125KHz-channel up-converter to receive the Oscar 100 satellite with a DVB-S2 decoder

125KHz-channel up-converter to receive the Oscar 100 satellite with a DVB-S2 decoder. A 125KHz-channel up-converter handling six different symbol rates to receive Oscar 100 on DVB-S2 ATV, with remote tuning control via an infra-red remote control (of any kind) and frequency auto-complete. 1. PREMISE 2. CHOOSING FREQUENCIES 3. SAVING THE SIX CHANNELS ON THE DECODER 4. THE PLL 5. THE ANALOGIC PART OF THE PLL 6. THE DIGITAL PART OF THE PLL 7. PLL MANAGEMENT SOFTWARE – 80ch.ino 8. HOW TO USE THE 80ch.ino PROGRAMME 9. THE MIXER, INPUT AND OUTPUT FILTERS 10. ADJUSTMENT 11. SHORTCUTS 1. PREMISE Most commercially available DVB-S2 decoders are 1MHz-channel. As a result, narrower channel signals cannot be correctly tuned and visualized. In addition, tuning can take some time and the signal – which can be monitored on https://eshail.batc.org.uk/wb/- often disappears before the process is complete. A 125KHz-channel up-converter with six different output frequencies, one for each symbol rate (which can be saved on the decoder and recalled by simply pressing a button) can solve the problem by providing greater flexibility and speed of use. The device outlined in the following pages consists of two different parts: • A PLL generating the conversion frequency (controlled through an infrared remote control, which may be the same as the one used for the commercial decoder). An ADF4351 controlled by an Arduino followed by a filter and an MMIC amplifier. • The converter proper, equipped with two filters, two MMIC amplifiers and a balanced mixer. The input and output ports have two F connectors through which the power supply coming from decoder is provided to the LNB. There are no buttons, only a small window for the IR sensor. The whole project is no-tune. 2. CHOOSING FREQUENCIES Using an LNB with a 9750MHz conversion frequency, the work band of the Oscar 100 (10491-10499MHz) is shifted downwards to 741-749MHz, which is clearly beyond the reception capabilities of a commercial DVB-S2 decoder. Consequently, an upward conversion is necessary to bring OSCAR 100 signals back within the receivable band. How far up should they be shifted? Two considerations: • The further up it is shifted, the farther apart are all of the spurious products of the mixer, the easier it will be to filter the desired mixer product. • The noise figure of this converter is quite low (it is placed after an LNB, typically with a gain of about 50 dB and a very low noise figure). The contribution to the overall noise of the system is negligible. Assuming the frequency of the local oscillator is around 1200MHz and considering 745MHz (median frequency) as the output frequency from the LNB, the resulting spurious products will be: Fig. 1 – Spurious products at the output of the balanced mixer The most troublesome frequencies are clearly 2110MHz (2xRF and 3xLO), 2690MHz (2xRF and 1xLO), 1655MHz (1xRF and 2xLO). However, they are very low and can be disregarded. Therefore, 1200MHz (approximately) is chosen as the conversion frequency. The Oscar 100 frequencies will be received by the decoder at around 1940MHz. The PLL described below will actually generate the 80 frequencies that will make it possible to receive all ATV channels of the Oscar 100, spaced by 125KHz (the lowest symbol rate), converted up to a single frequency for each symbol rate: 1940, 1941, 1942, 1943, 1944 and 1945MHz. In essence, what will be done is • Using the decoder as a fixed-frequency IF and • Vary the tuning only on the up-converter. The decoder will be used to decode the six different symbol rates (SR): 2M, 1M, 500K, 250K, 333K, 250K and 125K. 3. SAVING THE SIX CHANNELS ON THE DECODER The first thing to do is save six different channels on the decoder at six different frequencies (1940, 1941, 1942, 1943, 1944 and 1945MHz), each with a different SR: 1. 2M @Ch1 2. 1M @Ch2 3. 500K @Ch3 4. 333K @Ch4 5. 250K @Ch5 6. 125K @Ch6 If the decoder cannot be programmed for these six frequencies around 1940MHz, they will have to be saved as their corresponding in-antenna frequencies (i.e. +9750MHz). Ultimately, this is the list of the channels with the respective SR that will need to be saved on the decoder: 1. Ch1 @11690MHz and SR 2M 2. Ch2 @11691MHz and SR 1M 3. Ch3 @11692MHz and SR 500K 4. Ch3 @11693MHz and SR 333K 5. Ch4 @11694MHz and SR 250K 6. Ch6 @11695MHz and SR 125K From now on, the tuning process will be fully automatic, which means there will be no need to remember the frequencies or their symbol rates. • A reception frequency and SR is selected on the up-converter. The PLL will automatically switch to the required frequency. • The corresponding channel is selected (Ch1-Ch6) using the decoder’s remote control. In just two very quick and simple steps it will be possible to tune into any Oscar 100 ATV frequency with the desired symbol rate. 4. THE PLL The ADF4351 board can be found on eBay or Amazon, being careful to choose the appropriate reference frequency. This project uses a board with a 25MHz reference frequency. It is certainly possible to use a board with a 10MHz reference frequency, but it requires changing some of the register values. The values can be adjusted by using the relevant Analog Devices application, or a 25MHz reference frequency can be supplied through the SMA connector – on the left in fig. 2. Fig. 2 – Two of the many boards available on eBay or Amazon Fig. 2 shows two boards – the top one with a 10MHz reference frequency and the bottom one with a 25MHz reference frequency. They generate signals between 35MHz and 4.4GHz. They can be programmed through a 3-wire serial interface. In both cases, one of the two SMA connectors on the righthand side needs to be removed and replaced with a 50ohm resistor, possibly SMD. The board has two outputs, but only one is needed. The other must be closed on 50ohm. This is why one SMA is removed and replaced with a simple 50ohm R. As it is, the ADF4351 is certainly not the best there is. The VCO generates square waves between 2.2 and 4.4GHz (the lower part of the attainable frequencies is obtained by division and is very rich in harmonics). There is a very large number of even and odd harmonics at least up to 5 or 6 GHz, not many dB below the fundamental frequency. However, these harmonics are relatively easy to screen out – an effective band-pass or low-pass filter will do the job. What is impossible to filter out is the considerable phase noise. It can only be optimized by adjusting the PLL parameters using the above-mentioned AD application. ADF4351 ensures good stability and accuracy. Stability is the same as the quartz used as reference, hence adequate for most applications. Accuracy varies from unit to unit. In the five samples in my possession, the accuracy of the signal generated at around 1200MHz varies between +/-15KHz – compared to a reliable rubidium reference signal – hence it is sufficiently accurate to lock onto the signal from the antenna. This slight inaccuracy is clearly compounded by the LNB’s own inaccuracy. It is essential to use a PLL LNB, especially due to temperature variations. In any case, the decoder is certainly capable of tracking – and compensating for – these differences in frequency. 5. THE ANALOGIC PART OF THE PLL When using the ADF4351 the output power is programmable but not very accurate. The double balanced mixer needs around +10dBm, which requires an amplifier between 10 and 15dB. This can be built using an MMIC (50ohm in-out) like the SNA-586 and adjusting the R5 register to obtain +10dBm while keeping harmonics to a minimum. A slightly higher-than-normal quiescent current should be run through the SNA-586 as it is more important to have a good IP3 than a low noise figure, in order to avoid saturation of the stage and an increase in harmonics. About 80mA will do. Fig. 3 shows the layout of the analogic part of the PLL. A low-pass filter is placed before the amplifier with the SNA-586, cut-off frequency 1.6GHz. Why so high compared to the desired 1.2GHz? There are two reasons. • The first is convenience: the higher the filter frequency, the smaller the filter, which will be more mechanically manageable. • The second reason is to exploit one of the natural limits of microstrip circuits. Unlike circuits built with discrete components, the response frequency of microstrip circuits tends to be repetitive in the frequency domain – i.e. their pattern (with some distortion) tends to repeat at regular frequency intervals. Therefore, in the case on hand, if the cut-off frequency were set at 1.2GHz there would be a strong attenuation up to about 1.8GHz; then, an attenuation of just -10-15 dB at around 2.4GHz; then back up to -30-35dB and down again to -15dB at about 3.6GHz. in other words, it would have a tendency to let the second and third harmonics through, instead of blocking anything above 1.2GHz. Fig. 3 – The diagram of the analogic part of the PLL: band-pass filter and MMIC amplifier Considering the spurious products of the mixer, a strong attenuation is required between about 2.1 and 3.5GHz. When designing a fifth-order filter with inverse Chebyshev-type pole distribution, a couple of deep attenuations will appear in the “stopband” at predictable frequencies. By shifting the filter’s knee to around 1.6GHz the two attenuations will also shift, overlapping with – or moving very close to – the two most troublesome spurious products and cancelling them out almost completely. This will result in a smaller, more effective filter. Fig. 4 shows the Gerber file. The holes mark the via connections with the back side of the PCB, which has obviously been completely copper-plated. The PCB was built on a PTFE substrate, dielectric thickness 0.75mm, copper thickness 35um. The left-hand side of the PCB is the band-pass filter proper. The right part contains the amplifier built with the MMIC SNA-586. The size and position of the four holes at the corners match the LCD1206 display. The gbr file can be downloaded from the link below this article. Fig. 4 – The Gerber file of the analogic part of the PLL. NOT IN SCALE. 6. THE DIGITAL PART OF THE PLL It consists of three different parts: a board with the ADF4351, a 16×2 1602 LCD display board and a board with Arduino (Nano or UNO). The board with the ADF4351 has already been discussed above. The display is of the ordinary type with two lines, 16 characters each. The popular six-button display was not used for different reasons: • There is no need for buttons (the tuning is done via an IR remote control) • The buttons are too low, they should be at least level with the display. • The six-button board occupies nearly all of the Arduino’s pins. Arduino can be used in any of its versions (Nano, UNO, ESP8266 with Wi-Fi, etc.), each of which clearly requires a specific compiler. Arduino’s I/O – D10, D11, D12 and D13 – will be connected to the I/O LE, DATA, MUXOUT and CLOCK of the ADF4351 board, respectively. However, D10, D11 and D13 must be brought down to 3.3volt (maximum input voltage for the ADF4351), either by using a resistor divider or through a logic level bidirectional converter module from 5V to 3.3V. In this example, the latter solution was opted for (TE291). Fig. 5 – The filtered PLL emission spectrum at 1197.5MHz. Span 1GHz. Pout +10dBm Fig. 6 – TE291 logic level bidirectional converter module (5 – 3.3v) and diagram The I/O D2, D3, D4, D5, D6 and D7 need to be directly connected to the display. The infrared sensor input (remote control receiver) needs to be connected to Arduino’s D8 pin. The IT sensor is of the common type which can be found on eBay, Amazon or the bottom of any drawer. The recommended option is using one already mounted on a small board with three output pins (G, R and Y). The ADF4351 board needs to be connected as shown by fig. 7. There are many similar models available equipped with different inputs and outputs, especially as regards power supply. Some also have special serial interfaces for USB connection. It is important to keep in mind that, for the purposes of this project, the reference frequency must be 25MHz and that the key connections with Arduino include CLOCK, DATA, LE, MUXOUT and the RFout output (RFout+ or -, the two are interchangeable as long as the unused output is loaded on a 50 ohm resistor). The power supply tension, the type of connector, etc. all depend on the specific ADF4351 model used, but they are irrelevant for the purposes of this project. The remote control can also be of any kind – again, the best option is to choose one that has as few buttons as possible, just the essential ones, including ten numeric buttons (from 0 to 9), two buttons assigned to the UP and DOWN function of the Symbol Rates (SR Up, SR Down) and one button assigned to the DELETE function. Thirteen buttons in all; any extra button will be ignored. The procedure to assign a function to each button will be explained later and is very simple. The commercial decoder’s remote control may also be used, but the IR signal might also inadvertently change the decoder’s parameters. Using a different remote control greatly reduces this risk (different base codes). Fig. 7 – The PLL – The diagram of the digital part of the PLL 7. PLL MANAGEMENT SOFTWARE – 80ch.ino It consists of 280 lines, 44 of which are initial text. The hardware device (NANO, GENUINO UNO, etc.) must be chosen before compiling the programme. Any missing libraries can be downloaded from GITHUB, such as IRremote (https://github.com/z3t0/Arduino-IRremote), or other similar websites. The IR remote library is essential for the IR sensor to work but is physically incompatible with the normally resident library Robot IR Remote, as different files are designated with identical names. Consequently, the Robot IR Remote directory must be removed along with all of the files it contains. The hexadecimal codes specific to the buttons of the remote control in use must be entered in lines 61 to 73 of the 80ch.ino. To find these codes, the procedure is the following: • Select 13 buttons, including 10 numerical buttons 0-9, SR up, SR down and Delete. • On Arduino (NANO or UNO) connect the GROUND of the sensor, the R pin to +5volt and the Y pin to D11. • Compile and upload the programme IR_sensor.ino below and switch on the serial monitor. • Press the selected buttons and note down the hexadecimal codes appearing on the serial monitor (if a code with only F’s appears, it simply means the button was pressed and held). The programme IR_sensor.ino (attached below this article) is one of many readily available on the Internet: #include int RECV_PIN = 11; IRrecv irrecv(RECV_PIN); decode_results results; void setup() { Serial.begin(9600); irrecv.enableIRIn(); // Start the receiver } void loop() { if (irrecv.decode(&results)) { Serial.println(results.value, HEX); irrecv.resume(); // Receive the next value } delay(700); } Once the 13 codes have been noted down, they need to be copied into the respective lines (61-73) of the 80ch.ino programme (attached below this article). It is important to include an “0x” and “;” at the end of each line, as shown in fig. 8. Fig. 8 – Entering the IR codes in the 80ch.ino programme. The codes shown correspond to one of the many available remote controls. 8. HOW TO USE THE 80ch.ino PROGRAMME When switched on, the LCD1602 display will show an initial message for three seconds, then will automatically tune in to the beacon at 10492.5GHz with an SR of 2MHz (i.e. the 0 channel previously saved on the decoder – see point 3.), generating the conversion signal at 1197.5MHz. The Qatar-OSCAR 100 Wideband Spectrum Monitor (https://eshail.batc.org.uk/wb/) shows the frequency spectrum and signals present. For example: Fig. 9 – OSCAR 100 Wideband Spectrum Monitor Two signals are shown on the righthand side, one at 10497.512MHz – SR 125K and one at 10498.250MHz – SR 333K. The first can be tuned by simply pressing 75, the second by pressing 82. That is, ONLY the first two numbers following “1049” (a fixed number) are pressed. The programme will automatically complete the desired frequency, then switch to that frequency. For the symbol rate, the buttons assigned to this function must be pressed (in this example, a downward arrow and an upward arrow were chosen) until the desired SR appears on the display (125K in the first instance and 333K in the second). The programme will automatically calculate the frequency to be generated. When this is done, the corresponding channel (Ch 5 in the first example and Ch 3 in the second – see section 3.) can be selected using the decoder’s remote control. The video stream will appear on the display. Arithmetical note. While any digit from 0 to 9 can be used as the number of MHz, there are two digits that can never be used as the number of KHz: 4 and 9. This is because the frequencies corresponding to 125KHz-wide channels are the following: 125, 250, 375, 500, 625, 750, 875, 1000 of each MHz. As can be seen, none of these numbers starts with 4 or 9. As a result, if 4 or 9 are pressed as the second digit, the PLL will not accept the input and will stand by for a valid number. When an incorrect number is entered, the button assigned to the DELETE function can be pressed. The word “Deleted” will appear on the display, and the PLL will remain standing by for a new frequency or a new SR (in the latter case, it will use the most recent working frequency). 9. THE MIXER, INPUT AND OUTPUT FILTERS Fig. 10 – Mixer diagram Fig. 10 shows the mixer diagram. The signal coming in from the LNB enters a low-pass filter cutting out all frequencies above 770MHz, which are useless or even harmful for our purposes. The noise figure at this point depends essentially on the LNB’s noise figure, its gain and the loss of the drop cable. The printed low-pass filter loses around 0.4dB. In order to compensate for the loss of the drop cable, low-pass filter and passive mixer an amplifier equipped with a MMIC SNA-586 is added, which gains around 15dB. Its relatively low noise figure does not contribute to the overall noise figure of the system. The balanced mixer loses around 10dB but provides excellent resistance to intermodulation and, more importantly, solves all of the adjustment issues typical of a normal active mixer. Spurious products have already been discussed at point 2. The mixer shown is a SIM-63LH+, capable of handling signals up to 6GHz. It can be replaced with any mixer with similar features, as long as it can handle frequencies around at least 2GHz. It is not placed on the printed circuit for greater convenience. SMA connectors can be connected to any external mixer. Below is the Gerber file (also provided below this article): Fig. 11 – Gerber file of the mixer. NOT IN SCALE. The holes mark the via connections with the back side of the PCB, which has obviously been completely copper-plated. The substrate is regular FR4. The frequency loss is amply compensated for by the two MMIC amplifiers. The input low-pass filter has an impedance of 50ohm, while the drop cable has an impedance of 75ohm. Matching is achieved through a long line (quarter wave @745MHz) with a characteristic impedance of about 61ohm. The output of the second MMIC amplifier (Zout = 50ohm) is made of a 75ohm line. This slight mismatching produces a small loss, compensated for by the gain ensured by the amplifier. 10. ADJUSTMENT No adjustment is necessary. However, it is best to check the harmonic content in the output signal of the PLL: the fewer, the better. Though equipped with a robust SNA-586, when overdriven the PLL’s amplifying stage can start compressing and, as a result, loses linearity, thereby producing harmonics. For this reason, in case of an excessive number of harmonics, a simple solution is to reduce the ADF4351’s Pout to -4dBm by entering the value 0x902024 in register 4 (as instructed in the first 44 text lines of 80ch.ino). Unfortunately, the ADF4351 doesn’t have high Pout accuracy (among other limitations), so this is a test that should be run on a case-by-case basis. 11. SHORTCUTS Fig. 12 – Building of the mixer board Fig. 12 and 13 show the building of the up-converter with the indicated PCBs. However, this is not necessarily the only way to do this. The ADF4351 board is a stand-alone device, as is Arduino (UNO or NANO). Perfectly functional MMIC amplifiers can be bought pre-made on eBay or Amazon at a very small expense. This project requires three of them. The mixer can also be purchased pre-assembled. Fig. 13 – Assembling the PLL, including the ADF4351, Arduino NANO, MMIC amplifier and low-pass filter. As a result, the only parts that need to be specially built are essentially the three filters: • A 1600MHz low-pass • A 1940MHz band-pass • A 770MHz low-pass Below are the three Gerber files: Fig. 14 – The 1.6GHz low-pass filter on ROGERS RO4003 20mils/1oz laminate. NOT IN SCALE Fig. 15 – The 1940MHz band-pass filter on ROGERS 20mils/1oz laminate. NOT IN SCALE Fig. 16 – The 770MHz low-pass filter on FR4. NOT IN SCALE The three files are attached below this article. In all three, the holes mark the via connections with the back side of the PCB, which has obviously been completely copper-plated. By building the three filters and using already-made amplifier boards available on the Internet, the up-converter can easily be assembled with no need for any adjustment. Achille Galliena i2GLI i2gli.ag@gmail.com