Analog PTZ Camera: RS485 vs Control Over Coax
An analog PTZ camera receives its pan, tilt and zoom commands from the DVR in one of two ways: over a separate two-wire RS485 pair, or over the same coax cable that carries the video. With RS485, the protocol, address and baud rate set on the camera must match the DVR channel exactly. With control over coax, there are no extra wires, but both the camera and the DVR must support coax control for the video format you are using. Check which method your camera and recorder support before you run any cable.
This article is about cameras that plug into a DVR's BNC inputs. Yoosee PTZ cameras are generally network cameras that you move from the app or from a recorder over the network, which works differently; if that is your setup, see how to control a PTZ camera from an NVR instead.
Why video and movement travel separately on analog systems
On an analog system, the coax cable was originally designed to carry one thing: video, from the camera to the recorder. Movement commands have to go the other way, from the DVR to the camera, and older systems simply added a second, thin cable for that job. That cable is the RS485 pair.
Newer high-definition analog formats added a way to send small amounts of data back up the coax, so the DVR can talk to the camera without extra wiring. This is usually called control over coax, or "up the coax". On many DVRs, the same link is used to open the camera's on-screen menu or switch its output format.
The practical consequence: a perfect picture on the DVR tells you nothing about whether the camera will move. Video can be fine while the control path is wrong, missing or set to the wrong values.
Step 1: find out which method your camera supports
Before you look at any menus, look at the camera itself.
- Check the cable tail. Most analog PTZ cameras and speed domes come with a bundle of short leads. A BNC plug is video and a barrel or two-wire lead is power. If there is an additional pair of thin wires, often labelled 485+ and 485-, or A and B, or marked with two colours described in the manual, the camera supports RS485.
- Read the label and manual. Look for words such as "RS485", "coaxial control", "UTC" or "coax PTZ". Many cameras support both; some support only one.
- Note the video format. The manual or a switch on the tail will tell you whether the camera outputs TVI, AHD, CVI or standard definition. Coax control is tied to the format, so you need to know which one you are using.
- Check for address switches. Many RS485 cameras have small DIP switches under a cover, or set the address in the on-screen menu. If you can find a setting called "address" or "ID", note its current value.
If you are not sure whether your camera is a true PTZ or a fast dome with optical zoom, our guide to what a speed dome camera is explains the difference and how to read a listing.
Step 2: find out which method your DVR supports
Now look at the recorder.
- Look at the rear panel. A DVR that supports RS485 usually has a small screw terminal block labelled RS485, A and B, or plus and minus. No terminal block usually means no RS485 PTZ, although some models put it on an adapter.
- Open the PTZ settings for a channel. On most DVRs this sits under a menu named something like PTZ, PTZ Configuration or Serial Port; menu names vary by model and firmware. Pick the channel the camera is plugged into.
- Read the protocol list. You will see a list of protocol options. If one of them is named "COAX", "UTC", or after a video format, the DVR can send control over coax. The other entries are RS485 protocols.
- Check whether coax control is per format. Some recorders only support coax control on certain formats. If your camera outputs a format the DVR cannot control over coax, you will need RS485 instead.
Once you know what both sides support, choose the method they have in common. If both support coax control on your format, it is the simpler route. If they share only RS485, plan to run the extra pair.
Step 3: set up control over coax
If you are using coax control, the wiring is already done: the video cable is the control cable.
- Confirm the picture is stable first. If the DVR shows no picture, a rolling image or black and white, fix the format mismatch before anything else. Our guide to fixing a TVI camera with no picture on the DVR walks through it, and the same logic applies to other analog formats.
- Set the channel's PTZ protocol to the coax option in the PTZ menu.
- Save and open the PTZ control panel for that channel, usually by right-clicking the live view or tapping a PTZ icon.
- Test small moves: a short pan left and right, a short tilt, then zoom in and out.
- Test the menu call-up. Many DVRs open the camera's own menu over coax. If the menu opens but the camera does not move, the camera may not support coax PTZ, only coax menu control.
If nothing happens at all, check that you are not running the video through a device that blocks the return signal. Some video baluns, distribution amplifiers and long or poor-quality cable runs pass the picture well enough but weaken or block the control data. Test with a short, direct cable to rule this out.
Step 4: set up RS485 control
RS485 needs three settings to match between the camera and the DVR channel, plus correct wiring. If any one of them is wrong, the camera simply ignores the commands.
Match the protocol
The DVR's protocol list usually has several options. Set the DVR channel to the protocol your camera's manual names. If the manual lists two, choose one and set the camera to the same one, either with its switches or in its on-screen menu.
Match the address
Each RS485 camera has an address, a number that lets several cameras share one pair of wires. The DVR sends commands to a specific address, and only the camera with that address responds.
- Find the camera's address from its switches, its menu, or the startup screen that some cameras show when powered on.
- Enter the same number as the address for that DVR channel.
- If you have several PTZ cameras on the same RS485 line, give each a different address.
A common mistake is to assume the address equals the channel number. It does not, unless you set it that way. Some installers deliberately match them to keep things tidy, which is a good habit, but the camera does not do it on its own.
Match the baud rate
The baud rate is the speed of the control signal. Common settings include values such as 2400, 4800 and 9600, but the default differs between cameras, so check yours. The camera and the DVR channel must use the same value.
Wire the pair correctly
- Connect A to A and B to B, or plus to plus and minus to minus. Swapping them is the most common reason a correctly configured camera will not move. Labelling is not consistent between makers, so if a correctly configured camera still ignores commands, try swapping the two control wires at one end. Swapping A and B normally does no harm to RS485 equipment, but never connect the control pair to the power leads.
- Use twisted pair cable for the control wires, keeping both wires of the same twisted pair together. A spare pair in a network cable is often used for this.
- Run cameras in a chain, from the DVR to the first camera, then on to the next, rather than in a star of separate branches, where possible.
- Termination: long runs or several cameras may need a termination resistor at the far end of the line. Some cameras have a switch for this. The manual for your model gives the value and position.
After wiring, save the DVR settings and test small moves as in the coax steps.
What each symptom usually means
| Symptom | Likely cause |
|---|---|
| Picture fine, camera does not move at all | Wrong protocol, wrong address, wrong baud rate, swapped A and B, or no control path |
| Camera moves, but the wrong camera moves | Two cameras share the same address, or the DVR channel points at the other camera's address |
| Camera moves in the wrong direction | Image flipped for a ceiling mount, or a mismatched protocol variant |
| Pan and tilt work, zoom does not | Protocol variant mismatch, or the camera has no optical zoom |
| Camera moves only sometimes or jerks | Weak control signal from a long or untwisted cable, missing termination, or a poor power supply |
| Camera menu opens but no movement | Camera supports coax menu control but not coax PTZ; use RS485 |
Presets, patrols and the power supply
Once basic movement works, most DVRs let you save presets, positions the camera can return to, and patrols or tours that move between them. On most analog speed domes the presets are stored inside the camera, so they may survive a DVR swap, but check that the preset numbers still line up.
A PTZ camera usually draws considerably more power than a fixed camera, especially while the motors run with infrared on at night. If the camera resets, loses its presets or stops moving after dark, check the power supply rating against the camera's label. For mounting height, clearance and calibration, see our guide on how to install a PTZ camera.
Safety before you wire
Analog PTZ cameras are often mounted high on walls and poles. Switch off power at the supply before connecting any wires, and work from a stable ladder or platform with someone helping you. If the power supply connects to mains wiring, or the camera needs a new power point, use a qualified electrician.
When to get help
Get help from the seller or a technician if:
- You have checked protocol, address, baud rate and wiring, and the camera still does not respond.
- The DVR has no PTZ menu, no RS485 terminals, and no coax option for your format.
- The camera moves but keeps losing its position or presets.
- The cable runs through walls or roofs you cannot safely access.
Bring the camera model, the DVR model, the video format, and the settings you have tried. That saves a lot of back and forth.
Install or resell cameras?
Most analog PTZ call-backs come from settings that were never written down. A few habits help:
- Decide coax or RS485 before you order, after checking both the camera and the DVR, especially on an existing system you did not install.
- Set addresses and baud rates on the bench, before the camera goes up the pole.
- Run the spare twisted pair anyway on new jobs, even if you plan to use coax control, so you have a fallback.
- Label the cable tail and the DVR channel with the protocol, address and baud rate.
- Test every preset at night as well as by day, when power draw is highest.
If you install or sell cameras for customers, details of the Yoosee dealer program are at business.yoosee.com.
Frequently asked questions
Can I use RS485 and coax control at the same time?
Usually you pick one per channel in the DVR's PTZ menu. Some cameras accept both, but the DVR sends commands by only one method for each channel. Choose the one that works reliably and leave the other unused.
Can I control an analog PTZ camera from my phone?
Often yes, if the DVR has remote viewing set up, its phone app offers PTZ controls, and PTZ already works locally. The app sends commands to the DVR, which passes them to the camera over RS485 or coax. Fix any local control problem first, because remote control will not work better than local.
Do I need a separate keyboard controller?
No, not for basic use. The DVR's own PTZ panel is enough. A joystick keyboard is useful for guard rooms with many PTZ cameras, and it connects to the same RS485 line, so its protocol, address and baud rate must also match.
Why did my PTZ camera stop moving after I replaced the DVR?
The new recorder probably has different default PTZ settings. Set the protocol, address and baud rate on the new DVR channel to match the camera, and check whether the RS485 terminals are labelled the other way round. If you were using coax control, confirm the new DVR supports it for your video format.
Can an IP PTZ camera use RS485?
Some professional models have an RS485 port for special setups, but IP cameras normally receive movement commands over the network. If your camera is a WiFi or network model, set up control through the app or an NVR instead of wiring a serial pair.