Review of a DVI KVM fiber optic extender

In this article we review a DVI KVM fiber optic extender.

It is a device, composed of multiple parts, that provides a fiber optic link for carrying the DVI (Digital Video Interface) from the computer to the monitor, and also provides a KVM channel (Keyboard Video Mouse) which means that it transfers the signals of the keyboard and the mouse to the computer and back.

Having a pure fiber optic link separates electrically the monitor from the computer, so if the monitor is powered with smooth DC voltage with no electromagnetic noise, there will be less EM noise from the monitor.

Also the fiber optic cable doesn't emit any electromagnetic radiation at all, which is always better than a copper based video cable, which contains dozens of copper wires and carries voltages and currents at high frequencies, which certainly do emit some EM radiation in the surrounding, even if the cable is shielded.

Another advantage of this system is that the cable can be very, very long, up to many kilometers long. Of course we are interested in having a low EMF office with the computer in the same house or office, but anyway this products allows us to move the computer literally anyway in the house or office, with the fiber optic cable of the needed length.

The device is composed of a transmitter (TX) and a receiver (RX). The transmitter is supposed to be close to the computer, and connected to the computer with a generic DVI cable of limited length. The receiver is supposed to be on the desk not too far from the monitor.

Actually for our purpose of having less electromagnetic radiation around the desk, the DVI cable that connects the monitor to the receiver should be as short as possible, and of the maximum shielding possible. For example this short cable could be just 50 cm long.

This particular product supports at most digital video with the screen resolution of 1920x1080 pixels at the refresh frequency 60 Hz. This is certainly not the maximum screen resolution available today, but it is enough for a good picture quality, for normal office work, and also for watching Full HD videos full screen with a good rendering quality.

This product contains also a KVM system for a wired USB keyboard and a wired USB mouse. The two USB ports on the receiver box can't be used for other USB devices. So this product doesn't provide a full USB channel between the receiver and the transmitter. These are some of the things we can't do with this product:

Having a full USB channel between the desk and the computer is certainly useful, but not always essential.

This product provides also an audio output channel, which means a unidirectional channel for the audio signal produced by the computer and directed to the desk. We can connect a speakers set with audio jack to the audio socket of the receiver, we can connect a pair of headphones with audio jack, or a pair of ear plugs.

Of course, since the analog audio signal is generated inside the receiver box, which also contains digital video converters, it carries quite a lot of electromagnetic noise, so it is better to use a air-tube set for listening directly to this audio source with ear plugs. If instead we prefer a speakers set, it is better to use speakers that are very small and use very little power.

Both the receiver and the transmitter need a 5 V DC power source. At the computer side this could be provided by the original power adapter of the product, if the computer is far enough from us, in order to avoid the EMF generated by the switching mode power adapter. The power required by the transmitter device may be too high for a standard USB port of the computer so we can't use the 5V DC power of a USB port. At the receiver side instead we must use a linear power supply in order to have less electromagnetic noise and radiation.

The fiber optic cable required by this device is a standard single mode, single strand, fiber optic cable with standard SC connectors. Such cables have to be assembled on purpose, with the desired length. However cables of this type can be found from many online shops which make them at some fixed lengths, like 10 m, 15 m, 20 m, etc.... or can make them on request. The cost of these cables is relatively low.

A fiber optic cable of this type with length of 20 m typically costs around 35 USD. We suppose that this costs includes the cost of the work for cutting the cable, attaching the connectors, and testing the cable with professional instruments for fiber optic cables.

Fiber optic cables like this can be installed on walls by means of PVC guides. The cable can be bent in curves with a small enough radius to follow the corners of a room. We have to be careful in making the cable pass always far from sources of heat because that could damage the cable irreversibly. As the fiber optic cable is totally insensitive to electric and magnetic fields, and it doesn't create an electric or a magnetic field on its own, these cables can be placed close to electric cables of the mains network.

The receiver box and the transmitter box have the same shape and size which is just 127 mm long, 90 mm deep and 27 mm tall.

The exterior of these boxes is made of a metal alloy, so it stops most of the electromagnetic radiation of high frequency that is generated inside by the electronics. There could be a problem with the long sides of the box which could be just made of plastic.

During our test we didn't notice any strong high-frequency EMF from these boxes so probably the boxes are completely closed.

The product is sold with a 3m cable for testing it.

There is also another version of this product which doesn't have the KVM channel and costs a little less, but we think that having the KVM is useful afterall, even if it's not a full USB channel.

There is also another product of this kind but with HDMI ports instead of DVI, and without the audio connector, because HDMI carries also digital audio from the computer to the monitor, but we think that the DVI connector is better than the HDMI connector in terms of reducing the leakage of EM radiation. Furthermore our current modified monitor for having less EMF has a DVI connector so we can connect it directly to the DVI connector of the receiver with a short cable with DVI male connector at both ends.

As for the compatibility with computers and monitors, this product seems to have the EDID system which transmits the parameters of the monitor back to the computer, so the computer can select the corresponding mode of the graphic card.

However in our test the video output wasn't accepted by some of our monitors.

This is a serious limitation which means that we can't recommend this product.

Distributors and prices

We initially received a hint from a person about an offer of this product on AliExpress.

We tried to contact the vendor through AliExpress to get more information, but the vendor's answers were quite unsatisfying. Also we never bought anything from AliExpress before so we weren't accustomed with the site.

So we looked for similar products on Ebay and we found the exact same product from three different vendors, all from China. We contacted all of them through Ebay, but only one answered to our messages so we decided to go on with this vendor, which was also one with the lowest price.

This vendor is currently listed on Ebay with the code name tom94520181. The vendor is actually the company Primeda Telecom with office headquarters in Shentzen, Guandgong, (like thousands of other Chinese companies). Their website is www.primeda-telecom.com.

The price of this product was about 160 USD. The shipping was free, but the free shipping from China was very slow. So we asked for a faster shipping option, which required a cost of shipping of 25 USD, which is totally acceptable for a parcel travelling from Shentzen to Italy.

We also asked whether they could provide us with the fiber optic cable too, and they could, and they set up an Ebay item for a complete cable, 20 m long, of the needed type and with the needed connectors.

So the summary of our order was:

DVI extender set with KVM161.25 USD
20 m fiber optic single mode SC35.00 USD
total without shipping196.25 USD
shipping with fast service25.00 USD
total221.25 USD

Unfortunately when the parcel is brought to the first Italian office of the shipping company, they stop it and require the payment of VAT taxes and other customs duties. Anyway the total cost of this system is still reasonable.

Comparison with other fiber optic video cables

As we know there are several other fiber optic video cables in the market. We only consider the pure fiber optic and discard the hybrid cables because the latter do not provide complete electrical isolation and still have some EMF.

However the pure optic HDMI cables have generally higher prices, and also their price grows quickly with the increase of the length of the cable.

Instead with this system we can easily replace the cable with a much longer one at a small cost.

Comparison with other fiber optic KVM extenders

There are also a few complete KVM extenders that work on standard fiber optic cables, and provide digital video, keyboard, mouse and also full USB channel, but they are in the price range of 1500 - 2000 USD.

There is no intrinsic reason why these product should be so expensive, the only cause is that these are not products for the masses, and are used only by some industries in a few special situations.

These high level products provide also the complete USB channel, usually an USB 2.0 version, which allows the user to do many other things, but the price is too high to let these products be included in our low EMF office project, especially if we consider that we are not totally sure that these devices would be really EMF free, because of the emissions from the receiver box, and its power adapter, which we have to discard anyway.

Conclusion

This product is evidently incomplete, as it doesn't have the USB channel, even a modest USB 1.1 version, but the price and the other features would make it a possible product for our low EMF office project.

Unfortunately the product is not compatible with all monitors.

Other products from the same vendor

The same company also offers some USB fiber optic extenders, which do provide a complete USB channel, the cost is not negligible, but maybe buying the DVI extender and the USB extender together, with the needed fiber optic cables too, wouldn't be too expensive, and certainly it would be much less expensive than the special products that cost over a thousand dollars. In our next article we'll probably review the USB fiber optic extender available from this same vendor.