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.

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.


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

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