wrt54 antennas

IS there a distinction between the two antenna connectiond on the
WRT54 wireless routers. I had heard that one is for TX and the other
for RX but my router seems to work equally well with either antenna
disconnected. I cant tell a difference in performance unless I take
them both off.

Jimmie

On Tue, 22 Jul 2008 11:41:51 -0700 (PDT), jimmie68@gmail.com wrote:

>IS there a distinction between the two antenna connectiond on the
>WRT54 wireless routers.

No. The antennas area identical. However, the two ports are slightly
different. One is designated as "main" while the other is "aux". The
router will normally favor the "main" antenna and only switch to the
"aux" if the diversity receive algorithm determins that the "aux"
antenna has a better signal.

Unfortunately, I can't recall which is antenna is main or aux, or for
that matter, which antenna is considered "left" or "right". Sigh.
Looking at the inside photos at:
<http://www.linksysinfo.org/forums/showthread.php?t=47124>
I would *GUESS*(tm) that the antenna port with the long coax cable
running across the board would be the "aux".

>I had heard that one is for TX and the other
>for RX but my router seems to work equally well with either antenna
>disconnected. I cant tell a difference in performance unless I take
>them both off.

Some routers will only transmit on one antenna (i.e 2-wire). Routers
that have two antennas invariably use diversity receive and sorta
"scan" between the two antennas in receive. I vaguely recall that the
WRT54 transmits on the same antenna that it receives.

However, you should be able to tell the difference with only one
antenna attached. If you remove the antenna from the "main" port, the
stupid firmware will continue to favor the "main" port, even though
there's no antenna or signal. If you ping the router, you'll probably
find that the first ping will be lost using just the "aux" antenna.
That's not the case using only the main antenna.

If you insist on using only one antennna (a good idea if you're
attaching external antennas), some alternative firmwares have a means
of disarming the diversity switch system and just using one antenna.

Start reading here:
<http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008019f646.shtml>
especially the part about the golf course and using two different
types of antennas.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Jul 22, 3:53*pm, Jeff Liebermann <je...@cruzio.com> wrote:
> On Tue, 22 Jul 2008 11:41:51 -0700 (PDT), jimmi...@gmail.com wrote:
> >IS there a distinction between the two antenna connectiond on the
> >WRT54 wireless routers.
>
> No. *The antennas area identical. *However, the two ports are slightly
> different. *One is designated as "main" while the other is "aux". *The
> router will normally favor the "main" antenna and only switch to the
> "aux" if the diversity receive algorithm determins that the "aux"
> antenna has a better signal.
>
> Unfortunately, I can't recall which is antenna is main or aux, or for
> that matter, which antenna is considered "left" or "right". *Sigh.
> Looking at the inside photos at:
> <http://www.linksysinfo.org/forums/showthread.php?t=47124>
> I would *GUESS*(tm) that the antenna port with the long coax cable
> running across the board would be the "aux".
>
> >I had heard that one is for TX and the other
> >for RX but my router seems to work equally well with either antenna
> >disconnected. I cant tell a difference in performance unless I take
> >them both off.
>
> Some routers will only transmit on one antenna (i.e 2-wire). *Routers
> that have two antennas invariably use diversity receive and sorta
> "scan" between the two antennas in receive. *I vaguely recall that the
> WRT54 transmits on the same antenna that it receives.
>
> However, you should be able to tell the difference with only one
> antenna attached. *If you remove the antenna from the "main" port, the
> stupid firmware will continue to favor the "main" port, even though
> there's no antenna or signal. *If you ping the router, you'll probably
> find that the first ping will be lost using just the "aux" antenna.
> That's not the case using only the main antenna.
>
> If you insist on using only one antennna (a good idea if you're
> attaching external antennas), some alternative firmwares have a means
> of disarming the diversity switch system and just using one antenna.
>
> Start reading here:
> <http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note091...>
> especially the part about the golf course and using two different
> types of antennas.
>
> --
> Jeff Liebermann * * je...@cruzio.com
> 150 Felker St #D * *http://www.LearnByDestroying.com
> Santa Cruz CA 95060http://802.11junk.com
> Skype: JeffLiebermann * * AE6KS * *831-336-2558

Thanks Jeff, I am guessing that the traces on the board may form a
type of diplexer. If this is the case leaving one antenna disconnected
and the port unterminated would defeat the operation of the diplexer.
In this case one antenna connected to one port would work as well as
connecting it to the other. This would explain my experience of having
the unit work equally well with 1 antenna on either port. Having 1 or
2 antennas woud probably make little difference if ther is not a
multipath issue

Jimmie..

On Tue, 22 Jul 2008 15:27:51 -0700 (PDT), jimmie68@gmail.com wrote:

>Thanks Jeff, I am guessing that the traces on the board may form a
>type of diplexer.

Nope. It's a diversity switch. If you look carefully, there's a 6
lead chip sitting at the junction of the two i/o ports. The chip does
the switching.

>If this is the case leaving one antenna disconnected
>and the port unterminated would defeat the operation of the diplexer.
>In this case one antenna connected to one port would work as well as
>connecting it to the other.

Not exactly. The port with the long coax cable (aux) has a bit of
extra loss in the cable and exhibits perhaps 0.5dB more loss. Not
worth worrying about unless you're trying to squeeze every last dB out
of the system.

>This would explain my experience of having
>the unit work equally well with 1 antenna on either port. Having 1 or
>2 antennas woud probably make little difference if ther is not a
>multipath issue

Read the Cisco article. The problem is when you have two different
types of antennas. It's quite possible that the wrong antenna will
hear the signal first. The diversity algorithm doesn't continuously
test for the best signal. If it hears something on the FIRST antenna
that hears a signal, it could easily just sit there forever. The only
justification for switching antennas is if there is a signal loss, or
a rather high bit error rate. If you're planning to use just one
antenna, you should disable the diversity switch in firmware.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Jul 23, 12:58*am, Jeff Liebermann <je...@cruzio.com> wrote:
> On Tue, 22 Jul 2008 15:27:51 -0700 (PDT), jimmi...@gmail.com wrote:
> >Thanks Jeff, I am guessing that the traces on the board may form a
> >type of diplexer.
>
> Nope. *It's a diversity switch. *If you look carefully, there's a 6
> lead chip sitting at the junction of the two i/o ports. *The chip does
> the switching.
>
> >If this is the case leaving one antenna disconnected
> >and the port unterminated would defeat the operation of the diplexer.
> >In this case one *antenna connected to one port would work as well as
> >connecting it to the other.
>
> Not exactly. *The port with the long coax cable (aux) has a bit of
> extra loss in the cable and exhibits perhaps 0.5dB more loss. *Not
> worth worrying about unless you're trying to squeeze every last dB out
> of the system.
>
> >This would explain my experience of having
> >the unit work equally well with 1 antenna on either port. Having 1 or
> >2 antennas woud probably make little difference if ther is not a
> >multipath issue
>
> Read the Cisco article. *The problem is when you have two different
> types of antennas. *It's quite possible that the wrong antenna will
> hear the signal first. *The diversity algorithm doesn't continuously
> test for the best signal. *If it hears something on the FIRST antenna
> that hears a signal, it could easily just sit there forever. *The only
> justification for switching antennas is if there is a signal loss, or
> a rather high bit error rate. *If you're planning to use just one
> antenna, you should disable the diversity switch in firmware.
>
> --
> Jeff Liebermann * * je...@cruzio.com
> 150 Felker St #D * *http://www.LearnByDestroying.com
> Santa Cruz CA 95060http://802.11junk.com
> Skype: JeffLiebermann * * AE6KS * *831-336-2558

Interesing, this has got me wondering how hard it would be to alter
the software to use the the switch as a T/R switch. My thought is to
use one antenna for Rx with an antenna mounted LNA. I think I need to
check in with the guys over at DD-WRT.


Jimmie

On Sat, 26 Jul 2008 11:02:17 -0700 (PDT), jimmie68@gmail.com wrote:

>Interesing, this has got me wondering how hard it would be to alter
>the software to use the the switch as a T/R switch.

Fairly easy. If you lift the metal shield from the RF section, and
follow the RF path inside, the first part it hits is a 2.4GHz ceramic
bandpass filter. The next part is the T/R PIN diode switch, which
should be the same chip as the diversity switch. A bit of creative
wiring should be able to make it do what you want. No sofware
required.

>My thought is to
>use one antenna for Rx with an antenna mounted LNA. I think I need to
>check in with the guys over at DD-WRT.

The diversity algorithm is part of the firmware for the Broadcom
chipset. I think (not sure) that the interface is supplied as a
pre-compiled linkable library and cannot easily be tweaked. That's
also why you don't much in the way of MAC layer (RF) statistics from
Broadcom. There was some effort made towards reverse engineering the
interface library, but I have no clue what's happening.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Jul 22, 3:53*pm, Jeff Liebermann <je...@cruzio.com> wrote:
> On Tue, 22 Jul 2008 11:41:51 -0700 (PDT), jimmi...@gmail.com wrote:
> >IS there a distinction between the two antenna connectiond on the
> >WRT54 wireless routers.
>
> No. *The antennas area identical. *However, the two ports are slightly
> different. *One is designated as "main" while the other is "aux". *The
> router will normally favor the "main" antenna and only switch to the
> "aux" if the diversity receive algorithm determins that the "aux"
> antenna has a better signal.
>
> Unfortunately, I can't recall which is antenna is main or aux, or for
> that matter, which antenna is considered "left" or "right". *Sigh.
> Looking at the inside photos at:
> <http://www.linksysinfo.org/forums/showthread.php?t=47124>
> I would *GUESS*(tm) that the antenna port with the long coax cable
> running across the board would be the "aux".
>
> >I had heard that one is for TX and the other
> >for RX but my router seems to work equally well with either antenna
> >disconnected. I cant tell a difference in performance unless I take
> >them both off.
>
> Some routers will only transmit on one antenna (i.e 2-wire). *Routers
> that have two antennas invariably use diversity receive and sorta
> "scan" between the two antennas in receive. *I vaguely recall that the
> WRT54 transmits on the same antenna that it receives.
>
> However, you should be able to tell the difference with only one
> antenna attached. *If you remove the antenna from the "main" port, the
> stupid firmware will continue to favor the "main" port, even though
> there's no antenna or signal. *If you ping the router, you'll probably
> find that the first ping will be lost using just the "aux" antenna.
> That's not the case using only the main antenna.
>
> If you insist on using only one antennna (a good idea if you're
> attaching external antennas), some alternative firmwares have a means
> of disarming the diversity switch system and just using one antenna.
>
> Start reading here:
> <http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note091...>
> especially the part about the golf course and using two different
> types of antennas.
>
> --
> Jeff Liebermann * * je...@cruzio.com
> 150 Felker St #D * *http://www.LearnByDestroying.com
> Santa Cruz CA 95060http://802.11junk.com
> Skype: JeffLiebermann * * AE6KS * *831-336-2558

Hi, I discovered DD-WRT software does enable one antenna as RX and the
other as TX. This is user selectable. I dont know if the origonal
Linksys software allowed this or not but I doubt it. This may come in
handy because I want tot try using a 13cm LNA with mine to see what
happens.

Jimmie