 
   A chain of counter-parallel diodes is introduced into the antenna circuit, the purpose of which is to exclude shunting of the input circuits of the receiver by the P-circuit. A slight loss of transmitter power does not play a significant role. If desired, you can provide a separate antenna input of the receiver, or antenna switching.
2. 
   A button is connected parallel to the connector for connecting the key, for the possible use of a button instead of a key.

The transmitter is completed. It took 2-3 days off, I mean, that I was engaged in the transmitter of the transceiver without prejudice to other activities and duties.

I tuned the P-loop to a 75 ohm dipole. Checked the signal shape at the antenna output:

P-loop data varies over a very wide range, depending on the type of antenna. In my case: 25-28 turns are wound on a coil with a diameter of 12 mm, capacitors are about 500-1000 pF at the "hot" end and 2000-3600 pF at the antenna output. However, this information is for guidance only. It would be best to have variable capacitors of the appropriate capacity, or a matching device. But, for a "face-to-face meeting-test" it will be an overly complicated device that does not quite correspond to the half-joking "spirit" of this event. With the P-loop tuned to 75 ohms, the sine wave at the antenna output has no distortion when loaded, from about 30 to 100 ohms, with further mismatch, the waveform is no longer sinusoidal, i.e. distorted. The transmitter is built perfectly on a dipole.

The data of the “three-point” KG capacitors are also different, depending on the activity of quartz, etc., 43pf + 180pf, but also the data is purely for orientation.

Note- the light bulb really shines much more modestly, it happened in the photo.

The transmitter is assembled, then, after assembling the receiving part, this device will probably be tested in real conditions - in the forest. A similar transmitter and a similar planned receiver have been tested and performed very well. It doesn’t make much sense, but it’s a very interesting event - a practical test of the transceiver in the forest ...

A significant part of the direct conversion transceiver is assembled .... (The key terminals are closed with tweezers)

I turn to the assembly of the receiver: a coil is installed for the input circuit, a tuning capacitor, a zener diode, to power the microcircuit.

ULF assembled.

(For TNX transistors to Alexander U.A.9 LAK/ UN7! ).

Unlike the circuits I used earlier, I added a low-frequency choke in the output stage, in series with a 3.6k resistor, for better low-frequency amplification. The circuit, in fact, is designed to connect high-resistance telephones to the collector circuit of the output transistor, which are currently in short supply. You can use an emitter follower, if desired. Setting up the amplifier is simple - by selecting R3 and R4, set the voltage on the collector of the output transistor equal to half the supply voltage. With a 12 volt supply, I have a 6 volt collector voltage set.

Scarce (they were thrown away, as unnecessary), outdated low-frequency transistors were deliberately used: they have a low cut-off frequency of amplification and they will not amplify the local oscillator pickup, i.e. there will be no gain reduction for this reason.

I will repeat briefly. Let's say your bass amp has a gain of 40000. This is only when amplifying low-level signals. By applying 1 volt to the input, you will not get 40,000 volts at the output!

That is, the ULF gain for high-level signals decreases sharply. Yes, and in reference books, sometimes it is indicated: “Current transfer coefficient in small signal mode” ( For example: "Semiconductor devices: transistors", Energoatomizdat, Moscow 1983. page 109: MP104, MP105, MP106, MP114, MP115, MP116).

Practice has fully confirmed this. Field tests of "Friend-2" showed that when approaching the transmitter antenna, the signal in the phones practically did not increase. And when approaching very close, the receiver simply “shut up”.

The local oscillator signal that has entered the ULF input, when high-frequency transistors are used in the ULF, will be successfully amplified, respectively, reducing the gain.

And the pickup signal can very easily reach the level of tens of microvolts, which means that the sensitivity of the receiver will be significantly reduced.

Those. the use of HF transistors in ULF does not make sense and is fraught with a possible deterioration in the operation of a direct conversion receiver.

Modern capacitors in VLF PPP can generate, therefore, surprisingly, it is better to use old MBMs, etc. "tape" capacitors, it is not necessary to identify the generating capacitor, replace it with another one that can also generate. I prefer to put an outdated MBM capacitor, a guarantee that the VLF will work fine. (Although, out of 5 tested modern capacitors, one still did not generate. But, suddenly, in hot weather it will generate ....?)

A matching transformer is built in ... Please note that ULF, even on such rare transistors, does not take up so much space. LM-386, with "strapping", i.e. with electrolytic capacitors and resistors, according to my experience of its application (for TNX chips to Vladimir DL7 PGA!), takes up about the same amount of space, maybe a little less, but not significantly. This ULF is very economical.

As I reported, this variant of the receiving part does not require any adjustment, just hundreds of millivolts of local oscillator voltage must be applied to the heterodyne input of the microcircuit, and this value is very uncritical, the limits of this voltage must be found in the reference book for the applied microcircuit. But, no painstaking selection of the voltage value ( for me personally, the need for painstaking selection of voltage for the PPP mixer is absolutely not Like) is not required. The receiver works right away. You just have to pick up the taps for connecting the antenna and the microcircuit 1/4 ... 1/8 of the turns of the coil, from my experience, is suitable for connecting the input of the microcircuit and the antenna - a full-size dipole. The sensitivity of this receiver is better than 1 μV and on the 80-meter range its sensitivity, when a full-size antenna is connected, is clearly excessive. But, by selecting the taps for connecting the antenna and the microcircuit, the sensitivity can be set to the optimal value. Moreover, when connecting the antenna and the microcircuit to the taps from the coil, the load on the circuit decreases, which increases the selectivity and dynamics of the device.

In the manufacture of such a CCI for any other range, its high sensitivity can be fully realized. It takes a little effort to change the range: change the quartz and 2 coils - the input receiver and the coil in the P-loop.

The transceiver is fully assembled. No tweaking was required.

I collected this device for a little more than 1.5 months, in my free time, of course, without prejudice to other activities and duties.

73! Sincerely, UA1CEG, Yuri Alexandrov, Garbolovo village, Vsevolozhsk district, Leningrad region. LO-23,KP50FI.
Website: UA1CEG.narod.ru Direct conversion transceiver for 10.116 / 10.113 mhz "Friend-8".

Brief preface.

At a very fast pace, I began to assemble the Friend-8 direct conversion transceiver, the fact is that I most likely will not have the opportunity to assemble some kind of structure until late autumn. And, according to my criteria, in order not to turn into a lover of “talking”, wandering through numerous forums, you need to collect at least 2 completed structures per year. Simple, very simple, but in the form of a complete structure and fully functional, preferably in a relatively original scheme. At one time, in the QRP club, a homemade competition was organized at a full-time rally, a useful event!

By the way, the 5th month of this year is already coming to an end. There is not much free time, I had to work as quickly as possible.

Checking "Friend-8" in real time.
30.05.2010.

The construction was completed a couple of days ago, but on the air, in the forests, the fields have not been tested, continuous rains! Of course, "I'm sitting on pins and needles," but nothing can be done. Rain and +9 in the morning and almost until noon on May 30, 2010. However, in the lunch area, there was enlightenment! It didn’t take long for me to get ready: I ​​put the battery, “Friend-8”, phones, key and antenna into my bag and go!

Wet, but no rain, at least not yet. And I'm moving fast. No, not at altitude 109.0, which is what the antenna is designed for, by the time I get there, it will start to rain again. Move out to high ground where I work QRP/p when there's no time to move out further.

The acacia blossomed.

Rowan also does not lag behind, bloomed.

Solid wind at high altitude.

The antenna must be temporarily suspended in its working position.

I am a supporter of normal, full-sized antennas powered by coaxial cable. In this case, it is a dipole for 10 MHz.

I hook my right shoulder to a tree, since the cord is already thrown there and it remains only to hook the cord to the insulator. The central pole, to which I tie the central insulator of the dipole, is dug into the ground shallowly.

It became more fun, the right shoulder of the dipole is in the working position.

Similarly, I dig a hole for the left pole.

A little to the left, in the plane of the antenna, I drive a peg into the ground, for which the antenna brace will be fixed.

I wrap the guy around the pole, lift it up, dig it in with earth and tie the cord around the peg.

It all happens rather quickly.

Here is the photo of the left arm of the dipole.

Dipole in working position.

>The passage today is not very happy. Stations on the bands do not rattle, with the > exception of bigguns. RD9CX.
If Sergey says that the passage is unimportant, then this is true.

But let's hope. For quite some time I sent CQ de UA1CEG/p to 10113, silence, no one.

I switch to 10116 and have a QSO! Yes, what else!

With QRP station! I did not count on such luck. The transceiver works fine, I obviously overestimated the 9A0QRP report. Joyfully, quite understandably, I suppose.

I am returning to reality... The wind is driving a suspiciously dark cloud! You need to leave quickly. Dipole, not without regret, dismantle. He looked at the prepared hearth for the fire:

No, the planned leisurely tea party is being postponed, the cloud is approaching and growing menacingly in size.

I pick up the pace of 120 steps per minute and return home. However, the cloud slipped through Garbolovo without stopping, so ... a few drops fell, but this is not considered rain in our area. But, you won’t guess, you don’t want to get wet, and the transceiver check went perfectly!

The transceiver perfectly receives on a long LW, 80 meters, without the appearance of broadcasting stations, this is also very cool!

Receiver.
Direct conversion receiver, assembled according to a simple scheme, works as a direct conversion receiver, assembled according to a simple scheme. There is no need to make unreasonable claims to the apparatus of this class. At the same time, a properly adjusted simple PPP has very high characteristics. The performance characteristics of this device, given such minimal labor costs and components, are excellent!

Any complications, in order to dramatically improve performance, first of all dramatically increase the cost of labor, time and components, nullifying the main advantage - the ultimate simplicity of the apparatus. A superheterodyne of a similar class, with improved SPP, will require significantly less effort, with higher performance.

If on a simple IFR interference from broadcasting stations at 7 MHz will be heard in a double band, then if phase demodulation is applied, the same interference will be received in only one band. But, interference will take place and phase demodulation will not help. Of course, if you apply a lot of effort, you can at least reduce the leakage of interference.

This is for enthusiasts and originals... Personally, I would prefer, with much less effort and with better results, to build a superheterodyne.
Work starts:

Jacks: “Phone”, “Key”, connectors: “+12 volts” - 2 pcs, “Ant TX”, “Ant RX”. Clamp: "Body". And that's it.

We install the necessary terminals, connectors, etc. If a shortwave does this, then that's it, he will have an apparatus! Empty conversations end with the completion of the tasks of this stage. Only at the keyboard questions arise one after another, as soon as a specific work begins, that's it, no questions (chatter!).

The main block of PPP ULF.

it the best option ULF, tested in real designs, during real work on the air. The ULF is being adjusted simply - you need to select the values ​​\u200b\u200bof R3 and R4 so that the voltage on the collector of the third transistor is equal to half the supply voltage, 6 volts in this case.

I believe it is clear that the same circuit can be assembled on the famous ones: P27, P28, MP39B, MP40, P15, etc. change the polarity of the power supply and electrolytic capacitors and everything else is the same.

In the photo, the assembled ULF.

At the risk of being accused again that “the complete scheme is not published!”, I believe that this block diagram is more than enough, given detailed photos and detailed diagram ULF and heterodyne.
I can hardly imagine a shortwaver who is not able to assemble a PPP according to this description and numerous photographs, but ... you never know what happens, probably my message is simply not for him. I still hope that the radio amateur will be able to connect the microcircuit to the input circuit, supply power to the microcircuit and connect the transformer ...

Who will collect, he will collect.

Folk wisdom: “The road will be mastered by the walking one!”.

The ULF is built into the case and a tuning capacitor is added to adjust the input circuit.

We assemble the mixer 235PS1 (NE602, NE612, etc.). We connect a matching transformer from the radio receiver to the mixer, or any suitable similar one.

Photo of the working moment - setting the local oscillator. At this stage, you need to see how active the quartz you have is, and you may have to provide an emitter follower to reduce the load on the local oscillator. Here everything is decided really, practically.

input circuit. For microcircuits with a symmetrical signal input, for example NE602, NE612, a 3-turn coupling coil is simply wound (the number is practically specified) and connected to the corresponding inputs. I do not accept connecting an unbalanced output to a balanced mixer input.

Some explanation is required here.

The sensitivity of the receiver this version of the circuit can provide absolutely redundant, it simply cannot be implemented. And reducing the connection with the circuit dramatically increases the dynamics, the quality factor of the circuit will be very high, which will positively affect the selectivity. So far, the presence of interfering broadcasting stations, and this is the scourge of PPP, could not be found at all. And this is when connected to a full-sized delta. Of course, the final adjustments will be made after a real check in the live forest-fields.

I draw your attention to the fact that the high-quality circuit is used, on a frame made of ribbed high-frequency ceramics, and the tuning capacitor is with an air dielectric. That is, the quality factor of the circuit is high, this is fundamentally important for the high-quality operation of the device. No cardboard Chinese frames for coils, low quality capacitors and others "Modern Components" The device is going to work on the air .

A mixer on counter-parallel connected diodes shunts the circuit and completely loses to this option, without options. Practically tested. Of course, if you make a complete design, for practical use.

Of course, no one will forbid, to assemble something on a circuit board and, without false modesty, to list oneself as an expert in direct conversion technology.

In the photo, the first station heard on the air on this device, when used as a soldering iron antenna. This is RZ6MM, 21.03 MSK 20.05.2010 But, this is on the 4th floor, in stationary conditions. But still, pretty decent.

At this point, I decided that there are doubts about the activity of quartz and it is better to add an emitter follower after all. This is also determined practically.
On the 7030, for example, an emitter follower was not needed.

This completes the assembly of the receiving part of the transceiver. Some adjustments may be made during operation, and may not be needed. It will probably be possible to increase the sensitivity, given the extremely low level of interference in nature, at a distance from settlements. I remind you that in this version the gain margin is very large and the sensitivity is better than 1 μV without the slightest difficulty.
Transmitter.
It is known that transistors have a low-resistance output impedance, which creates certain difficulties in matching the low-resistance output of the transmitter with the relatively high-resistance input of the antenna, and some antennas simply have a high-resistance input. We have to painstakingly coordinate the P-loop at the output of the transmitter, which often requires a lot of effort, otherwise

and the introduction of a two-link P-loop.

I decided that the assembly of the so-called "binoculars" - a matching broadband RF transformer would require much less effort and provide load matching over a wider range.

The technology is simply ridiculously simple, a piece of shielded wire is cut off, for example, a coaxial cable, the braid is removed, 6-8 rings are put on and 4 turns of a relatively rigid single-core wire are pulled. Stranded is also possible, but it is flexible and more difficult to stretch.

Of course, if there is a desire, then it can be done better, using copper tubes ... In our case, a simplified version will do. Aesthetes can solder the screen, get hard tubes, which will be more solid. I simply do not have time for such a long work. And this option, as practice has shown, works great.

The braid (this is the "primary" winding) is included in the collector circuit of the output transistor, from the "secondary" winding the signal is fed to the P-circuit.

The work was "on the march", so on a piece of paper I sketched what I used in the transmitter, so as not to forget later.

I hope I won’t offend anyone if I draw attention to the fact that the broadband “binoculars” transformer is placed on a platform made of plexiglass, or another dielectric, not directly on the board.

Here is a photo of the transmitter. Doesn't look intimidating at all, does it?

And meanwhile, without “binoculars” I was fiddling, fiddling ... I couldn’t really coordinate the transmitter with a load of 75 ohms! I have KT920A installed in the pre-terminal cascade, which is a clear luxury, but I have run out of KT610.

KT911, which are available, I do not like, because of the tendency to self-excitation, KT603 is somewhere, but I did not find it.

Pay attention to the zener diode chain (D816, in this case) in series with the RF diode (KD503, in this case), this chain is visible in the photo.

This circuit should protect the transistor from high voltage breakdown, for example, you hooked the antenna or cable with your foot and disconnected the antenna from the antenna jack. As a rule, this leads to an instantaneous breakdown of the transistor.
A zener diode-diode circuit rated for voltages below the maximum allowable voltage of a given transistor reliably protects the output transistor.

And a large area of ​​​​the cooling surface reliably protects against thermal failure of the transistor - in this case, the transistor is securely screwed to the case. It is doubtful that the battery capacity is enough to heat the case to the maximum allowable temperature for a given transistor, and you will be indifferent to observe this long process.

The output signal has the form of a regular sinusoid in a very wide load change (active, finite resistors 75 ohms and higher) - from 37.5 ohms - in parallel 2 resistors of 75 ohms each (did not load below) up to 500 ohms. When the load is turned off, it is also the correct sinusoid. Obviously, the merit of the "binoculars" in the normal operation of the transmitter, when the load changes over a very wide range.

I do not indicate the frequency change capacitances, because they are selected individually for a particular instance of quartz. If quartz provides a much more extended tuning section, then in general it is possible to put a switch and provide for several operating frequencies, in this case there are 2 of them.

If desired, an emitter follower can be provided between the quartz local oscillator and the pre-terminal amplifier, but this is more of a reinsurance. But, if the quartz is not very active, there are doubts, it is better to provide an emitter follower. This will not cause you too much trouble and expense.

Working moment - connected the light bulb. In reality, the light bulb does not glow as brightly as it was perceived by the camera.
Self control.

Self-monitoring in a direct conversion transceiver is not a routine task at all.

Of course, if you put the toggle switch (button, pedal) "reception-transmission", then there is nothing to talk about. But, I want to do without buttons, toggle switches, pedals - you press the key and you are on the air.

You connect a multivibrator generating a frequency of 600-800Hz to the ULF. I pressed the key - a signal is heard in the ULF. Elementary, right? It is elementary, if it is not a device in hardware, but an imaginary, fictional one. You connect ... but the quality is not so hot, and it also works differently for different antennas. It wheezes, it's just annoying.

Oleg Viktorovich RV3GM also spoke about the difficulty of organizing high-quality self-control in the CCI, and he is a recognized practitioner in the direct conversion technique.

In the end, I built a capsule connected to a multivibrator and decided that this, if not the most optimal, then still a solution:


There was free space. Let the capsule work. I did not drill holes in the lid, the volume is enough. Maybe in the forest, when the wind is strong, it will be weakly audible, then you will have to make changes. But, it's incredible.

The photo shows a "creative mess", the stage of completing the assembly of the transceiver.

Soldering radio amateurs will not be surprised at all.

The so-called front panel. I always put LEDs, they signal the inclusion of the device and enliven the device. The second LED reflects the manipulation of the transmitter:

The most "ceremonial" view of the "Friend-8" transceiver:

This transceiver will have to work in forests, fields, in different weather, be subjected to shock and other mechanical influences, get caught in the rain, there’s nothing to say about fog, work in frost, etc. That's why I always take pictures of the devices before the start of field tests. There will never be a better appearance of this device, even the case will be scratched, and the covers will be dented.

There is nothing to say about pieces of paper with inscriptions, they will have to be updated several times.

05/28/2010 the transceiver is completed. It took time no terms: "weekend design" I don't recognize.

1. About transistors.

In general, all the detailed explanations in my messages are available ... But, you need to look at a few messages.

I will try, at least briefly, to give explanations, and those who wish can look in detail in the previous detailed messages in the club's RU QRP archive.

So, about my favorite MP101, P28, etc. Why not KT3102, KT3107, etc., or not imported consumer goods?

In ULF PPP, it is most expedient to use cascades with direct connections, any additional transition capacitors introduce additional noise, phase distortion, etc.
ULF in the direct conversion technique is the main amplifying element and must have a very high gain.

Let's say Ku = 50,000. I suppose that no one expects, by applying 1 volt of voltage to the input of an amplifier, to get 50,000 volts at the output?

The reference literature states: “The current transfer coefficient in the mode small signal ". With an increase in the input signal level, the ULF gain will decrease, up to the blocking of the ULF.
ULF on high-frequency transistors will have a very wide bandwidth; when the signal of its local oscillator leaks to the ULF input, the gain will decrease, up to its blocking.

The MP101 has a cutoff gain frequency of 0.5 MHz (!!), which is ideal for a direct conversion receiver (transceiver). Of course, RF transistors can also be used, but it is very likely that they will self-excite in the microwave and decrease the gain due to leakage of their local oscillator signal. Self-excitation is detected without difficulty, with an oscilloscope. But elimination, sometimes, requires a lot of effort, up to the need to replace the transistor (s)!

There is no point in using RF transistors, it is only fraught with unnecessary problems, and often blocking capacitors do not help to eliminate self-excitation. Personally, if I have specialized low-frequency transistors, I avoid using high-frequency transistors in ULF.

Now about the use of "tape" capacitors, such as MBM.

Again, modern, beautiful, elegant ceramic capacitors often begin to work in ULF not as capacitors, but like quartz, they begin to generate hundreds of kilohertz RF. The prospect of choosing non-generating capacitors does not appeal to me at all!

Here is a photo showing a sine wave generated by a very modern, very elegant capacitor. With a "ribbon" capacitor no problem!

Microcircuits in their composition have high-frequency transistors and leakage of the local oscillator signal to the input will reduce the gain, up to blocking the microcircuit.

Everyone, probably except me alone, the beloved LM386 makes noise like a primus stove, requires serious consideration of protection against HF interference, “eats” much more, and the gain is significantly lower than the ULF tested in “battles and campaigns” on domestic MP101, MP103 and etc. These transistors work flawlessly in the Chamber of Commerce and at -30 degrees.

So: I use MP101, MP103, in this case, not out of originality, not because of: “ ^ This modern element base is NOT interesting .", a due to the fact that this is the best option, really tested in assembled structures, which are really tested on the air, moreover, in forest-fields, under various weather conditions, up to brutal frost!
I don’t want to create difficulties for myself by using “modern components”, and then overcome them! It's for an amateur …

2. About microcircuits.

Regarding the use of microcircuits ... I have a number of imported microcircuits (TNX DL7PGA, Vladimir is my constant friend ... and opponent.) I prefer domestic 235PS1, not NE602. Although, objectively, these microcircuits are about the same class. Domestic ones are less noisy, have a metal screen, which eliminates extraneous pickups directly on the microcircuit case (NE602). And, domestic microcircuits have passed a rigorous selection for compliance with the parameters of specifications.

Next pair: 435UR1 and TL592. Here, the domestic microcircuit is clearly superior in terms of noise, efficiency, amplification, and shielding of the microcircuit housing is very important here. All this has been tested in practice.
More about imported microcircuits: in bulk, microcircuits of disgusting quality, an unknown manufacturer and simply non-working ones. Of the 3 stereo amplifier microcircuits purchased, 100% of the microcircuits had only one channel working, of course, not a single microcircuit produced any declared 20 watts of output power.
When I tried to purchase stabilizer chips, they immediately told me: “Don't take it! Rubbish, not workers!

Personally, I still prefer, if possible, to use reliable components. In a word, it is more difficult with microcircuits, if there is a guarantee that the microcircuits are branded, have passport performance characteristics, this is one thing. But if there is a clear substandard, an incomprehensible manufacturer, inscriptions at random, this is a completely different matter!
About domestic electrolytic capacitors.
At various forums, only a hopelessly lazy participant did not “kick” domestic components! Specially I demonstrate domestic electrolytic capacitors:

A box of such capacitors was in my possession at the beginning of this year, 2010. Packed, no one has energized these capacitors since the moment of manufacture. 1975 issue, by the way! I decided to check the condition of these solid age capacitors.

I parallelize a dozen of these capacitors and connect them through a current-limiting resistor and a diode to the network. Wonderful! No lumbago, crackling, rustling and other negative phenomena. After a while, I turn it off, pause, during which, as I assumed, the capacitors should be completely discharged and close the conclusions ... A wire with a diameter of about 0.5 mm was interrupted at the moment, a mark appeared on the screwdriver, and the volume of the discharge is comparable to a pistol shot.

By the way, I had full confidence in these capacitors and used them in the power amplifier on the GU-81M as a tribute to these glorious components. Great capacitors. And in parallel with them, in the UM, I soldered a resistor so that they would be discharged after turning off.

The following are great capacitors:

Capacitors brand "IT". 1970 of release (at that time I was in my 3rd year ...), this board was lying around somewhere, I don’t even remember where I got it from ... Constantly, when necessary, I unsolder these capacitors from the board and apply them. Work like new! Unfortunately, there are only 7 pieces left, the rest are in the works.

They look unpretentious, they are already about 40 years old, but they enjoy my full trust and respect. Great capacitors!

Another board of excellent capacitors. 1989, the capacity corresponds to the passport value, with a margin, the self-discharge is surprisingly low. No similar imports from "Chip and Deep" closely match in terms of parameters. But, in fairness, imported ones are smaller in size. Self-discharge and drying of imported capacitors, to put it mildly, are inferior to domestic ones ... Already, judging by one topic in the forum, electrolytic capacitors began to dry out in "thousanders". This is in the latest transceivers ...

And all sorts of good old R-250M, M2, R-309, Krot-M, R-326, etc. which has exceeded 40 years, work flawlessly. What can we say about my R-326M, which is only about 20 years old!

Final part.
As usual, best wishes to all of us! And see you on the air, including QRP/p!

73! Sincerely, UA1CEG, Yuri Alexandrov, Garbolovo village, Vsevolozhsk district, Leningrad region. LO-23,KP50FI.
Website: UA1CEG.narod.ru

Yu.V. Demin, UR5MMJ

Given below direct conversion transceiver made according to the scheme with direct frequency conversion and is designed for SSB and CW radio communications in the 1.8 MHz band. A distinctive feature of the circuit is the use of active filters in the ULF receiver and microphone amplifier, which improve selectivity and reduce the spectrum width of the emitted signal of the transceiver. Transceiver parameters Receiving path sensitivity not less than 2 μV

The bandwidth of the receiving path by level - 3 dB 2.5 kHz

Suppression of non-working sideband during reception and transmission of at least 35 dB

Carrier suppression not less than 40 dB

Output power 10W

Supply voltage 12 V (stable)

To eliminate interference of 50 Hz, the power supply is assembled in a separate housing. As a GPA (VT9), an inductive three-point circuit was used (Fig. 1). The operating frequency of the GPA is tuned by the capacitor C5.2 from 7320 to 7720 kHz. From the output of the source follower (VT10), the heterodyne voltage is fed to the TTL level generator (VT11, DD1), after which it is fed to the digital phase shifter - frequency divider by 4 (DD2). The DD3 multiplexer switches the phase shifter channels 0 and 90° between each other during the transition from reception to transmission. The heterodyne signals from the outputs of the multiplexer are fed to the engines of the balancing potentiometers (R9, R10) of the mixer.

The RF transceiver is assembled on a field-effect transistor VT1. The RF gain is controlled by a variable resistor R1, which changes the bias voltage at the second gate of the transistor. The input circuit of the URC is adjusted by the capacitor C5. i within the range of 160 m. The output circuit is low-Q, broadband. From it, the signal through the coupling coil L3 is fed to the mixer transformer. Diode VD3 prevents the circuit L2, C12 from being shunted by transistor VT1 when switching to transmission mode.

In a single-way mixer, a well-known scheme based on T-bridge RLC links is used as a low-frequency phase shifter. From the output of a single-band mixer, the signal comes through a two-link low-frequency filter but a ULF.

In the ULF, after the preliminary amplification stage, an active fourth-order filter (DA1) is used, which further increases the selectivity of the receiving path. In CW reception mode, an LC circuit is connected in parallel with the volume control. The ULF DA2 output chip operates in light mode for a 100-ohm load.

The microphone amplifier of the transmitting path also contains an active filter. The output of the active filter is loaded on the source follower (VT8). The function of the diode VD11 is similar to the function of VD3. For the CW mode, a separate tone generator (VT5) is used in the transmitting path. When transferring sound signal from the output of the microphone amplifier is fed through a low-pass filter to a single-sideband driver. From the output of the SSB shaper, the signal is fed to the transceiver's power amplifier. The power amplifier of the transceiver is three-stage. The final stage is assembled on a VT15 transistor according to a grounded collector circuit. From it, the signal enters the P-circuit, and then through the capacitors C89, C90 and the contacts K1.1 of the antenna relay to the antenna. The cascade on the VT16 provides a "self-listening" mode when working with the telegraph.

Transceiver design. The transceiver is placed on 6 boards (Fig. 2):

board 1 - GPA digital phase shifter, channel switch 0 and 90 ″, power supply TTL microcircuits; board 2 - URC;

board 3 - single-way mixer and passive low-pass filter; board 4 - ULF;

board 5 - microphone amplifier and 1 kHz generator; board 6 - preliminary stages of the transceiver power amplifier.

Boards 2 and 6 are located in the basement of the transceiver chassis. The power amplifier is placed in a separate shielded casing with a partition between the preliminary and final stages. All connections between the boards, except for the power wires, are made with a shielded wire, and the RF circuits are made with coaxial cables.

The most critical components of the transceiver are the GPA and the single-way mixer. Particular attention should be paid to the performance of the GPA circuit, since the frequency stability of the transceiver depends on it. The VFO frequency drift should not exceed 100 Hz per hour after the transceiver has warmed up for 10 minutes. The GPA coil is wound on a ceramic tube with a diameter of 6 mm and a length of 15 mm. As a frame

coils, the case of the KBG capacitor is used. To do this, the cheeks should be unsoldered from the capacitor and the contents removed. Then, with a file or sandpaper, cut the rings of the fasteners. They will be the contact points for the OUT winding. For a denser winding of the coil, it is necessary to pre-solder the outlet. After that, with tension, turn to turn, wind the coil, and solder its ends to the contact points. On top of the coil with epoxy glue, it is necessary to glue a textolite or another, for example, from the IF circuits of pocket receivers, a threaded sleeve, into which a standard 600NN ferrite core is screwed. Place the GPA contour on the screen.

Capacitors C76-C78 are soldered directly on the reverse side of board 1 between the positive and common terminals of each of digital microcircuits DD1-DD3. Capacitor C72 is located near the collector of transistor VT12. Such measures make it possible to completely avoid RF radiation through the power circuits of microcircuits. Pickups can be listened to by ear when received in the form of noise or hum with a certain sampling when the GPA is tuned.

Coils L6, L9, L10 of the mixer are wound with a wire folded in half, after which the beginning of one is connected to the end of the other winding. This tap is the midpoint of the coils. The winding data of the transceiver coils are given in Table 1. The size of the rings of all coils, except for the LF phase shifter coils 19, L10 and the LPF coils U1, L12, can be changed in any direction. Options for possible replacement of parts used in the transceiver are given in Table 2. The RES-47 relay was used as an antenna switch, however, any relay with a low contact capacity is suitable.