Fred points out this schematic for a rather interesting radiotelephone transmitter instantaneously powered by the operator’s voice. [via]
One of the neatest minimalist amateur radio transmitter circuits around – this one is voice powered – it provides DSB, (double side band)modulation and power from an ordinary 8-ohm speaker – if are in doubt that the circuit works, the maker has the contacts and the voice recordings to prove it!
Voice-powered RF transmitter - [Link]
Dimitris at users.otenet.gr/~meteo writes:
I make simple RF field strength meter to test the remote control from doors ,alarm e.t.c at frequency VHF-UHF, i used one μΑ meter ,2 diodes ,2 ceramic capacitors,a potentiometer,a box ,and one telescopic antenna. When I press the button at remote control, there is small RF current and with this meter it can be detected. In that way you can understand if the remote works.
Simple RF field strength meter - [Link]
This website details the design and construction Wave Bubble: a self-tuning, wide-bandwidth portable RF jammer. The device is lightweight and small for easy camoflauging: it is the size of a pack of cigarettes.
An internal lithium-ion battery provides up to 2 hours of jamming (two bands, such as cell) or 4 hours (single band, such as cordless phone, GPS, WiFi, bluetooth, etc). The battery is rechargeable via a mini-USB connector or 4mm DC jack (a common size). Alternately, 3 AAA batteries may also be used.
Output power is .1W (high bands) and .3W (low bands). Effective range is approximately 20′ radius with well-tuned antennas. Less so with the internal antennas or poorly matched antennas. [via]
Wave Bubble: a self-tuning portable RF jammer - [Link]
Low Power Radio Solutions (LPRS) has claimed that its easy-Radio allows you to ignore the radio link and treat it as if it were a wire. A simple TTL or RS-232 data source is all that’s required to move data from point A to point B, and vice versa, using a pair of easy-Radio transceivers. All of the messy encoding, decoding, and checksum calculations are achieved by the easy-Radio’s internal processor. easy-Radio uses frequency hopping and a maximum of 120 mW of output power to achieve a range of 500-m line-of-sight. My 900-MHz easy- Radios hop at 25 times per second over 25 channels, which, under the control of the internal microcontroller, is transparent to the data radio user.
RF Made Simple - [Link]
Here is a practical example how to use a XBee module with PIC18F452 to remotely control a led connected to the port of the recieving module.
Wireless Communication with XBee Radios - [Link]
Building large complex boards is very risky. If anything is wrong with the board, the entire board needs to be discarded sometimes after expensive components have been soldered onto them. Instead of have one big board, the display is split into module boards. These modules are the LEDPANEL( front panel with the lights and buttons ), LEDDRIVER( hardware to switch on and off the rows and columns ), and the PROCESSORBOARD( the board that contains the RF circuitry and microcontroller ). If something goes wrong with one of the boards, only that board needs to be redesigned or replaced. A secondary bonus is that the processor board can be redesigned for a different PC connection. An example would be a module with a USB connection to a PC rather then an RF link for cost savings.
A Scrolling Display with RF connection to a PC - [Link]
The Semtec DP1205 RF module is the core of the modem. This module is a Semtec XE1205 transceiver plus an antenna switch and other required discrete components that are not built on the XE1205 chip. The XE1205 is a very generic 900MHz FM module without any built-in protocol logic. It is very similar to the modules produced by Linx Technologies. The module has an SPI interface for changing between transmitter and receiver modes and for setting the RF frequency and the FM frequency deviation. The data connection directly drives the FSM circuity. For this project, the module uses a 100KHz deviation. The transmission power is 15DBm.
A FCC Legal Frequency Hopping Spread Spectrum USB RF Modem – [Link]
HC908VFO is a VFO software program that runs on a small, standalone collection of “daughtercards” that will be familiar to Micro908 users. What we did was simply connect the powerful HC908 Daughtercard microcontroller to one of the very popular DDS Daughtercards, and added an LCD and rotary encoder to form a very flexible signal generator in the RF range. We used some of the well-tested software modules from the Micro908 to consruct this simple VFO, then further simplified its operation by giving the user control over a multitude of features. [via]
HC908 VFO - [Link]
Rob Arnold writes:RF is just way too cool not to use in your designs. But if you’re a newbie like me it is difficult to successfully build solid RF transmitters and receivers. When I started out I didn’t realize that the larger breadboard I was working off of was causing a lot of the signal deviance because the metal traces on the breadboard worked like small capacitors and changed my circuit dynamics. So after much research I found the Reynolds Electronics RWS and TWS 434 RX/TX pair. I looked into a similar product by MING Microsystems and Radioshack but the Reynolds were superior in performance, cost and ease of use. So with that and two PIC16F84’s I started working on my serial RF link from my control interface (Joystick) to my robot. [via]
RF Modem Robotics Project - [Link]
This basically the frequency meter section of the frequency meter/pulse generator based on the AT90S2313 described elsewhere on this site, combined with the 100 MHz RF interface described in the page about the RS-232 to 100 MHz RF desktop channel adapter. Built and align this is the same manner as the 100 MHz RF desktop channel adapter. The frequency meter has a maximum input frequency of 4 Mhz and counts up to 65535. Time bases of 10 ms, 100 ms, 1 second, 10 seconds, and 100 seconds are selectable from the keyboard via the RF link. [via]
Frequency Meter with 100 MHz RF desktop channel - [Link]