"Robert F. Schaefer" wrote:
> > Can you clarify a few things....... > > > > When you say "hardware" do you mean Tx-Rx, Ants, RF Coax, etc.? > > Can you explain further "Recommendations for Topology"? (are you > trenching?) > > What do you mean by "incidental radiation with a highly directional > antenna." > > 1) hardware as in will a brace of off-the-shelf APs do what I want, or would > peaseas with wireless NICs be a better choice, or even something like a > Soekris Net4521 at each node. Probably I'll need a directional antenna for > some of the links, but the first one might be able to squeak by with a good > omni at each endpoint. I'm mainly looking for the link part here, as a > gateway will be taking care of encryption at each node. Ok, I understand now...... I have seen many wireless installations over the years that have tried to use "Consumer" grade equipment in a commercial / Industrial setting. To avoid service issues use a higher grade of equipment. Check out www.tessco.com for the proper hardware. > > > 2) topology as in point-to-point everywhere, or mesh network, or ? I'll be > starting with two nodes, but expect to have 6-7 before I'm done-- all > located within a less-than-one-mile radius and various minor obstructions in > between. I could probably grade them into primary, secondary, and tertiary > depending on expected traffic volume. Internet connections are currently > individual broadband or dialup links, I'd like to consolidate them into one > or two. Intranet traffic will probably account for less than 10% of network > traffic overall. > > (I'm hoping to accurately map the endpoints and any intervening obstructions > Real Soon Now, but my Copious Spare Time, isn't...) Topology in the RF world means something totally different, any way I suggest you perform some RSSI / BER measurements at each point. You also may want to measure the noise floor in the area. This will help you calculate the C/I (Carrier to interference ratio). Interference is going to be your main obstacle. The Zhao and Haggman formulas for OFMD are in the following PPT presentation on (http://www.ece.utexas.edu/~eerwa/wireless%20comm/OFDM1_presentation.pdf ) "Inter-Carrier Interference Cancellation in OFDM Systems" This will help you visualize some of the challenges you face. > > > > > Incidental radiation is generated by a device that radiates radio > frequency > > energy during the course of its operation although the device is not > > intentionally designed to generate radio frequency energy, antennas are > usually > > not considered incidental radiators. > > Well, I tried to talk the talk, but I guess I don't know as much as I > thought I did. I'm concerned about RF energy ending up where it's not > supposed to be. No problem- If you talk the talk you must walk the walk....... in the RF world this is not easy. For linking your access points I would recommend a Yagi or a Corner reflector. If you are concerned about "unwanted radiation" from your yagi you should look at Front to Back Ratio- Horiz Beamwidth- Vert Beamwidth- Ant Patterns- > I understand from lurking that with high-gain antennae even > low-power transmitters can be dangerous, as well as illegal. More illegal than dangerous, it will be pretty hard to exceed the Specific Absorption Rate (SAR) with an input of less than 1watt. > I may not be > overly fond of the guy across the street, but there's no reason for me to > carelessly irradiate him. Understand. > Several prospective endpoints are rather low to > the ground and somewhat concealed by trees, but a tall mast would not be my > first choice. If you do go with a tall mast don't forget to calculate signal loss do to the cable length. finding low loss cable @ 2400 Mhz can be costly. Any gain realized by high gain antennas will be lost and you will end up with a "Unity Gain" (no gain) situation. Again take RSSI /BER measurements before you make your final installation. > As my budget consists of unspent lunch money anything I can > build myself is a plus, and making my own directional antennae _seems_ like > a win, but perhaps I just don't have enough information to make a good > decision. > Ouch..... Lunch Budget Engineering I remember those days. I suggest you "Buddy-up" with some manufactures who will often "donate" equipment. I know they probably have been barraged with requests but try to find an "IN". Lucent, Moto, CISCO, etc. were always good to me when I was in school. Maybe a "grant" maybe in order. http://wifinetnews.com/archives/003234.html http://wifinetnews.com/archives/003128.html http://dailywireless.org/modules.php?name=News&file=article&sid=2344&src=rss09 > > > > > *In-tunnel coverage is difficult, at best, to predict with certainty. > Some > > Ah, I see one of my problems here-- when I said tunnel, I meant a secure > encrypted data path from point A to point B, not a physical tunnel. Sorry > for the mis-communication. Oh- My Bad, I guess I need to bone-up on my Wi-Fi Hi-Five "Slang"......... (Everything is literal for us Engineers aka Anal) -- NYCwireless - http://www.nycwireless.net/ Un/Subscribe: http://lists.nycwireless.net/mailman/listinfo/nycwireless/ Archives: http://lists.nycwireless.net/pipermail/nycwireless/
