TIA-AGC IF Amplifier

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The performance of a receiver or transmitter depends on careful impedance matching between its sub-systems: its mixers, filters, and amplifiers. Mismatches can cause loss of signal strength, inter-modulation distortion, and deep ripples in the audio passband that can make human speech hard to understand. A termination-insensitive amplifier (TIA) such as this one always presents a 50Ω impedance at both its input and output ports, providing a stable and predictable impedance to whatever it’s hook up to.

Adding automatic gain control (AGC) makes the audio coming out of the speaker or headphones stable as well. AGC boosts faint audio, and it keeps strong signals from blasting-out your eardrums. Though it’s far from a necessity, AGC is a nice thing to have. The TIA-AGC makes that easier. The circuit on which this broadband TIA IF amp is based was devised by Wes Hayward, W7ZOI, and Bob Kopski, K3NHI, and its AGC features were based on subsequent work by W7ZOI and Jeff Damm, WA7MLH.

The TIA-AGC broadband IF Amp has these features:

  • Input and output port impedance is always 50Ω and does not pass through or “telegraph” to the other port.
  • AGC responds to the input of a filtered DC voltage derived from the audio signal.
  • “Programmable” gain from 7 to 24dB.
  • Useful from 1 to 30MHz (with slightly-lower gain above 14MHz).
  • 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.

Available as a bare PCB, a kit of PCB and components (SMAs not included), or as a fully-assembled and tested unit. Fully-assembled units are produced on demand and may take up to 14 days for shipment.

Schematic diagram (PDF)

User’s guide (PDF)  AVAILABLE SOON!

Github Repository


PC board only $4.95 Buy on eBay Soon on Tindie
Kit of PC board with discrete components (SMA connectors not included) $12.95 Buy on eBay Soon on Tindie
Fully assembled and tested (SMA connectors not included)(produced on demand, shipment within 14 days) $19.50 Buy on eBay Soon on Tindie