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Offline dbannerTopic starter
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« on: May 14, 2015, 05:48:26 pm »
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I have reversed engineered a compass 77b PCB layout from a picture of the  circuit board underside. This is not the 77b automatic,but the 77b. Now I want to try to build it,but the problem I have is the coil specs. I know its a dd search coil resonating at 100khz,but  sometimes these coils are multitap. If the detector uses a colpitts oscillator for the tx coil then its easy. But some compass detectors tx signal consisted of an amplitude modulated frequency whose carrier wave is at 100 kHz. They achieved this by using a relaxation oscillator which required the use of a tapped coil to proved feedback to the tx transistor oscillator. The receiver section then discarded the 100 kHz signal leaving the audio signal to be amplified. If the 77 b used this method then without the coil specs I am doomed. Can anyone assist. Am I allowed to post the PCB layout?

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« Reply #1 on: May 14, 2015, 05:55:41 pm »
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   Yes you can post the schematic and Foil if you wish.  Compass is Defunct. 

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Offline dbannerTopic starter
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« Reply #2 on: May 14, 2015, 07:22:54 pm »
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The foil etc.

Posted on: May 14, 2015, 06:56:15 pm
Trying again

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77B frontPCB(0).jpg
77B%20foil.pdf
77B%20frontPCB.jpg
77B.pdf
77Bpcb.Backreverse_cropped.jpg


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« Reply #3 on: May 14, 2015, 08:48:30 pm »
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Nice work,but i can only open some of the files.
i cant open the files with %20 in them  Angry

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