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enter image description here This was salvaged from a dead "Bush" branded "walkman" style product a few years ago and has been rattling around in my parts bin ever since. The marking on the back simply says "M7." with no other markings at all. The white material seems to be plastic. The blue area looks very similar to the surface of a PCB and the "traces" are raised from the surface and can be detected by a fingernail scratching the surface.

My meter tells me there is less than 1 ohm between the middle and left pins but does not measure anything on the other pin combinations.

I wondered if it might be a fancy resistor or some sort or perhaps an exotic inductor. The part was upright and freestanding when installed in the product, but was near to the AM/FM radio receiver circuits. Could it be an antenna even?

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    \$\begingroup\$ Looks like a LC network of some sort, can you measure capacitance over open pins? \$\endgroup\$ – RoyC Jan 20 '17 at 9:48
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    \$\begingroup\$ but was near to the AM/FM radio receiver circuits. Could it be an antenna even? No, it is too small to be an Antenna for FM/AM, the wavelength at those frequencies is too large. My guess is that it is some kind of (IF) filter / resonator for filtering out the channel you're listening to. \$\endgroup\$ – Bimpelrekkie Jan 20 '17 at 9:57
  • \$\begingroup\$ I don't have an LCR meter unfortunately. My Fluke 179 doesn't register any capacitance on these pins, so it's probably very small (< nano Farads range). \$\endgroup\$ – Wossname Jan 20 '17 at 9:58
  • \$\begingroup\$ It looks like a BPF probably for the 88 to 108 FM band . \$\endgroup\$ – Autistic Jan 20 '17 at 10:35
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If both sides have only pcb patterns, it cannot be nothing else than a LC circuit - a filter or matcing network is my trivial quess. Seems to be quite complex due the coupling between the coils. No high power capacity.

Because it is a separate part which is not integrated into the main board proposes that it is selected differently for different marketing areas due different requlations. That is not a proof because the main board simply can have too lossy material.

The size proposes it is used at several hundred MHz. The stray capacitances and inductances of ordinary wires makes all measurements useless if proper UHF probes and instruments are not available.

Computer aided reverse engineering is possible by using high cost microstrip circuit analyzing software. But some idea of what to ask is a must.

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  • \$\begingroup\$ the little stub-looking pads between where the wires are bonded would support this being some kind of filter. \$\endgroup\$ – Sam Jan 21 '17 at 8:00
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I have the same component on a SHARP radio PCB it says CF1 where it is connected to the PCB it is connected in series with an IC

edit: I found the user manual with the parts list it said it was an FM Bandpass Filter

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  • \$\begingroup\$ Can you provide us with some photos of the part in your radio? \$\endgroup\$ – ThreePhaseEel Dec 19 '17 at 12:40

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