AP External Antenna question?

You only need or want one external antenna. The two antennas are for diversity reception, where the router selects which antenna has the best reception. The idea is to help deal with multipath and reflections. You can do that with two outdoor antennas, but it's neither necessary, or particularly desireable.

Once catch with your unspecified Linksys wireless device (why do you keep the model number secret), is that some wireless devices transit on only one of the antennas, while doing the diversity receive thing using both antennas. I can never remember which antenna and am too lazy to figure out which models. Just try one antenna and if it doesn't work quite right, try the other.

Another piece of trivia is that the cable lengths inside the box on many routers are different between the two antennas. Find a picture of the inside of your router, and select the antenna with the shortest coax, or preferably, no coax cable. That's worth about 1dB which might make a difference on a long distance link.

Reply to
Jeff Liebermann
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Dual antennas is called diversity and is used to compensate for multipath interference (reflections). The antenna with the strongest signal at that instant is used to receive and re-transmit the next frames. In your case you wont use diversity.Some APs allow you to turn off diversity and to select which antenna to use (left or right). MyLinksys WAP54g has this option.

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I want to install outdoor antennas to make connection between AP and Bridge. The Linksys devices each have 2 antennas. Do I have to install 2 outdoor antennas for one device? Some of Dlink's devices have only one antenna. What is the diffence between the two antennas device and the one antenna device? Thank you. GL

Reply to
G Lam

I have not bought any Linksys or Dlink device yet. I plan to implement a Wifi connection between two buildings 1600ft apart. External antennas are needed in my case to shot up the signal strength. I have to figure out what to buy and how to install the antennas up front. I want to use 9dbi gain antenna with 2 db cable/connector loss on each end; hopefully, I can get a total of 14 dbi gain. Thank you for your valuable information. It really helps. GL

"Jeff Liebermann" ??? news: snipped-for-privacy@4ax.com ???...

Reply to
G Lam

Do you know if the LinkSys WRT54GS V1.0 transmits only using one of the antennas?

That's a great tip! It looks like I should use the right antenna on the LinkSys WRT54GS V1.0, since it doesn't use no coax cable:


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Wrong. Co-phasing is a term used (almost) exclusively in CB radios.

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is also used in astronomy to describe the alignment requirement of segmented telescope mirrors.

Co-phasing is applicable for dual CB antennas, and other such abominations, because both antennas are operated simultaneously. This results in some "interesting" antenna patterns and cable length requirements to get a proper impedance match. The coax cable "phasing harness" allegedly forms a power splitter, where the cable lengths are critical.

However, the wireless access point has one additional piece of circuitry that is lacking in a typical CB radio and antenna system. It has a diversity switch located between the antennas and the radio. The switch scans between the two antennas, looking for the best receive signal. The algorithm varies by chipset, but is basically a stored antenna selection based upon the last successfully received packet.

When one antenna is selected and active, the other antenna is isolated from the radio and shorted to ground by the PIN diode switch diversity switch. However, the antennas are in sufficient proximity to create a somewhat directional pattern, and I agree that this pattern is highly dependent upon the length of internal coax cables. However, it is NOT critical by any stretch of the imagination, as demonstrated by the ability to orient the two antennas in any random manner and still have a functional access point. One can even remove or short one of the antennas, and see little effect on performance.

Anyway, since the coax cables are NOT part of some phasing, matching, power splitting, or beam forming network, and are impedance matched at both ends, the actual lengths are NOT critical.

Incidentally, I never suggested changing the length of the internal coax cable. My comments were in reference to the loss between the radio assembly and the antenna being slightly less on the port without the added loss of the coax cable. You are probably correct about not changing the internal coax cable length. I see some things in the circuit that look like the diversity switch is running at a much higher impedance than 50 ohms (to reduce switch loss), and that the coax cable (and a few components near the antenna connector without the coax) are part of a matching network. That will make the coax cable length critical to insure 50 ohms at the connector.

Reply to
Jeff Liebermann


This is also for antenna "co-phasing" or matching the two antennas to the


Do not change the length!!!!

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