[NLRS] 915 MHz ISM Band and Digital Modes

Tue Jul 12 16:51:12 EDT 2016

I see in the latest QEX that ARRL has a new book on the topic of ham 
high speed networks. "High Speed Multimedia for Amateur Radio." ARRL 
item number 0529. There's a slight chance there might be a copy at Radio 
City or Dan can order it and save paying postage, though the ARRL member 
price is better than Dan's, probably.

73, Jerry, K0CQ

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 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.
>
>
>
> 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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