For Everyone involved with radio transmitters needs some instruments to assess basic antenna functionality. Among these instruments, the best-known and most-used one is the Standing Wave Ratio meter. Some radio amateurs develop a cult for these little gadgets, having them in line all the time and watching the needles bounce while they chat.
- Wideband SWR meter - Transmission lines have a certain characteristic impedance, typically 50 or 75 Ohm for coaxial cable, and about 300 to 450 Ohm for open-wire balanced feedline. Such an impedance stating means that the cable is naturally suited to carry a ratio of voltage to current according to this impedance - for example, a 50 Ohm coaxial cable should carry 1A for every 50V applied to it, and the phase of voltage and current should be the same.
- Switch-out SWR Bridge - The circuit uses a double pole changeover switch (Measure or Operate), a SWR C/O switch Forward & Reverse, three 50 ohm resistors rated at 1/4 RF power, one RF diode (OA81), two 1nF capacitors, a series meter calibration variable resistor (10K) and a meter (100uA).
- Power and SWR Meter - The circuit uses bright LED's to display the power and SWR in binary coded format. This results in a very compact test instrument.The SWR/Power meter is powered by two internal "AAA" battery cells. The meter automatically powers itself down after a period of inactivity to conserve battery life.
- A Simple SWR Meter For QRP - This circuit should work with QRP rigs in the HF bands, although I have made no attempt to try it on other than 20 and 40.
- A Wifi (V)SWR Meter - The circuit on this page serves as a Voltage Standing Wave Ratio meter or VSWR meter for the VHF-UHF-SHF frequency range. This includes the Wifi (802.11b/g), 2m, 70cm and 13cm Radio Amateur bands.
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