At 10/14/2010 09:05 PM, Jason Bailey wrote: >Fred,many of those tvws channels are untouchable,unless you run your >tx at 40mw.A full duplex system has the ap at full power on one >channel,the s/u tx ing on a low power only channel in full >duplex.Many more channels are then available and you may now see the >reason for this...BTW,those low power channels are considered mobile >and wouldnt have all the restrictions.Do you see my point?Jason
And Brian added, >The request was made for the simple reason of being able to use the 40 mw >devices in a split radio architecture. If anyone caught my posting about how >far you can broadcast with 40 mw, it might make more sense. If you transmit >on one end of a link using 40 mw radio you could use a high gain antenna on >the other ends receiver to make up for the low power. Design a radio with a >separate receiver from the transmitter and you can have a multipoint system >that can operate in the first adjacent channels and still work for a WISP. >The key concept is that your transmitter does not use the same antenna as >your receiver keeping the power levels fully legal. The 40 mw devices in the >first adjacent channels do not have any HAAT limits. They are referred to as >mobile devices. Yes, I see what you're talking about; see my comments below. >There was a potential problem in the rules to make this >work. There was one little statement that said any transmitter and/or >receiver could not exceed the HAAT rules. It makes no sense for a receiver >to have to abide by that since it cannot cause interference. The FCC >apparently agreed. I don't read the new rules that way, but perhaps I'm missing something. I does talk about TVBD "devices", but I take that to be transmitting devices, based on the context of Part 15 and the surrounding words. FCC language is however sometimes ambiguous. Make that often ambiguous. So clarification is a good idea. >40 mw transmit into a no gain antenna is legal, a 15 dbi receive antenna on >the other end is legal to. Put one of each in all radio devices and we can >operate in the first adjacent channels, PLUS you can transmit and receive on >separate frequencies thus having 12 MHz to work with. Yes, I see the configuration you have in mind. I get how the 40 mW personal/portable rules allow adjacent-channel operation just outside the contour, so they fit in places that both 100 mW p/p and Fixed devices don't. It could be useful for some kinds of applications, especially, I'd guess, backhaul links, where FDX is most useful and big receive antennas aren't a problem. Dual antennas seems more unweidly for a subscriber AP. However, portables are only usable on channels 21 and up, so if your area has only channels from 2-20 available, or even say one channel above 20 (which is the case in some areas I've looked at), then you can't run much or any personal/portable devices, since VHF and 14-20 are Fixed only. Also, 40 mW, or more precisely -1,8 dBm/100 kHz spectral density (which is more constraining on narrowband modes), is not a lot of EIRP, especially for a rural WISP. 20 dB more makes a lot of difference. Even the 4W EIRP number strikes me as needlessly low, especially if it is highly directional gain. (1W TPO, on the other hand, seems quite generous.) I'd rather they had adopted, say, the 2.4 GHz PtP compromise, where extra antenna gain is partially, but not completely, offset by lower TPO. So it sounds to me like I should get some of my compadres together here and Petition to loosen up the HAAT restriction a bit. I'll probably ask them to allow operation there but with lower EIRP in the direction of any protected contour within some reasonable distance, but not zero, and allowable on any channel where Fixed devices can go. (I don't see why a device should have to lower the EIRP that's aimed away from any nearby protected contour.) Maybe something like the FM broadcast contour height/power tables in 73.333. Especially the 15 km curve. Offhand (very!) that looks like (compared to 75m) about 4 dB at 120 m, around 12 dB at 200m, and 18 dB at 1000m. Brian and Jason, thanks for clarifying the position. -- Fred Goldstein k1io fgoldstein "at" ionary.com ionary Consulting http://www.ionary.com/ +1 617 795 2701 -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: [email protected] Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
