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G8MNY > TECHNI 31.01.26 20:33l 261 Lines 13545 Bytes #4 (0) @ WW
BID : 51056_GB7CIP
Subj: 198 to 162kHz Off Air Standard
Path: JH4XSY<IW0QNL<OK0NBR<OK2PEN<VK6HGR<GB7CIP
Sent: 260131/1120Z @:GB7CIP.#32.GBR.EURO #:51056 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Oct 25)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have test converted a homebrew veroboard construction version of the BBC4
"198kHz LW off air reference" project. (from a Practical Wireless article Dec
1995 by G8JVE, and follow up Oct 1998) to a more universal off air locking
standard using 2 LM555s as locked dividing oscillators to convert 162kHz (or
198kHz) to the 2kHz used by the project. As it will be needed when 198kHz Tx
closes down now projected to be in 2026.
The 800kW 162kHz "French Inter", now branded "ALS162" with no AM modulation, is
also a Freq standard Tx and also carries time signal phase modulated, as BBC4
does, but it is about 10dB weaker in London. However it might also close down
in the future!
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 Clipper 555 555 ｳｳ
ｳ Manual ﾚﾄﾄﾄﾄﾄﾄﾄｿ Ref Freq ｳ ｳｳ Buff stage IC IC 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 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 of thet time encoded signals 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. A clipper can be used to remove any AM followed by an
attenuator to give 1mV RMS to trigger the LM555 to give 2% frequency
selectivity @ 18kHz and then lock another 2kHz LM555. And then feeding the
phase comaritor and using a very slow PLL loop filter of a fraction of a Hz, on
the AFC line will remove all the PSK data.
NEW SCHEME
ﾚﾄﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄｿ
ｳExternalｳ ｳ RF 2 ｳ ｳ Diode ｳ ｳ 18kHz ｳ ｳ 2kHz ｳ Rx ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ Lock
ｳ Active ﾃﾄﾄｴ StageﾃﾄﾄｴClipperﾃﾄﾄｴ LM555 ﾃﾄﾄｴ LM555 ﾃﾄﾄﾄ>ﾄﾄｴ ﾃﾄLED
ｳFerrite ｳ ｳBufferｳ ｳ ｳ ｳAstableｳ ｳAstableｳ 2kHz ｳ Phase ｳ
ｳRod Ant ｳ ﾀﾄﾄﾄﾄﾄﾄﾙ ﾀﾄﾄﾄﾄﾄﾄﾄﾙ ﾀﾄﾄﾄﾄﾄﾄﾄﾙ ﾀﾄﾄﾄﾄﾄﾄﾄﾙ 2kHz ｳComparatorﾃﾄ>ｿ+/-
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾙ ﾚﾄﾄﾄ>ﾄﾄｴ 4046 ｳ ｳswapp
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 ﾚﾄﾄｿ ﾚﾄﾄｿﾚﾄﾄｿ ﾚﾄﾄｿｳﾚﾄﾄｿ 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 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ﾃﾄｴ�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ﾙ
With 198kHz a 1/11 astable lock is needed to give 18kHz and then a 1/9 for 2kHz
clock. The 162kHz a 1/9 then also a 1/9 for the same 2kHz. Just the High Q
ferrite rod aerial and FET preamp determins the reference station selected. (If
a 1 kHz clock lock system is used instead then any LW / MW Standard Frequency
Transmission station could be used in Europe.)
With this new scheme the 2kHz is no longer an LSB mix image, so the varicap
sence need reversing to lock up. So on the phase comaritor Pin 1 not 13 now
used as mirrored O/P. Also it is important that the 2 astables are stable, so
their C & R components are stable types!
MODIFICATION IMPROVEMENTS
ﾚﾄﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄ+12V
Longwave ｳ ｳ 2K2
ferrite d 22K 1M ｳ 10n
rod g ﾃﾄﾄﾄﾄﾂﾄ15Kﾄｿ ｳ ｳ ﾃﾄｴﾃﾄﾂﾄﾄﾄﾂﾄ47Kﾄﾄ> Trigger
||ﾚﾄﾄﾂﾄﾄﾂﾄ>ｳFET ｳ ｳ ｳ ｳ ｳ/ ｳ ｳ 18kHz 555
||( ｳ ｳ\ ﾃﾄﾂﾄﾄ)ﾄﾄｴﾃﾄﾁﾄ>>ﾄﾁﾄｴﾃﾄﾁﾄｴ ｳ ｳ
||( === ｳ/\ sｳ ｳ 10n 4n7 ｳ\e _ｳ_ _ｳ_
||( ｳ === ｳ === ｳ /_\ \_/
||( ｳ /ｳ 4K7 ｳ10n ｳ ｳ ｳ
||ﾀﾄﾄﾁﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄ>>ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄ 0V
External Active Aerial BNC RF Buffer Clipper
With no AGC circut, a pair of 1N4148 diodes form a clipper to condition the
signal to feed the sensitve astable.
LM555 ASTABLES
These are quite sensitive to Pin 5 voltage control the less trigger signal the
narrower the lock.
+5Vﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾂﾄ
ｳ 4K7 ｳ+ ｳ 4K7
ｳ Preset ===10u ｳ Preset
ｳ8 ｳ ﾁ ｳ8 ｳ
ﾚﾄﾄﾁﾄﾄﾄｿ7 1K ﾚﾄﾄﾁﾄﾄﾄｿ7 1K
Conditionedｳ +ve dﾃﾄﾄﾄｴ R ｳ +ve dﾃﾄﾄﾄｴ R
Off Air ｳ ｳ6 10K ｳ ｳ6 10K
Signal ｳLM thﾃﾄﾄﾄｴ 18kHz ｳLM thﾃﾄﾄﾄｴ 2kHz
ｳ555 ｳ2 ｳ ｳ555 ｳ2 ｳ
oTP1 ｳ tﾃﾄﾄﾄｴ TP2 ｳ tﾃﾄﾄﾄｴ TP3
>ﾄｴ 5ｳ ｳ3 ｳ o 5ｳ ｳ3 ｳ o
1KﾃﾄｴﾃﾄｴCV oﾃﾄﾄﾄ)ﾄﾄﾁﾄ220KﾄﾂﾄｴﾃﾄｴCV oﾃﾄﾄﾄ)ﾄﾄﾁﾄﾄ>to phase discriminator
preset 10nﾀﾄﾄﾂﾄﾄﾄﾙ ｳ ｳ u1ﾀﾄﾄﾂﾄﾄﾄﾙ ｳ
ｳ 1ｳ 3n3=== C 1K 1ｳ 33n=== C
0V ﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄ
If you have a counter adjust the 2 presets for free running astables to give
exacty 18kHz on TP2 with TP1 grounded. Then again 2kHz on TP3 with the 1K
grounded.
Use a dual beam scope triggered to TP2, and check 18kHz astable, view TP1 for
mid range 1/9 162kHz lock (or 1/11 198kHz) to produce a locked 18kHz @ TP2.
The 1K preset adjusts the trigger sensitivity.
Then again for 2kHz astable, trigger from TP3 and view TP2 for mid range 1/9 to
produce a well locked 2kHz @ TP3. Check these are both stable hot to cold.
PLL FILTER
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 and 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 1 (originaly 13)
ｳ ｳ ﾀﾄﾄ1Mﾄﾄﾁﾄ220Kﾄﾙ ｳ1u
=== +ｳ100u ===
u1ｳ === ｳ
0V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 and 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, and 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 and
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 and keeps down any stray clock pickup/noise etc.
Off ~\ .-. _._ Power
Lock ｳ / \ / \__/~~ﾄ�..愷�-- Up ﾚ.__.-ﾄ-�..�-愷---
\__/ '-' ｳ
----------- 20 seconds ------------ --- 10 seconds ---
8/ MANUAL TUNE
My box had an ugly hole so added S meter/centre zero meter and 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, and I
needed a changeover. Leaving the pot in circuit and using T1 to short incoming
AFC line I achieved the same function, and 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 and 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 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ﾄﾂﾄﾄﾄﾄ
ｳ14 16ｳ 16ｳ 2kHz
10MHz ﾚﾄﾄﾁﾄｿ 10MHz ﾚﾄﾄﾁﾄﾄｿ 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ﾃｿ200 50ﾚｴ3 15ﾃﾂﾄﾁﾄﾄ>to Phase
ﾀｴ2 8ﾃｿ ｳ 9ﾃﾙkHz kHzﾀｴ4 9ﾃﾙ Comparator
ﾚｴ3 12ﾃｴ ﾚﾄﾄｴ3 ｳ 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 and 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 and 5V rails from centre
tapped 2x 6V transformer and single bridge to make 20V & 10V centre into their
respective regulators etc. The +5V is used for PLL tuning and 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), and 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 and can't be relied on to maintain high
accuracy over several years. This accurate source (better than 1 in 10^7
short term and 1 in 10^11 long term) enables checking of standards.
See my buls "Locking a Frequency with 555" "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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