Having done some research in to the AD603 which which was drawn to my attention by G6LBQ, I found a supplier who offers free next day delivery – RS Components for the sum of £9.60 each plus VAT.
I will put together a breadboard lash up of the AD603 circuit published in the EI9GQ “Building a transceiver” handbook and will post test results and schematics in due course.
Key points about this device:
- Low external component count.
- Fixed gain amplifier so no non-linear components created by AGC bias changes.
- Voltage controlled attenuator – neat.
- Input and Output impedance seems to favor 50 Ohm system architecture.
- Not obsolete.
- Available in DIP 8 discrete or SMD package.
Downside so far is the price, however the trade off in what appears to be published performance over variable bias amplifiers far outweighs the cost to me – watch this space!
9th of July 2017 – Proof of concept testing.
I have built a breadboard lash up of the AD603 variable gain amplifier following the schematic published in the Analogue Devices datasheet, so far it looks good but still not 100% as I am not getting the gain expected – currently seeing around 16dB, for a 1.3V peak to peak input I am seeing a 8.96V peak to peak output – not bad but not what I would expect based on the spec of the AD603 device, I also need to spend some time figuring out how the gain control works as applying a positive voltage decreases the gain but only by 10dB – see the video below for an explanation.