If you need a spot frequency antenna, you can build it yourself out of just about anything. A quarter-wave slotted sleeve balun is eminently suitable, and as for impedance matching, a 900 MHz dipole made of reasonably thick material will be closer to 50 ohms than 73 anyway.
Calibration remains the issue, but you can calibrate your dipole either against a known antenna, or (this is better) use the three antenna method and do the algebra to extract its antenna factor. The accuracy of your calibration will depend on your instruments. Or, figure aperture and efficiency at nominal, balun loss at 1 dB, and probably be close, just using theoretical figures. For what it is worth, it's possible to make an antenna that works pretty well out of coat hangers and a few ferrite beads. It does not, however, inspire a lot of confidence in those who see you using in it! Cortland ====================== Original Message Follows ==================== Well, only in the GSM band around 900MHz, and later in the 1.8GHz band as well. It just would have been convenient to re-use a good balun. The reason why I have been thinking about the dipole and not an LP or a horn, is that I do not want to use too directional an antenna, as I will be measuring fields in a room where the RF source is a transmitter located some tens of metres outside. I don't have some source in the room which I could aim a directional antenna at. I am therefore not sure of the angle of arrival of radiation when I'm in the room, and I can't be sure I'm measuring the peak field strength in this situation? I had done a quick calculation of the power I would expect with a typical AF of 28dB at 900MHz for a dipole in the HP11966H set, and at 10mV/m 80dBuV/m I should be looking at around -57dBm into a shielded spectrum analyser. I was planning to use a bandpass filter and preamplifier. Have a pleasant day! Kevin -- ----------------------------------------------------------------------- Kevin Williams, MIEEE Electromagnetic Software and Systems (EMSS) [http://www.emss.co.za] Technopark, Stellenbosch, South Africa email: [email protected] tel/fax: +27 21 880-1880 +27 21 880-1727 ----------------------------------------------------------------------- --------- --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], or [email protected] (the list administrators).
