[NLRS] 915 MHz ISM Band and Digital Modes

Mon Jul 11 22:16:33 EDT 2016

On 7/11/2016 8:32 PM, Doug Reed wrote:
>
>
> Jerry's comments are right on. I believe most of the interference is
> from frequency hopping spread spectrum Part 15 equipment. Most vendors
> choose FHSS because the rules let them use 1 watt RF power. I don't
> know how often you'll find Direct Sequence spread spectrum because
> there is ALWAYS a signal somewhere in the band. And single frequency
> Part 15 devices are seldom found because they must reduce RF output
> depending on duty cycle.
>
> With all the hash in the band, the only usable weak signal spectrum is
> at the lower end of the band. 902.100 is well placed to avoid the hash
> because the manufacturers don't want to get too close to the band edge
> since none of their equipment has a high accuracy oscillator..... FM
> repeaters are starting to use the lower end of the band for repeater
> inputs for the same reason. Hopefully most repeater coordinators are
> aware that 902.100 is weak signal and they should *not* coordinate
> repeaters +- 25KHz from there. OTOH, given the lack of FM repeater
> activity in the 902 band in and around Minnesota, it may never be a
> problem. But if you are near Chicago you may have trouble....

The 2015-2016 ARRL repeater directory in the 902 band plan shows 902.075 
to 902.125 for weak signal and EME. And 903 to 903.4 for weak signal, 
and allocates above that for all kinds of modes.

The band plan has been a topic of discussion at CSVHF conference 
business meetings intended to cause a submission to the ARRL band plan 
operation.

I see two 902 repeaters in Minnesota at Duluth inputs 902.4875 and 
902.6, 25 MHz splits.
And one at Eau Claire WI, and one at Waterloo, IA. There aren't very 
many around Chicago, the bigger lists are Ohio, Pennsylvania, and Texas. 
Id expect places with lots of part 15 digital traffic. Then the list is 
even longer for California including a repeater with input on 902.1 and 
output on 927.100. Maybe its linear. Or the weak signal out there has 
moved to 903.1. That move I'm sure depends on the FHSS activity and 
maybe the occasional beacon to chase frequency agile networks from the 
desired ham frequencies.

Then there's the K0LAV repeater in White Bear Lake with output on 919.1, 
input not listed.

The majority of the US repeaters on 902 use a 25 MHz split, low in and 
high out. There are a few with outputs around 921 +/- 2 MHz most without 
a listed input frequency. Maybe they are simplex data networks not 
otherwise identified.
>
> The upper end of the band is where most of the pagers are, mostly 928
> to 930+ with voice applications above that.
>
> Ubiquiti (ubnt.com) does make 900MHz WiFi equipment. They use DSS
> style dishes for the directional radios. Or if you want to play
> around, you can probably still find bits of the old Metricom Ricochet
> system laying around and on Ebay. The Ricochet modems were basically a
> 64Kbaud FHSS 1 watt data modem. The nifty thing is they used
> Hayes-style modem commands and you could have one unit "dial" another
> unit within range using just the ID code on the bottom. The TwinsLAN
> group was looking at using some of the Ricochet equipment for data
> links, but one of the first sites had a 400 watt 928MHz pager on the
> same roof...... There used to be a lot of info online, but I'm not
> sure how much still exists....
>
> 73, Doug Reed, N0NAS.

Pagers can be the nemesis of the whole band.

73, Jerry, K0CQ
>
>
>
> On 7/11/16, Russ Ramirez<russ.ramirez at gmail.com>  wrote:
>>
>>
>> Thanks Jerry. As I do not have a 'real' antenna up yet for 33 cm, I am not
>> very familiar with the congestion or QRM in general yet, but that will be a
>> good step 1 once I do and can get a look at/feel for the spectrum.
>>
>> 73, Russ, K0WFS
>>
>> On Mon, Jul 11, 2016 at 11:17 AM, Dr. Gerald N. Johnson
>> <geraldj at netins.net>
>> wrote:
>>
>>>
>>>
>>> I believe there are lots of signals across the 902 MHz band. We
>>> concentrate mostly at 902.1 for repeater inputs and narrow band because
>>> the
>>> broad band users have to avoid the band edges, but fill the rest solidly
>>> and some are not low power, like pagers. I was consulted years ago about
>>> a
>>> bank 915 link between a branch and the main office in Boone Iowa that was
>>> messed up by a pager located between the two locations. While good
>>> directional gain antenna can help the desired received signal strength it
>>> can also increase the undesired if that undesired is in the same
>>> direction.
>>> 915 with power and antenna gain should work but there will be lots of QRM
>>> from the unlicensed equipment spread all over the territory.
>>>
>>> 73, Jerry, K0CQ
>>>
>>>
>>> On 7/11/2016 10:48 AM, Russ Ramirez wrote:
>>>
>>>>
>>>>
>>>> Since David Palm asked a 902 MHz related question, I thought I would ask
>>>> a
>>>> another question about 33 cm.
>>>>
>>>> Are any of you doing any work with digital messaging or beacons up at
>>>> 915
>>>> MHz?
>>>>
>>>> Since as amateurs we are able to use the ISM band in ways that
>>>> unlicensed
>>>> makers cannot, this has been an area of recent interest for me as a
>>>> number
>>>> of microcontroller designs utilizing the RFM69HCW -
>>>> http://www.hoperf.com/rf_transceiver/modules/RFM69HCW.html have appeared
>>>> lately.
>>>>
>>>> For general wireless communication between microcontrollers, 915 MHz
>>>> works
>>>> far better than 2.4 GHz WiFi, BLE, or ZigBee do around your home/office,
>>>> and 915 devices are much easier on battery/solar power.
>>>>
>>>> For the amateur who might already have 33 cm loopers and amplifiers, the
>>>> use of these small devices opens up some interesting possibilities for
>>>> very
>>>> little investment.
>>>>
>>>> Thoughts?
>>>>
>>>> Russ, K0WFS
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