Connecting two wireless routers together

Hi,

As posted before, we are trying to set up a test bed with a bunch of Linksys WRT54GL routers. I would like to be able to cable the routers together so that they are not using OTA to communicate. Ideally, there would be an adjustable attenuator in the cable as well so we could simulate distance.

In a naive attempt at doing this we tried wrapping the routers in tinfoil (after removing the antennae) to isolate them. This worked pretty well. Then we tried wrapping a cardboard tube in tinfoil and connecting the routers by placing the tube over the antennae RP-TNC connectors on the routers. (the naive part!) This didn't work at all - no signals got through.

More research on the internet found me at this site:

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shows a test setup of wireless nodes connected with 'RF cable'. My questions are:

Would this actually work? Assuming it does: Are attenuators required so that the output from one router doesn't damage the other router? What cable is best to use for this application? Any other advice (note - we don't have any experience in this field)?

thanks, charlie

Reply to
Charlie
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"Charlie" hath wroth:

Yep. Been there and done that. What you want is a portable RF screen room or shielded box. Since you're only trying to block a small range of frequencies, this should be easy. See:

for examples. I'll spare you my photograph of the mylar foil and aluminum duct tape "tent" that I constructed for my first attempt at shielding. Search Google for "RF test enclosure".

Until they overheated. That's why I gave up on foil. Also, there was considerable leakage from the CAT5 cables on some routers.

Chuckle.

In the future, please wrap your URL's with so that they don't wrap.

Sure. However, there's quite a bit of detail missing. There are no combiners shown in the picture. You need some what to linearly combine all the tx and rx signals. A simple resistive combiner will do, or you can use a power splitter.

Be sure to terminate any unused ports. I use an 8 port device.

Getting attenuators that don't leak and are accurate is more of a challenge. You'll need to attentuate the maximum tx power down to the baseline noise level. That's about: +20dBm - -90dBm = 110dBm range. That's much more than can be easily found with the common switchable attenuator that might have perhaps 60dB of adjustable range. Fortunately, you only need half the 110dBm of each leg of the power splitter so a mess of common 60dB switchable attenuators will barely work. However, I suggest also buying a mess of fixed attenuators to make life easy on the attenuator.

One big problem will be calibration. You're going to have quite a bit of hardware floating around that may not necessarily be accurate at

2.4GHz. I strongly suggest you spend the time calibrating the attenuation of the various components at 2.4/5.7Ghz before you discover that your switchable attenuators were previously used as someone's dummy load.

Oh yes. LOTS of attenuators. The typical wi-fi receiver has a very limited dynamic range. My guess(tm) is that they can't really handle signals much stronger than perhaps -20dBm before blocking, saturating, or overloading. You might damage the receiver with anything over perhaps +30dBm (1 watt), but that's not possible. I've done some crude damage testing and found that most access points can handle at least +20dBm before doing any damage. However, that's because the diversity switch PIN diodes effectively limit the input power. I don't know what will happen is the PIN switch wasn't there.

Well, for TNC and SMA connectors, I use RG-400 and LMR-240. For N connectors, it's all LMR-400 or LMR-400 ultraflex. The stuff is really stiff. Make sure you use decent crimp connectors.

Yes. Find someone with microwave experience to help. Be prepared to buy some rather expensive RF test equipment.

Reply to
Jeff Liebermann

On Wed, 31 Jan 2007 09:56:11 -0800, Jeff Liebermann wrote in :

That's recommended practice, but _won't_ necessarily stop the unwanted wrapping. It notably doesn't help in Forte Agent.

Reply to
John Navas

John Navas hath wroth:

Wrong. I use Forte Agent 4.1/32.1088 for most of postings and have found that wrapping URL's in now prevents wrapping. Earlier versions just made a mess. If you look at any of my posting that include URL's, they don't wrap or do weird things to the line spacing. Version 4.2 just was released, and I have no idea what it does.

Reply to
Jeff Liebermann

Jeff Liebermann hath wroth:

I just installed Forte Agent 4.2/32.1177. No URL wrapping using the same URL as before:

Reply to
Jeff Liebermann

On Thu, 01 Feb 2007 08:41:28 -0800, Jeff Liebermann wrote in :

No, just different versions.

True. Which is what I meant. Agent lost its way IMnsHO with its change in basic architecture after version 1.93, which I still use, turning a lean mean fighting machine into sluggish bugware. (FYI, I dutifully reported some of those bugs, but failed to generate any real interest in fixing them.)

My original point remains: Wrapping URLs in , while a good standards compliant idea in general, _won't_ necessarily eliminate bad wrapping. That it works for you is great, but it won't work for lots of others, including me.

Reply to
John Navas

You might want to try again. The original writers of Forte Agent bought the company back from the clueless previous buyers and are again scribbling code.

I haven't seen much in the way of bugs lately. There have been 8 releases since 1.92.

Works for me in Forte 4.2. Also seems to work with Outlook and Outlook Express. However, Thunderbird 1.5.0.9 seems to word wrap.

All things come to he who upgrades.

Reply to
Jeff Liebermann

On Fri, 02 Feb 2007 01:46:42 GMT, Jeff Liebermann wrote in :

I know that. I'm talking about their new versions of Agent.

My bugs still exist as of the last time I tested. Likewise the sluggish performance.

The point is that framing in , while a good idea in general, is not any sort of assurance that bad wrapping won't occur.

Really?! Whatever happened to:

The effect is also self-perpetuating. Features get added faster than bugs get fixed. It's a natural law or something. This effect eventually results in a bloated monster ...

So, there we have the logic: In order to sell upgrades, it has to be noticeably buggy. In order to be sufficiently buggy, it has to be big and bloated. In order to look like an improvement, it has to have new features.

Software tends to grow faster than the bugs can be fixed. Bloat is in, quality is out. Eventually, reliability and scaleability will suffer. Bigger is better or at least sells better.

Few users would upgrade to the latest version just for the new and wonderful features that nobody really needs. They upgrade because there's a small hope that the new and improved release will have fewer bugs. This never really happens because features and functions get added faster than bugs get fixed resulting in a bloated application that's full of known bugs.

My conspiracy theory is that all software manufactories, intentionally leave bugs unfixed, so that the customer has an incentive to purchase upgrades and support. If the stuff actually worked out of the box, people would simply use the last version forever, and the software manufactory will go otto biz. Therefore, bugs are permanent and a good thing.

On a similar note, if some company accidentally produces something that actually works, an incentive to upgrade must be found. Manufacturing groups, consortia, and industry committees, meet in the inevitable smoke filled room, and conspire to introduce new technology, new acronyms, and standards in copious quantities. Soon, everything you own that actually works, is obsolete, incompatible, or unsupported. This is called progress.

Since the sales of MS NT4 have shown that the customers are unconcerned about reliability, stability, and performance, companies are forced to sell their products on the basis of features and support acronyms. Unfortunately, acronyms an features are added faster than bugs get fixed, resulting in bloated, oversided, feature infested, and buggy software. When the feature bloat grows to the point of non-functionality, a totally new product is invented to fill the product niche.

I've got a lean mean stable release with very few bugs. Tell me again why I should upgrade? ;)

Reply to
John Navas

Well, I must admit that I don't use every single feature in Forte Agent. Still, what I use works well enough.

Well, ok. I don't notice any sluggish performance on my systems which are certainly not state-o-de-art.

There is a line length limit where things autowrap. I don't mean the configurable limit that's usually set to 75 characters. I mean the

255 or so character limit probably caused by a fixed length buffer somewhere in Agent. That is sometimes a problem with Linksys URL's, which tend to be rediculously long. Otherwise, non-wrapping has worked just fine when I've used it in the last 3 or so versions.

Yep. I said that, I believe that, I even practice that. Give me features or give me death (of the product). Does the world really need MS Vista?

Yep. I said that. I won't go so far as to suggest that vendors intentionally introduce bugs in order to sell future upgrades. However, I will suggest that bugs are often ignored in favor of adding features, where time is limited. I gave up joining beta test ordeals after my bug reports were ignored, but my feature requests got their attention.

Yep. I said that. I don't think Forte Agent qualifies. There have been features added, but there have also be releases that are overwhelmingly bug fixes (i.e. version 4.1). There was a big leap in code size from 1.9x to 2.x, which I guess qualifies. However, as I understand it, the changes in architecture and design were required to supply new added features.

Yep. I said that. I think Vista might become a good example of this. Lots of features that nobody wants or is willing to pay for. Most of the customers that are bugging me about Vista are the ones that are having reliability problems with some part of Vista.

Yep. I said that. If the stuff worked, nobody would be asking questions in the newsgroups, nobody would need to read the manual, nobody would be upgrading to later firmware, and few would upgrade to the latest versions unless they needed the features.

Yep. I said that. Progress is measured in sales and stock prices. Those don't go up unless the company releases new products or upgrades on an almost continuous basis. Want to pump up the stock price? Just issue a press release announcing something new and/or improved. Know any company that has been selling the same version for a long time?

Yep. I said that. It's evolution in action. There's a good reason that the dinosaurs tended toward titanic growth. Being big is very defensible. Same with software. Want to avoid being eaten by the competition? Easy, grow big.

So you can have quoted URL's that don't wrap.

Reply to
Jeff Liebermann

If you can identify them, I might be able to test again.

YMMV. I use Agent 3.3 and its far from sluggish. Considerably more nippy than the other newsreaders I tried, in point offact. Maybe it was a h/w issue.

Sure. but Jeff's point is that it _does_ remove instances of bad wrapping the readers he tried.

V3 had enough new features, and no bugs that affected me, to make it worthwhile. YMMV of course.

Reply to
Mark McIntyre

On Sat, 03 Feb 2007 15:26:02 +0000, Mark McIntyre wrote in :

I doubt you'll want to go through the trouble -- the most critical bug for me only arises when Agent is accessing synchronized Briefcase or Offline Files (resulting in destruction of the files). I asked several times for a fix but never got any sign of interest in the issue, which is part of what's turned me off on Agent upgrades.

Agent v1 is resource lean and lightning fast by comparison with later versions. If, for example, a system is loaded with heavy multitasking and disk I/O, v1 performance will be acceptable, whereas the performance of later versions is too painful to be usable. That's not something I'd give up, especially given the showstopper bug (above), unless I got something important to me in return, and there's nothing in later versions that's terribly important to me.

Jeff actually made an _unqualified_ statement. My point is that framing in only helps in some newsreaders, making it a bit self-centered to insist that it be done for one's own benefit. Why shouldn't Jeff instead get a newsreader smart enough to avoid wrapping long URLs that aren't framed in ? It's not terribly hard to do from a design standpoint -- Agent v1 is already smart enough to properly parse URLs without framing, and it almost certainly would be simple to fix the wrapping issue without requiring framing.

YMMV indeed -- the new features in v3 aren't terribly important to me, especially as compared to what I'd have to give up to get them.

Reply to
John Navas

On Sat, 03 Feb 2007 04:58:51 GMT, Jeff Liebermann wrote in :

Because Agent v1 is an excellent newsreader, my own bar is higher than "well enough".

Agent v1 is resource lean and lightning fast by comparison with later versions. If, for example, a system is loaded with heavy multitasking and disk I/O, v1 performance still will be acceptable (to me), whereas the performance of later versions is too painful to be usable (to me). That's not something I'd give up, especially given the showstopper bug (to me), unless I got something important to me in return, and there's nothing in later versions that's terribly important to me.

My point is that framing in only helps in some newsreaders, making it a bit self-centered to insist that it be done for one's own benefit. Why shouldn't you instead get a newsreader smart enough to avoid wrapping long URLs that aren't framed in ? It's not terribly hard to do from a design standpoint -- Agent v1 is already smart enough to properly parse URLs without framing, and it almost certainly would be simple to fix the wrapping issue without requiring framing.

About as much as it needs Agent v3+ (IMnsHO at least).

Surely you're not so naive as to buy that? Especially since you don't seem to buy similar claims from Microsoft and others. ;) New features could have easily been added to the Agent v1 codebase. The major architectural change was to wxWindows (aka wxWidgets ) in order to facilitate portability, but at the cost of bloat, inefficiency, new quirks & bugs, and delayed features. And of course the upgrade wasn't free.

That's why I'll probably use Agent 1.93 forever -- it works very well indeed, is easy to use, lean on resources, rock solid, and has all the features I really want.

Sure, but not in the consumer market.

At the cost of bloat, inefficiency, and showstopper bug. No thanks.

Methinks you have a double standard for Agent versus Vista. ;)

I likewise continue to use Office 2000 -- there simply isn't enough of value to me in later versions to justify the cost and drawbacks of upgrading. And I'll likewise probably continue to use Windows XP Pro for years to come.

Reply to
John Navas

On Sat, 03 Feb 2007 04:58:51 GMT, Jeff Liebermann wrote in :

Good question. One would think Microsoft had learned its lesson and would make sure that Vista is at least fully compatible with XP, but such is not the case, a big reason not to upgrade:

Apple to Vista upgraders: 'Wait'

Apple has told iTunes users to "wait" before upgrading their computers to Microsoft Windows Vista, saying its music software may not work properly.

The company said it is aware of several issues including problems playing purchased files and synchronising data.

...

Compatibility issues

Apple outlined the compatibility issues and suggested workarounds for those already using Vista in a support document on its website.

Some problems listed were: failure to play music and video purchased from the iTunes store; poor animation performance; and a failure to automatically synchronize media, contacts and calendars.

Apple has also offered Vista users a downloadable tool that will "repair permissions for important files," but does not specify the precise nature of the incompatibility.

[MORE]

iTunes is a very popular Windows application, so there's really no good excuse for this.

One wonders how many more such land mines await unsuspecting victims ... er customers.

"Just say no." [for the foreseeable future]

Reply to
John Navas

Chuckle.

Anyways we got something to work well enough for our purposes. We wrapped the routers in tinfoil - 2 layers - and poked holes in it for ventilation. Of course, this is not a perfect RF shield but we found if we keep the routers about 1 foot apart they cannot see each other. A local shop here () helped us with a cable. It's simply a RP-TNC to N swedge, a 10 db attenuator, a 5 foot cable, and then swedge back up to RP-TNC. I realize this is far from ideal but it does what we want - allows us to direct our RF signals to a particular router. More importantly, it's cheap; about $35 CDN.

Thanks for all your help Jeff!

charlie

Reply to
Charlie

On 5 Feb 2007 11:11:56 -0800, "Charlie" wrote in :

In the future, please trim quotes down to the minimal relevant portion. Thanks.

Reply to
John Navas

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