Sunday, August 29, 2010

Power amplifier is working, 100 watts out on 20m, with 2 watts drive from exciter

2 watts PEP drive from the exciter into one IRF510 pre-driver which then feeds 4 IRF510's in a push/pull configuration. With this i am able to achieve approximately 100 watts out with about 20 VDC. Will try it with a 24 VDC supply shortly.

Amazing what you can do with a bunch of IRF510 MOSFETS.....

Friday, August 27, 2010

Portable tube pre-amp for the covert recording of live concerts

In college we were on a mission, to record a live show in Chicago with the best audio quality possible. For this reason i developed the small portable tube pre-amplifier shown here.

This amplifier runs on 12 AA batteries (in a separate battery pack) and should last 3-4 hours. Works well with microphones, electric guitars, and would be great in any portable/mobile application.

I recently have posted the schematic here and photos here.


Monday, August 23, 2010

20M SSB transceiver update: Exciter/LNA front-end module complete

2 watts PEP exciter and LNA/Driver and bandpass filter module
complete. Works quite well, the LNA is very quiet.

I am using a Norton type of feedback design with a discrete low-noise
NPN transistor (forget the name at the moment, but it is very small
and difficult to solder, NF<1 dB).

The TX pre-driver and driver consists of an AD8009 current feedback
op-amp driving an IRF510 N channel mosfet.

Tuesday, August 17, 2010

A Through-Dielectric Radar Imaging System, this month in Trans. on AP-S

Good news: my article in Transactions on Antennas and Propagation has been published. It is titled, 'A through-dielectric radar imaging system.' If you would like to read it click here.

A photo of the experimental setup is shown above. Yes, the measurements were made in my backyard :) The modeling and simulations were developed while i was a graduate student at the Michigan State University Electromagnetics Research Group. The radar system was built in my basement and my garage. This project shows you that you can build PhD level projects in your own backyard.

To learn more about the modeling and this radar system please see the project page.

Here is the abstract:

Through-lossy-slab radar imaging will be shown at stand-off ranges using a low-power, ultrawideband (UWB), frequency modulated continuous wave (FMCW) radar system. FMCW is desirable for through-slab applications because of the signal gain resulting from pulse compression of long transmit pulses (1.926–4.069 GHz chirp in 10 ms). The difficulty in utilizing FMCW radar for this application is that the air-slab boundary dominates the scattered return from the target scene and limits the upper bound of the receiver dynamic range, reducing sensitivity for targets behind the slab. A method of range-gating out the air-slab boundary by significant band-limiting of the IF stages facilitates imaging of low radar cross section (RCS) targets behind the slab. This sensor is combined with a 1D linear rail and utilized as a rail synthetic aperture radar (SAR) imaging system. A 2D model of a slab and cylinder shows that image blurring due to the slab is negligible when the SAR is located at a stand-off range of 6 m or greater, and thus, the two-way attenuation due to wave propagation through the slab is the greatest challenge at stand-off ranges when the air-slab boundary is range-gated out of the scattered return. Measurements agree with the model, and also show that this radar is capable of imaging target scenes of cylinders and rods 15.24 cm in height and 0.95 cm in diameter behind a 10 cm thick lossy dielectric slab. Further, this system is capable of imaging free-space target scenes with transmit power as low as 5 pW, providing capability for RCS measurement.

Thursday, August 12, 2010

adding an AUX jack to your stock car radio, 2 examples

I need to do this to the radio in my truck:

A Chrysler radio:

a foreign brand auto:

Thank you Matt Metts for posting these. I have been contemplating
doing this for a while now and have looked for years to try to see if
anyone has done this. Will try to fit it into the project schedule
this year.

Sunday, August 8, 2010

New audio derived AGC circuit, based on IIT Madras Lecture from Youtube

I was not really happy with the AGC circuits that i was finding in the ARRL handbook and other publications. My objective was to implement an audio derived AGC for my 20m DIY SSB transceiver.

I found this excellent lecture from IIT Madras yesterday, watched it end-to-end, and filled in knowledge gaps that i had from reading about AGC circuit designs.

Using the design example at the end of this lecture, with a number of modifications so that i could implement it with an opposite polarity variable gain IF amp and use the single-supply LM124 op-amp, i have completed the circuit shown in the photo above.

As explained in the lecture, it is a PID controller. It starts to take control of the gain just before saturation of the entire RF signal chain. The RF gain control on the front of my radio will allow this gain control point to be dialed back by the user if desired.

I am very happy with this audio derived AGC. It's performance is excellent! I will post schematics of this and the rest of the radio eventually once it is complete.

Saturday, August 7, 2010

NPTEL lectures on electrical engineering

I'm researching automatic gain control (AGC) for my DIY 20m SSB transceiver. I found an excellent lecture on AGC on youtube:

It turns out that India has a program where they are posting lectures on engineering topics, very good lectures, from the Indian Institutes of Technology and Indian Institute of Science:

As for the AGC lecture, it is very practical, i can actually design circuits from this. Not all academic lectures cover both theory and then dive into details on how to implement what was discussed.

Many thanks to IIT Madras for posting this lecture on AGC.