Hi I picked up a nice Roberts radio alarm at a car boot. It has a feature whereby it automatically sets the time on it's own via the Rugby[1] time signal. However, this feature isn't working & a scan through MW has little to no reception. I deduce from this that there's no reception of the 60kHz signal getting through. I'm not averse to taking it apart & having a look inside, I'm guessing an issue with the ferrite rod aerial inside? Anything else I should be looking for in particular?
Are you sure it gets its time signal from NPL Althorne? I ask because I have a Roberts radio, much more recent than yours by the sound of it, that gets its timing from the DAB signal. If the DAB signal is not available, you have to set the time manually and hope it keeps correct.
If you're certain yours gets its signal from Althorne, then try just moving the radio to a different place in the house, as in the past I've found the Althorne signal not easy to receive, and very dependent on receiver location. Does your radio have a telescopic aerial? If so, is it extended? Is 60kHz medium wave? I'm pretty rusty on that sort of thing, but it has to be long wave or beyond, surely (the long discontinued BBC Light Programme on Long Wave was at 1500 metres or
Probably a ferrite rod. Look for broken ferrite, or just a broken wire (if the former, then almost certainly the latter; probably if it's been dropped).
I have a Roberts radio alarm clock that uses the MSF signal. On the back it has a detachable aerial for the MSF which can be positioned for the best signal.
Whilst I like the idea of the clock being accurate, I have never thought that it worked very well. Some time ago whilst walking in Luxembourg I saw a similar radio in a shop, with a different brand name!
Yes, Roberts Radios are mostly marketed as Sangean around the rest of the world. It makes a mockery of the 'British' Roberts brand as they're made in the Far East somewhere I believe.
I doubt the same receive er is used for the time as is used for the radio am, but I guess both coils might share the same ferrite. What wavebands does it actually cover? I had a radio medium and long which was not good on those bands, somebody had dropped it and broken the ferrite rod in half and the wires from one of the coils were severed. No real way to repair it after that, sadly. Brian
It's also not a common ferrite for 22KHz to 60KHz. The ferrite rods, some of them, come from Russia.
The ferrite and coil are also resonant, and a C is added to the circuit which gives the desired resonant frequency.
The coil of wire can be smaller, because the "clock module" has to fit in all sorts of clock movements. Without the ferrite, the loops of wire require many many feet of material.
In this picture, is a 60mm rod, with a 20mm wide section of enameled fine wire. Under some black tape next to the flat coil section, is a capacitor selected for "resonance". The ferrite assembly in this case is tuned for 60KHz. Other ferrites-plus-cap are tuned for 77KHz or whatever.
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Alaso shown on the page, is a "receiver" assembly, with a glob-top chip on a module. The chip is raw silicon placed on the module, wire bonded to pads on the module PCB, then black plastic is poured over top. National Semi used to make some early digital clocks this way, with glob top chips. It's somebodies idea of a "money saver", which given the bother this causes, likely does not save any money.
You can buy the receivers as a separate item sometimes, and then the digital bits you design, have to pick up the "defacto standard" output of the module and do something with it.
Even wall clocks can use those module-solutions, for the RF to digital part of the thing.
This module is for the German LW transmitter, at 77.4KHz. it happens to have RS232 output (whereas other applications may not want the RS232 level shifter to be present, and instead, just have TTL or CMOS levels for the serial messages).
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You would connect a pre-tuned 77.4KHz ferrite plus capacitor, for easy reception (compared to running out in the back garden with a 20 pound spool of copper wire to make an "air core" antenna).
I think this may have been the site I visited years ago, with some of the details.
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And at the bottom here, is his "air core garden antenna".
90 turns of wire, on a square frame 2 foot per side or so, so about 720 feet of wire. The wire looks fairly substantial too. It's not 40ga magnet wire or anything. Probably an attempt at reduced loss due to resistance.
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"Without the high permeability ferrite the air cored loop has to be ca. 500 times the size for an equivalent ferrite rod antenna. This one has 90 turns in total. I used the same Mosfet pre-amp with this. It works well, about as good as the two, but not as good as the eight ferrite rod antenna."
So he built one ferrite antenna, with eight rods of ferrite inside.
There was a guy in sci.electronics who had some sort of evil plan to make an antenna with enough signal, it would go directly into his DSP solution :-) I don't know if he ever succeeded or not. People occasionally make a project out of this stuff, even when it's been reduced to "easy module" status.
yes. given that the ferrite is brittle and heavy, it's probly been dropped - the good news is that you SHOULD be able to glue any bits together and resolder any broken wires
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