A technical question about clock radios

[stephenb]

A technical question for those electronic experts out there. I know this sounds odd, but here it goes.

I am importing a retro clock radio from the USA (typical red LED type display) and naturally I'll need to look for a substitute transformer as it was designed to run on 120VAC.

My question relates to the power frequency. If I'm fortunate enough to locate a transformer with the correct voltage outputs, will it run correctly on 50Hz? Does the AC source frequency have any bearing on the clock function?

No point me acquiring it if it is going to run fast/slow.

Stephen

[Barrykgerdes]

You will need more information on the clock. The simple older types used the mains frequency to drive the timing. In which case the clock would be useless running slow.

However the modern types use clock chips that run from DC and use crystal control that is independent of the mains frequency and the AC mains voltage is used to derive the low voltage DC required for the electronics. Further to this the input voltages in the switch mode supplies these days usually are not critical of input voltage that can be anything between about 90 and 270 volts.

Barry

[Astro_Bot]

You may have problems with the radio, regardless of power. Radio channels in the US use a different standard to Europe (and Australia follows the European standard). If the tuning is all analogue, it should still work, but if there's any digital channel tuning, the channel widths/bands won't be aligned.

http://www.epanorama.net/documents/radio/radio_differences.html

You may be lucky and it may be switchable between the two schemes.

[mithrandir]

Adding to previous comments:

US mains 60Hz. Aus mains 50Hz. If it uses the mains frequency it will update by 50 sec per real minute. You'd need a converter that does 240V->110V and 50->60Hz using the 50Hz as a timing reference.

US AM station interval 10KHz. Aus AM station interval 9KHz. With digital tuning you would get 10% of stations. Some sets have a 9/10KHz interval switch to solve this problem.

US FM center freq 87.9-107.9MHz 200KHz steps. Aus FM center freq 88.1-107.9MHz in 200KHz step. Should be OK

You need lots more details.

[Astro_Bot]

European/Aus FM steps are 100kHz, not 200kHz, so a US radio won't tune to some Aus FM channels. Most Aus stations are actually on odd 100kHz multiples, though, so you only lose a few:

http://en.wikipedia.org/wiki/List_of_radio_stations_in_Australia

I'd have to refresh my memory on FM channel width to see if you'd lose signal (i.e. I can't recall what the US filters would do to an Aus signal).

[mithrandir]

In theory 100KHz. In practice 200KHz.

Australian VHF FM Radio Standard
Australia uses the ‘pilot-tone’ system commonly used throughout the world. Principal characteristics of the system used in Australia are set out below:
Frequency Range: 88 – 108 MHz (i)
Channel Centre Frequencies: 88.1, 88.3, ... 107.7, 107.9 MHz
Deviation: 75 kHz
Pre-emphasis/de-emphasis: 50 μseconds
Stereo Channel Subcarrier Frequency: 38 kHz
Pilot Frequency: 19 kHz
The stereo baseband signal occupies a frequency range of 53 kHz.

(i) Note : low power open narrowcasting services are licensed to operate in the band 87.5 MHz to 88.0 MHz.

Radio and Television Broadcasting Stations (Internet Edition, April 2013)

[Astro_Bot]

If you look at the link I posted above, you'll see the handful of stations that use even 100kHz multiples.

[Astro_Bot]

This is why people get fed up with forums - the discourse quickly departs the context of trying to answer someone's question simply, and becomes a battle of pedantry and egos (mine included).

I'll leave it here because I don't want to argue why one person wants to artificially add restrictions to the argument that favour them, while another is tempted to do the same in the other direction, and why one person makes simplifications so as not to write a thesis, in order that their answer is readable, while another adds ever finer levels of detail. And I'm not saying which side I'm on on that train of thought! ;)

IMHO, the question has been well and truly answered. If there's more to add, someone else can do it.

[stephenb]

thanks for replying all,

to clear up some points...

The radio is pure late 1980's analogue so there will be no issue with reception for either band. That part of the unit I am not concerned about.

I've solved the issue of input voltage with a 240-120 50W step down transformer. - tick

The only issue is if it the clock oscillator derives it's timing from the power source or has an inbuilt, self-contained oscillator.

I've been advised today by an authority in the field that often the clock chip in these bog-standard bedside clock radios have a dedicated pin which is connected to either ground or rail voltage, depending on whether it is running on 50 or 60Hz - I assume that makes it easier to export the same model to different parts of the world - then the only other internal change is the transformer.