Testing Circulator / Isolator - RF Cafe Forums

 Post subject: Testing Circulator / Isolator

Posted: Fri May 11, 2007 6:03 pm 

Greetings everyone.

Ive not new to here as I come here every time I could use some help and use the search feature mostly for antennas/vswr/smithcharts. However, I have not found anything on testing Circulators and Isolators. I have searched here and the net with very little luck, i believe wikipedia had the most info. Not that theory of operation on these items wouldnt hurt me, I am mostly searching on how to test them. Well, if I knew how they operated then I would know how to test them. However, after looking at the spec sheets of circulators/isolators on the net, are they tested by insertion loss?

I have a Motorola R2670 easily available, will this do the job? Its your basic comm test set (for those that dont know), and more. Im not sure on how to test a circulator (ie will this frequency pass with very little amount of reflection?). Im guessing I would use the Duplex function (generate Freq on RF IN/OUT while monitoring Freq on ANT port vs using Tracking Generator (?). THe Freq range supported by the test set is applicable to what I will be working on (make sure the circulator works / passes Freq with very little loss).

Thank you ahead of time. meanwhile i'll be playing with the test set.

 Post subject:

Posted: Fri May 11, 2007 6:12 pm 

learned some info...

environment is a radio with < 200Watts out to antenna (VHF range). all i gotta do is verify circulator/isolator work, was told a double circulator was in place... whatever that is

 Post subject:

Posted: Mon May 14, 2007 10:14 am 

Hello Lamini,
An isolator is nothing more than a circulator with the "final" port terminated in a "perfect" 50 ohm load (or whatever the characteristic impedance is).The purpose of these devices is to direct RF energy in only one direction thus protecting the device connected to one port from reflections from another port "downstream". Both of these devices are tested for 1) insertion loss 2) isolation between ports and 3) VSWR. You can use a VNA or a coupler/PM/Spectrum Analyzer to make the measurements. You don't indicated whether these are stand alone componets to be tested before insertion into a system or as part of a "circuit". I'll assume stand alone. Insertion loss can be tested by simply measuring the power into the device and the power out. The difference is IL. Isolation can be measured by applying power into device, using a coupler on output port 1, terminate output port 2 and measure the feflected power from port 2 on port 1. Continue around the circulator until all ports are tested. VSWR is measured by measuring the reflected power from the port of interest using a VNA or a coupler and PM or spectrum analyzer. I have always had good luck in contacting manufactures of components I have used and asking them what and how they test them.

Good luck,
RFTEjerry

 Post subject:

Posted: Thu May 24, 2007 12:02 pm 

I forgot to post my results from last week. I arrived to the test location and everything happened naturally. Was your basic Insertion Loss measurement;

0dBm in port 1 = 0dBm into port 2. 0dBm into port 2 to port 1 nothing = everything good. I used the Motorola/General Dynamics R2670 Communications Test Analyzer in Duplex mode to transmit/receive as neccessary with no problems.