(p.s. just because it's on the list doesn't mean it's any good..)
FRG-7700 :
Noise blanker mod - https://groups.yahoo.com/neo/groups/FRG-7700/conversations/topics/262 & https://groups.yahoo.com/neo/groups/FRG-7700/conversations/topics/1248
"Actually, the noise blanker looks to be well designed. It consists of a balanced diode-blanking switch made up of D20, D21, T09, and T10 that's controlled by Q23. The diodes are normally biased on and are switched off by Q23 when blanking is needed. There's a broadband noise amplifier made up of Q36, Q37, Q38, and Q39 that feeds an impulse detector made up of D35 and D36. It detects the noise impulses and feeds them to the base of Q23 through a low pass filter made up of C185, C186, C98 and R202. If a noise impulse is large enough, it will turn Q23 on and blank the audio to prevent the impulse from reaching the speaker. Here's the "rub", a voltage divider is formed by R202 (4.7k) in series and R88 (22k) shunt to ground which reduces the sensitivity of the blanking. ... I located R88 on the circuit board and clipped the looped lead end near the top ... The cut lead effectively takes R88 out of the circuit so that the full blanking impulse is applied to the base of Q23 for maximum blanking sensitivity. At first I thought I might adjust the value of R88 by trial and error to some higher value, but taking it out altogether worked great so I stopped there."
"I checked the results by observing the base of Q23 with an oscilloscope ... and noticed a great deal of blanking activity where non had occurred before ... Next I checked the audio with the noise blanker switched on and off for noisy signals and noticed a marked improvement with it switched on. At the same time, clear signals didn't seem to be adversly affected at all."
Active antennas :
http://g8jnj.webs.com/activeantennas.htm
Mainly whips & dipoles, but a good collection including active antenna designs by Chris Trask (though not the tuned loop).
http://www.qsl.net/m0ayf/active-loop-receiving-antenna.html
"A Wide Bandwidth Active Loop Receiving Antenna". Hmmm, o ... kay...
DDS :
A DDS Signal Generator - http://www.frankvh.com/dds-signal-generator/hardware.html
Another DDS-based signal generator - http://www.qsl.net/pa3ckr/signalgenerator/
Comparison of DDS vs (Silicon Labs) Si570 - http://www.hanssummers.com/ddssi570.html
DDS ALC - http://www.cwtd.org/May_6-2014.html
The Analog Devices AD5932 is a bit of a pain to program. These links were immensely helpful (note that the AD5930 is very closely related to the AD5932):
AD5930: CTRL usage unclear
AD5930 Gotcha's
Fixed AD5932 Control, 100 kHz to 1 MHz
AVR / Arduino:
FreqCount library - http://www.pjrc.com/teensy/td_libs_FreqCount.html
FreqCount example - http://interface.khm.de/index.php/lab/experiments/arduino-frequency-counter-library/
Single Display Frequency Counter - http://www.zl2pd.com/OneCounter.html (not really an AVR, but interesting - and has simple 1-transistor input buffer/amp; why reinvent the wheel?
Updated I2C Master library - http://dsscircuits.com/index.php/articles/66-arduino-i2c-master-library
Adding TOGGLE to digitalWrite() - http://forum.arduino.cc/index.php/topic,22934.0.html
Replacement ShiftOut() (arbitrary # of bits, & delay) - http://scott.dd.com.au/wiki/Arduino_ShiftOut
Compiling Optiboot:
Don't bother with the source in the Arduino bundle - outdated, only works with the old Arduino avr-gcc (and Arduino no longer includes make?!), and newer avr-gcc requires newer source (deprecated functions & different optimisations).
On OSX: install Macports, then avr-gcc & avr-libc from ports. May as well install avrdude too. Download latest optiboot source. Compile for NMU with make AVR_FREQ=20000000L BAUD_RATE=19200 LED_START_FLASHES=3 LED=D3 atmega328, & install using avrdude with -U lfuse:w:0xe0:m -U hfuse:w:0xde:m -U efuse:w:0xfc:m fuse settings.
