Homebrewing Thinking Outside the Kit · Multiband CW Transmitter . Initial Plan/Specification •...

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




• PCB Layout


– Fabricating Enclosures

• Machine Shop Experience

• Mills/Lathes/Acetylene Torches etc.

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




• PCB Layout


– 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)

http://www.linear.com/designtools/software/

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)


• 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.


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


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


• 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

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







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



Ansoft Designer SV

• Filter Design Sheet

Ansoft Designer SV

• Circuit Analysis and Frequency Sweep Screen


• 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

http://www.alibre.com/

Alibre Design Professional

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


• Assembly Screen – Shows Assembly of a Hybrid Coupler


• 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…


• 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

)


• 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.






• 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


• With Feedback – 50-ohm + 140nH Inductor

• Increased bias slightly to get more power output range.



• 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



• 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 – 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


– Solved – New Display

FCC-1/FCC-2 Issues



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

– Rolls off to +8dBm at 21 MHz


FCC-1/FCC-2 Issues






• 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









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

– All records of the PIC Program are gone

FCC-1/FCC-2 Issues









• 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

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

http://www.amqrp.org/

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

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

Homebrewing Thinking Outside the Kit · Multiband CW Transmitter . Initial Plan/Specification •...

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Transcript of Homebrewing Thinking Outside the Kit · Multiband CW Transmitter . Initial Plan/Specification •...