VSWR Measurement

You measure the forward and reverse power then calculate the VSWR.

http://en.wikipedia.org/wiki/VSWR

I'm doubtful a Spectrum Ananlyser would do the job, what's wrong with a VSWR meter?

http://www.nextmedia.com.ro/vswr/nmvw_d-rm_en.pdf

http://synergytelecom.tradeindia.com/Exporters_Suppliers/Exporter9124.140938/Thru-Line-Digital-RF-Power-Vswr-Meter-Schomandl.html

Using a spectrum analyser's tracking generator output as the reference source to the directional power head would allow the input of the spectrum analyser to display the VSWR over its frequency range.

Saves using a separate sweep generator and synchronised display with detector etc...

Also, those links point to single frequency VSWR measuring heads, using a spectrum analyser you can see the VSWR response with frequency... It was one of the main features of the Marconi spectrum analyser I helped design.

John.

All a bit OTT for a CB Radio antenna though surely?

What makes you think that the question is about an antenna or a fixed frequency CB channel?

Erm... Nothing, it was just a light hearted response as the main question had very little information to go on.

I use a $20 SWR meter when seeing if all connections are tight before transmitting on 2 meters.

John SE Texas WB5NWT

Might I ask what frequencies you wish to measure? Working in the GigaHz region is a bit different than say below 30 MHz.

I would use two directional couplers back to back... one measuring forward power only, and the other one measuring reflected power only. From these two readings, one can calculate the SWR. If I were doing this for real, I would feed the two signals from the directional couplers through A/D converters to a uController where I would do the math and then display the SWR on an LCD screen.

For the math:

SWR = (1+ sqr(Pr/Pf))/(1-sqr(Pr/Pf))

where sqr means square root, Pf is forward power, and Pr is reflected power.

Someone mentioned above a Marconi Spectrum Analyzer where you could excite your system with the internal tracking oscillator and measure the reflected power. I am curious if this machine had the brains to actually calculate and display the SWR or did it just display reflected power?

For more information on transmission lines I would recommend the ARRL Antenna Manual, www.arrl.org for the source. It is mostly antennas, but it has a good section on transmission lines. In fact I went over to my "work" computer, where I have it on disk to get the above equation.

Sincerely

Bill

With Spectrum analyser of any make / Model - May I measure about Vswr . How to calculate with Directional coupler ? - Please .

So , one more person also in need of this .