Ken, The added uncertainty is exactly as large as if you have a piece of cable (assume too short to have relevant losses) inbetween.
David Pommerenke -----Original Message----- From: Ken Javor [mailto:[email protected]] Sent: Friday, November 16, 2001 12:05 PM To: Pommerenke, David; 'ravinder ajmani'; [email protected] Cc: [email protected] Subject: Re: Pre-amps Note I am replying to all. What is the measurement inaccuracy associated with a mismatch if the transmission line is vanishingly short (relative to a wavelength)? ---------- >From: "Pommerenke, David" <[email protected]> >To: "'Ken Javor'" <[email protected]>, "'Ravinder Ajmani'" <[email protected]>, [email protected] >Cc: [email protected] >Subject: RE: Pre-amps >Date: Fri, Nov 16, 2001, 8:10 AM > > Dear Ken, > > I am thinking you are missing something (hope that I am correct). > If you simply shorten the cable to zero, the problem of the missmatch, and > the effect of an error that is not corrected for by the antenna factor still > remains. > > David Pommerenke > > -----Original Message----- > From: Ken Javor [mailto:[email protected]] > Sent: Thursday, November 15, 2001 5:51 PM > To: Pommerenke, David; 'Ravinder Ajmani'; [email protected] > Cc: [email protected] > Subject: Re: Pre-amps > > > If input VSWR for preamp and output VSWR for antenna are both bad, then it > seems a simple solution is to connect preamp input to antenna output and let > 50 Ohm output of preamp drive cable, solving two problems at once. Am I > missing something? > > ---------- >>From: "Pommerenke, David" <[email protected]> >>To: "'Ravinder Ajmani'" <[email protected]>, [email protected] >>Cc: [email protected] >>Subject: RE: Pre-amps >>Date: Thu, Nov 15, 2001, 7:49 AM >> > >> >> On the amps: >> >> For emissions there are the following electrical criteria: >> >> - Noise figure expect about 4 dB for a broadband amp 30 MHz - 2 GHz. >> The noise figure is often larger at the lower frequencies if the >> amplifier goes up to many GHz. >> >> - Input SWR. This is important. Most broadband amps (especially if they > go >> up to many GHz) >> have a bad input match at low frequencies. As the log-per antennas have > a >> bad mismatch too, >> you will have multiple reflections on the cable between the antenna and >> the pre-amp. >> This reflections will influence your measurement and cannot be > corrected >> for by the antenna >> factor. They may be as large as a few dB below 100 MHz. For that > reason, >> you may be forced >> to add a 3 dB attenuatore at the antenna. This increases your noise >> figure by 3 dB. >> >> - Gain. Of course, you need only as much gain as is needed to overcome > the >> cable loss (cable to >> the spectrum analyzer) and the noise figure of the spectrum analyzer. >> More gain will not help >> you. >> >> David Pommerenke >> >> -----Original Message----- >> From: Ravinder Ajmani [mailto:[email protected]] >> Sent: Wednesday, November 14, 2001 1:27 PM >> To: [email protected] >> Cc: [email protected] >> Subject: Re: Pre-amps >> >> >> >> >> Joe, >> HP (Agilent) make good Pre-amps for different frequency ranges. If you > are >> looking for an economical solution then you may try Com Power Corp. at >> (949) 587-9800. >> >> Regards, Ravinder >> PCB Development and Design Department >> IBM Corporation >> Email: [email protected] >> > *************************************************************************** >> Always do right. This will gratify some people and astonish the rest. >> .... Mark Twain >> >> >> >> >> >> MartinJP@appliedbiosyst >> >> ems.com To: >> [email protected] >> Sent by: cc: >> >> owner-emc-pstc@majordom Subject: Pre-amps >> >> o.ieee.org >> >> >> >> >> >> 11/14/2001 10:14 AM >> >> Please respond to >> >> MartinJP >> >> >> >> >> >> >> >> >> >> I am having some difficulties locating manufacturers that provide preamps >> with a 20-22dB gain. >> >> What manufacturer/model do you recommend? Why? >> >> Your assistance is appreciated. >> >> Regards >> >> Joe Martin >> Applied Biosystems >> >> >> ------------------------------------------- >> 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: >> Michael Garretson: [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: >> No longer online until our new server is brought online and the old >> messages are imported into the new server. >> >> >> >> >> >> ------------------------------------------- >> 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: >> Michael Garretson: [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: >> No longer online until our new server is brought online and the old >> messages are imported into the new server. >> >> ------------------------------------------- >> 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: >> Michael Garretson: [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: >> No longer online until our new server is brought online and the old >> messages are imported into the new server. >> > ------------------------------------------- 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: Michael Garretson: [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: No longer online until our new server is brought online and the old messages are imported into the new server.
