Replacing antennas on a wireless remote transmitter and receiver.

[ROV2022]

Good evening all, I hope this is the right place for my question(s).

To give a bit of context, I have an old military remotely operated vehicle which I am hoping to restore the basic functions of. The original electronics were completely beyond any use and had been bodged and mated with all sorts of controllers over the past 30 years and no longer worked at all. Having spoken to someone else who has undertaken such a task, they recommended that many of the functions can be controlled using one of these (image also attached to this post): DC 12V 15 Channel Relay Wireless Remote Controller Switch Transmitter + Receiver Board 10A for Large Power Appliances : Amazon.co.uk: Electronics & Photo

My knowledge of radio communication and the relationship between frequency and antenna type/length etc is fairly limited, so I was hoping to seek some clarification before I start removing the original antennas on both the transmitter and receiver and soldering on coax, different antennas etc. According to the specs on the amazon page, the receiver and transmitter is described as having: "Operating Frequency: 315 (Optional From 315 To 433MHz)".

1. When it is described as Operating Frequency: 315 (optional from 315 to 433MHz)" does this mean the frequency is anywhere between between these parameters as standard or is this something that can be changed by modifying the length of the already fitted coil antenna on the receiver?

2. I plan to extend the receiver antenna to be outside the main chassis of the ROV and utilize one of the unused external BNC fittings which are already present, to this I plan on attaching a 315MHz helical whip antenna. Would this be as simple as removing the existing coiled wire antenna, and soldering in a length of coax to bridge the gap between the receiver and the new antenna fitted externally to the vehicle?

3. I also intend to do something similar to Question 2 with the remote transmitter, and contain the remote in a more durable housing with a better antenna than the cheap telescopic one fitted. Could this also be achieved by using coax to connect to a more durable antenna with the same frequency of the receiver antenna?

I look forward to any comments or help that can be provided.

Regards,

Dan

 

[RFI-EMI-GUY]

It appears that the device normally ships on 315 MHz band with option for 433 MHz. Depending upon where you live on the planet the legality of 315, 433, or even 868 MHz for such an unlicensed device applies.

From the picture, it appears that a small board plugs into a vertical header at the bottom of the main receiver board. A helical coil of wire serves as the antenna.

In practice you would verify the frequency of operation by inspecting the receiver for markings or the chip part number. Obtain a 1/4 wave antenna cut to the operating frequency (about 9 inches at 315 MHz) and solder the center conductor to the point where the helical coil of wire now resides (after removal.) The outer conductor of the coax should be soldered to the nearest ground point on the receiver.

For the transmitter it would be same process. Bear in mind the parameters of these devices, while generally 50 ohms impedance, don't guarantee that a "better antenna" will yield better performance. I would experiment with the thought of putting it all back as normal and perhaps installing the entire receiver unit in a plastic box on the exterior of the vehicle.

Whatever you do, bear in mind that a loss of signal might be dangerous . I have no idea if this "military vehicle" is a bomb robot or Humvee.

 

[ROV2022]

Thanks very much for your response,

I'm located in the UK, so as far as I am aware from checking Ofcom, 433 MHz is what I am able to use legally. Despite quite a few UK retailers offering similar transmitters and receivers which operate on 315 MHz. I just need to work our how to switch this one to 433MHz if it isn't already there and adjust accordingly.

I'm currently away from my workshop at the moment so I can't check the part number on the receiver until later on in the week, although that will be the first thing I do when I get the opportunity as that really determines on how I'm going to progress further.

The plan to do this really came about with making the end product look as close to original as possible, and utilizing some of the existing fittings as there are two BNC fittings already attached externally for the original receiver. I just made the assumption it might be worth trying to use these given that the main board and receiver I intend to use was going to be housed internal to what is essentially a metal box.

I also plan on carrying out some tests on how the transmitter, receiver and the attached relays behave when there is a loss of signal. The manner in which the relays function should mean that they open the circuit when there's a loss of signal, thus stopping the flow of current. It's only for a small bomb robot which travels at walking pace, so it won't be smashing through walls or running people over!

 

[RFI-EMI-GUY]

Usually their is a pair of encoder or decoder chips that are separate from the transmitter and receiver which modulate and demodulate serial data that the TX and RX convey. A sort of UART device. If you can look up those chips, you might find them suitable to modulate a more powerful radio link. I would start with the chip on the receiver relay board that follows the socket where the actual receiver plugs in.

 

[RFI-EMI-GUY]

You might want to do some research here....

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