Schema Signal Detector 2.45GHz RF

This passive RF indicator is made from a few simple parts. A 100uA moving coil meter is used to display the relative intensity of the RF signal. This circuit can be used with some cellphones and many cordless telephones.

2.45GHz RF Signal Detector

Antenna Tuning Unit Schema

Antenna Tuning Unit Schema Description:
A simple passive (no power required) circuit to match an antenna to a radio receiver. This will be a useful addition to the short wave listener, but in addition a medium wave coil is almost used to tune the medium wave band.

Notes:
An aerial tuning unit (A.T.U.) is a useful accessory for any radio listener as it matches the antennas resonant length to the received frequency, increasing gain and reducing spurious signals. The A.T.U. does not provide gain, but provides a better match between antenna and receiver, which usually gives an increase on the signal meter of the receiver, due to the A.T.U's resonant filter.

The circuit is a standard Pi filter, consisting of two variable capacitors C1 and C2 and a multi tapped coil L1. Switch S1 is used to select the tapping points and C1 and C2 peak up on the received signal. In this circuit an additional MW coil, L2 is used. This has a value around 200uH and can be salvaged from an old AM radio. In this position the A.T.U. can tune down to the medium waveband.

Coil Details:
To make L1, which is an air space inductor, use a 1 inch diameter former, a short section of an old brush handle made from wood is suitable. The coil is made from 22 swg enamel covered copper wire. The coil has 60 turns and is tapped at 3,4,6,8,11,15,20,30,40 and 50 turns. Coil L2 is connected in series with L1 at the 60th turn. L2 is wound on a 3 inch length of 3/8 diameter ferrite and has 60 turns of 32 swg, or one can be salvaged from an old AM radio. Each tapping point is connected to the contacts on S1, to make this easier I used some small galvanised nails hammered into the wood former. Below is a picture of my A.T.U.

In use this Antenna Tuner works best with a Long or Random wire antenna. As little as 5 metres of copper or aluminium wire suspended and insulated at each end in a garden will make an efficient antenna. The noise will also be lower than if using a receiver indoors. In use, the receiver is tuned to a frequency, S1 is turned for strongest signal and then C1 and C2 adjusted for best reception.

Eduardo from Brazil has just finished making his ATU and a very nice picture of his ATU is shown below.

TV Antenna Booster 15dB UHF

This is an UHF band TV antenna preamplifier circuit With 15dB gain to build easily. It is formed based on BF180 UHF Transistor. The first stage is an band pass filter constructed by the C1, CV1, L1, L4, C7 and C3, the second stage is a base-common voltage amplifier with low input impedance to match.

TV Antenna Booster 15dB UHF Schema

Build the L1 ~ L4 as air core coil to obtain high Q-Factor. After assembling, pack it into a proper metallic box and connect the ground of the circuit to the box to reduce noise effect.

Audio Amplifier LM386 0,325W

The LM386 is a power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but the addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to any value from 20 to 200.

Audio Amplifier LM386 0,325W Shema

The inputs are ground referenced while the output automatically
biases to one-half the supply voltage. The quiescent
power drain is only 24 milliwatts when operating from a 6 volt
supply, making the LM386 ideal for battery operation.

Features
n Battery operation
n Minimum external parts
n Wide supply voltage range: 4V–12V or 5V–18V
n Low quiescent current drain: 4mA
n Voltage gains from 20 to 200
n Ground referenced input
n Self-centering output quiescent voltage
n Low distortion: 0.2% (AV = 20, VS = 6V, RL = 8W, PO =
125mW, f = 1kHz)
n Available in 8 pin MSOP package

Cut Phone Line Alarm Schema

Burglars, rapists and other criminals will often cut a phone line before they break into a home. The cut phone line will prevent many alarm systems from alerting the police. The battery powered circuit below will sound an alarm when the unit no longer detects the voltage present on an active phone line.

Cut Phone Line Alarm Schema

A bridge rectifier front end makes the circuit phone line polarity independent. It shows four 1N4004 diodes being used but you can also use a standard low current bridge rectifier package with a 200v rating or more. The bridge is wired so the output voltage goes negative relative to circuit ground. The phone line will typically be somewhere around 30v when in standby mode and drop to something less than 15v when a phone is connected to the line. In the circuit, this translates a negative voltage fed to the gate of the 2N7000 FET, which kept the transistor turned off. When the phone line is cut, the voltage fed to the gate of the FET will swing to +9v, which will turn on the FET. When Q1 turns on, it also turns on Q2, which routes power to a 555 timer circuit. The 555 timer is wired as a 1Hz square wave oscillator, which drives the transistor Q3. That transistor drives an alarm beeper. With the components shown, the circuit draws nearly zero current in standby mode. Therefore a good quality 9v battery should last for many years.

18v AC to DC Power Inventer

This is a classic linear power supply which produces a regulated 18v, rated at about 1 amp.

POWER INVENTER 240VAC TO 5VDC

This is simple way to power some 5v logic from a 240vac source. If a 120vac power adapter is used, the circuit will also work for 120vac power lines.