inside is a tiny metal reed!pic.twitter.com/VFsM2sVVan
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here's some unusual electrical components. these are tone reeds. they're used in older radio equipment, such as public safety radios and ham radios. they are used to send or receive CTCSS tones. let's take one apart!pic.twitter.com/rgWOvnv2VZ
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it's a little hard to hear so i put a plastic card to amplify itpic.twitter.com/AsRv4rPwCT
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on a scope, you can see the sine wave it creates. if you overdrive it, the reed bounces against the limits and the waveform distorts.pic.twitter.com/flCYp5Hz1P
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CTCSS=continuous tone-coded squelch system: let's say we have 10 radios (all on the same frequency) and we divide them into two groups using two different CTCSS tones. in my group i only hear my five buddies, and i cannot be heard by the other group.
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CTCSS works by sending a tone (like 192.8Hz) along with my voice whenever i TX and key up my mic. the RX side's squelch (aka mute, so you don't hear white noise when nobody is talking) will stay muted unless it also hears that exact tone.
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nowadays radios generate the tones digitally instead of using an actual, physical resonator. you can pick a wide variety of frequencies and you don't have to swap out the tone reed modules.
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here's the motorola datasheet, surprisingly still hosted on their website. https://www.motorolasolutions.com/content/dam/msi/docs/en-xw/static_files/Related_-_Vibrasender_and_Vibrasponder_devices.pdf …
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So on a CB radio that had 6 channels to choose from or whatever, were there 6 of these in there?
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these little reeds only make the CTCSS/PL tone (audible but low frequency). they don't set the tx/rx radio frequency, which is usually done using quartz oscillators. CB is simpler and doesn't use CTCSS. channel number = radio frequency, and you hear everyone in range.
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