Thursday, July 22, 2010
For those who are interested in tube audio I have posted the complete schematics of Frankenstein (which should be easier to read than my previously posted scanned notes), just scroll down the following pages:
Danger! Do not attempt to build any of this unless you have been trained to work with high voltage! High voltages can kill you easily and are extremely dangerous.
Sunday, July 11, 2010
I started with an audio derived AGC circuit from the 2010 ARRL handbook which uses 3 op-amps. I modified this slightly to work with the single supply LM124 op-amp. Additional modifications included changing the first stage from non-inverting to inverting and making it a gain stage rather than a buffer.
Results seem to be very good so far when testing the receiver with the signal generator and tuning in local amateur radio stations.
In final implementation i will leave room for further adjustments.
Thursday, July 8, 2010
Ok, so this project has been tough recently. I found out that my home-brew crystal filters using 4 Mc CPU xtals were no good (their response was far from ideal). So, i ordered a 2.5 KHz SSB filter from Inrad which was very inexpensive and provide excellent magnitude response. I should have ordered one of these in the first place considering the price.
The Inrad filter has a center frequency of 9 Mc, therefore i had to re-design the VFO, BFO, LPF's on each of these and the IF bandpass filters before and after the high-gain IF amplifier module. Alot of work!
With all of this complete i was able to tune in local amateur radio stations with ease.
Next step the AF and TX audio. I used a dual audio power amplifier chip, one half for RX to speaker audio amplification, the other half for TX audio. I purchased a surplus Motorola microphone from the MIT flea market for $5, found the schematic on repeater builder, and with advice from Mike Volz i biased it up.
I fed the output of one channel of the audio amp through a 100 ohm resistor to the IF port of the product detector. Wired the PTT switch from the surplus Motorola mic to the TX line of the bi-directional IF amp. Using my PARTS radio, i was able to listen to myself transmit using the DIY 40M radio! Success!
Next step: design the AGC system, then build it.
Next step: design the TX driver/power amplifier assembly
Next step: design the front-end LNA and TX/RX relay assembly
Friday, July 2, 2010
Registration is now open for the 2010 IEEE Symposium on Phased Array Systems and Technology.
At this conference the latest in phased array technology will be presented, discussed, and debated.
I strongly recommend attending if you are a fan of phased array technology, radar imaging, or antenna systems.