Make you own Roe Meter
This is a very useful tool for adjusting the antennas and transmitters of low and medium power.
is ideal for the experimenter because it can work with RF levels as low as 10 mw. and can make measurements at frequencies up to 144 Mhz.
Figure 1
For sensitivity, the device uses a DC transistor amplifier with the amplifier can be easily obtained current gains up to 100 times.
How does When J1 connects the end of the SWR meter to the transmitter, and the J2 end to the antenna, the RF current flowing through the central conductor L3, L1 induces a voltage directly proportional to the voltage on the line or conductor, L2 and a voltage proportional to the reverse voltage on same. The voltage detected by L1 is rectified by D1, and when SW1 is set to DIRECT, the rectified current is amplified by Q1 and indicated by the meter. When SW1 is in position reflected power, the voltage detected by L2 is rectified by D2 and turn amplified by Q1.
The meter reading gives a qualitative idea of \u200b\u200bthe RF power for a given control position sensivilidad R3, provided that it remains constant impedance load while making comparison.
The meter can be built for two different impedances, the impedance must be chosen to suit your needs, and according it using the impedance values \u200b\u200bgiven for R1 and R2.
As
weapon
This meter is built in a metal box (preferably aluminum) 6x6x12, 5 cm.
The transmission line section consists of an inner conductor (L3) and a piece of copper sheet gauge # 27 of 6x11 cm., Bending with the shape of the fig. 1, which form the outer conductor.
Figure 2
have to make two insulating supports (Fig. 2), or acrylic fiber serve to hold L1, L2 and L3 keeping the correct distance.
At the ends of the copper piece should glue the supports with a strong epoxy resin (with the holes made in advance with the measures Fig. 2).
When insulators are properly attached, we will hit the wires L1 and L2 acquisition and the central conductor L3, so that they protrude from insulators about 3 mm on each side to solder the resistors, diodes and coaxial connectors.
lands J1 and J2 should be well connected to the copper strip, as well as the DC amplifier.
The piece of copper must be connected to the metal box where the meter is assembled.
On the front panel mounted M1, SW1 and R3. Preferably M1 may be of the miniature.
J1 and J2 should be placed as close to the back of the box as possible.
In the protruding ends of 3 mm at L1 and L2 solder the resistors R1 and R2 and diodes D1 and D2 as close as possible to the insulation, then solder connections to the diodes short R4 and R5 and capacitors C1 and C2 . The other end of R4 and R5 can draw two wires that go to Sw1.
How
test
Connect the transmitter output to J1 using coaxial cable 50 or 75 ohms (as appropriate). J2 connect an antenna in phantom (resistance 50 or 75 ohms).
DIRECT With SW1 in position transmitter is turned on and calibrated R3 M1 full scale, is passed to REFLECTED SW1. The reading should be zero (0).
After this test, disconnect the antenna and connect the antenna ghost. Repeat with the antenna connected, with calibrated direct SW1 with R3 M1 deviation full scale, then with SW1 reflects back to pass and the scale reading is the reflected power or amount of stationary antenna is in .
These measures are qualitative, but if you want more precision can be gauged with the help of resistance or phantom loads. Example: with a resistance of 200 ohms have an ROE of 4 (200/50) with a resistance of 100 ohms SWR 2 (100 / 2), etc.
CE1RCH material, RadioClub Chiquicamata
