There are always several ways to skin that cat! 

Well the larger antenna would certainly allow you to decrease your back lobe
and increase power and the size of your ear.  

If the problem is interference at your site, a lot of this is going to
depend on how your site is built, length of the face of the tower, and
direction of all of your equipment.  

While I haven't done any current work with the 2 foot Gabriel professional
series I've been hearing enough good stuff about it that I ordered one to
play with and see if it worth deploying. 

What I like to do in situations like this is break out the Anritsu spectrum
analyzer and spend some time documenting the site.  Knowing the ambient
noise floor at the site is important before putting any additional equipment
up as it's likely to interfere with other equipment.  

Dustin Jurman

-----Original Message-----
Behalf Of Tom DeReggi
Sent: Wednesday, February 08, 2006 9:24 PM
To: WISPA General List
Subject: Re: [WISPA] BPSK QAM16 DSSS interference

Thanks, Charles and Dustin,

The challenge I'm working on is to determine if the degregation of my test 
link, is caused by

A) Distortion on the transmitter, at full power? or
B) Overload or lack of acuracy of the receiver. or
C) Or Just plain interference creeping in. (tested at about -80db)
note: multipath unlikely, as LOS link, 10 miles, parabolic antenna, o wall 
behind antennas, 100ft above other buildings.

In my Trango test case, w/ 2ft antennas, QAM16, at -55 db I got worse signal

Quality quality (packet loss) than at -65db. To me that would infer case A 
or B was happening.

What was interesting, is my Mikrotik test link w/ range5s, actually got peak

rssi (full power) of -47db apposed to Altas's peak signal of -55.
(note: path analisys calculated -55 db appropriate, so not a negative for 
the Trango, but a Plus for the Range 5, exceeding expectations).

With the Mikrotik, the higher the rssi radio power, the better the speed 
results, and lower the packet loss. So Mikrotik did not seem to be plagued 
with the same delimna. However, at a surprise, the Mikrotik performed at a 
slower speed, and had more packet loss, in its best link configuration, than

Trango had.  So the Trango at -65db QAM16, outperformed the Mikrotik 
at -47db.

I attribute those results partially, to how the radios deal with 
interference. One side of the link (AP/MU) had significant noise, causing 
the Mikrotik to lower modulation more frequently.  I proved this, by 
repeating speed tests with Trango using 5.3Ghz, which performed perfect 
links (no loss). However, the 10-11 miles was pushing the maxrange of 5.3, 
and I felt 5.3 was to risky, based on that. I actually had to turnup the 
Power a little over the legal limit to get the perfect link, but still lower

rssi than the 5.8G link.  But my point was, when noise wasn't there, the 
links worked much better.

So the decission I am trying to decide on is,
a) increase the gain (dbi) of the antennas and lower the gain (dbm) of the 
radio, to improve the link.
For example, upgrade from 2 ft dished to 3 or 4 ft dished.  or

b) get a better 2 ft antenna with more isolation.
For example, upgrade Gabriel cheap 2 ft para to the high performance 2 ft 
Gabriel Drum style antennas?

Either one could have a possitive effect. Its likely that my noise is 
comming from my colocated antennas at the same site. The Drum style antenna 
will likely have much better isolation comming from the sides.  Better F/B 
ratio is not jsut about an antenna behind me, but also beside me, and 
interference is not always cured by lowering the beamwidth, if the 
interference is comming from the side. So better isolation antenna could be 
the choice.

However, if the packet loss was from self generated noise, larger antenna 
would keep my gain up, even after lowering power. However, I actually would 
still have a gain improvement, because the antenna increases gain in both 
directions, where as lowering he TX power only does it in one direction. 
Because most of my interference is at the AP/MU side my paln was possibly 

Increase the antenna at the RU/Client, to a 3-4 ft dish. If packet loss 
at -55db was due to transmitting to high power, and loss was at MU/AP then 
it would be most importantto lower transmit power at the RU/Client side. 
Increasing dish size at RU would help this.

Then on the MU/AP side, I would add the high performance 2ft antenna, with 
better isolation, taking that most of teh interference may be colocation 
interference. Increasing the antenna size may not block interference comming

from the side.

But then again, if interference comming from the front (I have another site 
20 deg off to the left), its possible the larger dish and narrower beam may 
in fact also help isolate interference.

Now to make it complicated, what if the cause is not interference at the 
radio receivers? But instead its all the RF in between and reflections 
comming out of phase and distorting my signal before it gets to my radios?

Now I could just add 4 ft high performance drum antennas on both sides, and 
call the problem done, but then that would be $4000 just in antennas :-( 
But also means upgrading mounting pole and ballast hardware.

Which brings me back to my original post, is it just cheaper to buy better 
radios, and which have better C/Is and SNR threshholds?

The orthogon has more power, but no matter how good their path anal tool is,

and how good the reputation, when a large part of the problem is noise 
floor, I have a hard time believing that faster speed can be pushed through 
a narrower spectrum width, while hard setting speed in each direction.

So what I am learning is its not about whats the best radio, its what tool 
do you need to solve each unique problem. The hard part of this business is 
conclusively identifying what problem exists, to know the most cost 
effective way to solve it.

Decissions, decissions, decissions.

Tom DeReggi
RapidDSL & Wireless, Inc
IntAirNet- Fixed Wireless Broadband

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