The blurry and distorted photo you referenced above:
appears to be some manner of PIFA antenna. Very difficult to tell from the photos.
These are very common in laptops as that's about all that will fit inside the case. If it's a PIFA, it's a 1/4 wave bent monopole above a ground plane.
There are many forms of the PIFA antenna. I can't tell from the blurry photo which one is inside the x61t. Optimistically, it has an average gain of about -2dBi gain at 2.4GHz. Realistically, it's somewhat less.
If PIFA, it's probably a dual band antenna, which is considerably more complex:
From the polar graphs, it looks like an average gain of about -5dBi for both 2.4 and 5.7GHz.
If you're doing calculations, don't forget about the rather high coax cable losses.
Incidentally, the location of the antenna under the palm rest is not a good place to hide the antenna as the signal is blocked by the nearby metal components and shields.
What I'm trying to understand is much more than just the Lenovo X61t native antenna dBi so that's why I was hoping to just ask about that small missing piece of the puzzle in this post.
STOP READING NOW ... BELOW IS ONLY MORE DETAIL ON THAT STATEMENT!
The bigger picture is I'm trying to figure out what real-world equipment I need to communicate with various access points that my outdoor radio
+antenna sees (but it can't connect to them all) - and that my laptop radio+antenna does not see (but I hope to see with a USB WiFi extender).
In addition, I'd like to add a TV antenna to the top of my WISP antenna, so, AFTER I fully figure out the (more interesting to me) WiFi calculations, I'll adapt them for TV signal calculations (but I don't have ANY existing TV equipment yet to do any real-world tests).
For a WiFi example, just one (of many) interesting SSIDs found in my site survey shows a signal strength of -89dBm with a noise of -96dBm but I can't connect to it even though it's open. I want to calculate whether my current equipment has the capability to connect to it, and, if not, I want to understand how to calculate what I need to purchase (specification wise) that will connect to it successfully.
This then leads on to the 'second step' which is to take the FCC coverage information for TV signal to calculate what equipment I would need to pick up certain TV stations.
For example, tvfool.com indicates PBS is on station KVIE-DT, real channel
9, virtual channel 6.1, NM=-15.4DB, Pwr=-106.9dBm, path=2edge, and distance=82.3 miles away.
After I figure out what WiFi equipment I'd need to connect to every SSID that is of interest to me, I'd like to then use that knowledge to figure out what TV equipment I need to calculate what I'd need to receive NBC, PBS, CBS, etc. at my home.
All these calculations are not something that can be easily done in a USENET post - so - that's why I JUST asked about the laptop antenna spec. I was just fleshing out this starting-point chart of the capabilities of my existing equipment:
Lenovo X61t (Intel 4964AGN)
- TX=15dBm (30mW)
- Omni=2dBi ? (FRU 93P4365)
Ubiquiti Bullet M2
- TX=28dBm (630mW)
Linksys WRT54G v5 (CDFB)
- TX=18dBm (63mW)
- RX=-65dBm for 11g@54Mbps, -80db for 11b 11Mbps
And, I was investigating what this will be able to pick up if added to the Lenovo X61t Linux Laptop:
Alfa Networks AWUS036H ($28)
- TX = 20dBm (100mW)
- RX = -91dBm@11Mbps 802.11b CCK
- Omni = 2dBi
Once I understand the equipment specifications I need, THEN I will proceed to the calculations of what signals they can pick up. I am not doing this theoretically - I'm only interested in real live signals that I know are available to me such as what shows up in a site survey on my outdoor WiFi equipment above or what the FCC coverage maps tell me for TV (since I have no TV equipment as yet).
But, I figured I'd start simply with understanding what the capabilities were of the equipment that I had on hand. For that, I simply needed to figure out the specs.
I'm amazed that the dBi spec for the antenna on the Lenovo X61t is so hard to find!
The only thing I know is I found the antenna in my laptops on one side of the display. On my new hp, the card has two antenna coax connections. I wonder if that's for diversity or band change. I'm have not really pinpointed antenna location.
The built in antenna is for coffee shop use. For a complete system like a notebook, you won't find the antenna spec but rather a system spec.
You should really go USB. Note the Alfa Tube/U has slightly better specs than the plain 036. It has less power, but high power on one end isn't all that useful. Both are good devices. The RPSMA to N adapter is $5, so add that to the price of the AWUS036H.
If you want to mess with HDTV, I'd suggest getting a HD Homerun. I have the old version. It is hard to get test specs on consumer gear. The numbers exist since QA parameters need to be established, but on consumer gear, the numbers don't leave the factory.
The old HD Homerun works OK with XMBC. No idea about the current version. Installing MythTV is a kick in the groin. You can run the HD Homerun with VLC. If you know what you are doing, you can demod satellite streams with VLC. VLC has far more capabilities than most people realize.
Obviously the advantage to the HD Homerun is you can put it on that network you just set up.
In general it's negative (i.e. it's less that 0dBi).
You can only get gain in an antenna - a passive device - from directivity, so for any directions where it's positive then there are complementary directions where it must be negative. And as dBi is defined as a comparison with a lossless isotope in free space and as the Lenovo antenna is real and so has losses, the overall antenna has a gain of 0dBi minus those losses.
You'll needs to lubricate it with large dose of snake oil to achieve that.
I second that suggestion. I love my HD Homerun units. They just work, and that's more than I can say for the tuners I tried before the HR's. I'm using them with SageTV (bought by Google awhile back) and Win 7 Media Center.
Nope. I'm already sorry that I asked. No need to wait.
It's still backwards. Questions like yours (and answers like mine) make little sense without the proper context.
Ok, but first a short lecture. If you understand how things work, you can usually work out the details of how to make things work for your specific application. I like to supply theory and rules-of-thumb, rather than suggest you go out and buy some specific device.
In this case, the reason you can see more AP's than you can connect to is because it takes exactly one packet for the computah to announce that it can hear an AP. It takes far more packets, going in both directions, to associate with an AP, negotiate an encryption key, obtain a DHCP assigned IP address, and setup a route to the internet. Hearing one packet requires just luck. Making a connection, requires a good signal.
For Wi-Fi, the signal has two specifications. Signal level and signal quality, also known as SNR (signal to noise ratio). You could have a situation, where the signal level is adequate, but because of interference from other stations on the same channel, the signal quality sucks. This might be why you can't connect to the distant stations. You may be experiencing interference at either or both ends. A clue is to sniff the management packets going in both directions. The connection speed does *NOT* need to be the same in both directions. If there's a large difference in connection speed, in both directions, the end receiving the slow speed, probably has an interference problem.
So, now that you understand what it takes to get a decent connection, how is it calculated. Welcome to link calculations:
Plug in the numbers for the remote AP with which you want to communicate, assume a 20dB minimum fade margin, and see how close you get. If you have problems, post the numbers, and I'll use them as an example.
The basic idea is to have a sufficiently good SNR to insure reliable communications. So, what's reliable? See the SOM to % reliability to downtime table in the above URL. For a 20dB SOM (same as fade margin), you'll get 99% reliability, which will produce about 88 hrs per year of outage. If you can live with 15 minutes per day outage, you're done. If not, you'll need to add more gain somewhere in the system. Usually, the antennas are the easiest.
Enough on Wi-Fi calculations for now.
Bad idea. If they're too close, they'll affect each others antenna pattern. Keep them apart. I don't want to get into TV antennas in a wireless newsgroup.
That's because there is no single number that clearly describes the antennas. You could specify maximum gain, average gain, gain range, directivity, bandwidth for VSWR
I had never heard of the Alfa Network Tube/U which looks suspiciously almost exctly like the Ubiquiti Bullet M2 that I already have on my WISP antenna (only the 600mW Bullet M2 is powered by its RJ45 jack while the
1Watt Tube/U appears to be powered by a standard USB "B" cable).
Here's a link to the Alfa Network Tube-U(N):
I am only considering USB WiFi extenders for my Ubuntu laptop if their datasheet expressly says it supports Linux 2.6 (because I've been burned before).
Luckily, both the $28 Alfa Network AWUS036H and this previously-unknown- to-me $35 Tube-U(N) datasheets state they support Linux.
I had never heard of HD Homerun so I had to google it.
I like its premise that all the laptops in the house instantly become TV displays because the HDHomeRun apparently attaches to the home broadband router. Even the kid's iPhone (apparently) becomes a TV display.
But the "HD Home Run Dual" still needs a digital TV antenna (there is no cable where I live), so the reception calculations will still need to be made when I install the TV antenna.
Interestingly this $130 HDHR3-US requires a 100BaseTX high-speed network. I wonder what the star network is that I just put in a month ago? I seriously doubt its all that fast.
If you did it right, the Ethernet cables are capable of Gigabit and will only be limited by the speed of the connected devices. You can use tools like JPerf to test the actual throughput between two endpoints.
Yes, you still need an antenna. But my point is the HD Home run device works well. None of these receivers really have what I would call specs these days. Rather they have check marks. That is, it will do QAM and
8VSB. How well in terms of say the noise figure of the receiver is unknown.
Possible you could get a NEMA box and place it near the antenna, but that is another topic.
I didn't have any issues with the RL8187 chipset under linux. The other chipset (RALINK) they use in the high speed device has linux issues out of the box (i.e. whatever drive was in the last rev of opensuse), but I got it to work with the linux driver they supplied. The driver install was well documented, but certainly not trivial.
Again, you probably want to get a right angle N adapter to reduce the size of the "lever" arm that the Tube/U creates.
That implies having a negative value is inferior and an embarrassment, which misses the point. It is neither - it is just the simple maths of the physics involved. If Lenovo was designing a directional antenna with gain in one direction then it certainly would be a disappointment, but for their tablet notebooks they don't want a design where the signal could drop off just from moving or rotating the computer. Any time some antenna claims +ve gain, that specification must come with information on the direction of that gain, whether the antenna is a Pringles carton for Wi-Fi, a dish for satellite TV or a Yagi for TV or ham radio use. Wi-Fi antennas that claim to have +ve "gain", but in no particular direction, are just nonsense.