INSTALLERS: Mind those cable lengths

If you’re a longtime installer, your experience may be working against you. Any installer worth his (or her) salt knows that long cables mean high loss. A 250 foot run of RG6 is going to give you about 30dB of loss at 2150MHz, which is the high end of the satellite spectrum Even at 550MHz where the connected home (MRV) signal is found, you are looking at about 13dB of loss. That can be the difference between good signal and no signal.

Your experience may tell you that if the signal is -25dBm coming out of the SWM — and it should be — that you can run well in excess of 250 feet because we’ve all seen cases where receivers can still display a good signal with signals lower than -55dBm. The audio and video signal is actually very robust and works at ridiculously low levels.

However, there are two things you may not be considering. First of all, never underestimate the effects of a sunny day. You may get great results when doing the install and then you leave and the customer complains of 771 or 775 errors on the first rainy day. You can’t control rain fade, but by using the shortest possible cable you can keep signals strong when they reach the receiver.

Second, the connected home signal that is used for whole-home (MRV) and also for DIRECTV Residential Experience (DRE) at 550MHz is not as robust as the audio/video signal. Although you have less loss at that frequency, it can have a greater effect. If you start with -25dBm and split out to an 8-way, losing another 14dB, then lose another 13dB over a 250′ run, that puts you at -52dBm which is below the recommended -45dBm threshold for connected home communication. You may find that the customers can’t share programming or the DRE server can’t see the managed receivers.

Making matters worse, none of the commercial amps amplify that 550MHz signal effectively, and those amps that are designed for that bandwidth tend to be OTA antenna amps and can introduce a lot of noise into the satellite signal. The bottom line is that you can amplify in order to get more audio/video, but there’s no amp that will give you more range out of MRV. Remember, it’s not just a matter of one-way amplification like a satellite signal; the MRV signal needs to be amplified going both directions.

It’s a good idea to use a cable calculator like this one, and plan your runs to make sure you avoid long runs and large splitters. For long runs, RG11 cable is a decent choice, but it’s better to relocate SWMs. If this is a commercial install you may be able to do a single run to a neutral location and put the splitter closer to the individual residences with a band stop filter to keep the connected home signal from traveling unnecessarily.