IQ32 SDR TRANSCEIVER OPERATIONS MANUAL
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AGC Modes Explained
For those people interested in how our AGC (Automatic Gain Control) modes work, here is an
explanation from Charley W5BAA, who is the author of our AGC and many other portions of
our firmware.
The AGC control scheme controls two amplifiers in our CODEC (Coder/Decoder). One is the
PGA (Programmable Gain Amplifier), and the second is the DAC (Digital to Analog converter).
There are 4 modes of AGC operation: CW, Digi, SSB, and Off.
CW AGC
In the CW mode, the PGA's AGC is controlled by the peak (highest) magnitude found in any of
the FFT bins over the entire audio spectrum from 300 - 3500 Hz. Also, the DAC's AGC is con-
trolled by the peak magnitude in this mode.
Digi AGC
In the Digi mode, the PGA's AGC is controlled by summing only the magnitude bins from 2
pixels below the cursor through 2 pixels above the cursor. However, the DAC's AGC is con-
trolled by the peak magnitude, as described above for Mode 0.
SSB AGC
In the SSB mode, the PGA's AGC is controlled by summing the magnitude bins over the entire
audio spectrum from 300 - 3500 Hz. The DAC's AGC is controlled by the peak magnitude, as
described above.
Off
In the Off mode, the PGA's AGC is controlled by the RX_RF value which was set manually,
and the DAC's AGC is controlled by the RX_AF value, which was also set manually, on the
Settings screens.
There are two AGC values shown on a
H
OME
S
CREEN
: RF and AF. RF is the raw value being
sent by the AGC to the CODEC to control the PGA gain stage. It can range between 0 and 80,
which represents a range of gain from 0 to 40 dB. AF is the raw value being sent by the AGC
to the codec to control the DAC gain stage. It can range from -127 to +48, which represents a
range of gain from -65 dB to +24 dB.
When receiving signals, you will see these two values decrease with stronger signals and in-
crease with weaker signals.
