Hi Gert, Look at this another way. Receiver noise figure is -71- (-174dBm)-10log(120000) or approx 103 - 50 or approx 50dB receiver noise. To reduce this you are proposing a 6dBNF 24dB gain LNA without doing the calculation the overall noise performance will only decrease to approx 28dB If you cascaded a second 24dB gain amplifier, to overall noise figure would decrease to approx 9dB (again without actually calculating it) but this would still leave the equivalent noise at approx 20dBuV/m. It looks like you need a LNA with a noise figure of about 2 or 3dB and an overall gain in excess of 50dB (Add 50 to the cable loss and use that number as the minimum gain). This will need to be located immediately behind the antenna (before the feeder). You should also check that the receiver has the front end attenuator switched off (i.e. set to 0dB) If you measure any significant emissions, then you need to add about 6 dB attenuation between the antenna and the LNA - check that the measured emissions drop by the same amount as attenuation - this guards against measuring mixing products caused in the LNA or receiver. With this arrangement you should have reduced the overall NF of the receiver system to around 4dB so we have -174+4+20+10log(120000)+107 = 8dBuV/m which leaves plenty in-hand to allow for errors in my approximations. I hope that I have explained well enough. Regards Tim
************************ Tim Haynes Electromagnetic Engineering Specialist SELEX Galileo, A Finmeccanica Company 300 Capability Green Luton LU1 3PG (Phone () +44 (0) 1582 886239 (Mob )) +44 (0) 7540629920 (Fax 7)+44 (0)1582 795863 (Email *) [email protected] www.selexgalileo.com P Please consider the environment before printing this email. There are 10 types of people in the world-those who understand binary and those who don't. J. Paxman ________________________________ From: ce-test, qualified testing bv - Gert Gremmen [mailto:[email protected]] Sent: 25 May 2010 20:17 To: [email protected] Subject: [PSES] Radiated emission testing for automotive at low levels. *** WARNING *** This message has originated outside your organisation, either from an external partner or the Global Internet. Keep this in mind if you answer this message. Colleagues and friends, I have recently been asked to quote testing for automotive car manufacturers ESA specifications. Part of the specification is very low level testing, as low as 20 dBuv/m at 120 Khz BW above 1 Gig. Can any of you shine their lights/contribute 2 cents on the test configuration needed for that. I have run into the following problem: Our R&S analyzer has a noise floor at 120 kHz bandwidth of approximately -71 dBm. Adding a 6 dB preamplifier noise and 24 dB gain lowers the noise floor to 89 dBm (18 dBuV). Our horn antenna (3115) has a AF of >20 dB (@1m) and the resulting noise level field strength is about >38 dBuV/m What is your choice in solving this problem ? Gert Gremmen - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> SELEX Galileo Ltd Registered Office: Sigma House, Christopher Martin Road, Basildon, Essex SS14 3EL A company registered in England & Wales. Company no. 02426132 ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
