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SiriusHardware · 24th Mar 2020, 12:35 am

I think all that happened was that you shifted the output frequency when you put the lid on - as mentioned earlier, the 'transmitter' in the modulator is just a simple free-running oscillator and putting the metallic lid on it probably just made the transmitter frequency detune to one side a bit.

All you likely needed to do after putting the lid on (at which point the signal disappeared) was to retune the TV a little.

You can test this theory if you like: Tune it in as best you can with the lid on, and then flip the lid off - does the signal disappear? If so, tune around and find it again. Then, put the lid back on - does the signal disappear again? If so, tune around again until you find it again.

If everything in the previous paragraph is true, then all that's happening is that the modulator output frequency is changing slightly when the lid is present / is not present.

24th Mar 2020, 12:35 am	#159
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,553	Re: Zx81 I think all that happened was that you shifted the output frequency when you put the lid on - as mentioned earlier, the 'transmitter' in the modulator is just a simple free-running oscillator and putting the metallic lid on it probably just made the transmitter frequency detune to one side a bit. All you likely needed to do after putting the lid on (at which point the signal disappeared) was to retune the TV a little. You can test this theory if you like: Tune it in as best you can with the lid on, and then flip the lid off - does the signal disappear? If so, tune around and find it again. Then, put the lid back on - does the signal disappear again? If so, tune around again until you find it again. If everything in the previous paragraph is true, then all that's happening is that the modulator output frequency is changing slightly when the lid is present / is not present.