Hello! Sorry, my mailer is not handling the quoting of previous messages very well...
> Put your spectrum analyzer in Peak Hold, take the horn antenna in your > > hand, and spend several minutes sweeping the antenna methodically around > > the equipment location in the room, varying the polarization on successive > > sweeps. Now go read your spectrum analyzer; I think you will have a very > > high probability of having found the peak signal strength, regardless of > > the angle. The tricky bit is that I need to be able to plot a field strength map around the room. (We are involved in numerical modelling of this kind of situation, and it is required for validation.) I would like to be able to have a fairly systematic and repeatable measurement, if possible. > > > I had done a quick calculation of the power I would expect > > Now wait; did you want to measure field strength, in V/M, or power density, > > in W/M^2? Your assumed signal levels are too low to measure with a typical > > 3 axis bolometer power density meter. And you can't relate field strength > > to power density unless you know the wave impedance, which will be anything > > but 377 ohms if you are not in far field conditions. Yes, field strength. I was just referring to the power delivered to a spectrum analyser input! > > 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. > > Lessee... 80dBuV/m - 28dB AF = 52dBuV at the antenna output. Then, give > > about 4dB for cable loss, and it's 48dBuV into the spectrum analyzer. > > That's also -59dBm, but who cares? That's a very usable signal level. Why > > would you need a pre-amp? Also, why would you need a BP filter? Is there > > another strong signal in the room which must be discriminated against? The rooms I will be measuring in, have a fair amount of electronic equipment installed. Colleagues of mine have had cases of intermodulation causing fictitious peaks in a spectrum measurement in a lab, so it is just a precaution. It should also lessen the chance of any strong signals from affecting the linearity of the mixer. (Hmm. A preamp is maybe not necessary then. Although an email from a High-Priced equipment supplier re this issue recommended it... or did they just want to sell me one? ;-)) I have just picked up a paper, "A broad-band isotropic real-time electric-field sensor (BIRES) using resistively loaded dipoles", by Kanda and Ries. (IEEE TR.EMC 23(3), 122-132). This sensor is composed of three short, orthogonal, loaded dipoles. I see Boisvert et. al. (IEEE SYMP EMC, 1991, 214-219) say they have used a sensor based on this BIRES antenna, which they call BOTES (broad-band omnidirectional triaxial electrically small) for field strength measurements from commercial radio transmitting stations. Has anyone used something like this? Regards, 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).
