Sunday, July 31, 2011
Saturday, July 30, 2011
This is a great tutorial on how software defined receivers work and how to make your own.
You first must get past the funny 'plot line' (if you're making a youtube video why not have fun while doing it? :)
It's worth it because Jeri does a great job explaining signal processing concepts behind software defined radios without getting into too much detail.
Thursday, July 28, 2011
Making things as a kid, taking apart old TVs and radios and hooking things up to model railroad power transformers
My mother is an electrical engineer, i think because of this as a kid i enjoyed nothing more than to take apart an old TV set, radio, or appliance to learn how it worked. Eventually i started to learn how to hook things up to old model railroad power supply transformers such as car radios, lights, motors, and other cool things. After i while i started to use relays and was able to backwards engineer the power connections to almost anything. Things became interesting at approximately age 10 when my uncle described to me how to use transistors and i acquired my first oscilloscope. This lead to more interesting projects, including making power supplies, repairing more complicated appliances, and eventually the amateur radio license at age 13 thanks to encouragement by my mother who thought that i should try a more advanced hobby.
Tuesday, July 26, 2011
The power amplifier is complete. with -10 dBm in from the front-end mixer my driver will provide 10 watts out. My final power amplifier will provide 110 watts out with the 10 watts of drive power using a push-pull LDMOS transistor.
This is very exciting. Hopefully 100 watts will be sufficient to make some 10m and 6m contacts later this fall when the radio is complete :)
Sunday, July 24, 2011
Picked up this Yaesu YP-150 watt meter. Unfortunately it had a cold solder joint on one end of the 50 ohm load resistor that fell out causing the load to not be connected. This was obvious when an input of 20 dBm would cause a full scale meter reading.
To fix this i applied lots of flux and using a large iron i flowed solder back into the broken half of the load resistor.
I then checked the VSWR from HF to 150 MHz and it was good. Next i tried testing a 100 watt transmitter to verify that it was operating soundly and would not suddenly have a problem.
Good to go, i need this watt meter to test my driver and PA boards for my ARRL homebrew challenge 3 radio.
Friday, July 22, 2011
Submitted to Trans. on AP-S: A Through-Dielectric Ultrawideband (UWB) Switched-Antenna-Array Radar Imaging System
A through-dielectric switched-antenna-array radar imaging system is shown that produces near real-time imagery of targets on the opposite side of a lossy dielectric slab. This system operates at S-band, provides a frame rate of 0.5 Hz, and operates at a stand-off range of 6 m or greater. The antenna array synthesizes 44 effective phase centers providing $\lambda/2$ element-to-element spacing by time division multiplexing the radar's transmit and receive ports between 8 receive elements and 13 transmit elements. Laboratory measurements agree with simulations, the air-slab interface is range gated out of the image, and target scenes consisting of cylinders and soda cans are imaged through the slab. A 2D model of a slab, a cylinder, and phase centers shows that blurring due to the slab and bistatic phase centers on the array is negligible when the radar sensor is located at stand-off ranges of 6 m or greater.
(Hopefully the editors and reviewers will find this project interesting.)
Link to this project.
Wednesday, July 20, 2011
I've completed the AGC and signal meter circuit. My signal meter displays absolute signal level in volts at 50 ohms. The AGC circuit uses 4 op-amps and is audio derived. I've had good luck with audio derived AGC circuits in the past so i plan to use one again this time.
Monday, July 18, 2011
Creating the audio circuitry for a SSB transceiver is not a trivial task. Shown on the right is a green prototype board with the completed RX and TX audio and PTT circuitry.
Saturday, July 16, 2011
I am thinking about using an LDMOS RF Power mosefet push/pull pair for the homebrew challenge 3 radio.
I have prototyped an amplifier and am currently working through design issues. A colleague of mine came across these briefings on using LDMOS RF power mosfets.
Wednesday, July 13, 2011
A demo of my Colin B. Kennedy Model 20B console radio. Built in 1929 this radio still sounds great, especially when listening to vintage jazz music.
Monday, July 11, 2011
Recently we have posted some of the results and info on a very exciting project that i and a number of collaborators have been working on; a through-wall radar system.
It is a real-time through-wall imaging radar, providing a frame-rate of 10.8 Hz (nearly video frame rate), capable of imaging through 4", 8" solid concrete, and cinder block walls.
Tuesday, July 5, 2011
I restored this beautiful old console radio for two dance friends that we know who just got married. This was a fun project, hope that you enjoy!
Friday, July 1, 2011
Recently an article on the 20m homebrew SSB transceiver was posted on radioamateur.org, which is a French site dedicated to amateur radio. The author, F8BXI, describes the radio and provides the youtube video demo.
Thank you F8BXI for your write-up and kind words. Your article will help encourage others to create their own radio equipment.