Traditionally, over the last century, one single method has prevailed, which has become a classic one - rotating the tuning knob of a certain node inside the radio station (input circuit, local oscillator, synthesizer). That is, a setting associated with a mechanical or electrical change in one or more of them. This tuning method imposes a number of restrictions on radio operators. We can only receive transmissions from one station at a time. In order to listen to another station, we need to first of all lose the previous station and then tune in to the new one. And this is already a certain process that takes a certain time and excludes, in principle, a complex and complete perception of the radio broadcast as a source of information. The limitation of this method is that we cannot see the live broadcast. First, you definitely need to scan a certain area, and then expand the “frozen” image, as is currently implemented in most Yaesu transceivers.
In addition, as is known from the theory of constructing modern radio receiving devices, the main gain in superheterodyne receivers is provided by its intermediate frequency amplifier (IFA), which determines the real sensitivity of the receiver, i.e., its ability to receive weak signals.
Focused selection filters (FSS) of this path provide selectivity (selectivity) of the receiver in the adjacent channel. Quartz filters, which have steep characteristic slopes, cope best with this task.
The figure below shows the characteristics of the filter. Its passband (PB) is determined at a level of 0.7 K, where K is the filter transmission coefficient. The figure shows that the amplitude of the interference is significantly weakened relative to the amplitude of the useful signal: K2<К1.
From here it is obvious that the flatter the slopes of the characteristic, the less the interfering signal is suppressed and vice versa. Adjacent channel selectivity is a parameter characterizing the ability of the receiver to isolate the desired signal at a given frequency in a given band.
In addition to adjacent channel selectivity in superheterodynes, there is such a thing as mirror channel selectivity, which is determined by the design of the receiver input circuits.
But the most important feature of superheterodyne receivers is that the lower the value of its intermediate frequency, the more rectangular slopes of the characteristics of its bandpass filters can be obtained and the higher the selectivity over the adjacent channel. But, the lower the intermediate frequency value, the worse the selectivity in the adjacent channel. Therefore, we chose a compromise intermediate frequency value of 465 kHz for radio receivers produced in the USSR and 455 kHz for modern radio equipment. To improve selectivity along the mirror channel, it was necessary to use double and triple conversion circuits. But, at the same time, the receiver’s own noise increased, and an increase in the number of mixers also led to a deterioration in the dynamic range of the receiver and a decrease in the resistance of these receivers to intermodulation interference. Dynamic range determines the ability to receive a weak signal on a given frequency when another powerful station comes on nearby on a different frequency. It is determined by the linear portion of the characteristic and is limited “from below” by the receiver’s own noise, and “from above” by the nonlinearity of the elements of the mixer circuits. In modern broadcasting, the signal level in the receiver antenna can reach several hundred millivolts. At this level of the input signal, reception is no longer possible and is actually blocked. The concept of “dynamic range” describes the maximum levels of signals supplied to the receiver input at which the radio receiving path is able to operate normally and not be overloaded. Typical dynamic range figures for today's transceivers are 80...100 dB and allow you to work comfortably on the air on one band, even if there is a neighboring radio station with a power of 100 W within a radius of 1 km from you.
The main feature of transceivers made according to the classical scheme with several conversions is the increased level of thermal noise of all semiconductor elements of the path at the output of the radio receiver. The more conversion and amplification elements in the path, the correspondingly higher the noise level at the output. The noise of synthesizers and other generators is also added here. The use of automatic gain control has little effect on the overall noise of the path, because the number of amplification/conversion elements remains constant. This problem manifests itself as a constant annoying noise in the headphones or radio speaker, even with the antenna turned off. When connecting an antenna, this noise can be masked by the noise of the radio broadcast, but in this case the most important thing is lost - the transparency of the broadcast, clearly audible to any ear!
With the widespread use of digital technology and digital signal processing algorithms (DSP or DSP in English) over the past 20 years, DSP microprocessors began to be introduced into the IF processing path. This made it possible to significantly improve the quality of the main signal selection (filter band from 50 Hz, adjacent channel suppression levels up to -100 dB) and introduce many additional and useful functions, ranging from cleaning the spectrum of the received signal from noise and interference to decoding digital types of modulation.
By introducing several radio receiving paths with several IF and DSP paths into one package, manufacturers have learned to implement such a new and popular function as displaying a spectrum panorama on the operating range. The company that has been most successful in using this technology is ICOM.
However, when, with the use of DSP, selection on the adjacent reception channel was maximally improved, several problems came to the fore, which in previous implementations of the IF path were solved at approximately the same level as the IF path and were not so relevant. These are selectivity for side reception channels and the dynamic range of received signals.
In any variant of constructing a receiving path with one or several intermediate frequencies, side reception channels will always be present. These are the so-called mirror channels from IF frequencies and channels from harmonic conversion. Their appearance is associated both with the mathematics of signal conversion and with the nonlinearity of the conversion elements, which in principle cannot be avoided. The number of side reception channels can be very large and depends on the number of IFs and their rating. Manufacturers are trying to solve emerging problems in a variety of ways and tricks, coming up with new ways to suppress side reception channels. This includes minimizing the number of IFs, selecting IFs much higher than the frequency of the received signals, and using complex pre-selection schemes. Today, the typical figure for suppression of mirror channels is approximately -60...-70 dB. It is enough to be more or less comfortable in today’s overloaded airwaves.
Methods of direct conversion of signals from the radio frequency spectrum into the audio frequency spectrum and processing of the final signal using a phase method, where the main amplification and signal processing occurs not at an intermediate, but at a low (audio) frequency, will allow us to get rid of, if not all, then at least most of the problems described above. .
The principle of direct conversion was known back in the 30s of the last century. But at that time, with that elemental base, it was impossible to obtain acceptable reception quality. Radio amateurs returned to direct conversion receivers and transceivers already in the 70s of the last century. In our country, the pioneer in this was Vladimir Timofeevich Polyakov, who wrote many articles and published books on the direct conversion technique. The practical circuits of receivers and transceivers operating on the principle of direct conversion that he published were repeated by many radio amateurs, including beginners. But at that time, the element base did not allow achieving a tangible advantage, except for the cost compared to superheterodynes. Currently, with the advent of computers that have modern sound cards, on which the main signal processing is carried out, the direct conversion technique is experiencing its rebirth.
Today the computer is becoming more and more part of our lives. If earlier, some 15 years ago, the use of a PC was limited only to maintaining a hardware log, controlling the transceiver via the CAT interface and processing signals in digital communications, now all manufacturers of modern equipment are rapidly introducing the most advanced engineering solutions into the circuitry of modern transceivers. With the rapid increase in computing power and the miniaturization of integrated circuits, the possibility of widespread adoption of microprocessors has become possible. First, we processed the detected low-frequency signal, then we began to digitize the signal at a low frequency, close to the audio frequency – 12..48 kHz, and then programmatically encode/decode any types of modulation. The same technology of basic filtering and signal processing at intermediate frequency remains. The entire emphasis is on expanding the control and display service, until in 2004-2006 the Flex-radio company entered the radio communications market and began mass production of the Flex SDR-1000 transceiver (Software Define Radio), operating on the principle of direct conversion. Technologically, this made it possible to significantly simplify the circuit and reduce costs compared to classic transceivers. There are only a few components left in the design: a computer-controlled frequency synthesizer, a receive and transmit mixer, a low-noise ULF, receive/transmit switching nodes, a transmitter power amplifier and band-pass filters.
Since about 2005, several companies around the world, as well as individual enthusiasts, began to copy the SDR Flex-1000 transceiver with or without any modifications. The most famous and popular in Russia was the clone of the transceiver from Mr. Tarasov, UT2FW. Only thanks to his efforts, a 3-paid, largely improved clone version of the SDR Flex-1000 transceiver, as well as a 100 Watt fully finished version of the transceiver, became available to many Russians.
In Russia SDR transceiver They became known thanks to the Taganrog company Expert Electronics, which in 2007 began producing its own version of the SDR transceiver under the name Sun SDR-1. It is an improved copy of the Flex-1000 transceiver and has a fundamentally different control circuit. If the original Flex-1000 transceiver had control via an obsolete parallel LPT interface, then the Sun SDR-1 developers implemented transceiver control via a USB interface and wrote their transceiver program completely from scratch. Around the end of 2005 - beginning of 2006, a truly epoch-making event took place, which began a revolution in the world of radio and the widespread adoption of DDC architecture.
In the spring of 2012, the Russian company from Taganrog, Expert Electronics, announces the release of its new radio Sun SDR2.
At the end of the summer of 2012, they released their first ready-made transceivers for sale. The Taganrog team not only released a relatively cheap and functionally complete DDC/DUC transceiver for the HF band, but were also able to implement it in the VHF band, made wireless communication with the transceiver - full control via Wi-Fi, and also wrote all the software for the transceiver themselves from scratch.
Mixers used in modern receivers made using SDR technology are built using a double-balanced circuit and introduce a minimum of losses. Due to the fact that analog high-speed switches are used as mixer elements, such a mixer is practically silent. All amplification occurs at low frequency and is provided by specialized low-noise microcircuits. In order to maintain a high value of the dynamic range of the ADC, the ULF gain is selected as low as possible. It only compensates for losses in the mixer and input circuits. From the output of the ADC, the digitized signal is processed by software.
For example, in Flex SDR transceivers this gain corresponds to 20 dB. Additional gain is achieved by adjusting the low noise amplifier (LNA) at low frequency. Even without a preamplifier, the sensitivity of Flex SDR transceivers is -116 dBm - this corresponds to 0.35 µV. With the preamplifier turned on in the middle position, the sensitivity improves to a value of -127 dBm or 0.099 μV; with maximum gain, the sensitivity is already -139 dBm or 0.025 μV and is already limited by the noise of the preamplifier itself.
Compared to conventional transceivers, SDR is superior not only in sensitivity, but also in “noise,” which is one of the main subjective assessments of the quality of a transceiver.
The block diagram of gain distribution across the main blocks is shown below.
So, one of the most important characteristics of the radio receiving path is its ability to isolate a useful signal of the required band at any of the operating frequencies with minimal distortion and minimal unevenness.
Even the simplest SDR transceiver of the Flex family practically surpasses all devices in sensitivity, although it is inferior in dynamic range. The dynamic range of the AIC33 16-bit ADC is determined by its side-channel selectivity, mirror-channel selectivity, and compression point. In SDR transceivers, the compression point is usually set to a high level. Mirror channel selectivity in SDR technology is ensured by the correct symmetry and accuracy of the quadrature local oscillator signals and low-frequency processing channels. In fact, this is ensured by the manufacturability of the assembly printed circuit board, the correct wiring of the circuit diagram and the correct design of the circuit. All inaccuracies in the technological cycle are automatically compensated in the digital stream processing program.
In SDR transceivers, using a single mixer, the signal is transferred from the radio range to low IF (0-100 kHz) and digitized using a sound card, and then the required frequency band with the desired type of modulation is demodulated using software methods. To calculate using the phase method, a pair of maximally identical receiving channels shifted in phase by 90 degrees is required. As a result of signal conversion in 2 channels, we have a mirror channel spaced 180 degrees relative to the direct channel and easily suppressed by software methods by -100...140 dB. It is even easier to select a signal from an adjacent channel. When using DSP, the adjacent channel rejection level is approximately equal to the dynamic range of the DSP ADC - i.e. easily fits into the numbers -100...-120 dB with the filter squareness coefficient very close to 1.
It is in principle impossible to achieve such suppression figures when using analog filters. For comparison, suppression of the adjacent channel by a good quartz filter at a level of -60 dB occurs when detuned by 1...2 kHz. In a software filter, -100 dB suppression occurs with a detuning of only 50-100 Hz. This difference is clearly noticeable in the case when the adjacent signal comes with a level of 9+40...+60dB. On a classic analog transceiver, you lose air until you tune out from the neighboring station by about 5...25 kHz. When using an SDR transceiver, narrowing the software filter to 50-200 Hz, you practically stop hearing the interfering signal.
The presence of only one mixer in the signal processing path significantly increases the “transparency” of the airwaves. You hear the weakest signals and easily separate them from the strongest ones, you hear the “depth” with your ears and feel the “dynamics” of the radio broadcast. And integrated work with all signals in the 100 kHz band allows you to graphically easily expand the spectrum up to 200 kHz in real time and do with it what you want. No classic is capable of this with analog signal processing!
The block diagram of the Sun SDR2 transceiver is shown below.
A separate discussion concerns drawing the spectrum panorama. The maximum resolution of the monitor screen on which the spectrum is displayed is only 1080 pixels. Advanced video cards have the ability to stretch the spectrum across 2 monitors - the Windows video driver allows you to do this. The result is a maximum of 2160 points. Of the total number of points, the full width is often used very rarely; a small part of the points is occupied by borders and frames of the program window, and quite often the panorama spectrum window is kept expanded not to the entire screen, but only a small part of it, i.e. 30...60% of the maximum number of points is used.
When calculating the spectrum and filters, complex mathematical algorithms of fast Fourier transform (FFT) functions are used. The number of reference points during FFT processing is usually taken with a slight excess - 4096, 8192, and very rarely for specific tasks more than 16384 points. The more points are used, the more visually the spectrum looks beautiful and allows you to examine the signal elements in more detail when it is enlarged. However, the number of calculations, calculation time, and spectrum drawing time also increases. But even 32,768 thousand points are a mere minuscule compared to the 30...60 million samples that come from the ADC.
In addition to the main program (Expert SDR2), you can open windows of other programs, for example, a hardware log (UR5EQF Log 3), etc.
Below is a photo of the transceiver circuit board
It can be controlled from a computer using a separate WI-FI module, which is purchased separately.
Fans of the group PELAGEYA ("Polefans") VKontakte
Concert on Minin Square in Nizhny Novgorod May 9, 2013
Mini-concert in Magas (Ingushetia) June 4, 2014
Create a topic (if it has not already been created) on the forum http://ra3pkj.keyforum.ru
SDR HAM - Introduction
Attention! In winter, the CY7C68013 microcircuit may fail due to breakdown by static electricity, which accumulates in the air and on surrounding objects, and then flows down an unpredictable path. It is necessary that the equipment is grounded, and the SDR ground bus is connected to the computer case with a separate wire. Touch boards and parts on boards that are connected to the equipment only after removing static electricity from your hands, for example, by touching massive metal objects. I STRONGLY recommend connecting the USB connector body (which is on the SDR board) directly to the SDR ground bus, for which you need to short-circuit the parallel circuit C239, R75 (near the USB connector).
To purchase blank boards, contact Yuri (R3KBL) [email protected]
I’ll say right away - I didn’t make this transceiver, I’m just interested in the topic itself and the results. Moreover, the transceiver uses an AD9958 synthesizer of my design, and I also wrote new firmware for the USB adapter integrated into the board, which replaced the original outdated firmware “from the German” (this is discussed below).
General information
The SDR HAM transceiver is a clone of the SDR-1000, structurally designed by Vladimir RA4CJQ. The transceiver uses well-known circuit solutions developed by many radio amateurs. The difference from the well-known “Kyiv” clone SDR-1000UA is quite noticeable. Brief description of features:
1. Single board design.
2. Transmitter power amplifier of at least 8 W (those with talent can squeeze out more).
3. Frequency synthesizer on the DDS AD9958 chip with a low level of spurs (the synthesizer is described here:).
4. Transceiver control via USB ( The USB adapter is structurally described here: but there is special firmware for SDR-HAM!!!).
5. Power supply: +13.8V and bipolar +-15V.
6. Two-stage relay attenuator at the receiver input.
7. SWR and power meter.
8. Work without brakes in ANY Windows operating systems without installing a driver (the system HID driver of Windows itself is used), which became possible after replacing the firmware of the USB adapter integrated into the board (this is discussed below).
Information about firmware and software
The transceiver works with official PowerSDR from FlexRadio Systems versions no higher than 2.5.3 (starting from version 2.6.0, the SDR-1000 transceiver and its clones are not supported), but works with PowerSDR 2.8.0 from KE9NS, which in turn was adapted for SDR -1000 radio amateur Excalibur (the latest in fashion). Here's more about this version 2.8.0.
The AT91SAM7S controller (used to control the AD9958 synthesizer) should be flashed as described here:.
Now let's talk about the firmware and 24C64 memory chips, which are necessary for the CY7C68013 controller to function as a USB adapter. Historically, when the transceiver went to the masses, the firmware of the USB-LPT adapter from the “German” (described on my website) was “poured” into the memory chip (described on my website), but as it turned out, in versions of Windows higher than Windows 7-32, the firmware is human doesn't work. Brakes and problems with the digital signature of the driver!!! (owners of Windows XP and Windows 7-32 can sleep peacefully). The problem was solved after I wrote a new firmware that works in any operating system without any problems and also does not require driver installation (Windows itself will find an HID driver in its bins). The firmware was created by me in collaboration with US9IGY.
But there is a nuance - reflashing the memory chip located onboard, requires exercises with a soldering iron, since it involves lifting one leg of the microcircuit and connecting a temporary toggle switch (this will be discussed below). Flashing a CLEAN microcircuit into a board (i.e. in a freshly manufactured transceiver or when a memory chip is installed from a store) does not require additional exercises with a soldering iron. Both options for your behavior are described below:
1. A blank 24C64 memory chip should be flashed as described here: except that a special new firmware is used and the main working driver mentioned at the end of the page is not installed. Download the new firmware sdr_ham.iic: sdr_ham.zip. The firmware is flashed into the transceiver itself via USB (the same archive contains the sdr_ham.hex firmware for those who want to flash the memory chip outside the transceiver, i.e. using a programmer). Before flashing, do not forget to move the jumper on the board (which is about 24C64) to the programming enable position, and also do not forget to return it to its original position after flashing.
2. whoever will reflash the 24C64 memory chip (which has old firmware from the “German”) must do everything as described above in paragraph 1, but taking into account the following: temporarily unsolder pin 5 of the 24C64 chip (we pretend that we have clean microcircuit) and connect it via a toggle switch, move the jumper on the board (which is about 24C64) to the programming enable position and, with the toggle switch open, connect the SDR to the USB socket of the computer. Next, turn on the power to the SDR and run the flash program. Immediately before flashing, close the toggle switch. After flashing, turn off SDR and restore everything back.
For reference. The SDR (or rather its USB adapter) is defined by the computer as an HID Device, the properties of which have the following ID values: VID_0483 and PID_5750.
After all the hassle of flashing is completed, you can safely exhale and calmly place the Sdr1kUsb.dll file from RN3QMP in the folder with PowerSDR - download sdr1kusb_rn3qmp.zip. In PowerSDR, in the General -> Hardware Config menu, check the "USB Adapter" box.
Information for owners of various other SDR transceivers!!! In the firmware of the 24C64 memory chip (for CY7C68013), I limited myself to only what is necessary for SDR HAM. The firmware is not intended for upgrading USB adapters to CY7C68013 for SDR-1000 with DDS AD9854. This is confirmed by the UR4QOP experiment in the transceiver from UR4QBP - DDS AD9854 does not work! So I can state that the firmware is intended only for SDR HAM. I don’t have the time or motivation to adapt anything in the firmware for other applications (except for SDR-HAM).
Clean boards from yuraws
Clean boards with hole plating, solder mask and markings.
Straight side:
Reverse side:
Scheme
Download and unpack the diagrams (as well as board drawings on both sides) in PDF format: sdr_ham_shema_pdf.7z The same diagrams are shown below for general reference.
Input attenuator, UHF:
Range bandpass filters (in the diagram the Amidon rings are indicated in color - red T50-2, yellow T50-6):
Mixers, receiver and transmitter amplifiers:
Automatic control_1:
Automatic control_2:
Frequency synthesizer:
USB/LPT adapter:
Microcontroller for controlling the frequency synthesizer:
Transmitter power amplifier and ADC for SWR and power meter:
Pay
High-quality board drawings in PDF format are in the same document as the schematics (download in the previous paragraph). Below is a general view for your reference:
Design project
Download the project (with schematic and board): project_sdr_ham.7z AltiumDesignerViewer viewer on the official website: http://downloads.altium.com/altiumdesigner/AltiumDesignerViewerBuild9.3.0.19153.zip
List of elements
The list from RA4CJQ is generated automatically by the PCB layout program, so the names of many elements are not specific, but conditional. Keep in mind that such names are often not suitable for ordering items in stores. Download the list of elements in Excel format 2007-2010: sdr_ham.xlsx.
List from Steve (KF5KOG). This list also includes links to Mouser and Digikey stores (item names are clickable). The catalog names of these stores are indicated (they differ slightly from the names of the element manufacturers themselves): Parts List with Manufacturer part Numbers 18 Sep 2014.pdf
Bugs and improvements
Sometimes radio amateurs post messages on forums about noticed errors, and also suggest various improvements. I will publish them here as soon as possible.
#1. The board is mixed up designations resistors R90 and R94 in the wiring of one of the transistors RD06 of the power amplifier. The figure shows the correct designation (resistors are marked with highlight):
#2. In the UHF circuit, in the power circuit of the DA1 AG604-89 microcircuit, resistors R5 and R6 should be 130 Ohms each.
#3. It has been repeatedly reported that on clean boards from the manufacturer (link to the manufacturer at the top of the page) there are shorts in the area of the DFT elements. Moreover, the resistance of the shorts can be very different, for example, several Ohms and higher. In reception mode this is not particularly noticeable to the ear, but during transmission the output power is low. Shorties were also found in the area of the INA163 microcircuits, which was expressed in an imbalance of the signals supplied to the left and right channels of the sound card. Often short spots are not visible even at high magnification. In such cases, the short ones must be “burned out” electric shock low voltage but sufficient power.
#4. Please note that the DD6 chip on the board is initially rotated 180 degrees. compared to microcircuits DD4, 8, 9. That's right! You can mechanically solder DD6 in the same way as DD4, 8, 9 and this will not be correct.
#5. The transceiver requires an external bipolar voltage of +-15V (in addition to the +13.8V voltage) for power supply. In principle, it can be powered from a +-15V transformer source, but many radio amateurs use DC/DC converter microcircuits, putting up with a slight increase in noise from such converters. To do this, a scarf is made on which the microcircuit and wiring elements are soldered, and the scarf itself is placed on the transceiver board. They use MAX743 microcircuits (a converter from +5V to +-15V), link to the datasheet http://datasheets.maximintegrated.com/en/ds/MAX743.pdf, the datasheet has a drawing of a printed circuit board, the wiring of the microcircuit is quite complex. They also use microcircuits P6CU-1215 (from +12V to +-15V) or P6CU-0515 (from +5V to +-15V), which require fewer wiring elements, link to the datasheet http://lib.chipdip.ru/011/DOC001011940 .pdf. Also mentioned are the RY-0515D and NMV0515S microcircuits (both from +5V to +-15V), the latter makes little noise. It must be said that when using converters from +5V to +-15V, an enlarged radiator is required for the +5V stabilizer, because The current consumption of the converters is noticeable.
#6. To obtain an output power of 10W (or more), you should replace the RD06HHF1 transistors with RD16HHF1. Set the quiescent current of each transistor to 250mA. If the size of the radiator allows, then the quiescent current can be made significantly larger. Stew KF5KOG in the yahoo group suggests changing the values of the wiring elements of these transistors. Change capacitors C254,268 to 0.1 μm, and change resistors R91,102 to 680 Ohms.
#7. The HF transformer on the BN-43-202 binoculars at the output of the power amplifier gets very hot. It is proposed to replace the core with tubes 2643480102 FERRITE CORE, CYLINDRICAL, 121OHM/100MHZ, 300MHZ. Dimensions Dext.12.3mm x Dint.4.95mm x Length 12.7mm, material-43. Datasheet http://www.farnell.com/datasheets/909531.pdf (the photo on the right shows the previous transformer on the binoculars for comparison):
Stew KF5KOG in the yahoo group suggests replacing the core with a BN43-3312. Change capacitor C261 to 100pF, while the output power on the 6m range is at least 8W (using RD16HHF1 transistors). Secondary winding 3 turns!
A radio amateur with the nickname Lexfx (CQHAM forum) solved the problem differently. He installed an additional choke (in red in the diagram), while the middle output of the binoculars is no longer used. Choke core 10x6x5mm (probably 1000NN), 7 turns in two wires with a diameter of 0.8mm:
#8. Information from the yahoo group. To reduce UHF noise, you need to cut off the ground trace in one place (Bridge gap in the picture), and add SMD inductance in another place, breaking the conductor in this place (Cut Trace in the picture):
#9. To level out the noise track in the PowerSDR panorama, it is recommended to reduce the capacitance value of capacitors C104, 107, 112, 113 (at the outputs of the FST3253 receiver mixer) to 0.012 microns or even to 8200 pf.
#10. Error when wiring the board. Pins 2.3 (source, drain) of transistor VT2 IRLML5103, which supplies power to the UHF chip, must be swapped. Decide for yourself how to do this. Possibly wires. Datasheet IRLML5103.pdf
#11. Unsuccessful power amplifier bypass circuit. When switching to transmit, the bypass cable remains connected to the amplifier input, which drives the amplifier at 50 MHz. It is suggested to use the free contacts of the K26 relay to completely disconnect the bypass cable. Relay K26 has two groups of contacts. We unsolder K26 (if it was already soldered) and perform it according to the diagram and figure below. We use PEV winding wire for jumpers. You may have to bend the relay legs a little before soldering. It will be almost unnoticeable. On a fragment of the board, white lines show where the tracks are cut, and thin black lines show wire jumpers:
The radiator is an aluminum plate 3...4 mm thick, fixed to the bottom of the board on racks. The power amplifier transistors and the +5V stabilizer are soldered on the back side of the board and screwed to the heatsink.
Software Defined Radio - software defined radio, a new trend in construction amateur radio designs, where some of the functions of the receiver (sometimes the transmitter) are transferred to a computer (microprocessor, microcontroller). Let's take a look at the block diagram:
The signal from the antenna enters the input circuits, where it is filtered from unnecessary signals, can be amplified or divided, it all depends on the tasks of the device. In the mixer, the desired signal is mixed with local oscillator signals. Yes, yes, exactly with signals! There are two of them, and they are out of phase by 90 degrees relative to each other.
At the mixer output we already have signals audio frequency, the spectrum of which lies from the local oscillator frequency above and below. For example: the local oscillator is 27.160 megahertz, and the frequency of the useful signal is 27.175 megahertz, at the output of the mixer we have signals with a frequency of 15 kilohertz. Yes! Two again. They are also called IQ signals. The audio amplifier adjusts the level to the desired level and feeds it to the ADC. Based on the phase shift of IQ signals, the program determines whether the useful signal was above or below the local oscillator and suppresses the unnecessary mirror reception band.
By the way, the SDR transmitter works on approximately the same principles: a phase-shifted low-frequency signal from the DAC is mixed with a local oscillator in the mixer, and at the output we have a modulated high-frequency signal, suitable for amplification in power and supply to the antenna.
It should also be noted that even more modern SDR systems have appeared, in which the useful signal is directly supplied to a high-speed ADC.
In amateur radio equipment of the lower and middle segment, computer sound cards are mainly used as ADCs. Like built in motherboard, and external, connected via USB or inserted into the PCI connector of the motherboard. The reason for this is simple: usually the sound cards built into the motherboard do not shine good characteristics and this is compensated by installing external ones. The span (the band in which the sdr is able to receive a useful signal without tuning the local oscillator) directly depends on the sound card: the higher the frequency that it can digitize sound card, the wider the swath. Typically these values are 44 kilohertz (bandwidth 22), 48 kilohertz (bandwidth 24), 96 kilohertz (48) and even 192 (96) kilohertz. In high-end technology, high-quality and expensive ADCs are used, the signal from which is converted by a microprocessor built into the SDR to an understandable computer.
The main advantage of SDR technology in amateur radio practice: a large number of types of modulations, adjustable transceiver parameters (after all, signal processing is done in software) and a panoramic view of the range.
Since SDR transceivers and receivers are essentially direct conversion receivers and transceivers, it will be useful to familiarize yourself with the theory of the processes occurring in these devices. How exactly the required sideband is allocated or formed in SDR becomes clear after reading the document.
What's great about 2013 is that SDR enthusiasts finally have a choice rather than just bouncing between $20 RTL-SDR and $700 USRP. Several devices at once allow you to select a transceiver for a specific task. Let's look at the strong and weaknesses everyone.
The most affordable full-fledged SDR. This is not the first successful product of Michael Ossman, who in the past released the first budget Bluetooth sniffer Ubertooth (see the article “Hacker's suitcase” in the August “Hacker” last year). Michael has already run a successful Kickstarter campaign, raising about $600,000 for the production of HackRF. The first 500 pre-sale samples have already been distributed to beta testers, and based on their feedback, bugs will be corrected in the final product.
HackRF has a fairly wide frequency range available out of the box, from 30 MHz to 6 GHz, which is comparable to more expensive devices from the USRP family (50 MHz - 6 GHz). The sampling frequency is 20 MHz. This means that using the receiver it will be possible to analyze, for example, a Wi-Fi signal at a frequency of 5 GHz and high-speed LTE transmissions. The more expensive package comes with a Ham It Up converter, with which you can pick up a signal at a frequency of 300 kHz or more.
Among the disadvantages, it can be noted that HackRF works only in half-duplex mode, that is, at one moment you can either send or receive a signal. To switch between modes, you will have to send the corresponding command each time, which can add unwanted delay. However, if desired, you can combine two receivers and achieve full duplex support. Also, unlike bladeRF and more expensive USRP, HackRF uses USB 2, not USB 3. In addition, HackRF uses an 8-bit ADC (bladeRF has 12 bits), which negatively affects the accuracy of operation.
Another successful project from Kickstarter. BladeRF operates with a smaller frequency range than HackRF, from 300 MHz to 3.8 GHz, so it cannot reach a 5 GHz Wi-Fi signal. Work is also underway on an additional board that should allow signal reception at a frequency of 10 MHz or more.
A distinctive feature of bladeRF is the ability to operate in full duplex mode. Compared to HackRF, this receiver has a higher sampling frequency (28 MHz), a higher ADC resolution (12 bits) and USB 3.0 support. WITH using USB 3 is a concern in SDR receivers as it may introduce interference at 2.4 GHz, so the bladeRF comes with additional sensor shielding.
UmTRX
The device from Fairwaves does not fit into the review in terms of price, but is worthy of mention simply because it was developed by a Russian team. This is the only full (non-MIMO) dual-channel transceiver in this review. Two LMS6002D chips are used as radio chips, so frequency range and the bit capacity of the DAC/ADC are completely the same as bladeRF, which uses the same chip. The transceiver was developed with a greater focus on telecom, therefore the sampling frequency is the same as that of GSM and is 13 MHz. By replacing the reference oscillator, the sampling frequency can be increased to 20 MHz, and in future versions of UmTRX - up to 40 MHz. In addition to the standard firmware, there is firmware that supports four channels of reception without transmission.
In addition to two-channel distinguishing feature UmTRX is an industrial design, the use of “adult” 1Gb Ethernet instead of USB and the presence of an on-board GPS receiver to ensure the high accuracy of the reference generator required for standards such as GSM. All these bells and whistles explain the high price of the device.
USRP B100 Starter/B200
Two devices in the USRP family can be purchased at the same price. At the same time, the B100 is significantly inferior to the cheaper HackRF and bladeRF. It has a frequency range of 50 MHz to 2.2 GHz, and a sampling frequency of 16 MHz. In this case, the B100 uses USB 2 for connection. Full duplex mode is available in both models.
The B200 operates over a wider frequency range, from 50 MHz to 6 GHz. The sampling frequency is 61.44 MHz. The B200 uses USB 3 for connectivity. The more expensive ($1,100) B210 version has two transmitters.
The strength of USRP is that these products have been on the market since 2006 and during this time they have grown a huge amount third-party software and developments.
Conclusion
The future of SDR looks as positive as ever, with several affordable transceivers coming to market. HackRF, thanks to its price, capabilities and openness, will become good choice for novice users. More powerful bladeRF with its sophisticated FPGA and USB support 3 would be better suited for stand-alone projects, but the multifunctional USRP B100 and B200 bring the amateur market segment closer to the “adult” solutions of the N210 level.
