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While some might have started this process with building light controllers (or sequencing songs, or even picking out songs), here at PacificaLights we went with getting the radio transmitter set up first. In part, it was because it solved an everyday problem as well: it gave us a stereo system that worked throughout the house. The Federal Communications Commission allows for private individuals to broadcast low-power FM signals inside their own homes. What I’ve done here is to just boost up the signal a bit (actually, I attenuated it down) so that it can reach car radios on Grand Teton Drive. 
After searching in January and February 2007 for a good, inexpensive transmitter, I found that those two features are somewhat mutually exclusive. There are plenty of inexpensive ones and plenty of good ones, but not so many that have both.I knew I wanted a phased-lock loop (PLL) transmitter; a PLL is a highly stable electronic circuit that gives radio transmitters accurate, drift-free tuning. Some of the folks over at DIYC had been buying transmitters from China, and while some had poor luck with the results, others had been successful. One of the DIYC fellows took it upon himself to buy a handful of Vastelec one-watt transmitters on eBay and get a combined shipping price. After he had received the devices, he then resold them on a one-by-one basis, passing along the savings. There had been a number of people who had been burned using the .5-watt and .2-watt Vastelecs, so I thought I'd give the one-watter a try (at the time I was unaware of that the device might be considered by the FCC to be illegal). When I received the boards, I found the whole thing to be much smaller than I had anticipated and realized that I could fit it into an old SCSI enclosure, which had the added benefit of a good power supply. I had pulled the hard drive out of the enclosure years ago and hung onto it because I have trouble throwing anything away. 
My next task was to build an antenna. I bought a 25-foot RG-58 coax cable with BNC connectors at Radio Shack and built a di-pole antenna using 87.9 as my frequency.I determined this by visiting http://www.radio-locator.com/cgi-bin/vacant and entering my Zip code; 87.9 was deemed ”Best!“ by that database (it should be noted that when tuning an FM receiver in the car, the first commercial station that can be heard clearly on the FM dial is at 88.9). Then I used the dipole calculator at RadioBrandy.com to measure the length the wire. I did not use that page’s techniques; I merely soldered two pieces of 12-gauge, multi-strand copper wire to a female BNC connector. At this point I mounted the dipole on the wall of my basement office, starting the bottom lead about six inches from the floor and stapling the wire up the wall to almost the ceiling. My office is about four feet below grade on the street side of the house and at grade on the back-yard side of the house (which is on the downward slope of a hill). With this installation, I could easily tune in the broadcasts from 800-1000 feet away from the house, the further on the back-yard side of the house, the nearer on the street side. Though I had read a number of articles about FCC Part 15, I wasn’t clear on the concept that 200 feet was the furthest you should be able to receive a signal to comply with the regulations (and I realize that 200 feet is just a rule-of-thumb, and that actually complying requires a signal-strength meter, which I – and I assume most of us – do not have). A number of postings on various DIY Christmas forums made it clear that the 1-watt Vastelec straight out of the box would not meet the regulations.  (There were also postings about ”spurs“ from these transmitters, messing up other frequencies. I have not encountered this problem; I have driven all over the neighborhood in my 2004 car and searched all available frequencies, listening for spurs and haven’t found them. This may only be because the transmitter is situated below grade and is mounted in an all-metal enclosure.)A number of people had dismissed the problem of the over-powered Vastelec transmitter, suggesting that an attenuator could be installed between the transmitter and the antenna, which would cut back on the transmission range. I posted on another board, asking if anybody had an idea of what kind of attenuator to purchase. I was pointed to what turned out to be a 20db RF attenuator (FP-50 Trilithic), which I purchased for $20, including postage, on eBay. After the attenuator arrived and I installed it on the antenna end of the system, I did tests that indicate that it (coupled with the below-grade location of the di-pole) serve the purpose: you can’t hear the transmitter further than abut 200 feet from the house. Probably your next stop on the PacificaLights technical story should be the DMX transmitter. |