An RF probe is used to directly measure the level of
RF voltage present at a particular point and is one of the most useful
test instrument in the hands of the home brewer. It is normally used
with a digital multi meter to indicate the voltage level as dc voltage
which is equivalent to the RMS value of the RF voltage being measured.
However, the level of RF voltage being measured provides
useful information only when the probe has been designed for use with
a specific multi meter. The design of the RF probe is a function of
the DC input resistance of the meter we intend to use with it. If
a new meter with a different input resistance is used with the probe
the reading will be inaccurate.
Look at the figure below which shows the construction
of the RF probe. The rectified DC voltage at the cathode of the diode
is at about the peak level of the RF voltage at the tip. The value
of the resistor R1 is so chosen that when this resistor is connected
in parallel with the input resistance of the digital multi meter,
the peak value is about 1.414 times the RMS voltage. R1 has to drop
this excess voltage so the meter indication is accurate. If we know
the input resistance of the meter, we can calculate the value of R1
as follows. Usually, digital multi meters have an input resistance
of 11 meg ohms. In this example we shall take the input resistance
of the meter as 10 meg ohms which will make calculation easier to
understand.
7MHz
SSB Transceiver - Circuit digram and brief description of
7MHz SSB Transceiver for Hams. The circuit is designed around two numbers
of MC1496. It can push around 80 Watts with IRF840 in the final. You can
down load HTML version or the printer friendly word document.
Morse
Code Tutor - A program (23kb) written in C++. Morse code
uses dot and dash for communication. Still it is popularly used for communication
is short wave bands. The Archive contains program source code and executable.
AM
DSB Transmitter for Hams - circuit diagram of simple double
side band suppressed carrier (DSBSC) transmitter for hams. Circuit uses
crystal oscillator, crystal can be switched for multi band operation.
600
Volt Power Supply - simple 600 Volt DC power supply. Convert
230V AC to 300V and 600V DC.
Ham
Radio BFO- circuit diagram of beat frequency oscillator
using BF494 and how to listen amateur radio communication on ordinary
BC receiver.
Miniature
MW Transmitter - circuit diagram of simple medium wave transmitter
using BF494B. This simple transmitter have a range of 200 meters.
807
and 1625 Valves - data on vacuum tubes 807 and 1625 used
in ham radio transmitters. Describes various pin voltages and different
operation modes.
FM
Wireless Mike - low power frequency modulated transmitter
using two transistors. The circuit works with 9v power supply.
60
Watt RF Amplifier - Soild state RF power amplifier using
IRF840. Simple and easy to construct. IRF840 can handle a maximum power
output of 125 Watts.
Simple
RF Power Meter - simple RF power meter cum dummy load for
low power transmitters.
Touch
CPO - touch operated code practice oscillator using popular
timer IC555. Practice Morse code in a different way.
Modulation
Monitor - very simple and useful circuit used to monitor
on air transmission of your low power amplitude modulated transmitter.
Cheap
Crystal filter - Ladder filter using six 4.43MHz Crystals.
Building cheap side band filter for your bome brew SSB Rig.
RF
Dummy Load - make this simple RF Dummy Load for off-air testing
of your radio transmitter.
Mosquito
Repellant - very simple and easy to assemble mosquito repellant
using two transistors and handy components.
Ceramic
Filter BFO- Receive SSB and CW transmissions
on your BC receiver. Simple BFO is build around 455 KHz Ceramic Filter.
SSB
ADAPTOR - Build this simple adaptor to receive single side
band SSB on short wave AM receivers.
QRP
Keyer - very simple keyer circuit using only one transistor.
Designing
RF Probe - make your self simple and heighly useful RF probe.
An essential tool for every home brewer.
Shorty
Forty Antenna - Do you have space limitaion to put a 40 meter
dipole. Try this Compact 40 meter antenna.
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