Try to get a minimum of 2 wavelengths away and better up to 10. Past 10 you will have pattern distortion but the impedance and gain will be unaffected. Or, get as far as you can. If under 2 wavelengths expect weird behavior.
From: Christopher Gray Sent: Monday, March 14, 2016 10:43 PM To: [email protected] Subject: Re: [AFMUG] Antennas Behind Wood or Glass in Old Building? Chuck, How far back should an antenna be from an obstruction (if the obstruction is mandatory and space is limited)? I found a nice paper with information about empirical RF loss testing through various materials. The main drawback is the tests are for 0.5-2 GHz and 3-8 GHz (skipping 2-3 GHz). Found here: http://fire.nist.gov/bfrlpubs/build97/art123.html Glass test results starting page 141, and wood on page 147. Based on the published results, it seems I might expect signal loss in the 3 dB range when moving from behind glass to behind 1" boards, but I'm not sure I can be as far back as in their testing (1 m from the horn to the specimen). -Chris On Sat, Feb 20, 2016 at 6:38 PM, Mathew Howard <[email protected]> wrote: hmm... looks like bacon is the way to go, if you can't use glass or ABS On Sat, Feb 20, 2016 at 5:33 PM, Chuck McCown <[email protected]> wrote: Well, glass, silicon dioxide is a good dielectric. And dielectric materials can make RF lenses. So if it is flat, it will not refract the signal and should faithfully transmit it with low loss. The amount of loss, assuming you are out of the reactive near field range, is related to a factor called the loss tangent or dissipation factor. It is dependent on frequency. Air =0 (depends on weather and atmospheric parameters) Glass = .02 (decreases with higher frequency) ABS plastic I use for radomes = .01 Wood = as much as .4 Commonly in the .02 range @ 3 GHz if dry. Walnut wood = 1.4 @ 10 MHz Water = .157 Bacon (smoked) = .05 From: Christopher Gray Sent: Saturday, February 20, 2016 4:00 PM To: [email protected] Subject: Re: [AFMUG] Antennas Behind Wood or Glass in Old Building? The building is 200+ years old, so most of the glass is old enough. I've requested to replace some panes with acrylic sheets, but I don't think they will let me. Thanks for the feedback. It sounds like mounting behind glass is much preferred over wood. I have not found good loss estimates yet, but I haven't dug into it too far. On Sat, Feb 20, 2016 at 4:59 PM, Eric Kuhnke <[email protected]> wrote: Old windows are not so bad RF transparency wise. It's even possible to use 80 GHz through glass in high rise office buildings that predate 1982 or so, when metallic coatings and special IR/UV coatings on windows started to become possible. It's the *new* windows you have to worry about. On Fri, Feb 19, 2016 at 7:37 PM, Christopher Gray <[email protected]> wrote: I may have an opportunity to install some radios inside a steeple with some very specific requirements. I'm currently considering 5 GHz and 3.65 GHz radios for this location. I'd like to do some PTP and PMP links, but I cannot afford to lose too much. I have the option between mounting behind 1" thick solid boards, 2x 1" thick solid boards, or behind original windows. Are locations with such barriers even worth entertaining? If so, would it be best to ask for locations behind wood or glass? Thanks you, Chris
