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G8MNY > TECH 19.02.25 19:50l 170 Lines 7417 Bytes #6 (0) @ WW
BID : 26378_GB7CIP
Read: GUEST
Subj: AF 2 Tone Test Osc Design
Path: JH4XSY<IW0QNL<SR1BSZ<SV1CMG<SV1CMG<CX2SA<ED1ZAC<GB7CIP
Sent: 250219/1038Z @:GB7CIP.#32.GBR.EURO #:26378 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
TWO TONE AUDIO OSCILLATOR (Updated Jan 16)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
NEED
A two tone non harmonically related sine wave test oscillator is used for
setting up & testing basic linearity of linear amplifiers & RF Tx stages,
using a scope to see the RF waveform directly or AF/DC from a diode detector.
A simple solution may seem to use a DTMF encoder as it is a 2 tone generator.
But for SSB testing the 2 tone levels need to be independently adjustable, to
allow for the variation in mic response, mic amp response, & SSB filter shape
etc. to ensure the exact balance through the RF stages so the desired RF test
signal is obtained. However you may be lucky with the odd pair of DTMF tones
being just right for your rig, so give it a try & see the IN USE bit.
MY DESIGN FEATURES
POWER :- This unit run from a 9V PP3
On 12V it charges the PP3.
OUTPUTS :- Internal Hi Z LS (EARPIECE) high enough for acoustic coupling.
or jack for mic input hookup.
BALANCE :- A control for setting the relative tone levels
(as needed in Tx mixer for balance)
VOLUME :- A control for setting the AF output level for no Tx clipping.
RF IMMUNITY:- only 2 power transistor with base stoppers, so very immune.
BLOCK SCHEMATIC
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ｳPower Sine Osc 1ﾃﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄｿ _/ｳ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ﾀﾄｴ Gain ﾃﾄｴGainﾃﾄﾂｴ_ ｳL.S.
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄｴBalanceｳ ﾀﾄﾄﾄﾄﾙ ｳ \ｳ
ｳPower Sine Osc 2ﾃﾄﾙ ﾀﾄﾄﾄﾄﾄﾄﾄﾙ ﾀﾄﾄﾄﾄﾄ> Output
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
CIRCUIT
This uses 2 ferrite pot cores with 3 windings on each, 2 make a centre tapped
winding of about 32 mH, & the other winding about 1/4 of the turns giving a low
Z output. This forms the heart of the two power sine wave oscillators.
Each oscillator circuit is a single TO5 (BFY50) transistor connected in Hartley
configuration with a tuning capacitor across each centre tapped winding. The 2
tones must not be mathematically related e.g. harmonics etc. Mine turned out to
be 991 & 1352Hz. Each oscillator level is set by the 47k bias resistor located
at the transistor base, which also makes the transistor stage immune to RF!
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ EARPIECE
VOL ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄ 40R LS
POT<ﾄﾄﾄﾙ ｳ ｳ
200R ｳ ﾀﾄﾄﾄ LS
\ｳ/ ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ JACK
ﾚﾄﾄﾄﾄﾄﾄﾄBALANCEﾄﾄﾄﾄﾄﾄｿ ｳ
ｳ POT 100R ｳLow Z ｳ
ｳ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾂﾄﾄﾄﾄﾄﾙ
((() 991Hz ((() 1352Hz
= = = = = = POT = = = = = = POT
(((((((((() CORE (((((((((() CORE
ｳ ｳ ｳ ｳ ｳ ｳ ON/OFF
ｳ ﾀﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾁﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾂﾄﾄo/ oﾄﾄﾂﾄﾄ330Rﾄﾄｴ<ﾃﾄﾄﾄo +12V
ﾃﾄﾄｴﾃﾄﾄﾄﾄﾄｴ ｳ u47 ｳ ｳ ｳ Charge
ｳ u22 ｳ ﾃﾄﾄﾄﾄｴﾃﾄﾄﾄｴ +ｳ ｳ+ & or run
ﾃﾄﾄﾄﾄﾄｴﾃﾄﾄｴ ｳ ｳ === _ｳ_ External
ｳ u47 ｳ ｳ ｳ ｳ100u _ﾜ_ DC
ｳ ｳ/ ｳ ｳ/ ｳ _ﾜ_ 9V
ﾀﾄﾄ47Kﾄﾄｴ BFY50 ﾀﾄﾄ47Kﾄﾄｴ BFY50 ｳ ﾜ PP3
ｳ\e ｳ\e ｳ ｳ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄo 0V
The output windings feed the balance pot that works like a stereo pot selecting
the proportion of each tone. The tuned power oscillators have enough Q that the
output coupling via the 100R does not affect each oscillator frequency & the
outputs are quite good sine waves.
The 200R volume pot set the overall level in use. The internal LS was a old 40R
(4T) telephone earpiece that gives high AF level, ideal for putting next to the
Tx's mic.
Construction can be on PCB or ugly, & housed in any plastic or metal box. But
access to the controls is needed when a Tx mic is placed on top of the internal
LS.
IN USE
Using into SSB Tx, the resultant output once balanced & not overdriven it looks
like this on a scope as RF Envelope & as a loaded DC Detector display.
NORMAL
PEAK ｴ .ﾄﾄ. .ﾄﾄ. Round peak
RF ｳ /::::\ /::::\
ｳ ｳ::::::ｳ ｳ::::::ｳ Sharp Null DETECTOR
ｳ ｳ::::::::ｳ ｳ::::::::ｳVｳ PEAK ｴ .ﾄﾄ. .ﾄﾄ.
ｴX::::::::::X::::::::::X ｳ / \ / \
ｳ ｳ::::::::ｳ ｳ::::::::ｳ ｳ ｳ ｳ ｳ ｳ ｳ
ｳ ｳ::::::ｳ ｳ::::::ｳ ｳ ｳ ｳ ｳ ｳ
ｳ \::::/ \::::/ ﾀﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁ
ｳ `ﾄﾄ' `ﾄﾄ'
A scope connected to the RF output of a linear will produce the classic bridge
rectifier envelope. This can even be done at VHF & UHF using a suitably loaded
diode detector into the scope probe.
e.g.
Over drive ... shows up a flat topping of the envelope waveform.
Poor bias .... shows up as poor crossover on the envelope.
Instability .. at specific power levels shows up as fuzzy bits on the envelope.
CLIPPING Over Drive or Under Loaded PA
PEAK ｴ ____ ____ Flat peak
ｳ /::::\ /::::\
ｳ ｳ::::::ｳ ｳ::::::ｳ Sharp Null DETECTOR
ｳ ｳ::::::::ｳ ｳ::::::::ｳVｳ PEAK ｴ ____ ____
ｴX::::::::::X::::::::::X ｳ / \ / \
ｳ ｳ::::::::ｳ ｳ::::::::ｳ ｳ ｳ ｳ ｳ ｳ ｳ
ｳ ｳ::::::ｳ ｳ::::::ｳ ｳ ｳ ｳ ｳ ｳ
ｳ \::::/ \::::/ ﾀﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁ
ｳ ~~~~ ~~~~
POOR BIAS - CROSSOVER
PEAK ｴ .ﾄﾄ. .ﾄﾄ. Round peak
ｳ /::::\ /::::\
ｳ ｳ::::::ｳ ｳ::::::ｳ Wide Null DETECTOR
ｳ /::::::::\ /::::::::\V/ PEAK ｴ .ﾄﾄ. .ﾄﾄ.
ﾅｴ::::::::::H::::::::::H ｳ / \ / \
ｳ \::::::::/ \:::::::/ \ ｳ ｳ ｳ ｳ ｳ
ｳ ｳ::::::ｳ ｳ::::::ｳ ｳ / \ / \
ｳ \::::/ \::::/ ﾀﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄ
ｳ `ﾄﾄ' `ﾄﾄ'
NO BIAS - Class C PA
PEAK ｴ .ﾄﾄ. .ﾄﾄ. Round peak
ｳ /::::\ /::::\
ｳ ｳ::::::ｳ ｳ::::::ｳ Total Null DETECTOR
ｳ ｳ::::::::ｳ ｳ::::::::ｳV PEAK ｴ .ﾄﾄ. .ﾄﾄ.
ｴﾄｴ::::::::ﾃﾄｴ::::::::ﾃﾄｴ ｳ / \ / \
ｳ ｳ::::::::ｳ ｳ::::::::ｳ ｳ ｳ ｳ ｳ ｳ
ｳ ｳ::::::ｳ ｳ::::::ｳ ｳ ｳ ｳ ｳ ｳ
ｳ \::::/ \::::/ ﾀﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄ
ｳ `ﾄﾄ' `ﾄﾄ'
PARASITICS Instability
PEAK ｴ .ﾄﾄ. .ﾄﾄ. Round peak
ｳ n/::::\ n/::::\n
ｳ ｳ::::::ｳ ｳ::::::ｳ Sharp Null DETECTOR
ｳ ｳ::::::::ｳ ｳ::::::::ｳVｳ PEAK ｴ .ﾄﾄ. .ﾄﾄ.
ｴX::::::::::X::::::::::X ｳ n/ \n n/ \n
ｳ ｳ::::::::ｳ ｳ::::::::ｳ ｳ ｳ ｳ ｳ ｳ ｳ
ｳ ｳ::::::ｳ ｳ::::::ｳ ｳ ｳ ｳ ｳ ｳ
ｳ u\::::/u u\::::/u-Abnormal ﾀﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁ
ｳ `ﾄﾄ' `ﾄﾄ' Shape
See my Tech Bul "IC 735 No PA Bias Fault", "PA instability in ICOM IC735",
"T500M 12V 500W HF Linear", & "QRO 1kW HF Metered Dummy Load".
Why don't U send an interesting bul?
73 De G8MNY @ GB7CIP
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