Chris, We use an HP spectrum analyzer that allows you to program in the factors including pre-amps. Without a pre-amp, our noise floor would render our measurements useless, even in our semi-anechoic chamber. The noisefloor drops with the addition of the preamp when the preamp factors are enabled. Also, make sure that your attenuation is on manual and you set the attenuation that works for your circumstances. Otherwise, the noise floor will rise back up by an amount of attenuation that compensates for the preamp.
Another way to lower the noise floor is to use a narrower bandwidth. This is applicable to narrow band signals such as clock harmonics. The test I use to determine if a signal is sufficiently narrowband to use a narrower bandwidth is to look at the signal at 9kHz and then 1 kHz BW. If the level is the same using peak detect mode, it is narrow band. This is especially effective looking at clock harmonics in the fm band in an urban environment. Of course the span will be quite narrow also, perhaps .5 MHz to "see" through the fm forest, then narrower to analyze an isolated signal. Tedious but effective. I have also used a preselector. For my situation, the preselector did not work because the band was too wide. One band covered the entire fm band when it was fm ambients I was trying to get around. A preselector that allowed me to "slide" a narrow passband through the fm band would have been ideal, but the ones I found covered the entire band. If a situation such as the fm band is not your problem, maybe you should try one. Demos are free. If you are worried about harmonics of a huge ambient, a preselector will help that. Hope this helps some. Don Umbdenstock Sensormatic > ---------- > From: Colgan, Chris[SMTP:[email protected]] > Reply To: Colgan, Chris > Sent: Friday, March 24, 2000 4:34 AM > To: 'Emc-Pstc' (E-mail) > Subject: Receivers and spectrum analysers > > > Greetings all > > I have an Advantest spectrum analyser with a quasi peak detector that I > use > for pre compliance work. I am having trouble with the high noise floor > and > I am concerned about my measurements reading low due to overloading the > detector (no input attenuation due to the high noise floor etc etc). > > I have been told (mainly by sales reps) that by using a preamplifier > (cheap, > not a problem to buy) and a preselector (expensive, could be a problem) I > can obtain results that are virtually equivalent to a receiver (very > expensive). > > Has anyone tried the analyser/preselector approach and if so, how have you > got on? > > Regards > > Chris Colgan > EMC & Safety > TAG McLaren Audio Ltd > > mailto:[email protected] > > ===================================================== > Authorised on 03/24/00 at 09:35:59; code 37f48bf3B1A8A7D9. > > > ********************************************************************** > The contents of this E-mail are confidential and for the exclusive use of > the intended recipient. > If you receive this E-mail in error, please delete it from your system > immediately and notify us either by E-mail, telephone or fax. You should > not copy, forward or otherwise disclose the content of the E-mail. > > TAG McLaren Audio Ltd, The Summit, 11 Latham Road > Huntingdon, Cambs, PE18 6ZU > Telephone : 01480 415600 (+44 1480 415600) > Facsimile : 01480 52159 (+44 1480 52159) > ********************************************************************** > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
