G8MNY > TECH 16.05.25 08:15z 121 Lines 5373 Bytes #139 (0) @ WW BID : 32676_GB7CIP Read: GUEST Subj: MSF Time Signal Clock Feed Path: ED1ZAC<ED1ZAC<LU4ECL<VK2RZ<VE3CGR<VE6NAS<VE2PKT<GB7BED<GB7JED<GB7CIP Sent: 250516/0804Z @:GB7CIP.#32.GBR.EURO #:32676 [Caterham Surrey GBR] 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 & 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 _______ 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. 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, & 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! 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. | ³Tx | \ Á / ~-_ ~ - - ~ _-~ ~ - _ ~ -________ - ~ _ - ~ ~ -(__((((__()- ~ Ferrite Rod 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! ÚÄÄÄÄÄÄ¿ ³ ) ____ 1 turn === 60 ) (____ Balanced Drive wire ³ kHz ) ÀÄÄÄÄÄÄÙ 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 __.-~ ~-.__ ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÙ ÀÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄ>Freq 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 ÀÄÄÄÄÄÄÁ======================================================---Ù 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 ³Tx ___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 QRM SOURCES 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
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