A 3 Band QRP CW Transceiver

Richard Harris G3OTK g3otk@yahoo.com

1 Version 3.5

Tonight’s Presentation A look at what may be some of the more unusual features, at least for a home-brew CW transceiver, and the reasons for incorporating them.

I will describe my approach to minimising transmitted bandwidth and maintaining CW wave-shape in the receiver

2 Version 3.5

Headline Features

• 80m, 40m, and 20m CW Transceiver

• 3W RF output

• Auto-ATU

• Electronic keyer

• Integrates with logging program such as N1MM+ or SD

3 Version 3.5

Features - Receive

• DDS VFO

• 6 crystal linear-phase IF filter

• 3 crystal linear-phase post-IF filter

• RX input filter – 3 pole LC BPF

• 2 x 16 OLED display of frequency & S-meter

4 Version 3.5

Features - Transmit

• Efficient Class-E PA 3W output

• Output RF waveform rise and fall shaped to minimise transmitted bandwidth

• TX output filtered by same BPF filter as RX input

• Semi-automatic break-in CW operation with sent CW delayed by 0.4 sec

5 Version 3.5

Controlled by 7 PICAXE μPs

• A PICAXE is a PIC with an integral “PICAXE basic” interpreter – easy to program

• Interpreted programs run slower than compiled programs (e.g. Arduino)

• 8 and 16 bit integer arithmetic only

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Distributed Processing

• DDS Controller

• OLED Display Controller

• OLED Display Decoder (ASCII to characters)

• Electronic Keyer

• CW Delay, TX/RX & PA driver control

• Auto-ATU Controller

• Interface to PC running logging program

7 Version 3.5

Connectivity

8

Headphones Power & serial data

Morse key & paddle

Antenna

Version 3.5

Both 3.5mm and ¼ inch (6.35mm) jack sockets are fitted

Block Diagram

Band Pass Filter

Class E PA

CW Amplitude Modulator

Driver DDS

6 Xtal 5MHz Linear-Phase

Filter IF Amp

AGC

RS232 to PC ICOM Protocol

AF Amp

CW Delay

Morse Keyer/PC

Frequency and S-meter Display

Auto ATU

One per band

3 Xtal Linear-Phase

Filter

BFO

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DDS VFO

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Direct Digital Synthesiser

400 steps/rev Optical incremental

Encoder (from China) DDS Controller PICAXE 20X2

DDS PCB AD9851

(from China)

11

10.7288 Hz/steps, tuning by 400 steps/rev optical incremental encoder Normal tune rate 4.3kHz/rev Fast tune 39kHz/rev DDS update rate 1,000/sec

Version 3.5

Transmitter Section Controlling the Bandwidth

12 Version 3.5

TX Bandwidth - Licence Requirements

• Note (a) of the UK Licence states that:

The bandwidths of emissions should be such as to ensure the most efficient utilisation of the spectrum. In general this requires that bandwidths be kept at the lowest values which technology and the nature of the service permit.

• Excessive bandwidth CW transmissions are heard as “key-clicks” on adjacent frequencies

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Bandwidth and CW Readability

• Bandwidth of transmitted signal – The faster the rise and fall times of dots/dashes the

wider the bandwidth

– Sudden changes in the slope of the rise and fall times broadens the transmitted signal

• CW Readability - ARRL Recommendation – Non-fading circuit: 30 wpm, rise & fall times 10ms

– Fading circuit: 30 wpm, rise & fall times 5ms

(For detailed analysis see “Key-clicks and CW Waveform Shaping” on IVARC web site)

14 Version 3.5

CW Signal Bandwidth

• How can we define “bandwidth” of a CW signal? My thoughts:

• Consider:

– Wanted station A is strength S4 (easily readable)

– Nearby station B is strength S9 + 30dB

– B is 60dB stronger than A (6dB/S-point)

– If B is not to interfere unduly with A then sidebands must be about -60dBc in A’s receiver.

– So I use -60dBc to define bandwidth of a CW TX

15 Version 3.5

Shaping of Transmitted CW

60dB

1KHz

0.0

0.2

0.4

0.6

0.8

1.0

1.2

-10 0 10 20 30 40 50 60 70 80 90

Am

plit

ud

e

Time (ms)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

-5 0 5 10 15

Am

plit

ud

e

Time (ms)

4 Pole Gaussian to 6dB LPF Fc = 70Hz

On-off keying, no shaping

16

60dB

Version 3.5

40m during a CW contest

My Signal

7.000 7.010 7.020

University of Twente SDR (12 Nov 16)

Many signals have excessive bandwidth

17 Version 3.5

Class-E PA (40m Version) (Nathan Sokal WA1HQC – Class-E Power Amplifiers – QEX Jan/Feb 2001)

18

100n

IRF510

0V RFC

24u

C

C

V

C

C

V

0V

TX DRIVE

2.119u

(Cds = 81pF)

532p

580p

153p

CW Amplitude Modulator

Band PassFilter

Design Software at http://www.tonnesoftware.com/)

To RX INPUT

Designed for 3W into 50 Ohms

VRF is proportional to supply voltage

Version 3.5

40m TX/RX Band Pass Filter (Fc = 7.05MHz Butterworth Fbw = 1.5MHz L = 2.119 μH Rt = 50 Ω)

-60

-50

-40

-30

-20

-10

0

1 10

Inse

rtio

n L

oss

(d

B)

Frequency (MHz)

Simulated By SPICE

Measured

Termination 50Ω

Termination 50Ω

19

Qu = 235 I.L. = 0.35dB

Version 3.5

80m, 40, & 20m 3W TX Strips

20 Version 3.5

CW Modulator

21

Waveform shaping 4 pole Gaussian to 6dB

LPF F3dB = 70Hz

Supply to Class E PA

CW (on/off)

DC Amplifier

Version 3.5

CW RF shaped rise and fall times

22 Version 3.5

Transmit Board

CW Modulator CW Delay

PICAXE 20X2 OLED Controller

80m TX Strip

40m TX Strip

20m TX Strip

23 Version 3.5

Receiver Section CW Waveform Preservation

24 Version 3.5

IF Filter Amplitude & Group Delay Response

SPICE simulation using same crystals Blue - 6 crystal pre-distorted Chebychev 0.5dB ripple 650Hz design bandwidth Red - 6 crystal pre-distorted 0.5 deg ripple linear phase 310Hz design bandwidth

1 KHz 1 KHz

25 Version 3.5

6 Xtal Linear Phase Pre-distorted IF Filter

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Measured using the method that I described in QEX Nov/Dec 13

Filter Termination 1,000 Ohms

Version 3.5

6 Crystal Linear Phase IF Filter as Built

-60

-50

-40

-30

-20

-10

0

4,998.5 4,999.0 4,999.5 5,000.0 5,000.5

Inse

rtio

n L

oss

(d

B)

Frequency (KHz)

6 Xtal predistorted 0.5 deg linear phase filter with Fc = 4,999500Hz & Fbw = 275Hz design using Farnell 950-9909 Xtals Nos 6, 23, 55,

56, 72 & 89

Measured

Simulated By SPICE

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IF/AF Board

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TX/RX Changeover

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TX/RX Changeover

• Semi-automatic break-in used (similar to VOX)

– Goes to transmit as soon as Morse is key pressed

– Stays on transmit while keying (keying resets a timer)

– 0.4 sec after last dot/dash it then switches to receive

BUT

• The other station may start sending before the receiver is active, so can miss part of call sign

– In 80m Club Contest I read DQ6Q as IQ6Q

– I missed the first dash because still on transmit

30 Version 3.5

My Solution

• Delay transmitted CW by 0.4 sec

• Goes to receive just after last dot/dash is sent

• Delay now at start of sending so helping other stations using semi-automatic break-in

• PICAXE μP programmed to look after the delay, TX/RX control and PA driver control.

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CW Transmit Delay

Transmit Receive Receive

Morse Key

Transmitted Waveform

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Auto ATU

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Auto ATU

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Some Results with 3W RF Power

• Breadboard versions – Jul 16 – Low Power Contest – 2nd out of 6 entries in

3W Fixed category using 80 & 40m dipoles at 3m

• With completed transceiver: – 8 Jan – AFS Contest – 106 stations in 4 hours on 40m

and 80m using dipoles at 3m height (9th out of 14 entries)

– 19 Feb – Completed transceiver with 8m of wire indoors – worked US stations on 20m in contest

– 23 Feb – 80m CW Club Contest - 61 contacts – best DX SM and OK with dipole at 3m

35 Version 3.5

End

36 Version 3.5