Kevin M Gaukel

WB0POH

Computer-Aided Homebrewing

Computer Aided Homebrewing

• This presentation is a rough design review of a new CW transmitter.

• This design came about with the assistance of cookbook designs and computer simulation/modeling.

• This presentation shows the rough methodology that was used to create this design and how the average technically-minded ham can design a radio or circuit with these techniques.

Background

• Ham Radio

– Licensed May 23, 1975 as WN0POH (Novice). • Became WB0POH when the FCC dropped the Novice-specific calls.

– Upgrade to General in November, 1979

– Upgraded to Extra on May 13, 1985

– Operated primarily CW and FM (VHF/UHF)

– Briefly dabbled in Amateur TV

Background

• Ham Radio

– Licensed May 23, 1975 as WN0POH (Novice). • Became WB0POH when the FCC dropped the Novice-specific calls.

– Upgrade to General in November, 1979

– Upgraded to Extra on May 13, 1985

– Operated primarily CW and FM (VHF/UHF)

– Briefly dabbled in Amateur TV

• Professional

– BSEE – University of Minnesota, 1983

– MSEE – Arizona State University, 1994

– RF Engineer since Aug 1, 1983

• Presently Sr. Principal RF Engineer – Orbital Sciences

– Published Author, IEEE

– Received 4 patents

Homebrew Philosophy Computer Aided Design

Learning Homebrew – At work

• Worked in Industry as RF Engineer – EF Johnson

– Celwave/Radio Frequency Systems (formerly Phelps Dodge Comm.)

– EMR Corporation

Homebrewing Techniques

• Hands-on engineering – Design and Breadboarding Circuits

• Manhattan Construction

• PCB Layout

• Soldering Techniques

Homebrewing Techniques

• Hands-on engineering – Design and Breadboarding Circuits

• Manhattan Construction

• PCB Layout

• Soldering Techniques

– Fabricating Enclosures

• Machine Shop Experience

• Mills/Lathes/Acetylene Torches etc.

• Working with Aluminum, Copper, Steel, Plastic, PTFE(Teflon)

Homebrewing Techniques

• Hands-on engineering – Design and Breadboarding Circuits

• Manhattan Construction

• PCB Layout

• Soldering Techniques

– Fabricating Enclosures

• Machine Shop Experience

• Mills/Lathes/Acetylene Torches etc.

• Working with Aluminum, Copper, Steel, Plastic, PTFE(Teflon)

• Issue with doing this at home – No Test Equipment

– No Machine Shop

– No Money

“Virtual Homebrewing”

• To get around this, I used computer simulation tools. – RF & Electrical Design Software

• Simulate expected linear RF performance of circuits

– Active Component Simulations

• SPICE, PSPICE

• Simulates non-linear (and linear) circuits

• Limited RF performance modeling.

– Drawing/3D Modeling software for packaging.

• 3D drafting software to get a different perspective on an assembly

• Automatic Drawing Processor – locate holes and bend lines

Why Computer Aided

• Design and virtually test without expensive test equipment – Confirm existing designs work or show their potential shortcomings.

• Will this design work?

– Helps you know WHAT to look for.

• May design amplifier, but may find that is not very linear unless you boost voltage

• Could you do the same circuit in fewer components?

• Once you can build and test the unit… – Fewer Iterations

– Less trouble-shooting time

– Prevents purchasing of unnecessary parts.

Design Approach – CAD

• Past experience – Computer Aided Design – Drafting Software

• AutoCAD

• Solidworks

– RF Design Software

• Touchstone -> Agilent ADS

• Ansoft Designer

• Ansoft HFSS

– Had good success with getting design right the first time with minimal troubleshooting

Design Approach – CAD

• Past experience – Computer Aided Design – Drafting Software

• AutoCAD ($1200 for LT, $4000 for full)

• Solidworks ($3000-$5000/seat)

– RF Design Software

• Touchstone -> Agilent ADS ($10k-$20k)

• Ansoft Designer ($15k)

• Ansoft HFSS ($100k + $10k/year maintenance)

– Way too expensive for the average ham!

Design Approach – CAD for Less

• LT Spice

– FREE!!!!

– http://www.linear.com/designtools/software/#LTspice

– Simulates active circuits – both linear and nonlinear

• Includes DC operating points where applicable

– Extensive collection of Linear parts and Switching Transistors

• Siliconix

• International Rectifier (IRF510)

• Others

– Contains models for several common transistors and chips

• 2N2222 & 2N3904

• U309

• MRF901 (educational circuit area)

– Yahoo group exists that has an even more extensive collection

– Used often with homebrewers (see “Four Days in May” 2012)

LT Spice

• Example Circuit – 2n2222 amplifier similar to one used for the Tuna-Tin2

LT Spice

• First Analysis – Linear Sweep from 20-22MHz in 401 points

AC/RF Frequency Sweep

• Frequency Sweep complete. – Added an equation to show voltage gain between 50-ohm load an 50ohm source

– Solid (dark) line is dB magnitude (21dB gain)

– Dotted line is phase

• Log sweep available as well (more on this later)

Transient/RF Signal Analysis

• Simulated waveform with 0.25V amplitude RF Input at 21 MHz – Output Amplitude: 2.8V >> +19 dBm50W vs. 0.25V>> -2dBm50W

– Gain: 21dB (agrees with AC plot)

Transient/RF Signal Analysis

• Simulated waveform with 0.50V amplitude RF Input at 21 MHz – Note – positive swing goes higher than negative swing

– Non-linearity (2nd order) causes DC point shift.

Transient/RF Signal Analysis

• Simulated waveform with 0.75V amplitude RF Input at 21 MHz – Non-linearity much more pronounced.

Transient/RF Signal Analysis

• Simulated waveform with 1.00V amplitude RF Input at 21 MHz

Design Approach – CAD for Less

• Ansoft Designer SV (Student Version) – Linear RF Circuit Analysis

• Simulates lumped and distributed circuits

• Smith Chart Tool

• Filter Design Tool

– Stripped down of other features (optimization and macros), but no limit on circuit size

– FREE!!!!!

• Unfortunately – ANSYS removed the free link from their website.

• http://www.rfglobalnet.com/doc.mvc/Ansoft-Designer-SV-0001

– Must register with the site to gain access (free)

• http://www.gunthard-kraus.de/Ansoft%20Designer%20SV/index.html

– Site in German

Ansoft Designer SV

• Filter Design Sheet

Ansoft Designer SV

• Circuit Analysis and Frequency Sweep Screen

Design Approach – CAD for Less

• Alibre – 3D Drafting Software

– www.alibre.com

– Allows one to draw object in 3D

– Allows automatic drawing of 3D object in 2D

– Allows assembly of multiple parts (Professional and above)

– Sheet metal 3D design – incl. flat patterns with score lines (Pro and above)

– Direct 3D solid to CNC machine code (Expert only)

– Three entry points

• Alibre Personal Edition (PE) $200

• Alibre Professional $1000 + $300/year maintenance

• Alibre Expert $2000 + $500/year maintenance

– Less expensive than comparable software

• Solidworks $5000 + $1000/year maintenance

• Pro-E $7500 + $1000/year maintenance

Alibre Design Professional

• Solid Modeler – Showing layout of an 8-pole “hogout” cavity filter

Alibre Design Professional

• Assembly Screen – Shows Assembly of a Hybrid Coupler

Alibre Design Professional

• SMA End Launch Connector – 3D Model Assembly

Design Goal Multiband CW Transmitter

Initial Plan/Specification

• All HF Band CW Transmitter (80m-10m) – FCC-1/FCC-2 DDS VFO kit as a base oscillator

– Amplify output of VFO to 5-10 Watts

• Amplifier designed using Cookbook Circuits and LT Spice

– Install Low Pass Filter

• Filter designed using Ansoft Designer

• Still in process

Driver and Final Amps

Low-Pass Filter

FCC-1/FCC-2

• LCD Display and PIC-Chip interface – Standalone Frequency counter

• Counter Works to VHF

• Surprisingly accurate

• RF Section and Encoder – Surface Mount

– AD9834 DDS IC

• 75MHz Oscillator

– Interfaces with FCC1 for frequency display and memory.

– Tunable from 150kHz – 31MHz

– Allows for storing frequencies and two VFO settings

– Allows for frequency offset (receiver)

Amplifiers

• 2N2222A Driver Amp

– Based on Tuna-Tin 2 Final Amp

– Simulated using LT-Spice

• IRF510 Final Amp

– Homebrew Design based on many other circuits online.

– Simulated and Optimized with LT-Spice

LT Spice - Optimization

• Cookbook Amplifier

– 11 dB gain predicted at 14 MHz

– 12 dB gain measured at 14 MHz

LT Spice - Optimization

• Added 4:1 Bifilar transformer

– Lowered the input source impedance at FET to 12.5 ohms

• LT Spice: Gain would increase by 3.5dB at 14MHz

• Measured: Gain increased 4dB from 12dB to 16dB

Why would that work?

• FETs are high impedance input – relative to bipolar transistors

• Does not mean it’s infinite: – Output Switching Impedance is only 0.7 ohms

• Translates to roughly 10-15 ohms at class A.

– Finite Capacitance between gate and drain means some of the low impedance is seen at the input of the FET

• Lower input Z results, and gets lower with higher frequency (capacitive reactance)

• Not seen in general literature/ “cookbook” designs

Cascaded Pair

• Measured Gain: 41dB at 14MHz

• Power Output: 2W at 14MHz (1dB Compression!) with -8dBm input (158.5 mW)

• Saturated Power output 8W at 14MHz.

Vds = 13.5V Id = 700mA Pd = 9.45W

Design Done?

Design Done? - Nope

• After construction, several issues turned up

Issue #1: Heat sink for IRF510

• TO220 Transistor dissipating 10W

• Sheet metal plate used in prototype – not good enough at all. – Even with fan blowing on it.

• Standard TO220 heat sink nowhere near enough, either.

• Larger heat sinks require minimum non-refundable orders – Jameco actually cancelled my order because their supplier raised their prices by x10.

• What do you do?

Heat sink for IRF510

• What about Pentium Heat Sinks!

Heatsink for IRF510

• Pentiums and AMD Processors are known as power hogs, so they needed large cooling area and fans.

• Large amounts of old surplus machines.

• Found a bunch of these at a surplus store near HRO – including one made of pure copper.

• Drill and tap 4-40 to hold down the IRF510

– Insulate the IRF 510. The case is the Drain (+VDD)

– Drilling and Tapping Copper is tricky business. Lots of lubricant and patience.

Issue #2: Amplifier Gain Flatness

• Amplifier looks good – at 14MHz

• Looked ever better at 7MHz – 18.8dB gain

• No so good on 28MHz…

Issue #2: Amplifier Gain Flatness

• Wideband view indicates significant gain variation within the IRF510 itself. – 21dB Gain at 3.5MHz vs 9dB at 30MHz – 12 dB gain variation from 80m to 10m.

– Varies with bias

IRF510 Amplifier vs. Freq and Bias (Measured Data)

Freq (MHz)

Gai

n (

dB

)

Issue #2: Amplifier Gain Flatness

• 20dB Gain Variation over band is unacceptable – To get 40dB gain at 14MHz – we need only two stages

– To get 40dB at 28MHz – we would need 4 stages

– I am NOT going to use a switch-in amplifier

• How can we flatten the gain?

Issue #2: Amplifier Gain Flatness

• 20dB Gain Variation over band is unacceptable – To get 40dB gain at 14MHz – we need only two stages

– To get 40dB at 28MHz – we would need 4 stages

– I am NOT going to use a switch-in amplifier

• How can we flatten the gain?

• Negative feedback! – Classical trade off: Increase Bandwidth for reduced gain.

– Cascade additional stages to compensate

– RL circuit feedback

• Reduce the gain at lower frequencies

• Reducing the feedback (increasing gain) at higher freq.

• Referred to as “fly swatters” because they keep higher frequency amplifiers stable at lower frequencies to prevent low-frequency oscillation.

Issue #2: Amplifier Gain Flatness

• 20dB Gain Variation over band is unacceptable – To get 40dB gain at 14MHz – we need only two stages

– To get 40dB at 28MHz – we would need 4 stages

– I am NOT going to use a switch-in amplifier

• How can we flatten the gain?

• Negative feedback! – Classical trade off: Increase Bandwidth for reduced gain.

– Cascade additional stages to compensate

– RL circuit feedback

• Reduce the gain at lower frequencies

• Reducing the feedback (increasing gain) at higher freq.

• Referred to as “fly swatters” because they keep higher frequency amplifiers stable at lower frequencies to prevent low-frequency oscillation.

• Used LT Spice to optimize feedback design prior to construction

Feedback Amplifier IRF510 – LT Spice Simulations

• No Feedback

Feedback Amplifier IRF510 – LT Spice Simulations

• With Feedback – 50-ohm + 140nH Inductor

• Increased bias slightly to get more power output range.

Feedback Amplifier IRF510 – LT Spice Simulations

• With Feedback – 50-ohm + 140nH Inductor

• Increased bias slightly to get more power output range.

• Model shows virtually constant gain to 30MHz and beyond

-5

0

5

10

15

20

25

1 10 100

No Feedback

With Feedback

Feedback Amplifier IRF510 – LT Spice Simulations

• With Feedback – 50-ohm + 140nH Inductor

• Increased bias slightly to get more power output range. – 18W Dissipation (1.2A)

• Actual Gain: 13-14dB gain (vs 9dB in simulation)

Feedback Amplifier IRF510 – Cascaded

• New Design uses two IRF510s – Input stage biased at 500mA, Output stage biased 1.0A

– Flat gain around 26.5-29dB from 3-30MHz

– Output Power – 2W linear, 10W Saturated at 28MHz

Individual IRF510 stages

• Cascaded duplicate IRF510 amplifiers – One biased at 500mA, 13.8V

– Other biased at 1000mA(1A), 13.8V

Feedback Amplifier IRF510 – Cascaded – Experimental Results

Feedback Amplifier IRF510 – Cascaded – Experimental Results

Feedback Amplifier – 2N2222 Experimental Results

• Feedback is part of DC bias

• Circuit similar to a design used at EF Johnson for AIRFONE

• Gain between 18.7 and 20.6dB between 3.5 and 30MHz

5T

Ferrite Core

FCC-1/FCC-2 Issues

• Display hard to read in dark room – No backlighting

Example – FCC1 Display

• Solution – Get a new display!!!

Example – FCC1 Display

• LCD Displays – particularly parallel ones – have very common pin-outs.

• Backlit LCDs much easier to read in both dark and bright conditions

• This particular display can be found at MicroCenter as well as on www.sparkfun.com

FCC-1/FCC-2 Issues

• Display hard to read in dark room – No backlighting

– Solved – New Display

FCC-1/FCC-2 Issues

• Display hard to read in dark room – No backlighting

– Solved – New Display

• Power output varies – Puts out about 12dBm at 3-15MHz

– Rolls off to +8dBm at 21 MHz

– Rolls off to +3dBm at 30 MHz

FCC-1/FCC-2 Issues

• Display hard to read in dark room – No backlighting

– Solved – New Display

• Power output varies – Puts out about 12dBm at 3-15MHz

– Rolls off to +8dBm at 21 MHz

– Rolls off to +3dBm at 30 MHz

• No real band limiting – Does have band inputs, but they are not

set to ham radio bands

– Risk of sending out of ham bands.

FCC-1/FCC-2 Issues

• Display hard to read in dark room – No backlighting

– Solved – New Display

• Power output varies – Puts out about 12dBm at 3-15MHz

– Rolls off to +8dBm at 21 MHz

– Rolls off to +3dBm at 30 MHz

• No real band limiting – Does have band inputs, but they are not

set to ham radio bands

– Risk of sending out of ham bands.

• Kit is retired – no backup – Last FCC1 /FCC2 sold in August

– All records of the PIC Program are gone

FCC-1/FCC-2 Issues

• Display hard to read in dark room – No backlighting

– Solved – New Display

• Power output varies – Puts out about 12dBm at 3-15MHz

– Rolls off to +8dBm at 21 MHz

– Rolls off to +3dBm at 30 MHz

• No real band limiting – Does have band inputs, but they are not

set to ham radio bands

– Risk of sending out of ham bands.

• Kit is retired – no backup – Last FCC1 /FCC2 sold in August

– All records of the PIC Program are gone

• What happens if your kit decides not to work????

FCC1/2 Heritage

• Issue – PIC Chip program lost to posterity

FCC1/2 Heritage

• Issue – PIC Chip program lost to posterity

• Solution – Design your own controller!! – Decision made to abandon FCC1 as display and controller.

– Allows for more flexible mechanical arrangement.

• However – I do not want to learn machine code.

– I do not want to learn assembly code.

– C, C++, or BASIC only.

New Controller

• PICAXE – 28x1

– 28x2

• PIC Chip with built-in Basic Emulator

• Built in SPI and I2C controller – DDS is SPI controllable

• Supports Serial LCD

• Less need to know “machine/assembly code”

New Controller

• Cursor can be moved left with a “cursor left” switch and moved right with a “cursor right” switch.

• Band can be switched up and down using encoder with cursor on the MHz position.

• Frequency display limits at the ham radio band edges no matter what conditions.

• LCD is white back lit. Very bright

• PICAXE Inputs – Two momentary switches

• Cursor Left

• Cursor Right

– Two lines for Rotary Encoder • Grey Code Logic to ensure up vs down tuning.

• PICAXE Outputs – Present

• B.6: Serial out to Serial LCD

• B.7: SPI Chip Select to DDS CS

• SPI Clock and Data to DDS Clock and Data

Box Design – Alibre

• The fixture and first radio prototype housing was designed with Alibre’s Sheet Metal designer and used as a base assembly for the structure.

Box Design – Alibre

• The fixture and first radio prototype housing was designed with Alibre’s Sheet Metal designer and used as a base assembly for the structure.

• Generated a flat pattern, attached it to 0.031 Aluminum with Super 77 and folded the box using the pattern.

• Removed the 77 with “Goof Off”

Box Design

• Installed the 5V regulator, 28x1 Shield, Serial LCD, momentary NO switches, and PCB with encoder

• Installed a protoboard (Radio Shack) into the open space

• Installed a socket into the the protoboard, then installed the DDS-60 Synthesizer

DDS Design

• Although FCC2 is usable, a higher-frequency range DDS is being considered

• DDS-60 (www.amqrp.org) – Pre-built and tested (no kit required)

– Tuning range: 200kHz to 60MHz (vs 150kHz to 31MHz on FCC-2)

– Much smaller than FCC-2

• Designed to be a standalone oscillator - no other controls on the board.

• More flexibility in the mechanical design. – Device plugs into a motherboard instead of being “built-in” like the FCC-2.

Low Pass Filter

• The plan is to cover all HF Ham Radio bands – including WARC – with only 4 low pass filters – 3.5-4.0

– 7-10.150

– 14-18.168

– 21-29.7

• Switchable designs – Prefer fewer relays and control lines in this design.

• Not your standard “pi network”.

• Designed using Ansoft Designer SV and its “Filter Synthesis” subroutine.

• Parts ordered but not yet constructed – Effort halted with the decision to update the DDS and controller.

– Will start up once the Synthesizer and amplifier are tested together.

• Main tradeoff expected - higher insertion loss on the LPF due to the larger number of elements.

Simulation – 40/30m LPF

C=C

1

Q=Q

1

L1

Q=Q2

L2

Q=Q

2C

2

Q=Q

1

L3

Q=Q2

L2

Q=Q

2C

2

Q=Q

1

L1

Q=Q2

C1

Q=Q

1

Simulation – 20/17m LPF

C=C

1

Q=Q

1

L1

Q=Q2

L2

Q=Q

2C

2

Q=Q

1

L3

Q=Q2

L2

Q=Q

2C

2

Q=Q

1

L1

Q=Q2

C1

Q=Q

1

Simulation – 15/12/10m LPF

C1

Q=

Q1

L1

Q=Q2

L2

Q=

Q2

C2

Q=

Q1

L3

Q=Q2

L4

Q=

Q2

C3

Q=

Q1

L3

Q=Q2

L2

Q=

Q2

C2

Q=

Q1

L1

Q=Q2

C1

Q=

Q1

Simulation – 15/12/10m LPF

C1

Q=

Q1

L1

Q=Q2

L2

Q=

Q2

C2

Q=

Q1

L3

Q=Q2

L4

Q=

Q2

C3

Q=

Q1

L3

Q=Q2

L2

Q=

Q2

C2

Q=

Q1

L1

Q=Q2

C1

Q=

Q1

New Radio Layout

• Driver and Final Amps – Completed

• PICAXE Controller – in process – Display and tuner interface completed

– DDS SPI Interface Proven – working on correlating with encoder

– May need to shift to 28x2 due to memory constraints of 28x1.

• Can control freq. display, but no more room for other controls.

– Shifted to DDS-60 (www.amqrp.org) because of size and convenience

• LPF on hold due to DDS/controller effort.

DDS

PIC

AX

E 2

8x1

14.030000MHz

AGC Amp IRF510 Driver Amp

IRF510 Final Amp

LPF Bank

CS CLK

Data

Band Switch Cursor Position Key Switch

Rotary Encoder

Serial LCD Display

Goals for the New Design

• DDS Oscillator with new controller working by Thanksgiving

• Low Pass Filter working by end of 2012

• Final Box finished by February 2013

• On the air test by April 2013 (QRPTTF???)

• Plan to have this on the air by Field Day, 2013.

Goals for the New Design

• DDS Oscillator with new controller working by Thanksgiving

November 11, 2012

Appendix A – Update Status

First Prototype Oscillator

• DDS Oscillator Prototype working as of November 11, 2014

• Using PICAXE 28x1 AXE-201 Prototyping Board Set and a breadboard for interfacing with DDS-60 on a protoboard

DDS-60 Assembly

AXE201 with 28x1 PICAXE

Rotary Encoder

Tuning Resolution

Band Switch (below encoder)

Working Oscillator

Working Oscillator

December 12, 2012

Appendix B – Update Status

Updated Oscillator

• DDS Oscillator Prototype updated Dec, 2012

• Using PICAXE 28x2 with a AXE401 Prototyping Board Set – DDS-60 Mounted Directly on AXE401

– Band switching replaced by using the encoder with resolution set at “1MHz”. In that position, the band switches each “click” of the encoder as you turn dial.

DDS-60 Assembly

AXE-401 PICAXE Prototype board

Display

Rotary Encoder

Tuning Resolution

Front Panel – Updated Oscillator

Spectral Output at 21.000MHz