# Analog video transmitter
The Dragon SR stack supports analog video transmitters with extra hardware and software required.
While using analog VTx, Skynode S streams video over USB 2 connector to a companion computer that converts digital video to analog signal that is later forwarded to the VTx.
## Additional hardware required
* Companion computer
* SD card with DACNode image on it
* Analog VTx with antenna
* Cables and standard Skynode connectors
## Wiring
#### Connect the companion computer
Use [Interfaces](/hardware-integration/skynode-s/interfaces.md#usb-2) on Skynode S to connect the companion computer.
{% hint style="danger" %}
Always make sure that power requirements are below Skynode S limit while using 5V\_EXT output.
{% endhint %}
| Name | Skynode S | Companion computer |
| -------- | --------- | ------------------ |
| 5V Power | 5V\_EXT | 5V |
| GND | GND | GND |
| USB D+ | D+ | DP |
| USB D- | D- | DM |
#### Connect the VTx to companion computer
Connect the companion computer to the analog video transmitter by connecting the appropriate composite video output (CVO) to the relevant pin on the VTx (usually marked as VIDEO-IN). Refer to the VTx documentation to find the right pins.
#### Connect the VTx to Skynode S
* **VTx control:** connect the VTx Data (SmartAudio / Tramp) pin to the UART3\_TX (TELEM2 TX) on the Skynode S.
{% hint style="warning" %}
In order to use CRSF telemetry and VTx control at the same time, connect the VTx to SBUS\_IN pin and CRSF to UART3 (TELEM 2).
{% endhint %}
#### Connect the VTx to power
* VTx that support 5V input can be connected directly to any 5V\_EXT pin on Skynode S.
* VTx that requires battery voltage should be connected directly to battery voltage.
{% hint style="danger" %}
Always make sure that power requirements are below Skynode S limit while using 5V\_EXT output.
{% endhint %}
## Software setup
Download and install the Dragon SR Analog release. This release includes the VTx support app and an appropriate configuration for MC-Follow.
### VTx control
It's possible to change the video transmitter channel, band, power level and pit mode through the PX4 parameters (e.g. over AMC). For detailed configuration refer to PX4 documentation for Analog Video Transmitters.
#### VTx support app
The VTx support app is meant to simplify VTx configuration. The app can be accessed using the blue button located in the app’s container on the vehicle’s web page. Once opened, navigate to the corresponding tab. The web service provides three primary functions, which can be accessed through the sidebar.
**VTx terminal**: Supports editing VTx table (Band/Channel/Frequency settings and power levels) through `vtxtable` command.
**OSD Name Display:** In the second tab, the user can edit or update the vehicle name shown on the OSD screen. To change the default name, enter the new value and press **OK**. Displayed `vehicle_name` updates immediately. By changing the app setting *Device Name*, desired display name for the OSD screen persists after reboots.
**Import/Export PX4 Parameters:** The third tab allows saving, downloading, and editing PX4 parameters. This is useful for importing/exporting RC calibration or PX4 parameters related to VTX support.
## MC-Follow tracking initialization on mode activation
The key difference in analog workflow is the way the object can be tracked using visual tracking.
Dragon SR Analog release comes pre-configured with auto video-tracking initialization on mode activation - every time MC Follow mode is activated, it sends tracking init message with predefined relative object position:
* `MCFLW_TOA_X` : Relative x coordinate of the tracking init message in relative image coordinates.
* `MCFLW_TOA_Y`: Relative y coordinate of the tracking init message in relative image coordinates.
Default values of 0.5 for both `MCFLW_TOA_X` and `MCFLW_TOA_Y` will make the video tracking track whatever is in the middle of the camera image.
This feature can be disabled:
* `MCFLW_TOA` : Sends tracking init message on mode activation. Requires app restart.
{% hint style="warning" %}
The vehicle have to be armed for this video tracking initialization with MC Follow to work.
{% endhint %}
## Dynamic object selection by pixel nudging and zooming
{% hint style="warning" %}
Nudging is part of visual object tracking and requires Auterion tracking-service app to work.
{% endhint %}
{% hint style="danger" %}
Pixel nudging and zooming fully supports only Mode 2 RC transmitters. Support for other modes is experimental and can me configured via `TS_NUD_CFG` parameter.
{% endhint %}
Pixel nudging and zooming allows the pilot to manually select a target for tracking using the RC transmitter sticks. In particular, once MC-Follow mode is engaged and visual object tracking is active, the pilot can move the tracking window up-down and left-right using RC transmitter left stick horizontal (yaw) and vertical (throttle) axes (Mode 2). Zooming in and out is can be achieved using horizontal axis of the right stick (roll).
In case of poor RC calibration (sticks mid-point drift), the nudging may cause unintentional drift of video tracker. In such cases, the nudging dead-band should be increased using `TS_NUD_STK_THR` tracking-service parameter.
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