2 antennas on 802.11 device?
 

I'm trying to extend an 802.11 device using an external antenna. It
looks like a typical access point(It's actually a video extender) with
2 small moveable antennas on back. Internally, there are a couple of
connectors, which I beleive are MCX connectors.

My question is, is it OK to just connect ONE external antenna to ONE of
the connectors.

Thank you for the help,
Sam

I'm trying to extend an 802.11 device using an external antenna.

FYI, this may or may not be legal. The Part 15 rules require that
802.11 radios and antennas be tested and verified "as a single
system". Putting an arbitrarily-chosen antenna on an 802.11 radio
is likely to break this rule, and thus void the radio's certification.

[This rule is, of course, frequently broken, but I just thought I
ought to warn you.

The rule doesn't apply if you're using an 802.11 radio under Part 97
amateur-radio rules... but, in that case, your use of it must comply
with all of the Part 97 requirements e.g. which frequencies you use,
the requirement to ID periodically, the no-commercial-use rule, the
no-obscuring-the-content rule, the licensed-control-operator rule,
third-party traffic restrictions, etc.]

It
looks like a typical access point(It's actually a video extender) with
2 small moveable antennas on back. Internally, there are a couple of
connectors, which I beleive are MCX connectors.

My question is, is it OK to just connect ONE external antenna to ONE of
the connectors.

The answer is, I believe, "it depends". It depends on the internal
design of the device.

Many 802.11 radios have multiple antennas, with some sort of switching
arrangment (often a PIN diode switch), in order to implement a spatial
diversity system... this can help improve range and reliability quite
a bit, due to the signal's sensitivity to multipath reflections.

In these cases, the on-board MAC/PHY/micro will usually switch back
and forth between antennas, to figure out which one is receiving a
stronger signal from the peer device. Thus, for reception purposes,
having only one external antenna hooked up will probably work fine...
the device will select that antenna since it'll "hear" little or
nothing via the other (internal) antenna.

The tricky part is transmission. Some devices will transmit back out
of whichever antenna they had selected via the diversity polling.
Others always transmit out of a single, pre-chosen antenna. Others
might switch back and forth either randomly or deterministically.

I don't think there's any way to predict how a given device will react
to having only one "good" antenna hooked up. You'll have to test it.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Thanks for the great info,

About part 15... If I use a unity gain antenna, I should be OK right,
since I am actually decreasing signal strength through a longer antenna
run.

Dave Platt wrote:
I'm trying to extend an 802.11 device using an external antenna.

FYI, this may or may not be legal. The Part 15 rules require that
802.11 radios and antennas be tested and verified "as a single
system". Putting an arbitrarily-chosen antenna on an 802.11 radio
is likely to break this rule, and thus void the radio's
certification.

[This rule is, of course, frequently broken, but I just thought I
ought to warn you.

The rule doesn't apply if you're using an 802.11 radio under Part 97
amateur-radio rules... but, in that case, your use of it must comply
with all of the Part 97 requirements e.g. which frequencies you use,
the requirement to ID periodically, the no-commercial-use rule, the
no-obscuring-the-content rule, the licensed-control-operator rule,
third-party traffic restrictions, etc.]


It
looks like a typical access point(It's actually a video extender)
with
2 small moveable antennas on back. Internally, there are a couple of
connectors, which I beleive are MCX connectors.

My question is, is it OK to just connect ONE external antenna to ONE
of
the connectors.

The answer is, I believe, "it depends". It depends on the internal
design of the device.

Many 802.11 radios have multiple antennas, with some sort of
switching
arrangment (often a PIN diode switch), in order to implement a
spatial
diversity system... this can help improve range and reliability quite
a bit, due to the signal's sensitivity to multipath reflections.

In these cases, the on-board MAC/PHY/micro will usually switch back
and forth between antennas, to figure out which one is receiving a
stronger signal from the peer device. Thus, for reception purposes,
having only one external antenna hooked up will probably work fine...
the device will select that antenna since it'll "hear" little or
nothing via the other (internal) antenna.

The tricky part is transmission. Some devices will transmit back out
of whichever antenna they had selected via the diversity polling.
Others always transmit out of a single, pre-chosen antenna. Others
might switch back and forth either randomly or deterministically.

I don't think there's any way to predict how a given device will
react
to having only one "good" antenna hooked up. You'll have to test it.

--
Dave Platt
AE6EO
Hosting the Jade Warrior home page:
http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

wrote in message
oups.com...
I'm trying to extend an 802.11 device using an external antenna. It
looks like a typical access point(It's actually a video extender) with
2 small moveable antennas on back. Internally, there are a couple of
connectors, which I beleive are MCX connectors.

My question is, is it OK to just connect ONE external antenna to ONE of
the connectors.

Thank you for the help,
Sam

two antennas are for space diversity, which improves reception,
if the signal is better, it will stay on that one.

Doesn't matter. You can't legally modify it.

wrote in message
oups.com...
Thanks for the great info,

About part 15... If I use a unity gain antenna, I should be OK right,
since I am actually decreasing signal strength through a longer antenna
run.