> 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.
thus removing the cable, removes the reflections...
not necessarily the mis-matches, just the reflections on the cable.
Could the pre-amp-antenna combination be considered a 'unit' for antenna factors ???
- Bill
At 09:10 AM 11/16/2001 , Pommerenke, David wrote:
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:ken.ja...@emccompliance.com]
Sent: Thursday, November 15, 2001 5:51 PM
To: Pommerenke, David; 'Ravinder Ajmani'; marti...@appliedbiosystems.com
Cc: emc-p...@majordomo.ieee.org
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" <davi...@ece.umr.edu>
>To: "'Ravinder Ajmani'" <ajm...@us.ibm.com>, marti...@appliedbiosystems.com
>Cc: emc-p...@majordomo.ieee.org
>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:ajm...@us.ibm.com]
> Sent: Wednesday, November 14, 2001 1:27 PM
> To: marti...@appliedbiosystems.com
> Cc: emc-p...@majordomo.ieee.org
> 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: ajm...@us.ibm.com
>
***************************************************************************
> Always do right. This will gratify some people and astonish the rest.
> .... Mark Twain
>
>
>
>
>
> MartinJP@appliedbiosyst
>
> ems.com To:
> emc-p...@majordomo.ieee.org
> 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
>
>
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