I concur. When a 900 MHz access point (AP) is located "near" a
high-power paging (or other high-power) transmitter then a bandpass
filter is "cheap insurance" to avoid or minimize the AP receiver
"desensing" (overload) that the high-power transmitter may cause. It's
impossible to know in advance how near a high-power transmitter is "too
near". It depends on the AP receiver selectivity, the power of the
nearby transmitter, the antenna patterns, the separation distance and
the strength of the incoming signals from the WISP clients.
Bandpass filters will help. Physically moving further away from the
high-power transmitter will also help.
jack
P.S. - This is discussed on page 258 of my book.
John Scrivner wrote:
If you have an adjacent channel carrier which is running hundreds of
watts of power then you may not have a choice of whether to use the
bandpass filter or not. Your system may not operate in the upper part of
the 900 MHz band. What happens is that the adjacent carrier will "swamp"
your receiver and your base station will essentially become deaf to your
own, much quieter, client radios. The bandpass filter is the sole remedy
to this. I think many people use filters by default because they do
little harm to your system performance and may mean the difference
between your system working or completely failing in the presence of
higher-powered adjacent carriers.
I currently run Waverider 900 MHz systems and because of this I may have
a system which is more sensitive to adjacent carrier swamping than other
platforms. I simply do not know about other platforms to say one way or
another. I believe Charles has tested several 900 MHz platforms and may
be able to expand on this discussion. It is important to note that he
may have a bias toward Canopy as he now sells that platform. I can only
assume that his testing may have led him, in part, to this platform
choice for 900 MHz systems. Care to share your thoughts Charles?
If anyone out there has any past experience with swamped 900 MHJz
receivers, bandpass filters, different 900 MHz platforms, etc. then
please share your thoughts about the use/need for bandpass filters. I
would like to know more myself.
Scriv
Larry Yunker wrote:
While filters can help, the problem that I see is that filters are: 1)
expensive and 2) bulky. Last time I checked, a cavity filter for the
902-928 range was roughly $300-$400. I don't see it being practical
to install one of these at every customer site!
Cavity filters are fine for your broadcast sites, but that is of
little help when the 900Mhz paging systems bleed over so much that
they "deafen" the subscriber radios.
- Larry
----- Original Message ----- From: "Mike Cowan"
<[EMAIL PROTECTED]>
To: "WISPA General List" <wireless@wispa.org>
Sent: Thursday, October 26, 2006 7:32 PM
Subject: Re: [WISPA] Sprint / Nextel to use 900mz for iDen
Filters fix this problem quite handily. We recommend one on every
system needed or not. I don't see an issue here.
Mike
At 07:07 PM 10/26/2006, you wrote:
ISM 902-928.
Exact band and Power limit is relevant. Currently, the top 25% of
ISM 900 bandwidth (channel 4) is unusable, in MANY areas, due to
blead over from 930 Licensed high power gear (500W). If the same
thing were to occur at the lower portion of 900 ISM bandwdith, it
could kill Channel 1 also, horribly effecting WISPs using
unlicenced. They also may be requesting to use higher power on the
actual ISM bands, argueing Public Safety is more important than
unlicensed use. Iftheir request is granted, specifics should be
lsited on how they are going to prevent interference with existing
unlicensed band users. Remember that the goal may not only be to
use the spectrum. They have benefit in killing off all the 900Mhz
WISPs, that could compete with Sprint/Nextel Next generation WiMax
type Licensed 700M-900M solutions.
Tom DeReggi
RapidDSL & Wireless, Inc
IntAirNet- Fixed Wireless Broadband
Mike Cowan
Wireless Connections
A Division of ACC
166 Milan Ave
Norwalk, OH 44857
419-660-6100
[EMAIL PROTECTED]
www.wirelessconnections.net
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Jack Unger ([EMAIL PROTECTED]) - President, Ask-Wi.Com, Inc.
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