CWX Equipment (was Re: [NCLUG] Mesa Networks (broadband))

John L. Bass jbass at
Sat Aug 17 02:38:58 MDT 2002

	John, what are the issues using a standard recent-model 802.11b radio 
	(pushing 100mW)?  E.g., Cisco 350, Zcomax, Symbol, Senao (okay, it's 200mW, 
	so drop the power), ...  some of these can be picked up pretty cheap (except 
	the Cisco).

It's easy to build configurations with 200mw radios that exceed part 15 regulations
and are subject to $100,000 in fines if you make a configuration error, and criminal
charges if you intentionally violate the regs. There are good reasons to avoid these
unless your system is specifically engineered to be conforming regardless of driver
configuration and you have the equipment to actually measure the RF output levels
as required by Part 15 in case there is a driver or card failure in the power

They do not plug and play with Aironet link management diagnostics making the
link impossible to manage/debug when there are problems. This is a critical issue
trying to evaluate the link level retry rate to make sure the link has acceptable
margins. A poor link can consume 70-90% of air bandwidth with excessive retries
completely transparently (IE without loss) at the IP packet level. The Cisco350
partially works in this regard, we have two in our system, and I would prefer
they only be used when 4800 series radios are not available.

We have several links in our system with very marginal link performance, and
excessive link retries. And while they do not cause significant performance
problems for the network at large today, as we grow the excessive air resources
these sites use will have to be brought into an acceptable range. The link
level diagnostic tools in the Aironet/Cisco radios are a critical management
and link qualification tool.

There are plenty of used 4800 series devices on the market at prices that are
very price competitive with these products. The driver support for 4800 card
based products is standard with nearly every Linux release - so out of the box
installs work well.

Except where a notebook is used as a router gateway, I strongly suggest that
using PCMCIA cards with the mmcx pigtail be avoided. This connector is extremely
fragile and tends to fail in several ways, including mechanical damage in the
radio mmcx connector with frequent pluging and unplugging. Even then it's
highly recommended to mechanically strain relief the cable/connector and touch
it as little as possible. Also, the PCI4800 radio cards are much easier to
deal with since they do not require all the PCMCIA driver software which has
some significant querks in many Linux Distros/Releases.

Mike's system was installed with the help of a friend that was a licensed ham.
Because of the professional installation requirement for non-kitted systems,
and the knowledge/skills/equipment needed to troubleshoot we strongly suggest
most people find a friend or hire a contractor that is a qualified wireless
radio installer. Collins Communications is pretty cheap here, and can save
you many hours of fumbling with relatively simple problems.


	For cabling... you can get pigtails (e.g., MMCX connector to N-Male 
	connector short cable for Cisco/Aironet cards) and cables to get to the 
	antenna from with good quality and decent pricing.  19 inch 
	pigtails go for $21.  25 feet of LMR-400 "jumper" cable w/N-Male to N-Female 
	goes for $40.  For the roll-your-own types out there, LMR-400 is 0.62/foot, 
	LMR-600 is 0.83/foot.  (What's the difference you might ask?  LMR-400 loses 
	signal at about 6.5 dB per 100 feet, LMR-600 at about 4.5 dB per 100 feet, 
	so depending on how far your antenna is from your radio, choose 
	appropriately...)  N-type connectors go for about $4.50.

	I can't help hedge against the other costs.  ;-)

	ASCII art for the confused:
	(this is my installed configuration, which I believe is typical)

	  \  Dish             "Jumper" cable                 Pigtail      Linux
	   \                                                               Box
	    \    Lightning                                              _________
	     \   Arrester                                              |         |
	   |--|---[<=>]---------------//------------------> ]---------> ]radio   |
	     /    N | N                                   N N        M |M        |
	    /     | | |                                   | |        M |M        |
	   /      M | M                                   F M        C |C        |
	  /       a | a                                   e a        X |X        |
	          l | l                                   m l          |_________|
	          e | e                                   a e
	            |_______                              l
	        outside     |    inside                   e
	       (probably)   |

	PS: John, they've even got LMR-1700 for $6.95/foot!  Hoowahh!

	Michael Milligan  --  Free Agent  --  milli at

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