Ham radio is nothing new, however if your new to electronics, or interested in becoming a ham, we suggest reading one of Dan’s self-study guides. [via]
The RMS value of an AC signal is the voltage that causes the same power dissipation as
a DC voltage of the same value. (G5B07) For an AC signal with a sine-wave shape, the
RMS value is .707 times the peak value. 12 volts is the RMS voltage of a sine wave with
a value of 17 volts peak. (G5B09)
Conversely, the peak-to-peak value of an AC signal is 2 × 1.414 × the RMS value.
Accordingly, 339.4 volts is the peak-to-peak voltage of a sine wave that has an RMS
voltage of 120 volts. (G5B08)
Power is equal to the RMS voltage times the current, or
P (watts) = VRMS x I
Using Ohm’s Law, we can show that:
P = V2RMS / R
P = I2 x R
Amateur radio study guide has much information about electronics – [Link]
Here’s Jeri Ellsworth’s vlog showing her early progress on a homebrew software defined radio. Anyone who has considered SDR prototyping knows how complex this can be. We can’t wait to see the finished product.
UPDATE: Jeri has posted updates Part 2 and Part 3 to the above vlog.
Homebrew software defined radio, Jeri Ellsworth style – [Link]
NashblackCat writes to inform us of a chip that reads weather radio data: [via]
Silicon Laboratories makes an IC Weather Band (WB) radio called the Si4707. This IC is capable of using the specific area message encoding (SAME) and also supports the detection of the 1050Hz alert tone that is used by the National Weather Service. Currently no Arduino shields exist that could be used in a manner to receive, use, and/or display the broadcast alert data such as severe thunderstorm or tornado warnings. I think a shield like this would be great to implement all kinds of interfaces to this publicly available data resource. Some examples include Twitter alert system, VOIP streaming of audio broadcasts to your cellphone, and even a radio
Si4707 weather band radio receiver ICs – [Link]
Sean Michael Ragan writes:
This circuit is commonly credited to Japanese multimedia artist Tetsuo Kogawa. It takes audio input through a 1/4″ phono jack and, constructed as shown, without the optional antenna connections, will broadcast an FM radio signal about 30 feet.
Micro FM Transmitter – [Link]
Craig writes… [via]
I’ve made a half dozen battery-free crystal radios in about eight weeks. But I always wanted to try to stuff one inside of an Altoid tin for on-the-go. The short ground wire and long antenna wire that connect via an RCA plug, store neatly inside the tin. The 2000 ohm crystal earphone would fit in the tin if the long tube was chopped off. 200 turns of a 27 gauge wire on a 5/8” cylinder gets me tuning in the upper AM band. Perhaps I need to include a 3” copper ground spike to get a good ground in the field. Or would clipping onto a damp root be a better ground? Input?
Altoids Tin Radio – [Link]
The internet hosts lots and lots of online radiostreams, most of them with a certain theme, ranging from old time classics to Tibetian riverdancing. I must admit that I love to listen to them while I’m building stuff, as I can choose the music I like without listening to the same cd’s over and over again.
Build your own Wifi radio – [Link]
555 timer based AM radio receiver published on Tube Time is one of many entries for the currently running 555 contest. This project uses a 555 timer as AM demodulator plus amplifier to drive the speaker. The radio signal is tuned with an LC tank circuit. The 555 timer is configured as a PWM where a ramp signal is created with a capacitor and a potentiometer. The radio signal picked by the LC circuit is superimposed on the ramp signal which varies the duty cycle of the output PWM wave. The variation in the duty cycle corresponds to the audio signal in the radio waves.
555 Contest Entry: AM radio – [Link]
Traditionally, in a crystal detector radio tuned circuits, a mechanical type variable capacitor is used. For those of you who would like to eliminate this mechanical component, here is a modern version of the classic detector set. This radio, as shown on Figure 1, uses a varactor diode instead of the usual mechanical rotary device. [via]
Crystal Detector Radio Receiver Set – [Link]
This project shows how to build a simple AM radio transmitter based on 555 timer IC. The circuit parts are: the 555 timer IC, a NPN transistor three caps, three resistors and a potentiometer. The circuit is able to generate an amplitude modulation signal at 600Khz and you are able to receive it using a plain AM receiver. The range is about 30-40 feet. [via]
AM radio transmitter using 555 timer – [Link]