Long distance or high gain advice

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briester85
DD-WRT Novice


Joined: 02 Dec 2014
Posts: 2

PostPosted: Wed Dec 03, 2014 9:22    Post subject: Long distance or high gain advice Reply with quote
Hello all,

This is long, I'm sorry. I'm a bright guy, but I've never touched a router's firmware before, and have definitely never modded its hardware. I know I'm not alone, so I want to open the theory discussion here, and the only way I know how is to drone on and on about physics and what not so that maybe folks with experience will pitch their two cents in.

I've really been searching hard across the forum for someone in my shoes, but I've found that most folks are either genius or infant in their expertise. So I'm hoping that maybe this thread might be a collaborative effort to provide an entry point for solid IT professionals with loads of experience with computers but zero experience with routers. If this turns out to be of interest to others, I'll compile a comprehensive guide from my "gru-noob" perspective.

If you are able to contribute, please do so to the best of your ability. This guide is being built for intelligent/competent people with a solid background in physics. If we're to delve as deeply into the subject as we'd like, we must assume that everyone here can keep up. We will assume *zero* knowledge, but *infinite* ability to learn. So please, don't hold back.

BACKGROUND. SKIP THIS IF YOU WANT TO GET TO THE GOOD STUFF.

ANYWAY! On to the specifics. You'll find a sister thread to this one in general, where we can talk in more detail about the best router designs for specific purposes. This thread will focus on the hardware that makes it happen, and how the physical wifi signal can be improved.

The abstract scenario: There are surprisingly few categories that all router needs fall under. Excluding software needs, (VPN, security, intelligent transmission decisions...) people are generally looking for:
1. Hyper-speed, or if possible, ludicrous speed.
2. Long distance.
3. A great many simultaneous connections.
4. Material penetration.

The concrete scenario: I am CEO of a mid-size photography company. We often provide services to large organizations in which several photographers are generating and transmitting data in front of paying customers, who we want to treat courteously, i.e. get their photos to the server quickly. These photographers aren't technical people. The network has to be set up in an arbitrarily hostile environment, (e.g. unpredictable building materials, moderate distance to the router, fifty access points on the same channel, etcetera,) and it needs to adapt to that environment without excessive configuration.

HERE IS WHERE THE REAL THREAD BEGINS.

Fast, long-distance, polyfunctional. Choose two.

My intuition is that directional antennas have a better signal/noise ratio, and cut through crowded traffic more effectively than omnidirectional systems. Omni systems, of course, are more adept at communicating with several devices at once, but suffer from quadratic volume falloff. (Err... I mean they get slow with distance super fast outside their optimal bubble.) But you know what? You can throw money at the crowd issue. Speed and distance take actual expertise. So lets focus on that.

Amplifying signal strength is a task that could easily destroy sensitive hardware. Has anyone here successfully amplified their router's signal? How did you go about it? Were there unexpected lessons that you could share with us?

An excellent primer on the physics of this project can be found here:
http://www.antenna-theory.com/tutorial/txline/transmissionline.php

tl;dr: high frequency radio involves wavelengths comparable to the size of their transmitting hardware, and will either work in harmony with a line or destroy itself with dissonance, depending on how closely the length of the transmission line matches the wavelength of the signal. (Literally. Like, the physical length of the wire leading from our mod to the end of the line.)

If I'm not mistaken, the impedance of the line if its out of tune would manifest as heat loss? Or would it be worse than that? A cause of noise perhaps?

In any case, does anyone have specific hardware that they might recommend for an amp mod?

Oh, wow. 1:30 am. More later, if anyone hops in.

THANKS!
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Kronos69
DD-WRT Novice


Joined: 08 Nov 2014
Posts: 12

PostPosted: Wed Dec 03, 2014 15:37    Post subject: Reply with quote
Recent consumer hardware, at least, usually overrides bad user input regarding tx power: it's almost impossible to damage your router with an high tx power setting in DD-WRT, based on my little knowledge.
For example, the latest Broadcom driver doesn't even give you the opportunity to set that parameter other than auto.
Then, simply maxing the tx power of the router, unfortunately won't give you better rx, being that dependent on the client's own tx power.

Directional antennas between bridged routers and powerlines are two common solutions to avoid running cables through large homes.
The problem in office environment is that the more directional the antenna is, the less useful it obviously becomes to service multiple mobile clients, which is where most of the usefulness of the WiFi resides. If you keep a wider angle, directionals (like this cheap but functioning mod http://www.freeantennas.com/projects/template2/index.html) are useful if the unit has to be placed in a corner, but nothing beats the versatility of an omni placed in the center of the office room, IMHO.
If you really want to try with some antenna tweaks, remember that longer omnis usually add approx 1db gain every 10cm, if I do remember well, stretching out the "donut" shape of the covered area, and that would benefit both tx and rx, but you need to keep an eye to the bg noise, that gets amped as well.

In office environment, it should be no hassle to directly run an eth cable between the devices: usually, more of less powerful APs placed in the correct spots of the building, keeping an eye open on channel overlapping, do their jobs better than one/few more powerful units trying to cover up more space boosting their tx power. The latter seems to be more cost effective, until you discover that the router can reach the clients, but not vice versa. And buying an external adapter for every notebook isn't that cost effective. So, the real maximum range achievable, is based upon the clients' max range. DB gain antennas on the router as said MAY help, if the place doesn't suffer of much noise.

The new and faster AC standard relies on 5GHz networks, that, being at higher frequency than the "old" 2.4GHz networks,, are blocked more easily by common phisical obstacles (walls, etc.). 2.4GHz would be more cost effective requiring less units/sqft, seen that uploading pictures doesn't seem to require much overall bandwidth to me, but you have to consider network congestion, so dual band N units running at both 2.4 and 5 GHz may be the wisest choice in terms of benefits/costs, 5GHz N is way less congested than 2.4, that may be kept for legacy devices, and the unit's cost is usually way less than an AC unit.

You can easily map where to place your APs using free tools like inssider, and if you want to do an ever better job, you can buy one of those receivers that show the noise that can't be otherwise detected with standard wireless cards (cordless phones, microwave, radio remotes, etc.).
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