References for constructing DIY SWR bridges

Hello!

Can please someone point me to interesting literature about the construction and building of SWR bridges like that one used in combination with network analyzers and spectrum analyzers with tracking generator?

CU

For scalar measure with TG on SA, you can use directional coupler > 25 dB directivity for used frequence range. - Is usable to tuning cavity filters etc.

HP/agilent:s famous application note '95' (in different versions depend of years) in also very usefull source how to measure standing wave and S-parameters.

this case using directional coupler (very expensive wide band type in hp VNA) or kind of resestive wheatstone bridge (R&S) and instrument must measure phase angle between source and reflection wave and transmission wave and amplitude of all to calculate S-parameters - we talk of 12 unknow parameters per frequency to make perfect calibrate of systems and needs lot of complex math.

in old version of hp appnot 95 from 1968, using slide skrew tuner to pick up max and minimum SWR amplitude on transmissions line and distance of this to calculate
phase and amplitude (to S11 resp S22 parameters) by hand - ie _very_slow_ VNA-methode compare to day computer supported VNA - but still possible to make for people with very small budget without expensive VNA


I have appnote 95 from 1968 on paper but not in PDF.



/xxargs

Hello!

Thank you, but I am looking for literature about building the SWR bridges itself. The application of SWR bridges is known to me.

CU

Hi Pit,

Check the links below:


https://www.edaboard.com/viewtopic.p...ighlight=ha8et
hxxp://www.pollak.sulinet.hu/elektro/hidak/hidak.htm
hxxp://s53m.com/beacon/HA8ET%20merilni%20most.pdf

(replace xx with tt).

The GIE website is not alive anymore, if you need the articles, I will post them here

regards,
Al

Hello!

Thank you, the SWR bridges from HA8ET seems to refer to scalar measurements only. Do you have material about measuring the phase angle, too?

Interesting spec for a DIY bridge is:

40 MHz ... 3 GHz
~ 40 dB directivity
measuring forward and reflected power

I am thinking about a project of building an open hardware VNA. There is the AD8302 from Analog Devices that can measure power and phase angle (unfortunately not the sign of the phase angle so there is additional circuit required for that). With a good RF sweeper, two bridges and four power/phase angle detectors and a data processing unit (and a lot of software) one can build a simple VNA.

Pretty high goal, I know. There are a few DIY VNAs around, but they are all well below 1 GHz.


CU

A laudable goal! Go for it.

I think your problem might be one of terminology. "SWR" bridge specifically refers to a scalar measurement. This is the component that you would purchase to work with a scalar network analyzer.

Names that imply a vector measurement would be "Reflectometer" or "Impedance Analyzer".

You might want to get the repair manual for an HP 8714ES and see how they did it. I sincerely doubt you are going to find a component that has 40 dB directivity, you need to error correct for that.

I will think about it... the idea came to my mind as these devices are still pretty expensive, even in used condition.

This is my intention: use a bridge (whatever it's name is), measure forward and reverse power and phase and extract the information I want.

I will look for the HP data but I think that the ususal service manuals does not contain detailed information about the RF blocks.

CU

Hi Pit,

Search for HP8502A manual in hp folder of bama.sbc.edu website.
Search Elektroda too - long time ago somebody was uploaded here very nice inside photos of HP8502A. The name of topic was "ultra wideband directional coupler" or something similar.

BR,
Stoyanov

I noticed that Mini-Circuits provides some wideband directional couplers, however, at some frequencies, the directivityis less than 20dB, can it be used to build VNA without losing much of the accuracy? how much can calibration help?
Anyone knows the answer? thanks