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G8MNY > TECH 11.09.25 18:18l 371 Lines 18994 Bytes #7 (0) @ WW
BID : 40532_GB7CIP
Read: JN1VSI
Subj: 198kHz Off Air Standard
Path: JH4XSY<N3HYM<GB7YEW<GB7CIP
Sent: 250911/0908Z @:GB7CIP.#32.GBR.EURO #:40532 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jun 20)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I can no longer use my TV locked reference system (see my buls on "Off Air lock
for Ref Osc") for calibrating RF gear, as analogue TV has ended. So at a rally
I bought an old homebrew (cheap) veroboard construction version of the BBC
198kHz LW off air reference project. (from a Practical Wireless article Dec
1995 by G8JVE, to go with the Robin counter & follow up Oct 1998). The divider
chain in this design had a rearranged to give more useful reference frequencies
(different to article).
LAYOUT AE Mains 12V
ﾚﾄﾁﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ｳ ｳ~Trans- ~ｳ ｳ~~PSU~~~~~~ｳ ｳ
ﾉｵExternal Active Ferrite Rod Aerialｳ ｳ ｳ former ｳ ｳ board ｳ ｳ
ｺﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ｳ ~\_____/~ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ｳ
ｺ ｳﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿｳ
ﾚﾐﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ｳｳ RF Mixer IF Det OpAmp ｳｳ
ｳ Manual ﾚﾄﾄﾄﾄﾄﾄﾄｿ Ref Freq ｳ ｳｳ Buff IC LC IF ｳｳ
ｳ o .-. ｳ Meter ｳ .-. 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ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙｳ
ｳPower( ) ﾀﾄﾄﾄﾄﾄﾄﾄﾙ ( ) ｳ ｳﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿｳ
ｳ o '-' CZ =o Sig '-' ｳ ｳｳ10 Buff Counter Counter Phase ｳｳ
ｳ ｭ Not o o Lock (�) ｳ ｳｳMHz IC IC IC Comp IC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ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ｳﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙｳ
Ref Output ｳ SW Pot Meter SW BNC ｳ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾂﾄﾙ
This "type of design" might be usable in other parts of the world if there are
suitable accurate LW or MW stations.
OPERATION PRINCIPLE
SPECTRUM Carrier Rx Extracted
ｳ Image! Carrier
LSB MOD PSKｲPSK USB V ｳ
/~~~~~~~~~~~~~~~~~~~~~~~~~\ｲ/~~~~~~~~~~~~~~~~~~~~~~~~~\ ｳ
ﾄﾅﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾅﾄ>Freq ﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄ
191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 kHz 198.00000
As you can see from the spectrum, extracting a pure clean carrier is not quite
as straight forward, when there is phase shift keying to remove too. (PSK in UK
is used for power meter control?)
A close-up should look something like this..
ｳ
~~\ ｲｲｲｲｲｲｲｲｲｲｲｲｲｲｲ /~~~
ﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾁﾄﾄﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾄﾄﾁﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄ>
-20 -10 0 +10 +20 Hz
Where the PSK data sidebands cover the carrier, the data is encoded to have no
mean carrier offset. But no amount of sideband filtering will remove the PSK in
practice, but using a very slow PLL loop filter of a fraction of a Hz, it will
then be ignored.
So from this 198kHz (it used to be 200kHz a Standard Frequency Transmission,
until it had to conform to 9kHz EU region standard!) you can extract phase
control for a reference frequency oscillator.
SCHEME
ﾚﾄﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄﾄｿ
ｳExternalｳ ｳ RF ｳｳ ｳｳ 2kHz ｳｳ IFｳｳ IF ｳｳ IF ｳ Rx ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ Lock
ｳ Active ﾃ>ｴBufferﾃｴMixerﾃｴ LC IFﾃｴAMPﾃｴ Wien ﾃｴLimiterﾃﾄﾄ>ﾄﾄｴ ﾃﾄLED
ｳFerrite ｳ ｳ ｳｳ ｳｳFilterｳｳx10ｳｳFilterｳｳ x100 ｳ2kHz ｳ Phase ｳ
ｳRod Ant ｳ ﾀﾄﾄﾄﾄﾄﾄﾙﾀﾄﾄﾂﾄﾄﾙﾀﾄﾄﾄﾄﾄﾄﾙﾀﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾂﾙﾀﾄﾄﾄﾄﾄﾄﾄﾙ ｳComparatorﾃﾄ>ｿ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾙ ｳ200kHz S meter Local ｳ ｳ ｳ
ﾀﾄﾄﾄﾄﾄ<ﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄ>ﾄﾄｴ ｳ ｳ
ﾚﾄﾄﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄｿ ﾚﾄﾄｿ ﾚﾄﾄｿｳﾚﾄﾄｿ ﾚﾄﾄｿﾚﾄﾄｿ ﾚﾄﾄｿｳﾚﾄﾄｿ2kHzﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ｳ
ｳVariableｳｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳｳｳ ｳ ｳ ｳｳ ｳ ｳ ｳｳｳ ｳ ﾚﾄﾄﾄﾄﾄﾄﾁﾄｿ
ｳ 10MHz ﾃｴBufferﾃﾂｴ�2ﾃﾂｴ�5ﾃﾂｴ�5ﾃﾁｴ�2ﾃﾂｴ�2ﾃｴ�5ﾃﾂｴ�5ﾃﾁｴ�2ﾃｿ ｳMultipleｳ
ｳXtal Oscｳｳ ｳｳｳ ｳｳｳ ｳｳｳ ｳ ｳ ｳｳｳ ｳｳ ｳｳｳ ｳ ｳ ｳｳ ｳ Slow ｳ
ﾀﾄﾄﾄﾂﾄﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾄﾙｳﾀﾄﾄﾙｳﾀﾄﾄﾙｳﾀﾄﾄﾙ ﾀﾄﾄﾙｳﾀﾄﾄﾙﾀﾄﾄﾙｳﾀﾄﾄﾙ ﾀﾄﾄﾙｳ ｳ Loop ｳ
ｳ 10MHz 5MHz 1MHz 100kHz 10kHz 1kHz ｳ Filter ｳ
ｳAFC Frequency reference/marker outputs ﾀﾄﾄﾄﾄﾄﾄﾂﾄﾙ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ<ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
By using a low 2kHz IF, the superhet's unprotected image is @ 202kHz or @ 4kHz
of USB content. This will affect the phase & level stability of the extracted
carrier! Also using a high LO, then the IF goes down in freq for LO going down
too for a fixed Radio freq.
With this scheme it is important that the RF aerial tuned circuit & both the LC
& Wien filters, in the IF are properly centred on frequency, otherwise residual
AM will give asymmetrically phased sidebands resulting in apparent carrier
phase modulation. As it is the carrier's frequency we want, this is bad news!
WHY WAS MY UNIT CHEAP?
Well it sort of worked, but there was far too much Phase Shift Keying on the
reference output following the low speed PSK DATA on the 198kHz broadcast. As
well as that it was quite insensitive despite an extra RF buffer stage.
FAULTING
On testing with a scope I found the mixer was hard clipping very early, I found
it was incorrectly biased, & carefully following the circuit on the board this
was due to an uncut stripboard track!
The RF buffer was rebuilt to a simpler less lossy circuit. (see 6/ below)
The problem with the PLL I initially solved crudely with a 100uF & series 2k2
across the AFC line, then it gave a steady 10MHz note after a long lockup time.
IMPROVEMENTS
1/ Rx AGC
I found the mixer & other stages could overload & possibly add phase modulation
from the AM signal before the signal was tightly filtered, so I added an AGC.
I did not want to remove RF buffer's gain, as this is useful when in buildings
with weak signals etc. So I used an additional NPN to short out the external
FET preamp's supply, this gave a very good AGC, with no distortion from AGC
action & gave the S meter with usable log scale.
ﾚﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄ+12V
ｳ ｳ 2K2 ﾚﾄﾄﾄ>S meter
ferrite d 22K 1M ｳ 4n7 100K
rod g ﾃﾄﾄﾄﾄﾂﾄ15Kﾄｿ ｳ ｳ ﾃﾄｴﾃﾄ>Mixer preset
||ﾚﾄﾄﾂﾄﾄﾂﾄ>ｳFET ｳ ｳ ｳ 4n7 ｳ ｳ/ ｳ u1 IF
||( ｳ ｳ\ ﾃﾄﾂﾄﾄ)ﾄﾄｴﾃﾄﾁﾄ>>ﾄﾂﾁﾄﾄｴﾃﾄﾄﾁﾄｴRF Buff ﾚﾄﾄﾄﾂﾄ100Kﾄﾁﾂﾄｴﾃﾄﾄ*ﾄﾄ<OpAmp
||( === ｳ/\ sｳ ｳ 10n \ｳ ｳ\e ｳ ｳ+ _ｳ_ No Pin 1
||( ｳ === ｳ === AGCﾃﾄﾄﾂﾄﾄｿ ｳ ｳ === /_\ Series
||( ｳ /ｳ 4K7 ｳ10n e/ｳ === ｳ ｳ ｳ ｳ5uF ｳ R
ﾀﾄﾄﾁﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄ>>ﾄﾁﾄﾄﾄﾄﾁﾄﾄ)ﾄﾄﾄﾁﾄﾄﾄﾄ ｳ ﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄ
External Active Aerial BNC u1 ｳ AGC ｳ
ﾀﾄﾄ100Kﾄﾄﾄﾄﾄﾄﾄﾙ
The two 100K Rs set the AGC gain & with the 5uF sets the AGC time constant. It
is fast enough to remove some of the AM components below 10Hz, but still give a
stable AGC, leaving a fairly unmodulated carrier after the narrow IF filters
have removed the higher frequency sidebands.
2/ MIXER
I also noticed with the scope there was 2kHz IF beats on several of the Mixer
bias points, I changed decoupling capacitors from u1 to u47 & reduced this.
3/ LOCAL OSCILLATOR
The narrow 1:5 200kHz pulses fed to the mixer has been ramped a bit with an
additional 4n7 & 1K (was 10K), this yields 3dB more mixer gain (ideally a 100mV
square wave is best).
ﾚﾄﾄ>Mixer Pin10
4n7 ｳ ﾚ. ﾚ.
0Vﾄｴﾃﾄﾄｴ ｳ \_ ｳ \
ｳ10n ﾙ ~-ﾙ
===
74LS132 74HC390 ｳ 74HC390
+5Vﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄ
ｳ14 16ｳ 1K 16ｳ 2kHz
10MHz ﾚﾄﾄﾁﾄｿ 10MHz ﾚﾄﾄﾁﾄﾄｿ ﾃo200 ﾚﾄﾄﾁﾄﾄｿ o
Buffer>ﾂｴ1 11ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴ1 15ﾃﾄｴ kHz ﾚｴ3 15ﾃﾂﾄﾁﾄﾄ>to Phase
ﾀｴ2 8ﾃｿ ｳ 9ﾃﾄﾙ 50ﾀｴ4 9ﾃﾙ Comparator
ﾚｿ ﾚｿ
ｳｳ____ｳｳ
5:1
4/ 2kHz IF LC FILTER Q
I found the LC filter after the mixer was heavily loaded by the OpAmp 10k
circuit negating the high Q & narrow bandwidth possible, this may have been
partly due to different component values. Anyway I rewired the OpAmp for high Z
input & reduced the gain from 10 to 3.9, to stop it clipping, now the Q is much
greater (narrow bandwidth equals much less of the broadcast AM on the 2kHz IF!)
+12V ﾂﾄﾄﾄﾄ
47R
ﾃﾄﾄｿ
4u7 ｳ )|| ﾚﾄﾄﾄﾄﾄﾄﾄ390Kﾄｿ
=== )||L ｳ -ｳ\ ｳ
MC1496 _ｳ_ )|| ﾃﾄﾄﾄﾄｴ6 \ ｳ
Mixer ｳ u1 ｳ ｳ 7>ﾄﾄﾁﾄ>Wien filter OpAmp
Pin 12 >ﾄﾄﾄﾂﾄﾁﾄﾄﾂﾄﾄﾄｴﾃﾄﾄﾄ)ﾄﾄﾂﾄｴ5 /
ｳ2kHzｳ 100K ｳ+ｳ/ OpAmp common
=== === ｳ ﾀﾄﾄﾄﾄ1Mﾄﾄﾄﾄ<half rail
ｳ Cs ｳ u1===
ﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄ
After experimenting with the 2 Cs values for exact resonance of the L, the 1M�
OpAmp bias R does not load the tuned circuit, & the much better filtered IF
signal now has very little AM left on it. So the following Wien filter has less
to do to extract a clean carrier. But I did look at that too..
5/ 2kHz IF WIEN FILTER
The OpAmp has a gain of half, so it can be driven with a clipped signal from
the earlier OpAmp before its output to the level detector clips. By changing
the feedback R from a 22k to 2x 22k the gain is then 1 & the output to the
signal detector is true until the Wien OpAmp clips. The Wien filter Q is also
doubled, bringing the total IF bandwidth down to about �50Hz. The frequency
setting preset needs to be about 350R, so a suitable R across the multiturn
preset to provide this value at the centre of the preset is ideal.
Common ｳ\ ﾚﾄﾄﾄﾄ> Level Detector
half rail>ﾄﾄｴ3 \ TP2 ｳ
TP1 ｳ 1>ﾄoﾄﾄﾄﾁﾄﾂﾄﾄ>IF Limiter
x3 amp>ﾄoﾄﾄﾄ22Kﾄﾂﾄﾄｴﾃﾄﾂﾄｴ2 / ｳ
ｳ u22 ｳ ｳ/ ｳ Output TP2 is
ｳ ﾀﾄﾄﾄﾄ22Kﾄﾄ22Kﾄﾄｴ exactly 180deg
ｳ u22 ｳ (biggest AC difference)
ﾃﾄﾄﾄﾂﾄｴﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ out of phase to the
Freq R input TP1 when on tune.
500R ｳ
ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ
6/ LIMITER BIAS
With some AM modulation still on the 2kHz IF, there is slight asymmetrical
clipping on the following limiter stage. Slight biasing from +12V applied to
the -ve limiter input @ the 10K with a 560K gives more steady 1:1 symmetry.
+12V Common ｳ\
ｳ half rail>ﾄｴ13\
from 560K ｳ 14>ﾄﾄﾂﾄﾄ> 2nd 10x
Wien >ﾄﾄ10Kﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄｴ12/ ｳ Limiter
Op amp ｳ ｳ/ ｳ
ﾀﾄﾄﾄﾄﾄ100Kﾄﾙ
7/ PLL FILTER
Looking into the PLL jitter problem, there was a very high Z circuit using a 40
Meg ohm (4x 10M) as the R for a 40 second time constant. This obviously was not
working correctly on this layout, possibly due to leaky old PCB or varicap
diodes? (also discussed in the designer's follow up article)
Anyway I redesigned this bit using electrolytics, something avoided by the
original designer. But by using 2 identical electrolytics in series across the
well regulated 5V power rail, I solved most of the leakage problem & gained
instant half rail AFC voltage on power up, for a faster initial lock up time.
+5Vﾄﾄﾂﾄﾄﾄﾄ
+ｳ100u 4x 1N4148
=== ﾚﾄｴ<ﾃﾄﾄﾂﾄｴ<ﾃﾄﾄｿ Scope
Varicap ｳ ｳ ｳ ｳ o IC CD4046
AFC <ﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾅﾄｴ>ﾃﾄﾄﾅﾄｴ>ﾃﾄﾄﾅﾄﾄﾄﾂﾄﾄﾄ20Kﾄﾄﾁﾄﾄ< Phase Comparator
ﾃﾄﾄ4K7ﾄﾄｴ ｳ ｳ ｳ ｳ Pin 13
ｳ ｳ ﾀﾄﾄ1Mﾄﾄﾁﾄ220Kﾄﾙ ｳ 1u
=== +ｳ100u ===
u1ｳ === ｳ
ﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄ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ﾄﾄ
I enhanced the variable CR system with 2 more diodes & another resistor, so
initially PLL out of lock you have 20K + 200uF for a 4 Sec time constant, then
at �1V from lock it adds a 220K for a 50 Sec time constant, & at less than
�0.5V a further 1M for a 200 Sec "properly in lock" time constant.
The starting 20K + 1uF (20mS) is needed to remove the 5V 2kHz IF pulses &
reduce the residual 12.5Hz Phase Shift Keying data to below 0.5V ripple. This
however is a loop time constant that will oscillate, so I added a 4K7 in series
with the larger Cs to damp this oscillation, but the 4K7 is not big enough to
let much of the PSK data through to the AFC line. The u1 is used close to the
varicap diodes & keeps down any stray clock pickup/noise etc.
At lock, using the scope point with a x10 probe or on AC, & locked to a
fraction of 50Hz mains (e.g. 12.5Hz) you see.
_
+5V ｳｳｳｳｳｳｳｳｳｳ 2kHz phase
ｳｳｳｳｳｳｳｳｳｳ correction
ｳｳｳｳｳｳｳｳｳｳ needle pulses \/ PSK Data
..ﾁﾁﾁﾁﾁﾁﾁﾁﾁﾁ...__________.. Ripple Under
Mean 2.3V/ ｳｳｳｳｳｳｳｳｳｳ /\ 0.5V Swing.
ｳｳｳｳｳｳｳｳｳｳ
0V_ ｳｳｳｳｳｳｳｳｳｳ
SLOW P.S.K. DATA
/~~~~~~~~~~~\____________/
The PSK data pulls on the stored AFC voltage several times a seconds. A steady
2.3V is obtained with Xtal trimmer preset. With an SSB Rx you can hear the
10MHz oscillator (or harmonic of other outputs e.g. 29x 5MHz =145MHz) settle
down to a stable note after several diminishing 4 second cycles.
_
Off ~\ .-. _._ Power
Lock ｳ / \ / \__/~~ﾄ�..愷�-- Up ﾚ.__.-ﾄ-�..�-愷---
\__/ '-' ｳ
----------- 20 seconds ------------ --- 10 seconds ---
With the above modifications signal bandwidths down the Rx are now something
like this..
�7kHz �100Hz �50Hz (�10Hz Jitter) <0.005Hz
ﾚﾄﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄｿ
ｳExternalｳ ｳ RF ｳｳ ｳｳ 2kHz ｳｳ IFｳｳ IF ｳｳ IF ｳｳ Phase ｳｳ PLL ｳ
ｳ Active ﾃ>ｴBufferﾃｴMixerﾃｴ LC IFﾃｴAMPﾃｴ Wien ﾃｴLimiterﾃｴComparatorﾃｴFilterﾃAFC
ｳFerrite ｳ ｳ ｳｳ ｳｳFilterｳｳx3 ｳｳFilterｳｳ x100 ｳｳ ｳｳ ｳ
ｳRod Ant ｳ ﾀﾄﾄﾄﾄﾄﾄﾙﾀﾄﾄﾂﾄﾄﾙﾀﾄﾄﾄﾄﾄﾄﾙﾀﾄﾄﾄﾙﾀﾄﾂﾄﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾄﾄﾙﾀﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾄﾙ
ﾀﾄﾄﾄﾄﾂﾄﾄﾄﾙ 200kHz AGCｳ 2kHz
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ<ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
8/ MANUAL TUNE
There was an ugly hole in my box & a S meter/centre zero meter & switch fitted.
So I developed a circuit for these, to provide a manual Centre Zero mode with a
pot to fill the hole. (I did not have the follow up article then!)
The log pot (old Volume control) I used had a double make on off switch, & I
needed a changeover. Leaving the pot in circuit & using T1 to short incoming
AFC line I achieved the same function, & T2 shorts out the Green in lock LED to
indicate it is in manual off lock mode.
Varicap
ﾚﾄﾄﾄ> AFC
2x pot ﾚﾄ27Kﾄﾄｴ oﾄﾄﾄ< S meter circuit
+5V on/off ｳ \ｳ/ Loop Green ______/
ﾀo\___o\__ﾃﾄﾄﾄﾄﾄ47Kﾄﾄ6K8ﾄﾂﾄ<Filter LED ｳ oﾄﾄﾄﾄﾄ22Kﾄﾄﾄ>CD4046
ｳ Pot ｳ AFC ｳ ｳ+ CZ mode Pin 2
ｳ ｳ/ ｳ/ /~~~\
ﾃﾄﾄﾄﾄﾄﾄﾄﾄ3K9ﾄﾄﾄﾄﾄﾄﾄｴ T1 ﾚﾄｴ T2 ｳMeterｳ
ｳ ｳ\e ｳ ｳ\e \___/
ｳ _ｳ_ ｳ _ｳ_ _ｳ_
ｳ ｳ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄ3K9ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
As the pot was a log one the varicap angle-frequency action was not quite
linear (needed square law?) so 27K was put from the max end to centre & 6K8 to
the switched ground, this gave a really even feel to the offset (�5Hz @ 10MHz)
with 2.3V at the centre position.
The Centre Zero meter action was taken from pulses directly from the unused IC
pin 2 via a 22k, to set the meter sensitivity. If you scope that pin you see...
ﾚﾄﾄﾄｿ ﾚﾄｿﾚﾄﾄﾄｿ
ｳ ｳ ｳ ｳｳ ｳ The average changes a little depending on the two 2kHz phases.
ﾙ ﾀﾄﾙ ﾀﾙ
9/ OUTPUT FREQUENCIES
As my unit's dividers were not wired up as published, here is the arrangement.
74LS132 74HC390 ｳ 74HC390
+5Vﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄ
ｳ14 16ｳ 1K 16ｳ 2kHz
10MHz ﾚﾄﾄﾁﾄｿ 10MHz ﾚﾄﾄﾁﾄﾄｿ ﾃo200 ﾚﾄﾄﾁﾄﾄｿ o
Buffer>ﾂｴ1 11ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴ1 15ﾃﾄｴ kHz ﾚｴ3 15ﾃﾂﾄﾁﾄﾄ>to Phase
ﾀｴ2 8ﾃｿ ｳ 9ﾃﾄﾙ 50ﾀｴ4 9ﾃﾙ Comparator
ﾚｴ3 12ﾃｴ ﾚﾄﾄｴ3 ｳ kHzｳ ｳ
ﾃｴ4 13ﾃﾙ ﾃﾄﾄｴ4 13ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄｴ1 13ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ﾀｴ5 6ﾃｿ ｳ ｳ ｳ ｳ ｳ ｳ ｳ
ｳ 9ﾃｴ ｳ ﾚｴ14 12ﾃｿ ｳ ﾚｴ14 12ﾃｿ ｳ
ｳ 10ﾃｴ ｳ ﾃｴ2 7ﾃｴ ｳ ﾃｴ2 7ﾃｴ ｳ
ﾀﾄﾄﾂﾄﾙｳ ｳ ｳﾀﾄﾄﾂﾄﾄﾙｳ ｳ ｳﾀﾄﾄﾂﾄﾄﾙｳ ｳ
7ｳ ｳ ｳ ｳ 8ｳ ｳ ｳ ｳ 8ｳ ｳ ｳ
ﾄﾄﾄﾄﾄﾄﾁﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾁﾄﾄﾄﾁﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾁﾄﾄﾄﾁﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄ
o o o o o o
10MHz 5MHz 1MHz 100kHz 10kHz 1kHz
10/ OUTPUT PROTECTION
By adding a pair of 1N4148 diodes as a clipped attenuator the TTL chips are
protected from external static damage & small amounts of accidental RF (10W?).
o o o o o o
10MHz 5MHz 1MHz 100kHz 10kHz 1kHz
/ｳ\ +
ﾀﾄﾄﾄﾄｴﾃﾄ470Rﾄﾄﾂﾄﾄﾄﾂﾄﾄ(o Output
1u _ｳ_ _ｳ_ ｳ 1V p-p
\_/ /_\ ｳ
ﾄﾁﾄﾄﾄﾁﾄﾄﾙ
11/ 12V POWERING
The original circuit was mains only to provide +12V & 5V rails from centre
tapped 2x 6V transformer & single bridge to make 20V & 10V centre into their
respective regulators etc. The +5V is used for PLL tuning & must be accurate,
but the +12V is not so important, so I made a 12V input option to diode feed
both the regulators.
RESULT
I now have a very accurate marker for HF (VHF/UHF on harmonics with a steady
pure tone), & I can calibrate frequency counters, or lock them up to this
source, as well as lock up my 100Hz-1GHz PLL signal generator.
For VHF & UHF, Xtal oscillators age & can't be relied on to maintain high
accuracy over several years. This accurate source (better than 1 in 10^7
short term & 1 in 10^11 long term) enables checking of standards.
See my buls "Off Air Lock for Ref Osc.", "Comparing Off Air Freq Standards",
"Simple Crystal Oven", "Crystal Drift Compensation" & "Calibrating Frequency"
for more information.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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