That's right, a DIY SWR meter and it's good for 5.8GHz too! The bad part is you MUST ME A MASTER AT SOLDERING (did I say that loud enough?) in order to build it. It only requires a few parts and is quite simple to work.
1 - SMA directional coupler (you must use one that encompasses the frequency you intend to test)
1 - Microwave detector diode (standard diodes will not work) - I used an Agligent HSMS-286
1 - Resistor: Value should be about 1K or so. not that important.
1 - Capacitor: ~.01 uF works. Anything from .1 to .001uF works, actually.
1 - A small coaxial cable with SMA end (I used RG316)
How to build it:
Basically the entire thing is made at the end of a coaxial cable. It is nothing more than a diode, capacitor, and loading resistor. All you are doing is rectifying the output of the directional coupler.
1. Strip the coaxial cable. Pull the shield back and twist it up. Trim the insulation off of the center wire as close to the shield as possible. Tin both the shield and the center element with solder. Trim the center element so that the distance from the tip of the element to the shield is less than 1/4" (6mm).
2. Set you multimeter to diode test. Figure out which end of the microwave diode is which. Put a small dab of soldering flux on the pins of the diode. If it is a multiple diode chip, I suggest trimming off the extra pins. Place the diode on something sticky so it doesn't move during soldering. Heat up the solder on the coaxial cable and touch it to the positive pin on the diode. Do not heat the diode directly. 600-700 degrees is a good temperature. After solder has flowed, remove heat.
3. Trim your resistor leads very short. Solder the resistor to the shield of the coaxial cable. Now bend the other tab of the resistor to touch the negative side of the diode. Heat this joint and add solder.
4. Now add your capacitor to the circuit. Be careful not to desolder the connection to the diode. The capacitor should be in parallel with the resistor.
5. Add your leads. You are measuring the voltage drop across the resistor. The capacitor will stabilize this voltage so it it readable. Lead length is irrelevant since this is now DC.
6. Once done, cover the meter in some non conductvie glue so it does not pull apart. You can stick it to a small circuit board or piece of wood if you like.
First you need to calculate p. p is your reflection coefficient. Vr is reverse voltage, Vf is forward voltage.
p = Vr/Vf
Ideally p = 0. Thus perfect SWR is acheived when there is no reverse power.
SWR = 1+p/1-p
Below is a video on how to read this meter:
From the numbers you get, you can calculate your SWR.