CompuServe Messages

Hi, John…maybe this info will assist >>>What was the range of products that you included? I'm not involved in the lab testing, John, but I may be able to offer some experience with the 900 Mhz band. o With the short stubby antenna directly connected to the unit, the range will be limited to several hundred feet "direct line of site". I specifically say "direct" because I've had problems with the signal from these class of units with the stubby antenna passing signals thru walls. o NONE of these units are licensed therefore when one of these units is used you are taking a chance about local interference. As you are probably aware, the types of signals on this small 900 MHz band is everything from portable phones to CCTV signals to so called wireless LANs, to WAN bridges to pure digital signals. The problem turns out to be: any interference is up to you to correct. You would have no recourse from the FCC in any legal sense. The only possibility is if the interfering party violated the EIRP limits…assuming you, of course, could identify that interfering party. o Antennas are super critical if any distance is expected from these wireless unlicensed systems. I've used a 9-10 dBd (or in other units, 11-12 dBi) gain yagi with fairly good results over paths of 3 to 5 miles. I've had to use a "paraflector" type antenna (brand name) with super high gain to make one path reliable. o The feed line to the antenna is also super critical – The RG-58 type coax just won't hack it! The coax I recommend is the RG-214 type, minimum. The coax connectors are critical – I recommend the type "N" style good into the GHz range. Installation of the connectors onto the coax is also super critical – a major determining factor on whether your system will work or not. o Then there is the small problem of security – SPREAD SPECTRUM IS NOT ENCRYPTION!!!! Be aware than ANYONE including your competitors can and most likely will intercept your wireless signals and be able to produce clear text from them. The vendors of the spread spectrum systems tend to state that the possibility of interception by others is very low (note they don't say the signal cannot be intercepted). In these days of industrial espionage being the way of life from many (most?) companies, why hand the competition your company's secrets on a silver platter by broadcasting them to anyone that wants to receive these secrets? o And…there will be a time (soon?) where the effectiveness of the unlicensed spread spectrum systems, especially on the 900 MHz band, will approach zero. Consider…the CDPD techniques (spread spectrum) being deployed on the cellular band limit the number of users to 10 per frequency. Why? Interference or crosstalk, to use a copper cable term. Each new signal adds slightly to the "noise" of this 900 MHz band. A point will be reached where the spread spectrum receiver 'sees' nothing but noise. (BTW, John – a spread spectrum signal looks and sounds much like random noise, unless you happen to have a spread spectrum receiver set to the proper freq hopping or scan rate.) This is liken to carrying on a conversation in a crowded room…with two or three others talking, it's still easy to understand the speaker. But, consider a football game where thousands are talking…even yelling in the other persons ear doesn't make for understood communications. o About distances…be aware the "line of sight" horizon distance from 6' off the ground is about 5 miles – or less if there are trees, houses, buildings and/or hills. When these spread spectrum vendors talk of 20 miles, ask how high the transmitting and receiving antenna are above the ground <g>. Sorry, John…I get long winded at times. Enjoy the forum, John…and where wireless radio systems are involved – Buyer Beware! And finally, regardless of that the vendors says, these wireless radio systems should be installed by a RF professional. …JJ Read action !re 2865 Enter reply. (/EXIT when done) 1: Thanks for the long-winded reply! I like it that way. 2: I do plan to try to call FreeWave trfo o find out just how optimal 3: their conditions were then they determined the range to be 20 miles. 4: As I said, it's amazing, up they sabut they claim 60 miles on their 5: next 9600 baud device. 6: 7: It'a s apparent you won't be scared by a few numbers, so 8: here's what the literature says: error detec902-928 Mhz, 32-bit CRC, 9: frequency hopping, 3 inch whip provided, eats 10.5-18 volts DC, 10: consumes 180 mA transmit, 100 mZ \A receive, dimensions 11: 1/..6 "x3.9"x7.5", 340 grams. Sounds almost battery-powerable 12: and powrtable, sdoesn't it? 13: 14: With model DGR-115, they claim 115 kbps assuming 75% frequency 15: availability, with system gain of 135 dB, and range up to 16: 20 miles using supplied whip antennas. 17: 18: A single box can be set as repeater, with a commensurate 19: halving of the throughput. They do claim that a max range of 20: 60 miles, at data rate of 9600 baud.degrading to throughput of 9600 baud. 21: 22: So, it's a long way between "seveerral hundred feet" 23: and "20 to 60 miles." Tell me more about the 24: Paraflector. How much? Does it look high-tech? :-)Will it tlook high-tech 25: on the top of my old brick office building? 🙂 26: /post Message # 2867 posted