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The nickel tour continued...

Inside Look at Transmitter
A closer look at the transmitter. Yes, it's the famous 3-transistor bug your mother warned you about. When I built this in 1993 there was no internet to consult for technical knowledge, and yet it's served me well for a decade. The secret to keeping the frequency tolerance to ±10kHz are the two variable compression capacitors (arrows) trimming the oscillator tank and output. Tuning adjustments as delicate as ±1kHz can be made with these trimmers. Output is 2.5 Vrms, which delivers about 100 milliwatts to the antenna.

Radio Shack Frequency Counter
Because I didn't have AFC on this old transmitter, it was critical to monitor the oscillator's stability. Here is my hand-held Radio Shack frequency counter (no longer available) that helped me to stay somewhat in-channel. It cannot be coupled directly to the transmitter, so I had to find hot spots near it or under the antenna with enough signal strength to trigger a reading. The display in this picture shows I'm in a spot that produced a semi-accurate reading, so it's helpful to corroborate your measurement with a digital FM receiver.

Rooftop Antenna
Here is the antenna, where the signal ultimately lives or dies. It's a J-pole design, about 14.5 feet of 14-gauge wire wrapped lengthwise around a ten-foot section of 2" PVC pipe, secured by plastic wire ties. The connector is in a plastic electrical box stuffed with fiberglass insulation to keep rain from shorting it out. The whole thing's mounted on a coupling to the plumbing line on the roof and guyed low on the four sides. The low-angled guy wires prevent distortion of the radiation pattern. Of course, the tree isn't the best thing for the signal either, but at least it's at some distance. For a more complete description of the design, see Marconi's excellent page on the subject. From its height and 2.5dBi gain, I can obtain a quiet, usable stereo signal with a good receiver at my workplace a mile away.

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The nickel tour continued...
	A closer look at the transmitter. Yes, it's the famous 3-transistor bug your mother warned you about. When I built this in 1993 there was no internet to consult for technical knowledge, and yet it's served me well for a decade. The secret to keeping the frequency tolerance to ±10kHz are the two variable compression capacitors (arrows) trimming the oscillator tank and output. Tuning adjustments as delicate as ±1kHz can be made with these trimmers. Output is 2.5 Vrms, which delivers about 100 milliwatts to the antenna.
	Because I didn't have AFC on this old transmitter, it was critical to monitor the oscillator's stability. Here is my hand-held Radio Shack frequency counter (no longer available) that helped me to stay somewhat in-channel. It cannot be coupled directly to the transmitter, so I had to find hot spots near it or under the antenna with enough signal strength to trigger a reading. The display in this picture shows I'm in a spot that produced a semi-accurate reading, so it's helpful to corroborate your measurement with a digital FM receiver.

	Here is the antenna, where the signal ultimately lives or dies. It's a J-pole design, about 14.5 feet of 14-gauge wire wrapped lengthwise around a ten-foot section of 2" PVC pipe, secured by plastic wire ties. The connector is in a plastic electrical box stuffed with fiberglass insulation to keep rain from shorting it out. The whole thing's mounted on a coupling to the plumbing line on the roof and guyed low on the four sides. The low-angled guy wires prevent distortion of the radiation pattern. Of course, the tree isn't the best thing for the signal either, but at least it's at some distance. For a more complete description of the design, see Marconi's excellent page on the subject. From its height and 2.5dBi gain, I can obtain a quiet, usable stereo signal with a good receiver at my workplace a mile away.
	More...