Linksys WRT54G antenna system

Any place to score a copy of the technical service manual, schematic diagram
and/or information on how the diversity antenna system works?

I'm also curious if there is any practical way to switch the system to a
single mode antenna as my feeling is the diversity as provided by Linksys is
more marketing smoke and mirrors than an effective/functional option.

NotMe wrote:
> Any place to score a copy of the technical service manual, schematic diagram
> and/or information on how the diversity antenna system works?
>
> I'm also curious if there is any practical way to switch the system to a
> single mode antenna as my feeling is the diversity as provided by Linksys is
> more marketing smoke and mirrors than an effective/functional option.
>
>
>
I don't know about the stock linksys firmware, but you can set the
antenna to use for transmit and recieve (either single or diversity)
with the dd-wrt ver.23 drivers.

NotMe wrote:
> Any place to score a copy of the technical service manual, schematic diagram
> and/or information on how the diversity antenna system works?
>
> I'm also curious if there is any practical way to switch the system to a
> single mode antenna as my feeling is the diversity as provided by Linksys is
> more marketing smoke and mirrors than an effective/functional option.
>
>
>
Hi,
Diversity antenna system has three different ones. You can combine them
all to improve reliability/integrity of signal.
1. Polarization diversity. You use both horiz. and vert. polarized signal.
2. Space diversity. You use two antennas spaced in the multiple of
wavelength.
3. Frequency diversity. You use two different frequency.
Then you combine the received signal to produce more reliable output.
So you need at least two antennas, two TX/RX and two different signal
feeders(coax, waveguide, etc.)
Tony, VE6CGX

Jerry Park wrote:

> NotMe wrote:
>
>> Any place to score a copy of the technical service manual, schematic
>> diagram
>> and/or information on how the diversity antenna system works?
>>
>> I'm also curious if there is any practical way to switch the system to a
>> single mode antenna as my feeling is the diversity as provided by
>> Linksys is
>> more marketing smoke and mirrors than an effective/functional option.
>>
>>
>>
> I don't know about the stock linksys firmware, but you can set the
> antenna to use for transmit and recieve (either single or diversity)
> with the dd-wrt ver.23 drivers.
Hi,
Also TX power is adjustable.
Tony

"Tony Hwang" <(E-Mail Removed)> wrote in message
news:0EXBf.329909$2k.198190@pd7tw1no...
| NotMe wrote:
| > Any place to score a copy of the technical service manual, schematic
diagram
| > and/or information on how the diversity antenna system works?
| >
| > I'm also curious if there is any practical way to switch the system to a
| > single mode antenna as my feeling is the diversity as provided by
Linksys is
| > more marketing smoke and mirrors than an effective/functional option.
| >
| >
| >
| Hi,
| Diversity antenna system has three different ones. You can combine them
| all to improve reliability/integrity of signal.
| 1. Polarization diversity. You use both horiz. and vert. polarized
signal.
| 2. Space diversity. You use two antennas spaced in the multiple of
| wavelength.
| 3. Frequency diversity. You use two different frequency.
| Then you combine the received signal to produce more reliable output.
| So you need at least two antennas, two TX/RX and two different signal
| feeders(coax, waveguide, etc.)
| Tony, VE6CGX

Good over view but it's a bit more complex than that as the design of the
diversity switching/combination circuitry system itself can produce
significant difference in the resultant performance which is why I wanted to
get a look/see at how linksys was doing the deed.

I no longer have access to the lab so I can't run the necessary black box
test ergo I need to see what's inside and how they do what they claim they
do.

NotMe wrote:
> "Tony Hwang" <(E-Mail Removed)> wrote in message
> news:0EXBf.329909$2k.198190@pd7tw1no...
> | NotMe wrote:
> | > Any place to score a copy of the technical service manual, schematic
> diagram
> | > and/or information on how the diversity antenna system works?
> | >
> | > I'm also curious if there is any practical way to switch the system to a
> | > single mode antenna as my feeling is the diversity as provided by
> Linksys is
> | > more marketing smoke and mirrors than an effective/functional option.
> | >
> | >
> | >
> | Hi,
> | Diversity antenna system has three different ones. You can combine them
> | all to improve reliability/integrity of signal.
> | 1. Polarization diversity. You use both horiz. and vert. polarized
> signal.
> | 2. Space diversity. You use two antennas spaced in the multiple of
> | wavelength.
> | 3. Frequency diversity. You use two different frequency.
> | Then you combine the received signal to produce more reliable output.
> | So you need at least two antennas, two TX/RX and two different signal
> | feeders(coax, waveguide, etc.)
> | Tony, VE6CGX
>
> Good over view but it's a bit more complex than that as the design of the
> diversity switching/combination circuitry system itself can produce
> significant difference in the resultant performance which is why I wanted to
> get a look/see at how linksys was doing the deed.
>
> I no longer have access to the lab so I can't run the necessary black box
> test ergo I need to see what's inside and how they do what they claim they
> do.
>
>
Hi,
In old days, I worked on military long range comm. system based on
troposcatter link. Diversity will make the signal usable while disabling
it causes link to go down. Now there is something called MIMO on
routers. I don't exactly know what it does.
Tony

Tony Hwang wrote:

> Hi,
> In old days, I worked on military long range comm. system based on
> troposcatter link. Diversity will make the signal usable while disabling
> it causes link to go down. Now there is something called MIMO on
> routers. I don't exactly know what it does.
> Tony

Whilst the article is about testing MIMO it will give you some idea.
http://rfdesign.com/mag/511RFDF1.pdf

Bob

Tony Hwang <(E-Mail Removed)> hath wroth:

>Diversity antenna system has three different ones. You can combine them
>all to improve reliability/integrity of signal.

Actually, there are about 10 different types of diversity reception.
If you include the DSP based systems such as MIMO, the list doubles in
size. I belive the question is how does the Broadcom chipset in the
WRT54G do diversity.

>1. Polarization diversity. You use both horiz. and vert. polarized signal.

Not normally used by the WRT54G. You can point the antennas in all
manner of odd directions to improve the odds that an antenna will hear
a signal, but the antennas are normally both positioned vertically.

>2. Space diversity. You use two antennas spaced in the multiple of
>wavelength.

The distance between the WRT54G antennas is 14cm or a bit more than
one wavelength at 2.4GHz (12.5cm). Not even close to multiple
wavelengths.

>3. Frequency diversity. You use two different frequency.

The WRT54G only works on one channel at a time. However, you could
argue that OFDM works this way as it uses multiple carrier frequencies
to improve resistance to multipath. However, since OFDM can be done
with one antenna, that's not the diversity answer.

>Then you combine the received signal to produce more reliable output.

Combine? You can't just add them together with an RF combiner because
the odds are that the two signals will cancel rather than reinforce.
This will also create the rather dreaded inter-symbol interference
that is caused by a delayed or reflected signal arriving to trash an
incident signal. Since the WRT54G contains a diversity SWITCH, that
switches back and forth between antennas, and only one antenna is on
at a time, so that's not the diversity answer.

>So you need at least two antennas, two TX/RX and two different signal
>feeders(coax, waveguide, etc.)
>Tony, VE6CGX

So, how does the WRT54G (Broadcom chipset) do diversity? As far as I
can tell, from reverse engineering, the algorithm used is rather
crude. With a lack of signal, the WRT54G scans (switches) between the
two antennas waiting for valid data. When it hears and decodes enough
to extract a source MAC address, it stores the antenna number (L or R)
along with the MAC address. From that point on, it will use the
stored antenna to communicate with the stored MAC address. However,
if the WRT54G decodes errors, garbage, interference, or trash from
that MAC address, it will assume that the selection of antenna is no
longer optimimum and will try the other antenna. This will continue
until it receives a valid packet which defines the current "best"
antenna. In other words, it uses the antenna from which it received
the last good packet.

Disclaimer: I deduced the aformentioned from watching the waveforms
on the diversity switch and extracting what I could from the chipset
data. There's a chance that this could be wrong or incomplete.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann"
|
| So, how does the WRT54G (Broadcom chipset) do diversity? As far as I
| can tell, from reverse engineering, the algorithm used is rather
| crude. With a lack of signal, the WRT54G scans (switches) between the
| two antennas waiting for valid data. When it hears and decodes enough
| to extract a source MAC address, it stores the antenna number (L or R)
| along with the MAC address. From that point on, it will use the
| stored antenna to communicate with the stored MAC address. However,
| if the WRT54G decodes errors, garbage, interference, or trash from
| that MAC address, it will assume that the selection of antenna is no
| longer optimum and will try the other antenna. This will continue
| until it receives a valid packet which defines the current "best"
| antenna. In other words, it uses the antenna from which it received
| the last good packet.
|
| Disclaimer: I deduced the aforementioned from watching the waveforms
| on the diversity switch and extracting what I could from the chipset
| data. There's a chance that this could be wrong or incomplete.
|

Bingo! As I expected.

If that's the case the diversity is a PoS. The same system was use in the
original US cell phone systems (Chicago) by E.F. Johnson and is based on the
detection of 'rice clicks' (long story but a theory developed by a Japanese
PhD who's name was in fact RICE) in the received signal.

In theory (marketing's theory) this improved performance by 3db. In
practice -- less than worthless for voice, data was a nightmare.

Now to find out how to disable the diversity and work on a single port.

"NotMe" <(E-Mail Removed)> hath wroth:

>If that's the case the diversity is a PoS.

Not if your major purpose is to minimize the effects of multipath and
reflections. My limited testing shows that it has a substantial
advantage in a highly reflective environment (i.e. typical office).
Sorry, no numbers. It doesn't do anything useful for interference
reduction or when using two radically different antennas.

>The same system was use in the
>original US cell phone systems (Chicago) by E.F. Johnson and is based on the
>detection of 'rice clicks' (long story but a theory developed by a Japanese
>PhD who's name was in fact RICE) in the received signal.

I vaguely recall part of that story. I was running an Johnson/Comco
land mobile dealer at the time. The big thing in land mobile was
receiver voting systems to make low power handhelds useful. The idea
was to plaster the city with receivers, bring all the audio to one
place via lease lines or microwave, and decide on the fly which
receiver has the best S/N ratio. This works fairly well for VHF/UHF
voice and miserably for data. The problem was that GE and Motorola
had the patents on the easy ways to measure S/N on the fly, leaving
E.F. Johnson with whatever technology they could find. Counting noise
hits was what they contrived. I got to try it on one of their
repeaters in the LA area. It barely worked.

When cellular appeared, the first AT&T test system was in Chicago
using E.F. Johnson mobiles. I'm not sure who supplied the base
stations but I think it was also E.F. Johnson. I vaguely recall
reading something about a voting system being used. What happened
with the original system before it was politicked by Motorola?

>In theory (marketing's theory) this improved performance by 3db. In
>practice -- less than worthless for voice, data was a nightmare.

Just about all the voting system worked badly with data. There was no
dead air time to switch and they always induced phase glitches and
clock resyncs. However, the WRT54G does NOT work like a voting system
and is fast enough to switch between packets.

>Now to find out how to disable the diversity and work on a single port.

There doesn't seem to be any way to do that with the stock Linksys
firmware.
http://www.linksysdata.com/ui/WRT54G/v5/1.00.6/WAdv.htm
However, alternative firmware, such as DD-WRT, allows setting the
router to either antenna.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558