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Many homebrewing radio amateurs consider automatic gain control (to even-out the audio volume between loud and quiet signals) to be an unnecessary luxury. It may be, but so are fuzzy slippers, a hot-tub soaking, and Häagen-Dazs ice cream. A little self-indulgence won’t hurt you, and including AGC in your next rig could also help save your hearing. This ready-made PCB makes it easy to do so.
The Hayward-Damm design (published in the December 2007 issue of QST) has long been extolled as excellent, but its complexity and parts count has discouraged a number of would-be builders. Now, if you can stuff and solder a PCB you can have smooth and pop-free AGC. Even easier, this layout avoids the now-scarce TO-92 version of the J310 JFET and uses the surface-mount one instead. Don’t worry, though–these come preinstalled on the board! The other parts are readily available from major suppliers. For now, only the bare PCB (with the J310s) is available for purchase, but there’s a detailed parts list to help you obtain them.
The Hycas-AGC IF Amp has these features:
- 50Ω input and output.
- 100dB of AGC gain.
- AGC(off) gain 55-60dB.
- Gain adjustable with potentiometer.
- S-Meter voltage output.
- AGC on/off and mute control lines.
- Uses 12VDC power.
- PCB pads for edge-style SMA connectors (not included). Usable also for direct solder connection.
- Mounting holes for 4-40 (M3) screws.
- 4.25×2.63″ (10.7×6.5cm).
Available now as a bare PCB (with SMD J310s installed).
Schematic diagram (PDF)
Parts List (PDF) AVAILABLE SOON!
User’s guide (PDF) AVAILABLE SOON!
| PC board only (w/SMD J310s installed) | $12.95 | Buy on Tindie Soon on eBay |