The best dual-purpose router....

[lauzer]

Hey guys,

Brilliant site, brilliant people on here so thank-you in advance for your time & racking your brains.

Anyone know of any routers that will allow one external antenna to capture a wi-fi signal and the other external antenna to transmit? Preferably in black as all mt other electronics are. I'm happy to flex my inner-geek with any complex tweaking and/or additional firmware.

Cheers all!

Loz

 

[stevech]

Separate transmit and receive antennas aren't used in WiFi... because IEEE 802.11 (which the WiFi alliance uses), is a "half-duplex" protocol. That is, 802.11 cannot, by design intent, transmit and receive simultaneously.
Now with MIMO (options in 802.11n), there can be simultaneous transmissions but antennas for MIMO are typically internal and, like basic 802.11 (as above), the antennas are switched between transmit and receive.

So, the simple answer is that there's no need for separate transmit and receive antennas. It's essentially the same as using a handheld walkie-talkie radio - one antenna because it's a half-duplex communications method (the push-to-talk). In WiFi, to simplify, the push-to-talk is automated.

With other than the fanciest new MIMO 802.11n, there are often two external antennas. These are used in "switched diversity" - where the signal strength for each incoming data frame is measured in a few bits of the frame header for each antenna. The switch is made in a fraction of a microsecond. Then the "best" antenna is used for the rest of that frame. Later, a frame from other client device may be better on a different antenna.

The technical term is spatial diversity - with the basis being that in non-line-of-sight conditions, multipath and reflections may cause one antenna separated by a several wavelengths from the other, to "see" a quite different delay and reflection situation than the other. In high-end MIMO, they add Frequency Diversity - same concept, but the idea is that the conditions on a different channel (frequency) may differ. Then, to add multi-stream MIMO, the diversity ideas are applied concurrently, without switching antennas or frequencies - then there is a "vote" in a processor that chooses the best stream received vs. time, to get the lowest bit error rate.

Clear as mud?

 

[thiggins]

Anyone know of any routers that will allow one external antenna to capture a wi-fi signal and the other external antenna to transmit?

What are you trying to do?

 

[lauzer]

Crikey- I do feel somewhat privileged to have such elite attention to my mediocre query. Thank-you ever so much.

@Steve
Wow- after some brushing up online, I do believe I may have deciphered your very decisive explanation and feel all the more whole for the new understanding you have bestowed me. So, thank-you for your very wise words of wisdom.

@Tim
I am basically trying to pick up the very weak signal from my landlords WIFI(to which I have no access for tweaking) using a router with at least two external antenna inputs. I should then be able to attach all my local wired devices easily but would utterly love it if the router could also allow WIFI in my flat as the original signal is too weak for my WIFI devices to adequately pick up. I know of the AP/Bridge type routers but most are singularly solution specific which would result in the purchase of a second router to achieve local WIFI, forcing the AP/Bridge to become obsolete when I move and obtain my own ISP.

I'm aware some routers are dual-band, thus use the external antennas for the 2.4Ghz and some internal antennas for 5Ghz. Would it be perhaps be possible to have the 'externals' configured to pick up the weak present WIFI and then the 'internals' set to allow my WIFI devices to connect to?

I'm not too fussed about price at this point, however, we all love a good bargain. The only stipulation I have is a black casing so as to match all my electronics and to not induce a sore thumb.

I apologise if my lack of sleep has evoked a degree of ineloquent articulation. Thank-you eternally for your time in alleviating what has been several dozen agonising research sessions of failure.

Respectfully yours,

Loz

 

[thiggins]

You main problem is that the bandwidth you are going to get with a weak signal will be very low. For decent bandwidth, you are going to need a strong signal.

The best option would be to use two devices: one to pick up your landlord's signal and the other to redistribute it wirelessly. The first device would be a wireless bridge, the second could be your normal router.

You could try a wireless range extender or repeater if you opt for one device. But repeating the signal automatically reduces the bandwidth (throughput) available to you by 50%. Given the weak signal to start with, your Internet bandwidth would be unusable.

 

[stevech]

I suggest you pick up the landlord's signal (legally) using a WiFi bridge. Put the bridge in the ideal place to receive that signal - outdoors, window, attic, etc. Then run a cat5 cable from the bridge to the PCs. Or run it to an ethernet switch. Into the switch, you can connect PCs with cat5 ethernet cable, or you can connect a WiFi access point (AP) which will create another new WiFi coverage for you.

The bridge might need a high gain highly directional antenna- to get a strong enough signal to make this viable. If you want to go this route, I'd suggest trying an enGenious bridge with a built-in gain antenna (like 14dBi). These are $75 or so on Newegg.com. That 14dBi may not be enough if the signal is super weak.

 

[squigish]

I tried to do something similar this past summer, to share an internet connection between two adjacent family cabins. It was a lot of work, a lot of geeking out, and a little bit of success at the end.

Lessons I learned:

1. In almost every case, a wired connection is faster and more stable than a wireless connection.
2. Using a wireless repeater is really not a good option. The worst part is that your computer only knows that it's connecting to the repeater. If the connection between the repeater and the base station goes down, you don't get any notification.
3. Unless you use a repeater, you need two different radios for what you want to do. The only wifi routers I know of with two radios are simultaneous dual band routers, and some very specialized products. I think on most of the simultaneous dual band routers, the two radios still have to operate in the same mode (access point, client, or repeater).
4. A much better solution than a repeater is a pair of devices, operating on different channels, one connecting to your landlord's WiFi, and one broadcasting a signal for you.
5. Directional and high-gain antennas can be really helpful, even if they're only on one end of the connection.
6. Just because you will eventually go get a place of your own with your own internet connection doesn't mean a second device you purchase now will be useless. My summer project ended up involving a total of 4 wifi routers/access points, 3 of which were old "spares" that various family members had lying around. I've used spare routers in many different settings, as a wireless adapter for something with only an ethernet port, as a second access point connected by powerline networking in a large house, and others I can't recall at the moment.
7. EnGenius and Ubiquiti make several great specialized products for this type of application.

My other recommendation is that if getting the landlord to connect something is at all an option, you look into powerline/coax/phone networking. You can "sell" it as an improvement that will increase the value of his rental property: he can advertise it with internet included. If you share the same electric meter, then powerline networking has a good chance of working. All your landlord would need to do is plug a small adapter into a regular power outlet next to the router. Coax or Phone line networking have the potential to be faster/more stable, but have a smaller likelihood of the existing cables being in the right place.