Monday, December 23, 2013

FM Radio Station Part 4 Broadcasting

THE VOICE OF SCIENCE NOW BROADCASTING... Connected to a 9-volt battery, this is the first power on of the radio station. We're on the air, with an antenna so tiny, it's merely broadcasting to the other side of the table. This is the first successful test of the FM radio station with "across room range." There's always excitement when a "just built" project is switched on for the first time. It's always hoped that it works perfect the first time. Building projects is like a crap shoot - there's any number of things that can go wrong as Murphy's law dictates. In the case of projects, components often have a 10% failure rate and can cause some frustration in troubleshooting newly assembled projects. One can take a gamble and assemble the parts untested, or test each part for greater workability insurance. With this project, the radio station worked perfect the first time!
FM RADIO STATION transmitter broadcasting part 4
We're broadcasting into space! Who is listening?

This is the fourth installment about building your own radio station. On Monday December 23, two days before Christmas, at 10:00 pm, the radio station was turned on for the first time. A nearby FM radio was scanned across several transmitter harmonics, then settled onto the strongest signal. It's a success! "Testing, testing, 1, 2, 3..." came in loud and clear on the small portable radio tuned to the FM band.

The transmitter's coil was slightly adjusted to push the signal farther up the FM band to avoid several very strong radio stations around 98 to 100 MHz. The perfect test place was quiet at 101 and 102 MHz.

For initial testing, a tiny loop antenna is used which extends only about 3-inches high in the long direction when elliptical and is about 1.5-inches diameter when circular, perfect for across-room broadcasting.

The sensitivity is capable of overloading acoustical feedback and distance of the audible source to the mic is also sensitive. The orientation of the transmitter greatly effects reception and keeping it in one place is required. Hands near certain areas of the transmitter effect frequency and harmonics, although the portable FM receiver is ultra sensitive - a 10 band FM/MW/SW World Receiver model 6110 by Panda made in China. Its FM band ranges from 76 to 108 MHz with manual tuning and running from 3-volts. This radio was used for reception of objects in space such as the planet Jupiter and the Earth's Sun during the Lab's SETI program searching for extraterrestrial intelligence.

Radio Telescope Receiver

Don't Eat Us Safety Program Radio Telescope

Radio Telescope Adds Spaceweather Radio

Radio Telescope Observatory Lab 58

The FM band in this region of the country, serving up to 24 million people, contains strong stations in almost every position on the band from 76 to 108 MHz. Smaller stations serve a six million locality. Therefore the density of stations is unprecedented. Many of these stations may be underground as the government is working to license and annex these broadcast stations.

A weak station, or even one that has associated harmonics, will be lost in the signal hash, thus limiting the range.

The unexpected high quality of the FM transmitter is very good when trimmed and tuned. Voice is very audible close to the microphone. Backgrounds sound muted as desired although this requires more sensitive testing.

The high quality of such a simple circuit is attributed to the high quality of the parts used, i.e. the special am/fm, rf, amp, mix, conv, osc and IF ability of the 2SC1675 transistor, and the 1-watt output amplifier of radios in class B push-pull operations ability of the 2SC9013 transistor.

FM Radio Station Part 5 Index