The AMT5000 from sstran.com has all the high end features, including a power control for setting the final RF amplifier stage to an exact 100mW.
For fun, during early hours before the official broadcast day begins, I like to set the power input to the final RF amplifier down to minimum, which I’m guessing comes to about 40mW.
I could do the math using the simple formula provided in the Manual, but maybe tomorrow.
Prior to starting the internet stream and going to AM full power, we sometimes air the Alex Jones Show to get some idea how dire things are in the world, and this program comes in just over the morning skip from WPRR in Grand Rapids, Michigan, or KRJO in Monroe, Louisiana.
My radio is 36-feet from the transmitter, and if anyone else is receiving the broadcast they’d have to be within a hundred feet. Very private.
Private Material
By my own policy some material is not to be shared over the air. I use my FM transmitter to broadcast the audio when I view movies so I can use my Walkman with headphones. Knowing that there is potty talk in many movies I shorten the whip antenna so the signal is only heard about 10 feet from the transmitter with the intent that someone scanning the dial won’t hear it. It doesn’t seem to me to be a good idea for such material to be heard by neighbors via my signal since it can bring unwanted negative attention.
Lowering the transmitted signal level doesn’t guarantee they won’t hear it but it makes it very unlikely. I would use a hard wire for the phones but I like the mobility with the wireless setup.
Hear No Evil, See No Evil…
Then there are the IR headphones that use infra red light to transmit to the headphones.
Way To Do It
I use the C.Crane FM transmitter with it’s dinky whip for the same privacy when watching videos on Hulu. Of course there’s every chance the neighbors are watching movies on cable or DVD which contain X-rated words, but hearing on the radio still seems different somehow, and not as acceptable.
With Alex Jones, I don’t have permission to stream his show and so can only listen on part 15, and there’s no real reason to run it at minimum power, it’s just fun.
The Wind Was Quiet
Once a month I get up at 3 AM and do projects.
This morning I mapped out a chart showing power ranges for the carrier current transmitter from 100mW up to 10-Watts.
Then I started testing the transmitter at the different power levels and starting a collection of readings, including the peaks shown on the spectrum analyzer.
The lowest power adjustment is done by listening to an AM radio tuned to the frequency, then bringing power up just a tad until the first trace of a signal covers the noise. I call this setting “100mW” because it’s too low on the power meter to be observable as 1/10th of a Watt. At this low setting I see 35dBm on the spectrum analyzer, compared to 70dBm at 10-Watts.
On the TECSUN PL-310 radio’s field strength meter we observe 63/25, as compared to 94/25 at 10-Watts, with the radio at the World Desk in the front of the Internet Building.
For listening, this signal is very local, since every power pole outdoors reduces the signal as it travels down the electric line. A few buildings down the way it would be some feat for anyone to receive the 100mW carrier current signal.
By 7 AM it is realized how ridiculous it is, and it’s time for a nap.