Message 26410 in TECH.WW
From: G8MNY
Date: Wed, 22 Jul 26 09:32:00 Z
Newsgroups: TECH.WW
Subject: MSF Time Signal Clock Feed
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From: G8MNY@GB7CIP.#32.GBR.EURO
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 and 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.
CLOCK CIRCUITRY
These often have just 1 small ferrite 61kHz _______
To get the narrow bandwidth needed
circuit to the Rx. This gives less than |||( === B/W B/W
bandwidth and QRM from the Rx signal.
MSF MOVE
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, and said I doubt they will stay
working, and 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!
SIMPLE CURES
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
wrong direction.
~-_ ~ - - ~ _-~
~ - _ ~ -________ - ~ _ - ~
~ -(__((((__()- ~
Ferrite Rod
So try to relocate the clock (Rx) so that its' ferrite rod is perpendicular to
the Tx, and 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 and it hears the
MSF transmission for a few minutes a day and 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 and made of plastic trunking to house 30 or so turns and
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!
=== 60 ) (____ Balanced Drive wire
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 and monitor the field on the drive loop (e.g. scope/
diode probe & meter).
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.
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
\ polarised ground loop
\ ~-_ orientation needs to
QRM SOURCES
Do not put loop aerial too near mains wires running vertically in walls.
TV sets and computer screens, have strong high frequency AC magnetic fields and
can cause problems. SMPSU in computers, economy lamps and 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 and de-tune the loop as well as reduce
the Rx signal.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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