Hi, Please allow me to take the liberty of fwding this note in another discussion forum. Michael was talking about OATS validation using networm analyzer. -barry ma ------------- From: Michael Foegelle [mailto:michael.foege...@emctest.com] Sent: Friday, June 16, 2000 9:15 AM To: Tim Harrington (AEI); Kefeng Liu Cc: 'patentlaw...@ieee.org' Subject: RE: Site Attenuation Measurement / Antenna Factors
Gentlemen: Unfortunately Clifford's response cut off Doug's e-mail address, so hopefully you can forward this or post it to the discussion group. Here at ETS we've used vector network analyzers for antenna calibration and site validation for the past five years. They provide results that are far superior to that possible from a spectrum analyzer/tracking generator configuration due to the excellent dynamic range, linearity, and external signal rejection. If you perform a full two-port calibration, you can also eliminate the necessity of pads since the calibration can correct for mismatch. However, there is one significant limitation and a couple of pitfalls to be aware of. Clifford is quite correct that the first issue is the height scan requirement and the lack of max-hold functionality on network analyzers. I've tried to get HP (Agilent) and others to listen and convince them that there is an untapped market here if they'd just add max-hold to their firmware, but so far I've been unsuccessful. Thus, the only way to use the network analyzer is to perform the max-hold from test automation on the PC. In order to do broadband scans with a large number of points, this also requires height stepping of the tower, since the sweep time becomes too slow to maximize on the fly. An additional danger to be aware of is a limitation (I consider it a defect) in the popular HP line of analyzers (HP 8753, 8720, etc.). If the cable length is too long, the path delay becomes longer than the step period, thus the transmitted signal does not reach the tuner before it steps to the next frequency. Thus, the tuner is not centered on the received signal. In minor cases, this results in a 10 dB error or so, but the inexperienced user is not likely to realize where the problem comes from or even that there is a problem. (Worst case, the receiver sees the noise floor because it's stepped so far that the received signal is outside the bandwidth of the receiver.) For broad span measurements, this will typically be indicated by falling steps in the signal as you sweep to higher frequencies. For narrow span measurements, you'll never notice the effect, since the receiver bandwidth will typically still cover the incoming signal, but it will be recorded at a different frequency point on the display. The result would be that a resonance would appear to be at different frequencies depending on the bandwidth, frequency span, and number of points. The only solution is to forcibly slow the sweep speed (typically by narrowing down to 10-30 Hz bandwidth) which greatly increases the test time. We've pointed this problem out to HP, but they do not seem to be interested in fixing it. We've tested the newest analyzers from Anritsu/Wiltron and they do not seem to suffer from the same problem. I've been told that the new Rhode & Schwarz units do not either, but I haven't had the opportunity to test one yet. As far as ANSI testing, the next revision of C63.5 will contain more generalized wording that make it clear that network analyzers and automated measurements are acceptable for performing the calibrations specified in the standard. After all, a network analyzer is really just a high quality signal generator and receiver with a few additional features over a spectrum analyzer/tracking generator combination. It's just that in their current incarnation, none of them have the max-hold automation built in. All-in-all, vector network analyzers are great pieces of equipment to have around, and if you have one that's going unused, I suggest you take a look at it. Chances are, you've only scratched the surface of its potential! (Ok, so I got my Ph.D. using an 8753B! It allowed us to perform measurements and see things that had never been seen before, so I'm definitely a fan! =) Sincerely, Dr. Michael D. Foegelle ------------------------------------------------------- Dr. Michael D. Foegelle | 2205 Kramer Lane Senior Principal Design Engineer | Austin TX, 78758 EMC Test Systems, L.P. |(512) 835-4684 x650 _______________________________________________________________________ Why pay when you don't have to? Get AltaVista Free Internet Access now! http://jump.altavista.com/freeaccess4.go _______________________________________________________________________ ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org