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Mr 1936 · 1st Oct 2022, 9:42 am

Hi

I still have the Binatone Worldstar version of this set, which seems to work much better than it has a right to. A quick search revealed that Manuals and Circuit diagrams are freely available online.

It was rather ingenious of the designers to equip it with two separate front ends, one for 88 to 108 MHz "FM" and another for 108 to 174 MHz "VHF". The dial cord wraps round two tuning drums, and the 10.7 MHz IF output coils are just summed by putting them in series. This relegates band switching to DC and saves all the difficulties of alignment and switching coils at VHF.

Although "VHF" is tuned as one band, it enjoys no less than three printed tuning scales; Aircraft, Weather and High. All helps to look more impressive I suppose !

Looking at the detection arrangements, there is just one FM ratio detector for both these bands and the alignment instructions call for an FM modulated signal generator for both bands. This would have fitted with the use of FM in the USA for two-way and marine radio on the "high band" plus the weather broadcasts around 162 MHz. I guess the AM voice transmissions for aircraft on 118 to 136 MHz would have been a bit of an afterthought, with deliberate mistuning needed to resolve them. At least the "VHF" band has no AFC to spoil this workaround.

The squelch (only for the "VHF" band) has D10 and D11 as a level detector, with adjustable offset by R44 to set the threshold. This then gates the audio via Q9 and Q10. From memory it sort of works.

There is also D13 and D14 plus Q11 and Q12 as an IF level detector which drives a red "Tuning" LED D12. The LED sits in the tuning pointer which looks quite neat.

1st Oct 2022, 9:42 am	#16
Mr 1936 Heptode Join Date: Mar 2017 Location: Romsey, Hampshire, UK. Posts: 524	Re: Unknown Radio Hi I still have the Binatone Worldstar version of this set, which seems to work much better than it has a right to. A quick search revealed that Manuals and Circuit diagrams are freely available online. It was rather ingenious of the designers to equip it with two separate front ends, one for 88 to 108 MHz "FM" and another for 108 to 174 MHz "VHF". The dial cord wraps round two tuning drums, and the 10.7 MHz IF output coils are just summed by putting them in series. This relegates band switching to DC and saves all the difficulties of alignment and switching coils at VHF. Although "VHF" is tuned as one band, it enjoys no less than three printed tuning scales; Aircraft, Weather and High. All helps to look more impressive I suppose ! Looking at the detection arrangements, there is just one FM ratio detector for both these bands and the alignment instructions call for an FM modulated signal generator for both bands. This would have fitted with the use of FM in the USA for two-way and marine radio on the "high band" plus the weather broadcasts around 162 MHz. I guess the AM voice transmissions for aircraft on 118 to 136 MHz would have been a bit of an afterthought, with deliberate mistuning needed to resolve them. At least the "VHF" band has no AFC to spoil this workaround. The squelch (only for the "VHF" band) has D10 and D11 as a level detector, with adjustable offset by R44 to set the threshold. This then gates the audio via Q9 and Q10. From memory it sort of works. There is also D13 and D14 plus Q11 and Q12 as an IF level detector which drives a red "Tuning" LED D12. The LED sits in the tuning pointer which looks quite neat.