HILNA HF w/ AGC User Manual
Rev ‐
9
The HYSTERddd command defines the amount of change needed in the RSSI value before the AGC loop
makes any change to attenuation. The value for the HYSTER is approximately 16 counts per 0.5 dB (e.g.
HYSTER032 would equate to an approximate 1 dB change required before any attenuation is added or
removed). This setting prevents the AGC loop from constantly adding or removing attenuation due to a
small signal level change. Table 10 lists SPEED, ATACK, and DECAY settings for 4 different attack / decay
times.
Table 11: AGC settings for various attack / decay times
Time (mS)
Speed
Attack
Decay
10
SPEED3
ATACK018
DECAY018
100
SPEED6
ATACK009
DECAY010
250
SPEED6
ATACK003
DECAY003
500
SPEED6
ATACK002
DECAY002
These times are based on a 30 dB delta on the incoming signal level. Initial approximations for attack /
decay times can be calculated with some knowledge of the incoming signal. To approximate the attack
time, apply the following formula:
∗ ∗
∆
The same formula also applies to decay times. For example, with settings SPEED6, ATACK010, and a
∆
dB
of 40, we see that:
∗ ∗
Note that these calculations are close approximations and do not take into account the processor
overhead or decisions made by the estimator as to how much attenuation change to make.
