G8MNY > TECH 09.07.18 10:33l 120 Lines 5372 Bytes #999 (0) @ WW
BID : 28251_GB7CIP
Subj: MSF Time Signal Clock Feed
Sent: 180709/0812Z @:GB7CIP.#32.GBR.EURO #:28251 [Caterham Surrey GBR]
To : TECH@WW
By G8MNY (Updated Oct 08)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Dave M1CTK reminded me of a cure for the weak 60kHz time signal, I have used
for Radio Studio Clocks that would not work in metal framed buildings due to
the weaker signal & local QRM sources (PC/TV Screens). The system is also
usable for the clocks tuned to the more distant German DCF (Deutchlandfunk)
time standard Tx on 77.5kHz.
These often have just 1 small ferrite 61kHz _______
rod tuned to 60kHz, but on a German ===== |||( ³
clock, I have seen 2 rods used at 90ø, (((() |||( ³ 60kHz
the idler one being tuned a few % off ³ ³ |||( === To Rx
frequency, giving true omni Rx. À´ÃÄÙ |||(__³____
To get the narrow bandwidth needed
with a TRF design, often a Xtal element ÚÄÄÄÂÄÄÄÄÄÄÄÄ´ÃÄÄÄÄÄÄ
at 60kHz is in series with the tuned |||( ³ 5kHz 1kHz
circuit to the Rx. This gives less than |||( === B/W B/W
1kHz & is ideal way to remove unwanted |||(___³__________________
bandwidth & QRM from the Rx signal.
Now that the MSF Tx has moved from its central UK site at Rugby, to Anthorn
Cumbria near Scotland, the signal in London has dropped 12dB. This is at a time
when there is more & more QRM on the frequency, from broadband telephone wiring
digital TV, computer PSU etc. etc.
Just before the MSF Tx changeover, I visited a commercial radio station that
had several radio controlled studio clocks, & said I doubt they will stay
working, & I was right, they all stopped receiving the signal! They had to move
clocks outside weekly for 30 mins, in order to have any sort of time keeping!
One reason for lack of service with a weaker signal is of course QRM, or poor
location in a metal framed building, or just mounted with the aerial in the
| ³Tx |
\ Á /
~-_ ~ - - ~ _-~
~ - _ ~ -________ - ~ _ - ~
~ -(__((((__()- ~
So try to relocate the clock (Rx) so that its' ferrite rod is perpendicular to
the Tx, & away from QRM sources like TVs (4x 625 line TV timebase 62.5kHz!) or
PC screens all SMPSUs & mains wiring. Then you may be lucky & it hears the MSF
transmission for a few minutes a day & stays in reasonable time lock.
MY WEAK SIGNAL CURE
I used an external tuned frame aerial, to feed a set of these clocks. The frame
was about 60cm square & made of plastic trunking to house 30 or so turns & a
fixed capacitor (selection of) to tune it to 60kHz. Remember to make it water
proof, e.g. drill holes in the bottom to let any tapped water out!
³ ) ____ 1 turn
=== 60 ) (____ Balanced Drive wire
³ kHz )
With an indoor location a variable capacitor can be used. Tuning will need some
sort of 60kHz Rx or a GDO etc. Or drive the loop with the capacitor in series
from a signal generator & monitor the field on the drive loop (e.g. scope/diode
probe & meter).
_______ ÚÄÄÄÄÄÄ¿ level :":
³Sig gen³ ³ ) ____ to Scope or ³ | |
³ 50-70 ³ === 60 ) (____ Diode Probe ³ / \
³ kHz ÃÄÄÙ kHz ) ³ __.-~ ~-.__
test circuit 55 60 65 kHz
One turn is added to take the drive away on a balance line. The balanced drive
line feeds 20 turns on a small ferrite rod glued on the back of every clock
beside it's ferrite rod aerial.
ÚÄÄÄÄÄÄ¿ clock1 clock2 clock3 clock4
³ DRIVE³ (((() (((() (((() (((()
³ LOOP ³ LS wire up to 100m ³ ³ ³ ³ ³ ³ ³ ³
The clocks are all paralleled up to the line, small chock block screw
connectors work fine at 60kHz for this. Such a drive system from a large loop
should provide ample signal. Further optimisation of the ferrite couplers can
also be done with series tuning C tuned up as in the main loop, if maximum
sensitivity is wanted.
LOOP AERIAL ORIENTATION
___³___ As MSF is vertically
\ polarised ground loop
\ ~-_ orientation needs to
\ ~-_~ - _ _./³_ _ - ~ _ be in the vertical plane
\ ~-_ ~- _ /_ ³ _ - - ~ _ with one edge pointing
~-_ ~ - _ ³ _ ³ _ - - ~ at the Tx for the maximum
~ - _ ³ _/ _ magnet field Rx signal.
³/ component of RF
Do not put loop aerial too near mains wires running vertically in walls.
TV sets & computer screens, have strong high frequency AC magnetic fields & can
cause problems. SMPSU in computers, economy lamps & even remote controls, can
all cause QRM, but normally only to weak signals.
Do not use it beside metal framed windows/doors/tin foil backed board walls, as
these can effectively be a shorted loop & de-tune the loop as well as reduce
the Rx signal.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
Read previous mail | Read next mail