[HamWAN PSDR] 902 MHz Band Plan? Hardware?

Bart Kus me at bartk.us
Fri Nov 21 15:59:35 PST 2014

Are you sure a Mikrotik host board won't just run a 902MHz card like the 
XR9?  If it's possible, that'd allow us to keep the same software stack 
we have right now, keep TDMA, and provide the MIMO we're seeking.  The 
other thing I'm curious about is the frequency agility of the XR9.  Does 
it support 2.5MHz/5MHz channels?  What are the quantization steps on its 
tuning ability?  What is its tuning range?  Are there other 902MHz 
miniPCI(-e) cards on the market?

I'd still like to see sectorization since it's hard to scale otherwise.  
The band is 26MHz wide, which is enough for 5MHz sectorization.  Perhaps 
the sectorized spectrum can be arranged to avoid the most 
likely/frequent users of this band, but I don't think you're gonna have 
any luck by trying to comply 100%.

If someone has any suggestions about other technologies, such as CDMA 
spectrum sharing, I'd like to hear them.  One of the things to keep in 
mind about 902MHz HamWAN service is that it's aimed squarely at mobile 
users.  Can't assume high gain directional antennas at the user 
terminal.  I'd like to support things like whips on car rooftops with 
near-continuous coverage as the car drives around.

As some of you are aware, I'm not satisfied with the available power 
levels for any of this equipment.  Mobile stations will be behind 
buildings and trees, at close to ground level.  I'd like to bring things 
up +20dB or so over stock (ie: 50W range).  If you know of any 
affordable 902MHz amplifiers that can be used with these radios, let me 
know.  The requirements are RF-sensed TX triggering from signals as low 
as 100mW or so, bidirectional signal handling, about a 1us TX/RX delay 
time, and linear amplification since these modems use amplitude 
components to carry data.  Running off a standard 12V car power system 
would be a bonus.  The combination of reduced frequency and increased 
power ought to drive a far more available service than we have with the 
6GHz offering right now.  However, experiments can begin right now with 
just stock power levels to get a better feel for propagation properties 
and noise levels of this band.


On 11/21/2014 10:34 AM, Ryan Elliott Turner wrote:
> Hey folks,
> I'd love to get rolling on testing some 900 MHz gear here in Memphis. 
> I've got a few high-level questions about it, though, and I'd love to 
> find out what others have already settled.
> Do we want to do sectors and multiple channels? UBNT sells a AM-9M13 
> that looks pretty slick; 120 degrees, 2x2 mimo; spec sheet here: 
> http://www.streakwave.com/mmSWAVE1/Video/AirMax900Sector_DS.pdf
> Mikrotik sells a metal 9hpn that's 27 dBm @ 11Mbps to 24dBm @ 54 Mbps 
> (500 mW transmitter), but that's single chain. From what I read, dual 
> chain MIMO mitigates about 3dBm of noise, which may be worthwhile. 
> These devices don't play nice between vendors, though, and I think the 
> preferred dual chain 900 mhz device is the UBNT XR9. We'd lose TDMA by 
> going with this but gain another chain. Thoughts?
> Apparently the ARRL band plan is pretty outdated and unrecognized 
> (http://www.aracc.org/33cm900mhz.pdf ). Around here, we have an 
> organization named SERA that has specified a 900 MHz band plan; it is 
> available at the following URL: 
> http://www.sera.org/pdf-files/SERA%20902%20MHz%20FUP.pdf
> So, here we've got
>   * 922<=f<928
>   * 910<=f<916 (it says ATV...)
> And that's it. So, if we were to sectorize, we don't even have 3 
> channels to use here.
> Thoughts? Looks to me like omni, TDMA, and single 5 MHz channel 
> (911-916?) is the best way to go for this.
> -- 
> Ryan Turner
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> PSDR at hamwan.org
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