Can I Convert HDMI to HDMI via an Old Coax Cable and Utilize HDMI ARC?

Many homeowners are faced with the challenge of updating their home entertainment systems with modern TVs that require HDMI connectivity. Unfortunately, in many cases, the old coaxial (coax) cable installations left in houses from the 1970s and 1980s do not support such high-bandwidth connections. A common question arises: can an old coax cable, previously used for television and radio signals, be repurposed for HDMI signals, particularly to support the HDMI Audio Return Channel (ARC) feature?

Finding the Solution

The short answer is that it is possible, but the chances are slim. To understand why, let's break down the potential solutions and their limitations.

1. Direct Conversion

Directly converting an HDMI signal to coax and back to HDMI is complicated due to the fundamental nature of the signal types. HDMI is designed for a bidirectional flow of data, including video and digital audio, while coax cable is unidirectional and designed for analog signals. Therefore, a direct conversion would require specialized hardware that can handle the bidirectional nature of HDMI, which is not widely available and can be expensive.

2. Ethernet to Coax Conversion

One approach to leveraging an old coax cable is to convert it into an Ethernet backbone using a protocol like MoCA (Multi-channel Serial Data Over Cable). MoCA is designed to provide Internet connectivity over coaxial cables, effectively turning an old coax cable into a high-speed Ethernet cable. However, even with MoCA, the HDMI signal needs to be converted to Ethernet and back to HDMI, which leads to the next section.

3. HDMI to Ethernet Adapter

Using an HDMI to Ethernet adapter with HDMI ARC support can solve part of the problem. These adapters allow an HDMI signal to be transmitted over Ethernet cabling, which can then be transferred back to HDMI. The key limitation is that the coax cable must be recent enough to handle the required bandwidth for HDMI signals.

Practical Considerations

While the idea of repurposing an old coax cable for modern HDMI signals is intriguing, several practical considerations should be taken into account:

1. Coax Cable Performance

The age and quality of the coax cable play a critical role in the success of this setup. Older coax cables may not be able to handle the bandwidth required for modern HDMI signals. Newer coax cables, specifically those designed for data transmission, such as those used for cable Internet, are more likely to support the necessary bandwidth.

2. Cost and Feasibility

The cost of the necessary equipment, including specialized converters and potential cable upgrades, can be high. Additionally, professional installation may be required, adding to the overall cost. The likelihood of this setup working, especially for a DIY project, is less than one in a hundred.

3. HDMI ARC Function

The HDMI Audio Return Channel (ARC) feature allows for the automatic transmission of audio from the television to the sound system. While ARC is typically supported over Ethernet in modern setups, the conversion back to HDMI and the quality of the audio transmission may not be ideal if the coax cable and associated hardware are not up to the task.

Alternatives

Given the limitations of repurposing an old coax cable for modern HDMI purposes, several alternative solutions are available:

1. Cable Replacement

The most straightforward and reliable solution is to replace the old coax cable with a new cable that is specifically designed for data transmission. These cables are typically more resilient and can support the required bandwidth for modern HDMI signals.

2. Combination Cabling

A hybrid approach could involve using an old coax cable for video and a separate Ethernet cable for audio. This setup would require the use of a MoCA adapter to convert the coax signal to Ethernet for the sound system, ensuring both video and audio functionalities are supported.

While the idea of repurposing old coax cable for HDMI signals is appealing, the challenges and limitations make it a less practical solution. For a reliable and high-quality home entertainment system, it is generally recommended to invest in modern cabling and equipment that can support the required bandwidth for HDMI and HDMI ARC.