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Set-Points
The Variable Gain Board is operated / configured with in total 12 set-points. These different set-points are programmed with a μ-controller by means of the I2C protocol. This page is meant as a user reference page of the functioning of set-points on the Variable Gain Board. For how to actually program the IC's registers with the I2C protocol, the datasheets should be consulted for the details.
| Vsph |
| Description: |
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Vsph sets the decay speed during the DECAY state for the AGC in Hang-Mode. Usually a relatively fast decay speed is used. With the speed specified by Vsph, the Vslow control voltage is decayed until it equals Vfast again and the AGC re-enters HANG state.
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| Location: |
AD5306 IC19, pin 3, Channel-A. |
| Type: |
Analog output, 8-bit DAC. |
| Usage: |
Directly by the operator. |
| Steps: |
255 |
| Reference Voltage: |
5.0V |
| Minimum Value: |
1 |
19.6mV, 6.06dB/s, 21.6s/131dB |
| Maximum Value: |
255 |
5.0V, 1546dB/s, 84.8ms/131dB |
| Step Size: |
19.6mV |
6.06dB/s |
| Recommended Default Value: |
32 |
194dB/s, 0.675s/131dB |
| Vspa |
| Description: |
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Vspa sets the decay speed for the AGC in Attack/Decay-Mode. Usually a relatively slow decay speed is used for quiet operation of the AGC. With the speed specified by Vspa, the Vslow control voltage is decayed until it equals Vfast again.
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| Location: |
AD5306 IC19, pin 4, Channel-B. |
| Type: |
Analog output, 8-bit DAC. |
| Usage: |
Directly by the operator. |
| Steps: |
255 |
| Reference Voltage: |
5.0V |
| Minimum Value: |
1 |
19.6mV, 6.06dB/s, 21.6s/131dB |
| Maximum Value: |
255 |
5.0V, 1546dB/s, 84.8ms/131dB |
| Step Size: |
19.6mV |
6.06dB/s |
| Recommended Default Value: |
8 |
48.5dB/s, 2.7s/131dB |
| Vleak |
| Description: |
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Vleak sets the decay speed during the HANG state in Hang-Mode. The speed can be 0 but usually a little amount of leaking is configured to have the AGC follow slow QSB during HANG state in Hang-Mode. A voltage divider with buffer is used to provide a more fine grained and smaller output value.
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| Location: |
AD5306 IC19, pin 5, Channel-C. |
| Type: |
Analog output, 8-bit DAC. |
| Usage: |
Directly by the operator. |
| Steps: |
256 |
| Reference Voltage: |
5.0V |
| Minimum Value: |
0 |
0V, 0dB/s |
| Maximum Value: |
255 |
0.455V, 140.7dB/s |
| Step Size: |
1.78mV |
0.551dB/s |
| Recommended Default Value: |
4 |
7.14mV, 2.21dB/s |
| Vfloor |
| Description: |
Vfloor sets the compensation for the noise floor of the diode detector. Vfloor is subtracted from the output of the diode detector in order to obtain a Vagc control voltage that starts close to 0V at the beginning of the control range. A voltage divider with buffer is used to provide a more fine grained and smaller output value. In practice Vagc will start at plus minus 300mV for the given default value.
Rather than to adjust Vfloor to have Vagc start at 300mV in closed-loop, Vfloor should be used to precisely set the end of the control range. The exact end of the control range is set by Vfloor to correspond with the strongest input signal that the signal path can handle. The alignment is simple. Apply a precise +3dBm 9MHz input signal to the input of the Variable Gain Board and adjust the value of Vfloor such that Vagc = 3.894V, which is exactly the end of the range. If no calibrated signal generator is available, use an uncalibrated 9MHz signal source plus oscilloscope and attenuator to obtain 893mVtt in 50Ω. The value found for Vfloor should be around 150.
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| Location: |
AD5306 IC19, pin 11, Channel-D. |
| Type: |
Analog output, 8-bit DAC. |
| Usage: |
Once, configuration only. |
| Steps: |
256 |
| Reference Voltage: |
5.0V |
| Minimum Value: |
0 |
0V |
| Maximum Value: |
255 |
0.763V |
| Step Size: |
2.99mV |
0.1dB |
| Recommended Default Value: |
151 |
0.452V, 15.1dB |
| Vath |
| Description: |
|
Vath sets the threshold value used for automatically choosing the AGC strategy. Signals with Vslow below Vath will use Attack/Decay-Mode. When Vslow is above Vath, Hang-Mode will be used. Given the default value (112) input signals below S9 will use Attack/Decay-Mode and above S9 Hang-Mode.
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| Location: |
AD5306 IC18, pin 3, Channel-A. |
| Type: |
Analog output, 8-bit DAC. |
| Usage: |
Directly by the operator. |
| Steps: |
256 |
| Reference Voltage: |
3.894V |
| Minimum Value: |
0 |
0V, -131dBm |
| Maximum Value: |
255 |
3.894V, 0dBm |
| Step Size: |
15.3mV |
0.515dB |
| Recommended Default Value: |
112 |
1.71V, -73.3dBm, S9 |
| Vhth |
| Description: |
|
Vhth represents the hang threshold value used to set the direction of the hang integrator. If Vfast + Vhth < Vslow, then the integrator moves towards the DECAY state, otherwise it moves towards HANG state. In other words: Vhth defines the window in dB that the Hang AGC allows Vfast to decrease during HANG state to maintain its preference for HANG state.
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| Location: |
AD5306 IC18, pin 4, Channel-B. |
| Type: |
Analog output, 8-bit DAC. |
| Usage: |
Once, configuration only. |
| Steps: |
255 |
| Reference Voltage: |
3.894V |
| Minimum Value: |
1 |
15.3mV, 0.515dB |
| Maximum Value: |
255 |
3.894V, 131dB |
| Step Size: |
15.3mV |
0.515dB |
| Recommended Default Value: |
20 |
0.305V, 10.3dB |
| Vloop |
| Description: |
Vloop has a dual function:
-
For small values (< 80), it determines the voltage that is subtracted from Vfast to produce Vfast2. Usually a value that represents 6dB is used in order to minimize the gain modulated IMD produced in a closed loop AGC. This value depends on the loop bandwidth provided by the attack/decay times of the FAST path. In this mode it is an analog output.
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For large values, Vloop is used to mute the AD602 amplifier that provides signal to the diode detector. In this mode it is a digital output. To open the AGC loop for manual gain control mode use 255.
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| Location: |
AD5306 IC18, pin 5, Channel-C. |
| Type: |
Analog output, 8-bit DAC. |
| Usage: |
Indirectly by controller logic. |
| Steps: |
256 |
| Reference Voltage: |
3.894V |
| Minimum Value: |
0 |
0V, 0dB |
| Maximum Value: |
255 |
3.894V, 131dB |
| Step Size: |
15.3mV |
0.515dB |
| Recommended Default Value: |
12 |
0.184V, 6.2dB |
| Vgain |
| Description: |
|
Vgain is used to set the maximum allowed gain of the signal path. This control is usually called IF-gain or RF-gain in most receivers. When the loop is opened by means of Vloop, Vgain provides pure manual gain control.
|
| Location: |
AD5306 IC18, pin 11, Channel-D. |
| Type: |
Analog output, 8-bit DAC. |
| Usage: |
Directly by the operator. |
| Steps: |
256 |
| Reference Voltage: |
3.894V |
| Minimum Value: |
0 |
0V, 109.6dB gain |
| Maximum Value: |
255 |
3.894V, -21.5dB gain |
| Step Size: |
15.3mV |
0.515dB |
| Recommended Default Value: |
0 |
0V, 109.6dB gain |
| Vspd |
| Description: |
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Vspd sets the maximum hang time of the AGC in Hang-Mode. This is the interval starting when the hang integrator begins to integrate towards the DECAY phase until DECAY phase is actually reached. The 8-bit 100KΩ digital pot-meter is used to create 256 hang integrator speed steps from 0V to 5V.
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| Location: |
AD5242 IC16, pin 15, pot-meter-2. |
| Type: |
Analog output, 8-bit digital pot-meter. |
| Usage: |
Directly by the operator. |
| Steps: |
255 |
| Reference Voltage: |
5.0 |
| Minimum Value: |
1 |
15.3mV, 31s |
| Maximum Value: |
255 |
5V, 122ms |
| Step Size: |
15.3mV |
| Recommended Default Value: |
15 |
0V, 2.0s |
| Attack |
| Description: |
|
Attack sets the attack time of the AGC in both Attack/Decay-Mode and Hang-Mode. This is implemented directly with the 8-bit digital pot-meter used as a variable resistor in an RC-time constant.
|
| Location: |
AD5242 IC16, pin 3, pot-meter-1. |
| Type: |
Analog output, 8-bit digital pot-meter. |
| Usage: |
Directly by the operator. |
| Steps: |
256 |
| Minimum Value: |
0 |
0Ω, 73ms |
| Maximum Value: |
255 |
100KΩ, 400ms |
| Step Size: |
392Ω |
1.3ms |
| Recommended Default Value: |
10 |
0V, 85ms |
| Vhot |
| Description: |
|
Vhot is the "hang on transmit" bit. If set, the hang integrator is forced deep in to HANG state quickly. This bit is most relevant if the receiver is used in combination with a transmitter to maintain the receiver's AGC level during short transmissions.
|
| Location: |
AD5242 IC16, pin 1. |
| Type: |
Digital output port. |
| Usage: |
Indirectly by controller logic when a forced hang is needed. |
| Minimum Value: |
0V |
HOT Disabled |
| Maximum Value: |
5V |
HOT Enabled |
| Vmute |
| Description: |
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Vmute is used to completely mute the signal path. If set, all AD600's in the signal path are disabled. This bit is most relevant if the receiver is used in combination with a transmitter in half duplex mode to mute the IF during transmission.
|
| Location: |
AD5242 IC16, pin 13. |
| Type: |
Digital output port. |
| Usage: |
Indirectly by controller logic when receiver mute is needed. |
| Minimum Value: |
0V |
Signal Path not Muted |
| Maximum Value: |
5V |
Signal Path Muted. |
This concludes the Set-Point reference of the AGC Control Path. Please follow the links below to read more about the other aspects of the Variable Gain Board.
Signal Path
Control Path
Closing the Loop
Set-point Reference
Back to Variable Gain Board
Back to the TOC
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