I am putting this out not as the best solution necessarily, but as a solution. It will be interesting to get several different techniques and see whose is most accurate, fastest, requires least equipment.
I would install a 10 dB pad at each discontinuity (consecutively, not simultaneously) and measure the difference each time. If you measure precisely 10 dB less, there was no vswr. Anything different from 10 dB means there was a reflection. There is a way to get from the reflected amount to what the vswr actually is, but in your case you don't need a vswr reading as much as you want to bound the errors. The biggest mismatch is from 30 - 80 MHz between the antenna and the attached coax. Another source of reflections is if no internal attenuation is selected and the spectrum analyzer mixer is a poor match to 50 Ohms. HP used to warn about this. Along those lines I recall Don White (does anyone hear from him anymore?) critiquing a paper at the 1989 EMC Symposium in Denver. The paper was something about how accurate this facility was in making RE measurements. Don asked the speaker if they used a pad to match the antennas to the coax when making NSA measurements, and the speaker said of course. Then he asked if they took the pads out in order to get usable sensitivity for RE testing. Again the answer was in the affirmative. Don didn't have to say another word. The sneer on his face said it all. on 9/26/02 6:01 AM, Gordon,Ian at [email protected] wrote: > > > Everybody > I need to assess the uncertainty of radiated emission and immunity > measurements and thus need to measure the mismatch between components in the > systems. The frequency range of interest is 30MHz-1GHz) > Is there a way in which I can measure the VSWR of a > cable-antenna-receiver/amplifier combination without having to purchase a > directional coupler or network analyser? > The equipment I have at my disposal is: two power amplifiers (150kHz-30MHz & > 80MHz-1GHz), a spectrum analyser with tracking generator (9kHz-2.6GHz), > signal generator (150kHz-1GHz), RF power meter (9kHz-1GHz) and a receiver > (9kHz-2.6GHz). > Any suggestions would be appreciated. > Thanks > Ian Gordon > > _____________________________________________________________________ > This e-mail has been scanned for viruses by the WorldCom Internet Managed > Scanning Service - powered by MessageLabs. For further information visit > http://www.worldcom.com > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > http://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list" > -- Ken Javor EMC Compliance Huntsville, Alabama 256/650-5261 ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
