VSWR measuring test setup help
I am about to build a VSWR meter and have researched a bit about the same.
Now i need to know low level requirements of a VSWR measuring setup.
Like what kind of dummy load i need to buy and the cables required and the signal to be fed and where can i buy these peripherals.
Any help is appreciated
It would help us to help you if you stated the range of frequencies in which you are interested.
Hello and thanks for the reply
The frequency I am looking for is up to 250 MHz
The meters I have built were for the h.f. band, 3 to 30MHz.
One used the moving coil meter from a commercial v.s.w.r. meter, and I also calibrated its sensitivity control in power for f.s.d.
The other used a small microammeter which I calibrated in power, 30W and 3W.
But any resistive load from a respected manufacturer will be suitable. For low power, one of the widely available BNC terminations for instance.
You will of course need a signal source; a laboratory signal generator is an obvious one.
Achieving a known mismatch to calibrate intermediate points below 1:1 might take some ingenuity. If it were me I would mark them simply as a proportion of f.s.d.
But I suspect that there are better ways of doing it.
For any RF band there are structures known as reflectometers. They utilize a swept-frequency signal generator., best having 10 to 100 mW output. Between the generator and a load you connect a directional coupler, with 10-dB coupling loss.
The coupled output of it is connected to a wideband detector, and its output to an oscilloscope Y-input. The X input is driven by a voltage used to sweep the frequency.
As the coupled detector output corresponds to a reflection from a load, if the load is well matched (RL ~ 16 dB or more), the detector output will be close to zero. An open or shorted line at the load position causes the highest output. Using a calibrated variable attenuator, you can measure load reflection loss over a frequency band of interest.
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And the reflection loss can be used to determine VSWR if you need.