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RAT5 Manual version 1.2.0 

 

 
RAT5 Information Manual version 1.2.0   © GW4GTE 2010                    

Page 4 of 29 

 

1. Introduction 

 

What is it? 

The  RAT5  is  a  single  conversion  AM  receiver  for  80m  and  160m  (operation  on  other 
frequencies is also possible).  
 
The  receiver  is  based  on  the  TDA1072A  AM  receiver  IC  which  although  obsolete  is  still 
available  in  quantity  from  at  least  one  source  and  a  reasonable  number  has  already  been 
obtained for kit builders.  
 
The  low  cost  and  ease  of  construction  make  this  an  ideal  club  project,  and  to  this  end 
component  values  are  also  provided  to  cover  the  Medium  Wave  where  signals  to  tune  into 
are plentiful. No previous experience of kit-building is required, just basic soldering skills. 
 

What does RAT5/FAT5 mean?  

For  some  years  now  the  author  has  been  playing  about  with  home  brew  solid  state  AM 
transmitters, largely based on solid-state Class-E designs using low cost FETs. This is the so-
called FAT5 series. 
 
The FAT5 name came from the original idea of making a solid state version of the AT5, using 
FETs. So, FET-AT5 became truncated to FAT5. RAT5 is an AM receiver to go with the FAT5 
transmitter project. Maybe the complete RX/TX could be the FAT-RAT project? 

 
Is there a kit? 

Yes. Based around a 3”x2” drilled and tinned single-sided fibre-glass PCB the kit contains all 
the  components  for  the  project.  All  that  is  required  in  addition  is  an  antenna,  power  source, 
loudspeaker,  control  knobs  and  case.  For  ordering  details  check 

www.s9plus.com

  or  email 

the culprits below. 
 

It’s a big manual for a little kit? 

This is the complete reference document containing everything about RAT5. To just build the 
kit  most  of  the  sections  can  be  ignored.  Please  read  the  entire  document  before  starting 
construction. 
 

Project Support 

This is a supported project, with free advice offered before, during and after construction.  
 

Who to Blame 

Circuit design and PCB layout by Dave GW4GTE.  
PCB production and kit distribution by Eric GW8LJJ. 
 

Contact Points 

Dave GW4GTE:  gw4gte @s9plus.com; address is QTHR or see QRZ.com 
Eric GW8LJJ: [email protected] ;  address is QTHR or see QRZ.com 
 

Acknowledgements 

The  author  extends  grateful  thanks  to  ‘Ferric’  Eric  GW8LJJ  for  the  production  of  such 
excellent  PCBs  at  ham-friendly  prices.  It  is  no  exaggeration  to  say  this  and  several  other 
designs  would  never  have  seen  the  light  of  day  as  completed  projects  without  Eric’s 
enthusiasm and support. 

 

Summary of Contents for RAT5

Page 1: ...nstruction and operation This manual refers to RAT5 hardware version 1 2 Please check you are reading the latest version of this document by checking www s9plus com for any updates Please read this do...

Page 2: ...Single Conversion AM Receiver Kit for 160m or 80m RAT5 kit of parts Easy to Build This kit is suitable for constructors with little or no previous experience of kit building A basic level of solderin...

Page 3: ...on 10 4 Testing and Alignment 13 4 1 Power off Tests 4 2 Power on Tests 4 3 Local Oscillator alignment 4 4 IF and RF Alignment 4 4 1 IF Alignment 5 Interfacing 18 5 1 Connection Method 5 2 Connections...

Page 4: ...ith the FAT5 transmitter project Maybe the complete RX TX could be the FAT RAT project Is there a kit Yes Based around a 3 x2 drilled and tinned single sided fibre glass PCB the kit contains all the c...

Page 5: ...detailed below Changes to the PCB The PCB to which this manual refers is version 1 2 The previous PCB was version 1 1 New IF filter PCB Version 1 2 incorporates a different 455kHz filter We have now m...

Page 6: ...sumer equipment In amateur use a squelch feature is useful and this has been designed into the circuit Low power consumption RAT5 consumes typically less than 50mA from a 9V to 15V supply making it su...

Page 7: ...et parts of the spectrum The image frequency for 3615kHz is 2705kHz and the image frequency for 1963kHz is 2873kHz Compare with say a low side LO on 160m which would produce an image frequency in the...

Page 8: ...use with a frequency display future add on project and to assist with setting up 2 2 3 IF Filter The IF tuned circuit L2 C4 is tuned to 455kHz giving a good match into the IF filter FL1 a 6 pole ladde...

Page 9: ...signal to inaudible levels When a carrier is received such that the AGC line at U2 pin 2 goes more positive than the level on pin 3 the comparator output will drop to zero cutting off Q1 and enabling...

Page 10: ...2 5 below shows an actual frequency response plot of a prototype unit The steepening LF roll off is caused by the increasing reactance of C27 which becomes significant at lower frequencies 2 3 3 Audio...

Page 11: ...hen check all holes are drilled The boards will have been carefully checked but as they are hand drilled there is always the chance a hole could be missed It s easier to correct any problems now rathe...

Page 12: ...referred Orient the capacitors such that the values are visible from the same side __ Solder Q1 VR1 and D1 taking care not to mix them up they look similar Follow the case orientation shown on the PCB...

Page 13: ...U1 16 U2 4 and U3 4 U2 3 and U3 3 will read to earth via RV2 and RV3 sliders respectively when the controls are fully CCW vary the controls to confirm Before inserting the ICs carefully check all sol...

Page 14: ...aid __ With no leads connected using a multi meter measure the resistance across the power input pins PL3 1 2 Connect the positive red meter lead to PL3 2 A typical reading is 24k ohms after allowing...

Page 15: ...counter is available use an oscilloscope Failing that assume the LO is running and search for the signal on a receiver Decide on a receive centre frequency to use 3615 kHz for 80m or 1950 kHz for 160m...

Page 16: ...requency of 3615kHz with VC1 set to minimum the tuning range is typically 20kHz With VC1 set to maximum and L1 re adjusted for 3615kHz the tuning range is typically 150kHz 4 4 IF and RF Alignment IF R...

Page 17: ...te core from its preset position tuning for a maximum S meter reading The tuning will be quite broad but it should be possible to establish a centre position for the core It s a good idea to monitor t...

Page 18: ...sing the squelch Further signal generator based squelch tests Set the squelch so that it just mutes the receiver Apply a carrier of 3uV PD Check the squelch opens at this level Apply a 1V PD carrier C...

Page 19: ...Wires can also be soldered directly to the pins of PL3 but the recommended method is to use the companion socket strips Again wires can be soldered directly to the strips but the method preferred by...

Page 20: ...onsequence A 10k series variable resistor can be used to set the meter level as required 5 3 1 Calibration Calibration of the S meter can be attempted If a calibrated signal generator is not available...

Page 21: ...able trips then Maplin s Hybrid battery range is worth a look They self discharge much more slowly than other rechargeable types 5 7 Choice of enclosure and boxing the unit In the UK Maplin carry a st...

Page 22: ...U1 16 U2 4 and U3 4 U2 3 and U3 3 will read to earth via RV2 and RV3 sliders respectively when the controls are fully CCW vary the controls to confirm If all continuity checks read ok insert all Ics a...

Page 23: ...ow Violet Orange Red R13 22k Red Red Orange Gold R14 10k Brown Black Orange Brown R15 10R Brown Black Black Red R16 10k Brown Black Orange Brown R17 2k2 Red Red Red Gold C1 47p 80m 150p 160m 390p MW 4...

Page 24: ...p Cut to length as needed Non PCB item SK1 2 3 Header socket 10 way Cut to length as needed Parts List by value R C only with idents Value Component Marked as 10R R15 Brown Black Black Red 22R qty 2 R...

Page 25: ...RAT5 Manual version 1 2 0 RAT5 Information Manual version 1 2 0 GW4GTE 2010 Page 25 of 29 Appendix 2 Circuit Diagrams...

Page 26: ...RAT5 Manual version 1 2 0 RAT5 Information Manual version 1 2 0 GW4GTE 2010 Page 26 of 29...

Page 27: ...RAT5 Manual version 1 2 0 RAT5 Information Manual version 1 2 0 GW4GTE 2010 Page 27 of 29 Appendix 3 PCB Layout Version 1 2...

Page 28: ...squelch but a sustained level from a carrier will trigger the squelch after a few seconds The downside is that the start of an AM transmission is missed but of course during a QSO the squelch can be l...

Page 29: ...n 1 2 0 GW4GTE 2010 Page 29 of 29 Appendix 5 Builder s Gallery Excellent example built by Eric GW8LJJ for club demonstration in this build the controls are not directly soldered to the PCB The amazing...

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