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WiFi Antenna Location Sensitivity

 
 
Jeff Wisnia
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      03-14-2009

I'd like to learn why sometimes moving a wireless adaptor's antenna by
just a few inches can cause a significant performance difference.

Ex: Today SWMBO came down to my office (We both work in our own
business' office.) complaining that internet access on the computer in
her office was slower than molasses in January.

We use a Linksys WAP54G router to service the five computers in our
business. Her computer has a Linksys WUSB54G adaptor plugged into it.

I gave her my usual reply that MY computer was connecting just fine and
that she has so much junk and obsolete files stuffed in her computer
that it probably needs an enema to get its performance back to where it
used to be.

That strateguy didn't work, so I hauled my ass down to her office and
had a look.

She was correct, internet access on her computer was awfully slow, even
though none of the other computers in the office were in use then.

Her computer is the closest one to the router, only about 25 feet away
with nothing more than a couple of drywall partitions in the way. The
adaptor software reported excellent signal strength and I checked to
make sure that the wireless channel we were using was still unoccupied
by any of our neighbor's wireless systems.

To make a long story shorter and less boring, I solved problem by simply
moving the wireless adaptor about four inches sideways on the bookshelf
it sat on, and her computer instantly regained its usual internet access
speed.

I understand how multipath signals can cause RF nulling, but I'd expect
that the adaptor's software would report "poor signal strength" under
those conditions. It's the "good signal" report combined with lousy
performance that has my inquiring mind wondering what's really going on.

Thanks guys,

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.
 
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Mike Easter
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      03-14-2009
Jeff Wisnia wrote:
> I'd like to learn why sometimes moving a wireless adaptor's antenna by
> just a few inches can cause a significant performance difference.


Because it is a radio transmitter-receiver and "all kinds of crazy things"
can affect the quality of the signal getting around. Including
interference.

> Her computer is the closest one to the router, only about 25 feet away
> with nothing more than a couple of drywall partitions in the way.


.... and other stuff. Gee, /only/ 25 feet of walls and all of the things
that are next to and inside walls and in between walls on the floorspace.
Imagine trying to shine some kind of light-like beam which can penetrate
some things better than others from some kind of undescribed 'adapter'
back and forth to some kind of router antenna.

> The
> adaptor software reported excellent signal strength


Sometimes that information is worthless.

> It's the "good signal" report combined with lousy
> performance that has my inquiring mind wondering what's really going on.


3 quick adages. I would rather be wired than wireless. I would rather be
able to see (with my eyeballs) one antenna from the other than not. And
you can't trust 'excellent' signal strength to mean excellent clear
reception/transmission.



--
Mike Easter

 
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Helpful guy
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Posts: n/a
 
      03-15-2009
"Jeff Wisnia" <(E-Mail Removed)> wrote in message
news:gphbhp$ihn$(E-Mail Removed)...
>
> I'd like to learn why sometimes moving a wireless adaptor's antenna by
> just a few inches can cause a significant performance difference.


See Mike Easter's reply.

Moving a flashlight a few inches can cause it to completely miss the window
25 meters away.
RF (Radio Frequency) is not very different. If you could see it like you can
see light you would immediately see the answer to your question.

If you want a reliable network use wires.


 
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Helpful guy
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      03-15-2009
"Helpful guy" <(E-Mail Removed)> wrote in message
news:gphkoj$7ac$(E-Mail Removed)...
> "Jeff Wisnia" <(E-Mail Removed)> wrote in message
> news:gphbhp$ihn$(E-Mail Removed)...
>>
>> I'd like to learn why sometimes moving a wireless adaptor's antenna by
>> just a few inches can cause a significant performance difference.

>
> See Mike Easter's reply.
>
> Moving a flashlight a few inches can cause it to completely miss the
> window 25 meters away.


Same with 25 feet


 
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chuckcar
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      03-15-2009
richard <(E-Mail Removed)> wrote in
news:(E-Mail Removed):

> On Sat, 14 Mar 2009 21:14:11 -0400, "Helpful guy" <(E-Mail Removed)>
> wrote:
>
>>"Jeff Wisnia" <(E-Mail Removed)> wrote in message
>>news:gphbhp$ihn$(E-Mail Removed)...
>>>
>>> I'd like to learn why sometimes moving a wireless adaptor's antenna by
>>> just a few inches can cause a significant performance difference.

>>
>>See Mike Easter's reply.
>>
>>Moving a flashlight a few inches can cause it to completely miss the
>>window 25 meters away.
>>RF (Radio Frequency) is not very different. If you could see it like you
>>can see light you would immediately see the answer to your question.
>>
>>If you want a reliable network use wires.
>>

>
>
> What you're speaking of is misconceived as "line of sight".
> What most people mistakenly think of when they believe that in order
> for the antenna to receive a signal, it MUST be pointed in the
> direction of the transmitter.


Wrong. We're talking microwaves here. That's line of sight. That's *why*
weather radar (and plain radar) works.

--
(setq (chuck nil) car(chuck) )
 
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Helpful guy
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Posts: n/a
 
      03-15-2009
"richard" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Sat, 14 Mar 2009 21:14:11 -0400, "Helpful guy" <(E-Mail Removed)>
> wrote:
>
>>"Jeff Wisnia" <(E-Mail Removed)> wrote in message
>>news:gphbhp$ihn$(E-Mail Removed)...
>>>
>>> I'd like to learn why sometimes moving a wireless adaptor's antenna by
>>> just a few inches can cause a significant performance difference.

>>
>>See Mike Easter's reply.
>>
>>Moving a flashlight a few inches can cause it to completely miss the
>>window
>>25 meters away.
>>RF (Radio Frequency) is not very different. If you could see it like you
>>can
>>see light you would immediately see the answer to your question.
>>
>>If you want a reliable network use wires.
>>

>
>
> What you're speaking of is misconceived as "line of sight".
> What most people mistakenly think of when they believe that in order
> for the antenna to receive a signal, it MUST be pointed in the
> direction of the transmitter.
>
> Radio signals don't give a damn when or where they get transmitted.
> Is that antenna on the back of the router a specialized directional
> unit? Not likely. It is what we call "omnidirectional". That is, the
> signal gets transmitted in a globular pattern equally.


Don't worry I know what an omnidirectional antenna is.

>
> The receiving antenna, however, is generally of a yagi type. What's a
> yagi? Look on any roof top and you'll find one. The old standard
> broadcast tv antenna is a yagi.
>
> The yagi aids in pinpointing the source. A more direct line equals a
> stronger signal.


I think you should go back to wireless networking school.
When did you last see a laptop user carrying a Yagi around with it?
The Yagi antenna is a Japanese invention but not relevant to this thread.



 
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Helpful guy
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Posts: n/a
 
      03-15-2009
"richard" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Sat, 14 Mar 2009 22:06:58 -0400, "Helpful guy" <(E-Mail Removed)>
> wrote:
>
>>"richard" <(E-Mail Removed)> wrote in message
>>news:(E-Mail Removed). ..
>>> On Sat, 14 Mar 2009 21:14:11 -0400, "Helpful guy" <(E-Mail Removed)>
>>> wrote:
>>>
>>>>"Jeff Wisnia" <(E-Mail Removed)> wrote in message
>>>>news:gphbhp$ihn$(E-Mail Removed)...
>>>>>
>>>>> I'd like to learn why sometimes moving a wireless adaptor's antenna by
>>>>> just a few inches can cause a significant performance difference.
>>>>
>>>>See Mike Easter's reply.
>>>>
>>>>Moving a flashlight a few inches can cause it to completely miss the
>>>>window
>>>>25 meters away.
>>>>RF (Radio Frequency) is not very different. If you could see it like you
>>>>can
>>>>see light you would immediately see the answer to your question.
>>>>
>>>>If you want a reliable network use wires.
>>>>
>>>
>>>
>>> What you're speaking of is misconceived as "line of sight".
>>> What most people mistakenly think of when they believe that in order
>>> for the antenna to receive a signal, it MUST be pointed in the
>>> direction of the transmitter.
>>>
>>> Radio signals don't give a damn when or where they get transmitted.
>>> Is that antenna on the back of the router a specialized directional
>>> unit? Not likely. It is what we call "omnidirectional". That is, the
>>> signal gets transmitted in a globular pattern equally.

>>
>>Don't worry I know what an omnidirectional antenna is.
>>
>>>
>>> The receiving antenna, however, is generally of a yagi type. What's a
>>> yagi? Look on any roof top and you'll find one. The old standard
>>> broadcast tv antenna is a yagi.
>>>
>>> The yagi aids in pinpointing the source. A more direct line equals a
>>> stronger signal.

>>
>>I think you should go back to wireless networking school.
>>When did you last see a laptop user carrying a Yagi around with it?
>>The Yagi antenna is a Japanese invention but not relevant to this thread.
>>
>>

>
> Actually I have. I've seen a couple of truckers with yagi's mounted to
> the mirror. Know of a few people that have them for in the home
> because otherwise they'd have no signal at all.


Ok and how is this relevant to what the OP asked??
Do you suggest he gets a Yagi for all of his users?
Or would 25 feet of wire and a few holes in the drywall be a more economic
and reliable option?


 
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PeeCee
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Posts: n/a
 
      03-15-2009
"Jeff Wisnia" <(E-Mail Removed)> wrote in message
news:gphbhp$ihn$(E-Mail Removed)...
>
> I'd like to learn why sometimes moving a wireless adaptor's antenna by
> just a few inches can cause a significant performance difference.
>
> Ex: Today SWMBO came down to my office (We both work in our own business'
> office.) complaining that internet access on the computer in her office
> was slower than molasses in January.
>
> We use a Linksys WAP54G router to service the five computers in our
> business. Her computer has a Linksys WUSB54G adaptor plugged into it.
>
> I gave her my usual reply that MY computer was connecting just fine and
> that she has so much junk and obsolete files stuffed in her computer that
> it probably needs an enema to get its performance back to where it used to
> be.
>
> That strateguy didn't work, so I hauled my ass down to her office and had
> a look.
>
> She was correct, internet access on her computer was awfully slow, even
> though none of the other computers in the office were in use then.
>
> Her computer is the closest one to the router, only about 25 feet away
> with nothing more than a couple of drywall partitions in the way. The
> adaptor software reported excellent signal strength and I checked to make
> sure that the wireless channel we were using was still unoccupied by any
> of our neighbor's wireless systems.
>
> To make a long story shorter and less boring, I solved problem by simply
> moving the wireless adaptor about four inches sideways on the bookshelf it
> sat on, and her computer instantly regained its usual internet access
> speed.
>
> I understand how multipath signals can cause RF nulling, but I'd expect
> that the adaptor's software would report "poor signal strength" under
> those conditions. It's the "good signal" report combined with lousy
> performance that has my inquiring mind wondering what's really going on.
>
> Thanks guys,
>
> Jeff
> --
> Jeffry Wisnia
> (W1BSV + Brass Rat '57 EE)
> The speed of light is 1.8*10^12 furlongs per fortnight.




Jeff

What Philo says is right, multipath can cause distortion as well as nulling.
Think of a TV picture with ghosting in it, the signals are strong but arrive
at differnent times and distort the picture.
In the case of WiFi the data bits are what get distorted so the routers
spend all their time resending packets because the checksums don't add up.

Mike's advice is also worth noting:
Use wire if you can.
Wireless works best when you can eyball antenna to antenna.

It's also worth noting that WiFi is slow compared to Wired networking.
Even the new 'N' standard is slow compard to the Gbit Wired NIC's most PC's
come with today.

Best
Paul.

 
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Evan Platt
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Posts: n/a
 
      03-15-2009
On Sat, 14 Mar 2009 22:43:09 -0400, richard <(E-Mail Removed)>
wrote:

>And you don't know jack. I held an FCC license for 5 years. I know
>what I'm taliking about.


A CB license? Wow.

Must have been tough. I'm sure the toughest part was making out the
check to the FCC.

What license do you have now?
--
To reply via e-mail, remove The Obvious from my e-mail address.
 
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Jeff Wisnia
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      03-15-2009
PeeCee wrote:
> "Jeff Wisnia" <(E-Mail Removed)> wrote in message
> news:gphbhp$ihn$(E-Mail Removed)...
>
>>
>> I'd like to learn why sometimes moving a wireless adaptor's antenna by
>> just a few inches can cause a significant performance difference.
>>
>> Ex: Today SWMBO came down to my office (We both work in our own
>> business' office.) complaining that internet access on the computer in
>> her office was slower than molasses in January.
>>
>> We use a Linksys WAP54G router to service the five computers in our
>> business. Her computer has a Linksys WUSB54G adaptor plugged into it.
>>
>> I gave her my usual reply that MY computer was connecting just fine
>> and that she has so much junk and obsolete files stuffed in her
>> computer that it probably needs an enema to get its performance back
>> to where it used to be.
>>
>> That strateguy didn't work, so I hauled my ass down to her office and
>> had a look.
>>
>> She was correct, internet access on her computer was awfully slow,
>> even though none of the other computers in the office were in use then.
>>
>> Her computer is the closest one to the router, only about 25 feet away
>> with nothing more than a couple of drywall partitions in the way. The
>> adaptor software reported excellent signal strength and I checked to
>> make sure that the wireless channel we were using was still unoccupied
>> by any of our neighbor's wireless systems.
>>
>> To make a long story shorter and less boring, I solved problem by
>> simply moving the wireless adaptor about four inches sideways on the
>> bookshelf it sat on, and her computer instantly regained its usual
>> internet access speed.
>>
>> I understand how multipath signals can cause RF nulling, but I'd
>> expect that the adaptor's software would report "poor signal strength"
>> under those conditions. It's the "good signal" report combined with
>> lousy performance that has my inquiring mind wondering what's really
>> going on.
>>
>> Thanks guys,
>>
>> Jeff
>> --
>> Jeffry Wisnia
>> (W1BSV + Brass Rat '57 EE)
>> The speed of light is 1.8*10^12 furlongs per fortnight.

>
>
>
>
> Jeff
>
> What Philo says is right, multipath can cause distortion as well as
> nulling.
> Think of a TV picture with ghosting in it, the signals are strong but
> arrive at differnent times and distort the picture.
> In the case of WiFi the data bits are what get distorted so the routers
> spend all their time resending packets because the checksums don't add up.


That's the answer I was seeking, the TV ghosting analogy was appreciated.

Thanks,

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

>
> Mike's advice is also worth noting:
> Use wire if you can.
> Wireless works best when you can eyball antenna to antenna.
>
> It's also worth noting that WiFi is slow compared to Wired networking.
> Even the new 'N' standard is slow compard to the Gbit Wired NIC's most
> PC's come with today.
>
> Best
> Paul.


 
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