I use a ULTRA SMALL 25db (1.1db NF)70Mhz to 4Ghz octave Preamp that mounts on the end of the antenna. This sucker is FLAT - <1.3db over span. Not much bigger than a N-m to N-m adaptor. It has a great match to the antenna thru the input matching network and is powered thru the coax with a DC Block in the shield room. With a string of ferrites on the cable at random spacing to decouple the feed line coax we see almost nothing in the way of secondary emissions. The Preamp was built to our specs. by MITEQ and I am very pleased with it's performance. I sure would recommend MITEK if you need an octave preamp.
As a side note I also use a co-axial rotary joint on the end of this to prevent cable flex-twist with polarity changes. It also serves as a sacrificial connector to protect the preamp connector from wear and damage. (available from Pasternack or surplus market) Regards, Michael Taylor PE, NCE Hach Group Danaher Corp. From: [email protected] [mailto:[email protected]] Sent: Monday, January 05, 2004 11:42 AM To: [email protected]; [email protected] Subject: Re:Extending Pre- complince test set to 2GHZ. E. Donald, Bilog antennas are nice because you don't have to swap antennas if you only have one mast. The problem with them is they tend to have high loss toward the ends of their spectrum. We have a Bilog antenna and at 2Ghz it has a correction factor of almost 32db. When you factor in the cable loss at 2Ghz, you will need a receiver/spectrum analyzer will a fairly sensitive front end to be able to obtain any kind of headroom for accurate measurements. You will want to have at least 10db of headroom between the noisefloor of your receiver/spec Analyzer (after all the correction factors have been plugged in) and the limit you are trying to measure. You may want to look into just replacing the log antenna if you can find one which performs well up to 2Ghz. If your losses are too high I would look into low-loss coax. If you consider using a pre-amp, that creates additional concerns. A good low-noise broadband pre-amp can be hard to find and be expensive. There is the problem with high adjacent signals throwing off your readings, too. Good luck, Brian Kunde LECO Corp. ____________________Reply Separator____________________ Subject: Extending Pre- complince test set to 2GHZ. Author: [email protected] List-Post: [email protected] Date: 1/05/04 10:10 AM Group: I am currently face with extending my pre-compliance RF emissions test system from a 1GHz upper limit to 2 GHZ to address FCC requirements for clock speeds beyond 100Mhz. My existing system consists of two antennas a bicon for the lower 30 to 300 MHz band and a Log periodic rated for the 200 to the 1Ghz band. I have review some options to specifically address the 1 to 2 GHz but it appears to me that because of the limited dynamic range and cost involved it may be wise to considering replacing both these existing antennas with a broad band combi-antenna which could address the additional bandwidth requirements and eliminate the need for multiple antenna. I suspect that with the increasing trend to high and higher processor clock speed I am not unique in this regard. Could any one else who has had to address this issue share their experience? Donald McElheran Ross Video Ltd. This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: with the single line: This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [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: http://www.ieeecommunities.org/emc-pstc
