Ed, Thanks for the info on the Empire Devices dipole. I have both Empire and Stoddart/Eaton Ailtech dipole sets. I have both the Eaton equivalent of the EMCO 3115 and a Stoddart original 1-10 GHz logconical or log spiral. The problem is I need to make field intensity measurements of cell phones (850 MHz) and PCS devices (1900 MHz) transmitting up close, closer than 1 meter. I am afraid the larger apertures and distributed structures of the horn and logconical, respectively, will cause the antenna factor to change as I approach either of these antennas from the one meter antenna factor calibration distance. Whereas I know that the gain of a dipole is relatively constant once you are a half-wavelength away, which means I can come much closer.
Ken From: "Price, Ed" <[email protected]> List-Post: [email protected] Date: Tue, 14 Nov 2006 06:09:09 -0800 To: [email protected] Subject: RE: balun info From: Ken Javor [mailto:[email protected]] Sent: Monday, November 13, 2006 4:20 PM To: [email protected] Subject: balun info Experts, I need to build/buy a 1.9 GHz PCS band dipole receive antenna. Haven't found anything to buy. What is a suitable material and balun design to go from 72 Ohm balanced to 50 Ohm coax? Could I use an old T3 balun (400 - 1000 MHz tunable dipole) and just modify the elements? I will need to build two so I can calibrate an antenna factor. I will transmit 0 dBm or less. Thanks in advance! Ken Javor Ken: A dirty little secret about the old Empire T3 Dipole was that it's balun didn't work all the way to 1000 MHz. Everything was sweet until about 950 MHz, and by 975 MHz, the balun could be causing about 5 dB more loss than expected. At 1000 MHz, you would be down about 8 or 9 dB. The competing Stoddart / Singer 90330-2 dipole used a sliding short in addition to adjusting the arm lengths (was that a J-match?). This worked well up to about 1300 MHz. One of the nicest and most flat matches was achieved by Schwarzbeck. They put a little film resistor network at the junction of the dipole arms, creating a purely resistive match. The only drawback was that you sacrificed some sensitivity, and you had to be careful to not use that antenna with a signal source above a few milliwatts. At 1 GHz, you are high enough that horns are not too huge, so why not consider building / buying a rugged little horn like an EMCO 3115 or even an ancient Polarad CA-L? Ed Price [email protected] NARTE Certified EMC Engineer & Technician Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (FAX) Military & Avionics EMC Is Our Specialty - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
