security alarm circuit

The 4X4 Slimtenna - Development of the Slim Jim antenna for HF

Z-Match Antenna Tuner project - This Z-Match is a link coupled all-band tuner. Two all band tank circuits cover 3-14mhz and 14-30mhz. The tank output links are selected with a very heavy duty SPDT rotary switch.

Variacs - Variable Autotransformer - Use these Variac auto transformers for specific application requirements that include, but are not limited to, home coffee roasting, tube amps, and more.

Adding 160 meters to the Heathkit SB-220 - There will be radical changes to this Heathlit SB-220. There will be the addition of 160 meters along with many other circuit and design changes.

SB-220 Repairs and Modifications - Heathkit SB 220 mods, replacing the Zener ZD1, replacing the plate-voltage voltage divider, adding a keying circuit for solid state transceivers

Transistor PA Biasing - Here is a simple circuit that can deliver the peak base current needed for linear ssb operation

Integrated Circuit Audio Amplifiers - Circuit designs for IC audio amplifiers by N1HFX

Design Guidelines for JFET Audio Preamplifier Circuits - Design Guidelines for JFET Audio Preamplifier Circuits By Mike Martell N1HFX

Adjustable Regulated Battery Charger - This battery charger circuit is regulated and adjustable to make this circuit able to charge the mosto NiCAD battery.

A NiCAD Battery Charger - A NiCAD Battery Charger with Current and Voltage Limiting

RF Dummy Load - The use of dummy load is mandatory for off-air adjustment of the transmitters. Build one.

DC RF Sensing PA Switching - Circuit for dc/rf sensing pa switching from g8mny

Noise Bridge Tuner Tuner - Noise bridge circuit to tune your tuner

About Cavity Filters - Cavity filters are tipically circuitry behind a duplexer that allow only certain frequencies to pass

RF Sampler - This circuit will let you look at the signal and frequency output of your transceiver.

A low cost morse Trainer / Keyer - By Prof. T. K. Mani - VU2ITI

FT290 CW KOX Circuit - This is not actually break-in but just KOX circuit. It can only be used on the CW mode otherwise it keys up the Tx

Non-relay instant RF Switching - Coax lines to do the RF switching. The advantages are instant switching, no power wasting DC control circuits.

An Accurate Power Meter For QRP Ops - A circuit using two junkbox transistors and a garden variety op-amp that will let you accurately measure your rig\'s flea power down to milliwatts.

Circuit Improvements for the TS-440S - Some improvements for the Kenwood TS-440S, including distortion level in SSB in transmitted signals, Lack of crispness in the RX audio and Limited transmit frequency coverage.

Grip Dip Oscillator - Originally eveloped by I1FLC, uses seven plug in coils covering 3.0 to 30Mhz in a Colpitts oscillator circuit.

Build a Test Meter - This article include a circuit that allows a cheap 0-1mA meter to be used as a micro-ammeter or a milli-voltmeter

Make your own multimeter - Homebrew a multimeter with this article

Oscilloscope Tester - Circuit to assist in the setting-up and calibration of oscilloscopes

RF Probe circuit - This RF probe circuit allows RF to be measured in the presence of DC