To achieve enough rf signal pickup, an outside long wire aerial is required, of at least 25 feet anchored to a pole. No aerial balun must be used.Exploring the Anthorn MSF UK Time Signal.
Here are some links to Anthorn information of background interest:MSF link here: http://www.npl.co.uk/science-technology/time-frequency/time/products-and-services/msf-radio-time-signal
TR1 & TR2 form an asymetrical squarewave multivibrator local oscillator (LO), running at a frequency close to 60khz.
TR6 is the LO buffer stage, between the LO output and mixer/detector input.
TR3 operates as a LO-switched, mixer and detector.
TR4 is an af amplifier having a signal voltage gain of 10.
TR5 is an emitter follower, delivering a dc blocked, low impedance source to the pc mic input.Prototype
RFC1 artificially lengthens the aerial wire and together with C2 acts as a low pass filter to broadcast stations. RFC2 inhibits detector rf leakage to the audio stages. RV1 reduces signal overload to the detector and helps to partially null the decoded MSF second harmonic.
The multivibrator output to the mixer is buffered, so varying lengths of aerial "long wire" or variations of signal strength, do not influence or load the oscillator. Its switching pulse output is designed asymmetrical, as formed by the circuit crossover components.
Ref the spectrum analyser sweep picture: As no signal information is needed at the lower and upper audio frequencies, then C4 limits the low audio frequency response and Tr4 & Tr5 together form a three-pole low pass filter, having a band stop at 10khz.
While the whole circuit is centered on a 700hz output, the LO frequency unavoidably drifts with large changes in ambient room temperature. But afc action in SpectrumLab, tracks this drift without alterations in the program's performance. Manual variation of Ct1, allows compensation back to 700hz as required.
The prototype receiver proved particularly useful after building, as I needed an external reference source for adjustment within the ham radio slow scan picture program MMSSTV. This screenshot shows my laptop pc under test running the calibration aspect of that program and having precise reference MSF applied, to exactly set picture slant correction for true vertical straightness against the dotted green cursor line.
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