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Related Manuals for ozQRP MST400
Summary of Contents for ozQRP MST400
- Page 1 ONSTRUCTION ANUAL MST Construction Manual – Issue 1 Page 1...
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Page 2: Table Of Contents
ONTENTS Introduction ................................4 Block Diagram ................................5 Circuit Description ..............................6 SSB generator..............................6 Transmit mixer ............................... 6 Power amplifier ............................. 7 Receive mixer ..............................7 Receive audio ..............................8 Parts List .................................. 14 Main Board Parts ............................14 Band Specific Parts ............................ - Page 3 List of Figures Figure 1 MST Block diagram ............................5 Figure 2 SSB generator ..............................9 Figure 3 Transmit mixer ............................. 10 Figure 4 Power amplifier............................11 Figure 5 Receive mixer ..............................12 Figure 6 Receive audio ..............................13 Figure 7 Component overlay ............................ 22 Figure 8 Front panel drilling guide ........................
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Page 4: Introduction
12. No complicated coil winding required. Uses inexpensive commercial coil assemblies for tuned circuits. A range of kits containing PCBs and hard to get parts for the MST and the DDS VFO are available from www.ozQRP.com. MST Construction Manual – Issue 1 Page 4... -
Page 5: Block Diagram
LOCK IAGRAM Receive Path Transmit Path Figure 1 MST Block diagram MST Construction Manual – Issue 1 Page 5... -
Page 6: Circuit Description
IRCUIT ESCRIPTION 3.1 SSB GENERATOR Transistor Q1 is configured as a Colpitts oscillator and acts as the 10MHz carrier oscillator in transmit and beat frequency oscillator (BFO) in receive. The frequency of crystal X1 is set by trimmer capacitor TC1 to a frequency slightly above the upper crystal frequency response. This results in LSB being generated. -
Page 7: Power Amplifier
A link coupled winding provides a low impedance output for the pre-driver built around transistor Q9. The collector load is another IF transformer (T8) and resonated to the transmit frequency in the same way as T7. In practice the two transformers form a 2 pole band pass filter and adjusted to give the desired passband. -
Page 8: Receive Audio
3.5 R ECEIVE AUDIO The 10MHz SSB intermediate frequency (IF) signal from the crystal filter is applied to the product detector U2. The product detector is formed with another SA612 and mixes the IF signal with the 10MHz BFO signal to produce an audio output. The BFO is adjusted slightly above the crystal filter upper response so that Lower Side Band signals are detected correctly. -
Page 9: Figure 2 Ssb Generator
Figure 2 SSB generator MST Construction Manual – Issue 1 Page 9... -
Page 10: Figure 3 Transmit Mixer
Figure 3 Transmit mixer MST Construction Manual – Issue 1 Page 10... -
Page 11: Figure 4 Power Amplifier
Figure 4 Power amplifier MST Construction Manual – Issue 1 Page 11... -
Page 12: Figure 5 Receive Mixer
Figure 5 Receive mixer MST Construction Manual – Issue 1 Page 12... -
Page 13: Figure 6 Receive Audio
Figure 6 Receive audio MST Construction Manual – Issue 1 Page 13... -
Page 14: Parts List
ARTS 4.1 M OARD ARTS Quantity Comment Designator 22pF 50V disc ceramic NPO C6, C9 68pF 50V disc ceramic NPO C12, C14 82pF 50V disc ceramic NPO C11, C13, C15 100pF 50V disc ceramic NPO C4, C5, C26, C29, C33, C64, C66 220pF 50V disc ceramic 470pF 50V disc ceramic C34, C42... - Page 15 Quantity Comment Designator 500R vertical multi turn trimpot 20K horizontal trimpot 1N4148 signal diode D1, D2, D3, D4, D5, D6, D7, D8, D9, D11 1N4004 1A power diode 9.1V 0.5W Zener diode 6.8V 0.5W Zener diode ZD2, ZD3, ZD4, ZD5 2N3904 NPN transistor Q1, Q2, Q3, Q4, Q8, Q9 2N7000 MOSFET...
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Page 16: Band Specific Parts
4.2 B PECIFIC ARTS Quantity Designator 6.8pF 50V disc ceramic NPO 33pF 50V disc ceramic NPO 56pF 50V disc ceramic NPO 390pF 50V disc ceramic C21, C23, C68, C71 470pF 100V monolithic 820pF 100V monolithic ceramic C59, C60, ceramic C0G C61, C62 1.1uH T50-2 15 turns 0.5mm 2.2uH T50-2 21 turns 0.5mm... -
Page 17: Construction
ONSTRUCTION 5.1 G ENERAL The MST is a built on a high quality fiberglass PCB. The PCB is doubled sided with tracks on the bottom side with the top side being a continuous ground plane. The holes are plated through and so it is not necessary to solder both sides to make connections. - Page 18 Step 4: Trimmer capacitors and trimpots The type specified for the trimmer capacitor is quite small and has one lead electrically connected to the screwdriver adjustment slot. Use a multimeter to determine this pin and solder to the hole in the PCB connected to the ground plane. Note that the carrier balance trimpot is a multi-turn vertical mount while the bias trimpot is a horizontal mount type.
- Page 19 Step 10: Coils Output transformer T6 T6 is wound on a 13mm two hole ferrite balun former type BN-43-202. The edges of the holes are quite sharp and can scrape the enamel off the wires. To reduce scraping and the risk of shorts, cut two lengths of 3mm heat shrink and feed into the balun former holes.
- Page 20 Transformers T1 and T4 Use a FT37-43 ferrite toroid and 0.5mm enamelled copper wire. T1: 4 turn primary (balanced modulator), 3 turn secondary (output) T4: 10 turn primary (U1), 3 turn secondary (output) Scrape the enamel off the ends of the wires and tin with solder before installing in the PCB.
- Page 21 Step 11: Crystals The crystals are mounted close to the PCB but not touching it. This is to avoid the metal case of the crystal shorting pads underneath. A space of about 1mm is all that’s needed. Once the crystals for the filter are installed solder a wire across the top of the metal cases and down to a spare pad in the PCB groundplane set aside for this purpose.
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Page 22: Figure 7 Component Overlay
Figure 7 Component overlay MST Construction Manual – Issue 1 Page 22... -
Page 23: Enclosure
NCLOSURE Now that your MST board is completed you’ll want to put it in an enclosure and try it out. The PCB was designed to fit inside a plastic instrument enclosure 200mm wide by 155mm deep by 65mm high. A suitable type is catalogue number H0480F available from www.altronics.com.au. It can be purchased with aluminium panels or you can easily make them yourself from 1.5 or 2mm thick aluminium sheet. -
Page 24: Front Panel Label
If you plan to design your own then use the dimensions shown in Figure 8 as a guide. Once you have either your own file or the downloaded file follow the procedure below to produce the label: 1. -
Page 25: Figure 8 Front Panel Drilling Guide
Figure 8 Front panel drilling guide MST Construction Manual – Issue 1 Page 25... -
Page 26: Fitting The Dds Vfo
6.5 F DDS VFO ITTING THE The DDS VFO is simply screwed to the inside of the front panel. The DDS VFO PCB is set back from the panel using threaded spacers to allow room for the LCD. If you use the specified LCD the distance will be 22mm and is made up of a 10mm spacer and 12mm spacer. -
Page 27: Wiring Up
IRING UP The wiring diagram is shown in Figure 10. Use light duty hookup wire of different colours for each connection and twist the wires together. It was found that shielded cables were not required. Most PCB connections utilize 2.54mm pitch polarized headers and mating plugs. These are inexpensive, give a professional looking appearance and allow easy disconnection and removal of the PCB if required. -
Page 28: Figure 10 Wiring Diagram
13.8V DC Antenna Loudspeaker AF gain Mic gain PWR LED Mic socket Figure 10 Wiring diagram MST Construction Manual – Issue 1 Page 28... -
Page 29: Testing And Alignment
ESTING AND ALIGNMENT 8.1 G ENERAL A suggested list of basic tools and accessories to undertake testing is shown below. Digital multimeter. 50 ohm dummy load capable of dissipating at least 5 Watts. QRP wattmeter or oscilloscope. ... -
Page 30: Receive
8.3 R ECEIVE Set the VFO to a frequency in the middle of the band you will be using. Turn the AF gain control to halfway. You should hear some low level hiss come from the speaker indicating that the audio stages are working. ... -
Page 31: Figure 11 Typical Circuit Voltages
Location V DC Receive V DC Transmit U1 pin 8 +6.8V U1 pin 5 +5.6V U2 pin 8 +6.8V U2 pin 5 +5.6V U3 pin 7 +13.3V U3 pin 6 +6.7V U4 pin 6 +13.7V U4 pin 5 +6.7V Q1 collector Q1 emitter 5.6V 5.6V... -
Page 32: Carrier Frequency Adjustment
8.5 C ARRIER FREQUENCY ADJUSTMENT The suggested carrier frequency is 10.000MHz which places it just above the passband and on the upper skirt of the crystal filter frequency response. The frequency response shown in Figure 12 was obtained from a completed prototype MST board. Note the passband is approximately 2.5KHz. -
Page 33: Operation
PERATION Operating the MST is very easy as there are no complicated controls and software menus to navigate. It’s simply a matter of connecting a power supply, microphone and antenna and talking. Operation of the DDS VFO is covered in the DDS VFO construction manual. In receive mode apart from the VFO there is only the AF gain control to adjust.