HF Amateur SSB Receiver PCB Set for radio club project http://rhelectronics.net
PCB for DIY HF Amateur SSB Receiver 20M The receiver is a simple syperheterodyne type with quartz crystal filter. The circuit is based on two NE612 mixer IC s and one audio amplifier LM386. The electrical circuit as it described below in the manual is intended for 14.000MHz 14.350MHz upper single side band receiving of amateur radio transmissions. However, the PCB allows modifying it for all others amateur SSB radio bands, or making it 2 bands receiver if required. If you are beginner it s strongly recommended to ask someone from your local radio club to help you with components selecting and receiver assembling. The syperhet calibration requires you to have an oscilloscope, DDS HF signal generator, LC Meter, multimeter and soldering tools. Moreover, it requires some basic knowledge of how it works for correct preset of the board. That s why I recommend to ask help of someone experienced if you get trouble with receiver calibration. Each rectangle represent separate operational block. The package includes only 3 PCB s without electronic components: 1. Receiver PCB 2. Band Pass Filer PCB 3. Mini Balun PCB for Beverage Antenna You need to supply all components on the list below. The circuit is designed for 20M receiver. Some components has critical value, please check carefully the part list of the project: You need LC Meter to check precision values of C2, C4, C5, L1, L2 and also compare the inductance of L3 and L4 coils with circuit value. for Band Pass Filter 20M band: C1 = 5pF-20pF trimmer green 6mm C2 = 220pF NP0 (use LC Meter for precision value) C3 = 5pF-20pF trimmer L1 = 10µH axial inductor +-1% (use LC Meter for precision value) L2 = 10µH axial inductor +-1% (use LC Meter for precision value) for Receiver 20M: C4 = 56pF NP0 (use LC Meter for precision value) C5 = 220pF NP0 (use LC Meter for precision value) C6 (optional) C7 C8 (optional) C9 = 10n C10 = 10n
C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 C33 C34 C35 C36 C37 C38 C39 C40 C41 C42 C43 C44 C45 C46 C47 C48 = 220µF 16V = 100pF = 100pF NP0 = 5pF-30pF trimmer green 6mm = 100pF = 10pF = 100pF (optional) = 220µF 16V = 10n = 100pF = 10n = 470µF 10V = 100pF = 10pF = 100pF = 47n = 10n = 47n = 470µF 16V = 10µF 16V = 47µF 16V = 220µF 16V = 10µF 16V CD1 = BB910 CD2 = 1SV149 from same batch! CD3 = 1SV149 CD4 = 1SV149 CD5 = 1SV149 Q1 = 4.194 MHz all crystals have to be +-200Hz max. Q2 = 4.194 MHz Q3 = 4.194 MHz Q4 = 4.194 MHz Q5 = 4.194 MHz Q6 = 4.194 MHz L3 L4 L5 L6 L7 L8 L8b R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 = 2.8µH 28 turns T30-6 Amidon Toroid = 1.0µH 17 turns T30-6 Amidon Toroid = 10µH (variable inductor preferable) = 10µH (variable inductor preferable) = 56µH axial inductor = 10µH (variable inductor preferable) = additional axial inductor for BFO shift trimming = 10R = 220R (optional) = 10K + 1K (10-turns potentiometers for analog tuning) trimmer (can be substitute with 10K-100K value) = 10K = 220R (optional) = 1K = 1K = 10R = 10K
R18 R19 R20 R21 R22 R23 R24 R25 R26 R27 R28 R29 T1 T2 T3 IC1 IC2 IC3 IC4 IC5 IC6 = 1K = 1K5 = 10K = 10K = 10R = 10R = 10R = 220R = 470R = 500R potentiometer = 2K trimmer = 2N3904 = 2N3904 = 2N3904 = NE612 = NE612 = LM386 = LMC7101 (optional) = LMC7101 (optional) = LM317 Mechanical Parts: 28 AWG Copper Magnet Wire for coils winding DIP Socket 8pin 3pcs 3M Screw 6pcs 3M Standoff 6pcs Pin Header 40pin breakable row 2.54mm 1pcs BNC Panel Jacks (analog of A97548-ND) 3.5mm Phones Audio Jack for Panel Toggle Switch On/Off Barrel Power Panel Connector 2.1mm (analog of CP-5-ND) Knobs for potentiometers 50ohm cable for antenna connection Aluminum Project Box for mini Balun 1:9 and Beverage antenna: FT37-43 Amidon Toroid 32 AWG Copper Magnet Wire for Balun winding BNC Panel Jack for PCB (analog of WM5514-ND) Binding Post Banana Plug (analog of 501-1094-ND) Plastic screw 2.5x8 with nut and 2 washers Stranded electrical wire 5-25 meters for Beverage antenna Miniature Plastic Box All crystals for IF filter have to be selected from same batch and have up to +-200Hz difference! To select crystals for your filter use simple Colpitts Crystal Oscillator circuit, connect a frequency counter or digital oscilloscope to the output and find 6 crystals with no more than +-200Hz difference. Here is less important to see exact 4194302Hz frequency output of each crystal, but the frequency difference within all 6 crystals is playing major role! If you have problem to find 4.194MHz crystals you are free to use different IF frequency with respect of proper modifications for rest of the circuit components.
When you choose Intermediate Frequency take into consideration the mirror channel is created and it possible to fall into powerful AM broadcast station. That s why strong interference may happen. Here is the link to download useful software for calculating VFO and IF frequencies and avoid IF spurs: IF Spurs Calculator by Relayer http://dspview.com All varicaps for crystal filter have to be from same batch to reduce parameters difference. What is optional mean? In my circuit I use LMC7101 rail-to-rail OPAMP sot23-5 SMD for varicap control. Operational amplifier buffer helps to improve varicap linearity and split high frequency from power line. If you get trouble to solder SMD, or have no available LMC7101, don t worry! This is optional improvement and it can be easily removed from the circuit by installing two wire links marked as ---- on the PCB s silkscreen. Check components list for all parts marked as optional and exclude it from your project if you do not use LMC7101. To create the wire links you can cutoff metal leads of the installed resistors. When LMC7101 is used you DO NOT need wired links ----! When you exclude LMC7101 you have to install 100K resistor instead of 220 ohm R3. Frequency trimming potentiometer R4 is multiturn type. SSB stations are very narrow band so it require precision trimming. You can use 10-turn 10K-100K Bourns multurn potentiometer. For better usability you can combine R4 with 2 multiturn potentiometers for coarse and fine tuning. The ratio distribution has to be 100%/10%. For example 10K for coarse and 1K for fine adjustment. DDS trimming. If you want to use digital trimming, the PCB allows you to connect AD9850 DDS module. Connect module output to pin#6 of IC1 through 10nF cap. If you connect DDS then following components are not used: C14, C17, C9, C10, C15, C16, C6, C8, C11, IC4, R4, R3, R1, L4, CD1. Variable inductors for L5, L6 and L8 are preferable, but can be replaced with axial type green inductors. L8b intended for additional shifting of BFO when required. All resistors are 0.25W and all ceramic capacitors are multilayer type for better stability.
The circuit use Single Tuned Input configuration of NE612. It works fine for one band receiver. The PCB design is flexible and allows you to make any band SSB receiver you want, including modifying it for 2 or 3 bands radio. In that case use Untuned Input configuration. My circuit is created for 20M band and you need to recalculate all critical block with respect to your preferred band if making the modification. Audio Gain Control LED. The PCB has place to install LED for auto-gain controlling. Personally I do not recommend to use that way, that s why the electrical circuit is not showing the LED. But if someone find it useful they are free to do that.
Receiver Calibration. Here are several calibration procedures you have to perform for successful results. First of all, it always better to wash the board with flux remover or isoprhyl alcohol. Clean and accurate soldering is important. Still do NOT install NE612 and LM386 into the sockets!! Trim LM317 output for 7V DC. Connect regulated 9V power supply and trim R29 for the 7V voltage output on pin#2 of LM317. After that check all VDD points read correct voltage. Check with the scope that LM317 output does not oscillate for some reason. Install LM386 and connect phones. Insert weak audio signal of several mv to check that audio amplification stage is working. Be careful not to overload LM386 input with powerful signals, you can inject small signal by using potentiometer divider. Check Crystal Filter Bandwidth. Connect oscilloscope to pin#1 of the IC2 DIP socket (NE612 still not installed). Connect HF DDS sinusoidal function generator to pin#4 of IC1 DIP socket. Insert IF frequency signal of 4.194MHz from DDS. The amplitude of the signal need to be 200mV-400mV VPP. Sweep the generator +-10KHz. Check the filter bandwidth does not exceed 4KHz. Use R5 to trim the bandwidth and L5, L6 for filter matching. I use slow oscilloscope horizontal scanning for that purpose and sweep DDS manually to observe the amplitude of the output filter signal. Write the filter frequencies pandpass, for example it will be something like 4.193-4.197MHz. Later you ll readjust R5 a little with real signal receiving. BFO frequency adjustment. Insert IC2 into the socket. The L8 coil intended to shift down BFO Q6 crystal frequency. Connect frequency counter or digital oscilloscope to BFO control point. f audio = f IF - f BFO Let's say that the resulting crystal filter had -6dB points at 4.193 and 4.196MHz (bandwidth of 3kHz). The location of the BFO relative to the passband sets the audio frequency response of the radio, so if you want your bandwidth from 400 to 3400 Hz you would set the BFO 400Hz from the edge of the passband. Varying the BFO allows you to trade off between high and low frequency response. Generally you don't want to get much below 300 Hz because there is less rejection of the carrier and opposite sideband. There is some room for adjustment here because the crystal filter won't have perfectly steep sides. But which side of the passband? That depends on which sideband you want. If the BFO is above the passband (4.200 MHz) you will get lower sideband (LSB), and if the BFO is below the passband (4.190 MHz) you get upper sideband (USB). Unless, of course, the receiver uses high side injection (frequency difference) in one of the mixer stages, which causes a sideband reversal. Usually for frequencies below 10MHz LSB is used, and for frequency over 10MHz USB is in use. For CW or digital stations you need narrow 200Hz-400Hz bandwidth. For voice receiving the bandwidth need to be between 2200Hz-3500Hz.
VFO frequency adjustment. Insert IC1 into the socket. The frequency of the VFO depends on L4, C10, C16, C15, CD1 values. Connect frequency counter or digital oscilloscope to VFO control point. VFO Frequency range for 20M and 4.194MHz IF: 9800KHz - 10160KHz Example for station with frequency of 14.100MHz: 14.100MHz = 4.194MHz(IF) + 9.906MHz(VFO) For analog manual trimming I recommend to wire two multiturn resistors of 10K+1K for R4. Be sure that you cover all range of 9800KHz-10160KHz for VFO. If your range is bigger than required then measure DC varicap voltage range you need for 20M band and use additional resistor before or after R4 to limit it. If you use frequency synthesizer for trimming, the NE612 works fine with AD9850 or any other HF generator. The amplitude of the signal can be 100mV-200mV VPP connected to pin#6 of IC1 via 10nF capacitor.
Band Pass Filter. To reject the out of band station it requires to use band pass filter in the antenna input. The input filter intended to cut all radio signals outside the 20M band. This part of the project requires fine adjustment. The filter is 50ohm input and output impedance. Connect it to the main PCB to BPF connector pins. Connect the scope to pin#1 of the IC1 DIP socket (IC1 is not installed). Insert 14.100MHz signal from the second side of the filter and adjust C1 and C3 for better amplitude results. The adjustment is very sensitive. With just half of a millimeter over-twisting you can skip the correct position. Try it until you get the best results for both caps. 14.000MHz-14.350MHz BPF for 20M Receiver:
1:9 Balun for Beverage Antenna: Beverage antenna is a long wire antenna. This is the simplest HV antenna that every beginner can make. Ideally, the minimal length of the wire need to be equal to ¼ of the radio wave length: that means 5.3 meters minimum or full 21 meters wire for 14MHz band. Hang stranded long wire on your balcony or outside the building. The position of the wire do matter for stations direction, but you can play with it later. The problem with long wire antenna is that the impedance is far from 50 ohm. To match the impedance with BPF input you need to use 1:9 balun. The balun is build with miniature FT37-43 Amidon ferrite toroid. For receiver antenna we do not need large power dissipation, so it possible to use miniature size core ring and 32 AWG magnetic wire for winding. Make 9 or 10 turns over the toroid ring. It s important to wind 3 wires together with every lap, as it presented on the picture below. The balun can be mounted inside miniature plastic box on the window or balcony door where the Beverage antenna is inserted to the building. To connect balun outpu to receiver use 50 ohm cable with BNC jacks, such as RG58 or RG174. During thunderstorm I would recommend to disconnect the receiver BNC cable from the balun box.