Ralph - for someone who has 30yrs of Experience in RF and 10yrs of "RF Engineering" you sure don't know much do you other then how to toot your own horn?
Please give us ALL a lesson in "radio".... Please give me the calculations of 150ft of LDF4-50A using a 250mw amplifier with a 17db RX gain...... and then compare this to a 250mw radio at the top of a tower (which by the way will exceed EIRP limits if going into an Omni) Your original posts to the group were and are misleading by saying that using heliax or LMR600 to go up to an antenna is the "wrong" way to do things..... Therefore I call it B *cough cough* S.... JohnnyO -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ralph Sent: Saturday, March 17, 2007 5:47 PM To: 'WISPA General List' Subject: RE: [WISPA] LMR600, LMR900, Heliax If EVERYONE is misled, then EVERYONE needs a lesson in radio- especially you Jonny-O. My "BS" as you call it comes from over 30 years in 2 way and data radio and over 10 years in RF Engineering. But before you tell folks to leave radios on the ground, you'd better check your sources again. I'd love some of your $1.50 per foot 7/8" Heliax. 7/8" Heliax was $3.00 per foot 25 YEARS AGO! Back then, 1/2" Heliax was about $1.80 per ft. I'm surprised that the price hasn't changed that much since then, but I'll bet there's not as much copper in it. I know the center conductor is copper clad aluminum now. Maybe your $1.50 7/8" Heliax was the piece that got water in it and was discarded by the radio shop. For 900 MHz, 1/2" would possibly *adequate* but I would not recommend it at all. For 2.4 GHz, you might consider 7/8", but for 5.8, better forget anything less then 1 5/8", but most real users use waveguide. Heck- even XM Radio uses elliptical waveguide at their frequency of about 2.3 GHz for their terrestrial transmitters- and they have 100 watt power levels! I can send you a picture right now! Putting the radios at the antennas saves vast amounts of costs in feed line. Your tower owners are happier, and your rent might be cheaper. I know that we charge the other WISPs we rent space to much less because they use CAT5. The best use of $ for RF is to use antenna gain. You have nearly wasted that if you long feed lines of improper sizing. As far as justifying my statements- I don't really need to. Anyone can do the calculations, taking feed line and connector loss and subtracting it from antenna gain and radio power. The procedures and the numbers are there and speak for themselves. Andrew makes a spiffy calculator for this purpose and it is available, free, at http://www.andrew.com/downloads/ilcalc/default.aspx All of the following figures include a pair of Andrew N type male connectors. A 100 foot long piece of Andrew LDF4-50A (1/2") at 2450 MHz has a loss of 3.64 dB. That's over half of your power wasted. List price (cable only) is $1.56 per foot. The connectors are $20.00 - 45.00 each depending on material. A 100 foot long piece of Andrew LDF5-50A (7/8") at 2450 MHz has a loss of 2.1 List price (cable only) is $3.58 per foot. The connectors are $34.82 each A 100 foot long piece of Andrew LDF7-50A (1 5/8") at 2450 MHz has a loss of 1.28 dB List price (cable only) is $9.33 per foot. This cable is very heavy so figure in a lot of freight as well. The connectors are $153.22 each Now if you would like to use a very efficient feed line, you can use EW20-25 Elliptical waveguide, which is technically the correct cable for microwave frequencies like these. It will cost you $33.40 per foot. The connectors are only about $1570.00 each, but you will have onlt .45 dB of loss in 100 feet! Remember that these numbers are only for 2450 MHz. 5.2 and 5.8 loss is higher, but waveguide for that frequency is lots smaller and lighter and has only 1.35dB loss at 5200MHz. $23.5 per foot and only $500.00 per connector. I'm not going to justify my statements on amplifiers either. You can (and should) read Part 15 for yourself. Go try to get Teletronics to give you an FCC waiver, or go ask your AP manufacturer, assuming they are even building certified equipment. The problem I see with many of today's WISPs is that they are making up their own rules to suit themselves. Recently I saw a WISP post a recommendation to another WISP to set up a device to intentionally interfere with Wal-Mart's 900 MHz RFID systems. Nothing I say can stop or even sway any of you- that will have to come from someone with that kind of clout. Maybe a competitor who follows the rules will come into your market, or maybe you'll cause a problem with something licensed and you'll have a white Ford Explorer with a government tag and antennas hidden in the headliner pull up at your tower- but why would it even have to come to that. WISPS are taking technology that was designed for in-building LANS and doing remarkable things with it. A few years ago it was a pipe-dream to be able to do this stuff. Now we do it with off the shelf devices and do a damn good job. Let's just make sure we set the good example! (wow- I feel like Patrick) <grin> -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of JohnnyO Sent: Saturday, March 17, 2007 8:32 AM To: 'WISPA General List' Subject: RE: [WISPA] LMR600, LMR900, Heliax Importance: High Jeez Ralph - your post is misleading to EVERYONE that is reading this. -- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.446 / Virus Database: 268.18.13/725 - Release Date: 3/17/2007 12:33 PM -- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
