I don't understand that. You only get standing waves when a mismatched transmission line is a significant fraction of a wavelength. If the transfer of power from antenna to amplifier is in question, then you could do what another list member suggested: calibrate antenna and amplifier together as a unit. Problem solved.
---------- >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, 12:36 PM > > 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.
