W7ZOI did a seminal piece on a Hybrid Cascode AGC Circuit. This same circuit was used in my JABOM rig. (JABOM = Just A Bunch Of Modules and published in QRP Quarterly)
The original article for Hayward's circuit was published in QST.
Originally published in the December 2007 QST, Figure 1 is similar to what was presented in yesterday's Blog Posting. Hayward found that this circuit, however, was sensitive to Vdd dropping below 12VDC.
Figure 2 with a simple change of J2 to a 2N3904 enabled using as little as 8.5VDC to give peak performance. The issue was portable battery operation where a fully charged battery in short order drops below 12VDC.
The full-blown circuit is shown below.
Homebrewers are indeed fortunate as Todd, K7TFC sells the circuit board for the HyCAS Module which uses the J310 configuration and so that removes 60% of the effort to replicate your very own HyCAS.
Below is an actual build from N6QW as used in the JABOM. This was the subsequent refinement by W7ZOI where the J310 and 2N3904 transistors were used. My board also includes the SBL-1 Product Detector located behind a shield.
I can attest that switching in the AGC is like night and day. It really works but does require more parts than one FET and two resistors.
So, I will stop here with any further talk about AGC and as I said most of my rigs use the Armstrong method (manual adjust of the volume control).
TYGNYBNT. Don't eat your pet!
73's
Pete N6QW
