Ha-1197 Am - diyAudio
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Old 27th August 2005, 10:10 PM   #1
approse is offline approse  United States
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Join Date: Apr 2005
Location: Tennessee
Default Ha-1197 Am

Greetings all,

I don't have the expertise so I'm hoping someone is familiar enough with this AM demodulator chip to help me. Most circuits for I've seen are very similar for this chip but if it would be helpful I'll try to make a small scan and upload it.
I'm having trouble with what seems to be an overloading condition input. When there's a spike in the signal input (as in Lightining) or even I can hold my hand on the ferrite antenna to suppliment the signal a little, the circuit will go into an oscillation that locks the whole of the circuit. Sounds like about 1-3khz, in that area. Switching the circuit off and then back on resets the circuit until the signal overloads again. I found I can prevent it happening by removing the 33k mylar cap that bridges from signal out to the b+ but I have the feeling all I'm doing here is lowering the gain of the chip? I'm past my understanding of the circuit here. Only thing I do know is there's no AGC in the circuit unless it's built into the chip itself. The frontend itself is purely vcap tuning, all amplification is done at the chip and post output. Thanks in advance!!

Ron
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