Carrier Current Sanity Check

PhilB · 2012-12-02T08:24:33Z

Lately, there seems to be a resurgence of interest in Carrier Current transmission. This is a technology that goes back to the 1940s. There seems to be perception that Carrier Current offers a way to achieve a much wider coverage area within the confines of the Part 15 rules. In the heyday of Carrier Current (1950s - 1970s), it was widely used on college campuses. A typical configuration involved distribution of RF from a central source over coax lines to individual amplifiers located in each building. The output of the amplifiers was then coupled into the power wiring in each building. It was well known that the signal would not go much beyond each building due to blocking by the AC power distribution transformer, but was very strong within the building. More often than not, the signal had an annoyingly high level of AC hum, but that was generally tolerated because the concept of actually having a college radio station was more important. Subsequently, AM carrier current was replaced with an FM transmitter and/or by on-campus distribution over TV cable. Until recently, there were only two remaining manufacturers of carrier current equipment in the US: LPB Communications and Radio Systems Inc. Since LPB has stopped sales, Radio Systems is the only one left. Obviously demand has waned. A Google search for Carrier Current doesn't turn up any information that supports the idea that a wonderful new expanded coverage area is actually achievable. In fact, documents from LPB that still linger on the web specifically state that reception beyond the AC distribution transformer falls off greatly and coverage of more than one campus building from a single injection point is unlikely. The present-day scenario for Part 15 carrier current mainly focuses on the transmitter being located in a single home served by an AC distribution transformer which also serves a small cluster of maybe 10 to 15 other nearby homes. The transformer blocks the signal beyond those homes, so coverage is limited to those homes at best. A 5 to 10 watt transmitter is required to overcome the extreme losses encountered in the AC wiring. Often, it is mentioned optimistically that the power company may have RF bypass devices across the transformers that would allow the signal to propagate over a wider area. These are called "CT Couplers", www.narucmeetings.org/Presentations/current-telecom0704.pdf, and are part of the Access BPL (Broadband over Power Line) system. BPL has been deployed in a limited number of areas for test, has proven to cause RF interference, and in many cases has been taken out of service. It is not likely to continue into widespread deployment. So, this new interest in Carrier Current doesn't seem to make much sense. Of course, it has been proven to work within its known constraints, but it doesn't sensibly offer expanded range relative to a good single Part 15.219 transmitter installation. In fact, given the typical single-home scenario, it seems to offer a smaller or, at best, equivalent range.

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i have discovered 15.221 wont work here. neutrals, cold water and ground are all tied together at service entry. the neutrals on the main grid here are also broken up and not tied together. i am about 10ft above ground over a parking garage so independent ground is useless here. too much ground lead radiation would result. so i can not tried cold water pipe distribution either.

Posted : 04/12/2012 12:54 pm

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