Here's an old thread on using optical devices in an AGC for the Bitx40, but not the H11F3M:
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/g/BITX20/topic/5619869#31012Middle of page 6 for the H11F3M datasheet shows an AGC circuit, claims 70dB dynamic range:
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Capacitance across the H11F3M's detector is 15pF, and minimum on state resistance?
is several hundred ohms.? So only useful as an attenuator at audio frequencies.
Don measured 20 dB dynamic range using a $0.02 2n7002 FET, but that was at RF.
I wonder how the $0.02 2n7002 compares with the $2.50 H11F3M at audio frequencies.
The audio pre-amp is limiting our dynamic range, as Henning pointed out.
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/g/BITX20/message/32043For a large dynamic range, the H11F3M would have to be in front of the pre-amp.
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Jerry?
On Wed, Mar 28, 2018 at 12:55 pm, Sandy T wrote:
Has anyone tried a H11F3M for the AGC on the newer uBITX ??It's a Photo FET Optocoupler made by ON Semi and actually shows an application note with AGC use. You could drive it with the existing second amplifier, minimal extra components, and a 6-pin socket which will fit on the board near the amplifier. I would also put in an 8-pin socket on the TDA2822M/NJM2073D amplifier for future convenience.....might as well, while you are messing around with the board. Just received some to try out.
73 Kees K5BCQ
