This project will explain the function of a simple RF field meter. The unit will be in great help to tune transmitters for best performances. At the bottom left corner you will see a voltage divider. This divider is to produce a virtual ground of 4.5VDC. Above you will find the dipole antenna. The dipole antenna will pick up some radiated energy and the diode will rectify the RF signal to a DC voltage at VRF. This voltage is still quit low and needs to be amplified before it can control the panel meter. The signal then enter the OP which amplifies the voltage to suitable level set by the `Gain` potentiometers`. The second OP acts as a voltage follower and set the offset (zero) for the panel meter. The panel meter is connected to the board via two wires (5meter long). To prevent any RF signal to be induced in this long wire I have added 2 ferrite block which will act as high impedance units.
You can use any ferrite block or large inductor (10uH).
The block diagram at right show you one easy way to measure the RF filed strength. To the left you find a dipole antenna.
The antenna should be cut to match the receiving frequency.
The length of antenna is not a critical at all.
Length = 0.95*300/(4*freq) <= (freq = Mhz)
The RF signal is then rectified in a diode and the DC voltage is then amplified in an OP-amplifier. To display the voltage I use a panel meter. The amplifier gain can be set with a potentiometer and I have also added a bias voltage to set the zero level of panel meter.
This unit will not show you the exact power like a power meter, but it will show you the relative power transmitted out from your transmitter and antenna. The panel meter is connected to the PCB with 5 meter long wire.
In this way I can put the field-meter 5m away from where I am and still be able to watch the panel meter.
I will tell you how I use my filed meter.
I place the RF field meter 5 meter away from my transmitter.
I then put all variable capacitor to middle.
I switch on the transmitter and go to my RF filed meter. I then set the gain (with potentiometer) so I get half of max reading on the panel meter. I then switch off the transmitter and set the offset (with other potentiometer) so I get zero reading on the panel meter.
I repeat this tuning process unit it looks good.
Now I can start tuning the transmitter and watch the panel meter.
All I need to do is to tune for max reading on the panel meter. Then I know the RF field is at max strength.
I also advice you too receive the signal you are transmitting to check that it sound good.
I also check the current to the transmitter so it don't get to high.
Usually the current go down when good tuning has been done and you got max power.
Another good thing to monitor is the temperature of the transistors.
Don't let them go to hot.
3DPrint.com g2 Maker Conrad Farnsworth's recent contribution to MakerBot's Thingiverse is pretty unusual as projects go. In fact, it's doubtful that there is widespread demand for Farnsworth's 3D-printed Geiger counter, but the project speaks
Control Design "Units don't require any power other than what the signal can produce, just like analog ." ... “After the NTM proved to be successful, I needed to get back to the digital panel market, but I couldn't find an LED to satis
The Borneo Post Among the tampering methods discovered by the team was the usage of a remote switching relay with a receiver circuit board to bypass the which will then disrupt the full flow of electricity to the meter and will only register
The group also indicated that homeowners will be given step-by-step instructions on how to replace water with the plastic plugs. The estimated average charge for water is around €240 per household per year. But the Commission for Energy&nb
gulfnews.com Sharjah: Sharjah Transport has started penalising taxi drivers who swindle passengers by tampering with taxi . The move came after the taxi company received complaints that taxi drivers were illegally charging additional amou
Popular Science Electric Wheels (Top View). A top view of the gears driving the counter wheels. Revolutions of the shaft on which the big aluminum wheel rides turn the gold colored shaft in this picture, which in turn drives all of the count