#IRSignalTransmission

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Additional features of twisted-pair HDMI extenders: Transmitting the infrared signal

When purchasing a twisted-pair HDMI extender, it is useful to check if it has any additional functions. One of them is the ability to transmit the IR signal. In this article, we will look at the types of IR transmission, and explain what they are needed for and how they are implemented.

Let's look at an example of two extenders: Lenkeng LKV372AE-4.0 and Lenkeng LKV676E (twisted-pair HDMI extenders up to 230 feet)

IR signal pass-back

The Lenkeng LKV372AE-4.0 is a simple twisted-pair HDMI extender that has the additional function of sending the IR signal back. This means that we send an HDMI signal from the transmitter to the receiver (i.e. from the TV tuner to the TV) and we can send an IR signal back (i.e. from the TV to the tuner).

In other words, if your TV tuner is in the living room and you want to watch TV in the bedroom, you need to lay a twisted pair from the tuner to the TV in the bedroom. Then connect an HDMI transmitter to the tuner and a receiver to the TV, as in the diagram above.

Now we need to ensure a comfortable switching of the TV tuner channels. To do this, we additionally connect the IR blaster (included with the extension cord) to the HDMI transmitter and attach it to the TV tuner with the included double-sided adhesive tape. Connect the IR receiver (also included in the package) to the HDMI receiver, and attach it with double-sided tape in a convenient place where we will direct the IR remote control. Usually, this is the frame of your TV set.

Now the video signal will be transmitted over twisted pair from the tuner to the TV, and the IR signal will go back from the TV to the tuner.

And this is the principle of IR signal pass-back.

Bi-directional IR signal transmission

Bi-directional IR transmission can be explained in the example of the Lenkeng LKV676E twisted-pair HDMI extender.

On the body of the transmitter and receiver, you can see two ports to connect the IR: In and Out. Depending on the task we have to use the right input.

If we have already solved the first problem (the IR signal pass-back), then why should we transmit the IR signal from a transmitter to a receiver?

This is more used in commercial applications, e.g. the TV is in the lounge in the cafe, and the TV set is somewhere at the bartender's workplace. The bartender wants to turn off the TV, or switch the input source without going close to the TV set. So with the feature, we are kind of extending the IR remote control signal of the TV over a long distance.

In this way, we get a more versatile transmission of the IR signal in both directions. This does not mean that you have to buy a device with a bi-directional IR signal function. Just think if this scenario is required or not.

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Review twisted pair HDMI extender Lenkeng LKV375N

We had another twisted-pair HDMI extender up to 230 feet for testing - Lenkeng LKV375N. This is an inexpensive extender that works on HDBaseT technology. This means it is interchangeable with equipment from other manufacturers that work on the same chips

Main Features

The Lenkeng LKV375N is a ready-to-use kit for transmitting HDMI signals with up to 4K@30Hz resolution over a twisted pair at a distance of up to 230 feet. Additional features include additional IR signal transmission in both directions.

External view

The set is packaged in a gray package. Such packaging is found in almost all professional devices. This emphasizes that "wrapping doesn’t matter, but the content does".

If you open the box, you will immediately see the transmitter, receiver, and instructions. The rest of the accessories (power supply unit, IR transmitter, and IR receiver) are located under the black blister.

The transmitter and receiver are of average size for such devices and are made of quality metal.

There are a lot of vents in the housing of the devices, which seem to hint at increased heat dissipation. We will test this during the testing. There are also threaded holes on the sides of the housing. They may be used for additional mounting ears which we did not find in the kit. Moreover, there is not a single word about it in the manual. Still, we consider it to be a useful feature for fastening the box to various surfaces.

The kit also includes an IR transmitter and an IR receiver for remote control of either a display device or a video source. Remember that the kit has two-way transmission of the IR signal. Of the disadvantages, note that the double-sided adhesive tape is supplied separately and not already glued to its seats. But this is not a significant drawback.

After removing the cover, we found a rather large radiator on the main chip. Now it is clear why there are so many holes in the housing – they provide for better heat dissipation. You can also note the slightly skewed adhesion of the radiator to the chip. This does not affect its capabilities but should be noted as a fact.

Otherwise, there is no question about the quality of soldering - all is neat and high quality.

Performance testing

When connecting we use our test cable twisted pair CAT6 230 feet. Initially, we feed the image at 1080p at 60Hz. The set is up and running. The video was transmitted with no visible delay and no degradation in quality.

As the next step, we decided to test the claimed 4K video transmission at 30 Hz at a distance of 115 feet, which the manufacturer claims in the manual. Initially, we purposely set the frequency to 60 Hz. As expected, the video did not transfer. When we changed the frequency to 30 Hz it worked. There is not enough bandwidth to transmit more frames.

Conclusion

At first glance, the tested set showed the usual results, as the declared characteristics were shown during the test. But mind one significant thing - the price. The transmitter and receiver kit is cheaper than many other manufacturers' HDBaseT transmitters or receivers sold separately. If it's the transmitter and receiver kit you need, it would be a good choice in terms of price.