Teletronics amp toasted my D-Link 900AP+

Actually, it toasted two of them.

I needed a little bit of a signal boost to get from my access point (a
DWL-900AP+) to the client location (DWL-650+ PC Card in a laptop)
located beyond a thick belt of trees. The teletronics 1 watt SmartAmp
amp I bought says it is designed for DSSS applications, and is
bi-directional - boosts tx signal to +30dBm and amplifies rx signal by
up to 15dB. I couldn't mess with the client location, so this seemed
like a good solution.

I inserted the amp in line between the AP and antenna, and all seemed
fine. When I went to test the setup 30 minutes later, it didn't work
at all. Upon examination, the 900AP+ was putting out *zero* signal at
the antenna port. (I tested this with a spectrum analyzer). OK, I
thought - the 900AP+ is brand new - maybe it was just faulty. So I
got another one and plugged it in. Watched it closely this time, and
noticed the link quality at the client site quickly degrading. I
pulled the plug on the amp after about 10 minutes of this. Put the
second 900AP+ on the analyzer and what do I find but that it is now
broadcasting 25dBm lower than it was before.

Seems like my amp is burning out my D-Link access points. Has anyone
else run into a similar problem? Can anyone give an explanation as to
why this may be happening? Any suggestions would be welcome, 'cause
I'm scratching my head at this point. Obviously, I don't want to try
hooking this thing up to anything else (read - different brand of AP)
until I can figure this out.

Cheers,

Rik.

Thanks for the suggestions, but I don't think they are causing the
problem.

I didn't say +15dBm. I said "amplifies rx signal by up to 15dB".
There is a big difference between the two. Signals from the antenna
are not coming into the AP at +15dBm, they are coming in 15dB higher
than they would in an unamplified state. An example would be a weak
signal picked up by the antenna - say at -80dBm - would get boosted by
15dB to -65dBm. This is indeed how the amp performs; I've hooked it
up to the scope and watched it do just that.

I was worried that perhaps the connectors on the amp had been labeled
incorrectly, so I scoped that too. No such "luck" - it is labeled
correctly and I was using it correctly.

Incidentally, I figure that if you *do* hook it up backwards by
mistake, you're not likely to cause much damage to anything. Here's
why: The default mode of operation for the amp is to be in "rx gain"
mode - it boosts any signals coming from the antenna by about 15dB.
The trigger level for the "tx gain" mode of the amp is +4dBm, and it
only flips into tx mode when it detects a signal coming from the radio
that is +4dBm or higher in strength. If you plug it in backwards,
then the "radio" side of the amp will be listening to the antenna
instead, and it is very unlikely that a +4dBm or higher signal will
come from that direction. The strongest signal I've ever picked up
on any antenna I've scoped was -20dBm, and we thought that was pretty
damned loud. On the other side of the amp, the "antenna" port will
now be listening to the radio, and quite happily boosting that signal
by approx 15dB (say from +15dBm to +30dBm)

If you plug it in backwards, what you seem to end up with is a 15dB
boost to your tx signal, and no rx signal at the AP at all. Feel free
to correct me if anyone thinks I'm wrong.

The AP is hooked up to a 90deg sector, which I can't change as it is
serving other clients in that sector. At this point, installing a
repeater at the midway point is looking better and better, but I still
want to know *why* this thing fried my AP in the first place.

One line of inquiry I'll be following tomorrow (when I'm back at work
and near my tools) is to check if the amp is DC-open or DC-short. I
suspect it may be DC-short, and the D-Link 900AP+ doesn't like that -
or vice versa perhaps. Stay tuned tomorrow.

Thanks again.

Rik.

"Jeremy Parr" <(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>...
> With the +15dbm RX gain of the TT amp, you are sending WAY too much power
> into the AP radio.
>
> Are you sure you have the amp connected in the right direction? The antenna
> port is connected to the antenna?
>
> BTW, what antenna are you using? If you have an omni at the AP side, it
> might be better to use a directional antenna rather than an amp.
>
> Jeremy
>
> "R. Ling" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) om...
> > Actually, it toasted two of them.
> >
> > I needed a little bit of a signal boost to get from my access point (a
> > DWL-900AP+) to the client location (DWL-650+ PC Card in a laptop)
> > located beyond a thick belt of trees. The teletronics 1 watt SmartAmp
> > amp I bought says it is designed for DSSS applications, and is
> > bi-directional - boosts tx signal to +30dBm and amplifies rx signal by
> > up to 15dB. I couldn't mess with the client location, so this seemed
> > like a good solution.
> >
> > I inserted the amp in line between the AP and antenna, and all seemed
> > fine. When I went to test the setup 30 minutes later, it didn't work
> > at all. Upon examination, the 900AP+ was putting out *zero* signal at
> > the antenna port. (I tested this with a spectrum analyzer). OK, I
> > thought - the 900AP+ is brand new - maybe it was just faulty. So I
> > got another one and plugged it in. Watched it closely this time, and
> > noticed the link quality at the client site quickly degrading. I
> > pulled the plug on the amp after about 10 minutes of this. Put the
> > second 900AP+ on the analyzer and what do I find but that it is now
> > broadcasting 25dBm lower than it was before.
> >
> > Seems like my amp is burning out my D-Link access points. Has anyone
> > else run into a similar problem? Can anyone give an explanation as to
> > why this may be happening? Any suggestions would be welcome, 'cause
> > I'm scratching my head at this point. Obviously, I don't want to try
> > hooking this thing up to anything else (read - different brand of AP)
> > until I can figure this out.
> >
> > Cheers,
> >
> > Rik.

"R. Ling" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> Thanks for the suggestions, but I don't think they are causing the
> problem.
>
> I didn't say +15dBm. I said "amplifies rx signal by up to 15dB".
> There is a big difference between the two. Signals from the antenna
> are not coming into the AP at +15dBm, they are coming in 15dB higher
> than they would in an unamplified state. An example would be a weak
> signal picked up by the antenna - say at -80dBm - would get boosted by
> 15dB to -65dBm. This is indeed how the amp performs; I've hooked it
> up to the scope and watched it do just that.

I understand that, guess I wasn't too clear in my description. Where is the
amp located in relation to the access point and antenna? If your antenna is
RXing a signal of -20, and getting a +15dbm gain by the amp, your D-Link AP
is gonna see a signal level of -5dbm. Obviously that is enough to toast the
RX side.

Assuming you have a long cable run, the amp should be up against the
antenna, not up against the AP. The cable should attenuate the signal enough
so it won't swamp the RX side of the AP.

Jeremy

"Jeremy Parr" <(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>...
> "R. Ling" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) om...
> > Thanks for the suggestions, but I don't think they are causing the
> > problem.
> >
> > I didn't say +15dBm. I said "amplifies rx signal by up to 15dB".
> > There is a big difference between the two. Signals from the antenna
> > are not coming into the AP at +15dBm, they are coming in 15dB higher
> > than they would in an unamplified state. An example would be a weak
> > signal picked up by the antenna - say at -80dBm - would get boosted by
> > 15dB to -65dBm. This is indeed how the amp performs; I've hooked it
> > up to the scope and watched it do just that.
>
> I understand that, guess I wasn't too clear in my description. Where is the
> amp located in relation to the access point and antenna? If your antenna is
> RXing a signal of -20, and getting a +15dbm gain by the amp, your D-Link AP
> is gonna see a signal level of -5dbm. Obviously that is enough to toast the
> RX side.

Hmmm... you have a point there. I'll have to check 1) whether the amp
is smart enough to *not* amplify very strong rx signals (i.e. rx
signals greater than, say, -20dBm) 2) what the loudest signal the
reciever on the 900AP+ can handle without incurring damage is.

> Assuming you have a long cable run, the amp should be up against the
> antenna, not up against the AP. The cable should attenuate the signal enough
> so it won't swamp the RX side of the AP.

This isn't an outdoor amp; it's an indoor one. Unlike the outdoor
models which have a separate injector and amplifier, this is all one
unit. It appears to be designed to be mounted near the AP.

Info on the amp can be found here:

http://www.teletronics.com/tii/produ..._24_1w_in.html

Cheers,

Rik.

Further update: I tested the ports on the amp today with a
multimeter. The antenna side of the amp is DC-closed, while the AP
side of the amp (labelled, somewhat erroneously "to injector", as the
injector is built into this one) is DC-open.

The 2dBd dipole that comes with the 900AP+ is also DC-open, so I guess
there's no problem there.

Guess I'm going to have to bite the bullet and call Teletronics and/or
D-Link and straight up ask them.

....sigh...

Rik.

I still think you are overdriving the RX side of the AP. Get the amp as far
away from the AP cable wise as you can. I almost jumped out of my chair when
you said you were seeing signal at -20

"R. Ling" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> Further update: I tested the ports on the amp today with a
> multimeter. The antenna side of the amp is DC-closed, while the AP
> side of the amp (labelled, somewhat erroneously "to injector", as the
> injector is built into this one) is DC-open.
>
> The 2dBd dipole that comes with the 900AP+ is also DC-open, so I guess
> there's no problem there.
>
> Guess I'm going to have to bite the bullet and call Teletronics and/or
> D-Link and straight up ask them.
>
> ...sigh...
>
> Rik.

(E-Mail Removed) (R. Ling) wrote in message news:<(E-Mail Removed). com>...
> "Jeremy Parr" <(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>...
> I still think you are overdriving the RX side of the AP. Get the amp as far
> away from the AP cable wise as you can. I almost jumped out of my chair when
> you said you were seeing signal at -20

Now why on earth would I use an amp if I were seing signal at -20dBm?
What I said was that the loudest rx signal I've *ever* seen *anywhere*
on *any* antenna was around -20dBm, and that was in the lab with 2
antennas practically touching each other.

Anyway, I've put a call in to Teletronics. We'll see what they say.

Thanks again.

Rik.