CFR47 Part15.247 900 MHz GMRS Link

[Batman]

anyone ever try to use 900 MHz FHSS Radios under part 15 as a voter link for remote receive sites or linking 2 repeaters?

GMRS has one downfall that i can tell and that is portable coverage in mountainous area's can be terrible.

part 90 and 97 users solve this with remote receive sites and voters.

GMRS has regulatory issues regarding remote control and interconnection to PSTN.

anyone see any regulatory issues in using 900 MHz license free (under part 15, Not Part 95 or 97) P2P links for remote receive sites to improve portable coverage?

just something i dreamed up in my sleep.

ideally you could centrally locate a TX Site and set some small voter sites throughout the Tx's coverage area to improve the portables ability to get into the repeater.

i'm sure there is off the shelf transceiver or transmitter units for 900 mhz and this can be tied to a off the shelf voter and you can use something like maxtrac's as remote receivers with 2 bay folded dipoles.

the main tx site could have a MSF5k standard Repeater/voter with a DB-420.

the 900mhz links could be horizontal polarization using dishes or corner reflectors for antenna's to keep interference from others user of the band to minimum.

i know some of the more high end gear (specifically part 15 STL systems for b,cast) have security features to prevent unauthorized users from hijacking the link.

any input?
_________________________
Thank You,

Rev. Robert P. Chrysafis
Universal Life Ministries
http://www.ulc.org

Moderator: Hunterdonfree

Owner & Moderator: freestuffwarrennj

[Batman]

it may be part 15.249. can't remember which one allows for 200 Watt ERP for p2p links on 900, 2.4, and 5.8 bands.

[d119]

The issue is that those FHSS radios are likely digital, not analog. The entire purpose of voting is to obtain the receive signal with the least amount of noise.

If you used digital FHSS radios as links, it would play hell with the voter. In installing and setting up voting systems, each remote receive site must return its audio back to the comparator with the same levels and quality as all the other sites. This is so that when a true user signal is placed on the system, the system can make an educated decision on which receiver to select. We all know how digital audio tampers with speech. Imagine a voter trying to figure out the amount of noise on a signal after going through all that analog to digital to analog conversion.

When you tamper with audio quality, run through too many links, etc, you affect levels and audio quality, and the voter can then make a "bad decision" about which site to select.

I've seen systems set up using RF links and receivers that were manufactured by different companies, with different transport methods (some telco here, a little microwave there, some RF here) and the system never works properly. It votes sites that are much noisier than others, etc.

• Guidelines in setting up signal-to-noise based voting are
• Always use receivers of the same manufacturer and model
• Use telephone company or microwave links where ever possible to ensure identical audio parameters between sites. Equalization may be required to obtain even audio characteristics.
• When using RF links, again, use all the same equipment at each site and ensure 100% quieting between all sites and the voter to prevent voter falsing due to link path noise.

The other issue with using FHSS radios is that they are not continuous duty devices by any means. If you are going to do true status-tone based voting, your links would have to be continuously keyed, and you would be continuously replacing FHSS radios.

I believe if you delve into the guts of the rules regarding GMRS, you cannot interconnect to the PSTN (as you stated), you cannot link multiple repeaters together, and you cannot interconnect to other services. FHSS radios would likely be considered as operating in another service (ISM).

Amateur radio operators can pull this off 100% legally in that the 900MHz, 2.4GHz and 5.8GHz bands are also licensed amateur bands.

Hope at least some of this helps.

[Osprey]

I believe if you delve into the guts of the rules regarding GMRS, you cannot interconnect to the PSTN (as you stated), you cannot link multiple repeaters together, and you cannot interconnect to other services. FHSS radios would likely be considered as operating in another service (ISM).

This is it, and it unfortunately ends any attempts for GMRS licensees to do almost anything that would be considered rudimentary in terms of commercial radio. With the state of FRS/GMRS hybrids these days, though, I suppose we could be glad the commission permits repeaters and MDC. :/

Many people in the GMRS community have spent some time trying to carve a bit more functionality out of the service, but the only place the FCC has relented is DOS. And even then they probably only did because of the ridiculous Garmin Rino ruling.

If you want to get this involved, incorporate and get Part 90'd. PCIA fees and a tax ID will most likely be cheaper in the long run than an NAL...

[alex]

Many people in the GMRS community have spent some time trying to carve a bit more functionality out of the service, but the only place the FCC has relented is DOS. And even then they probably only did because of the ridiculous Garmin Rino ruling.

What happened with the Garmin thing? I don't really follow the GMRS world all that much, but I'm curious now that you bring it up.

-Alex

[Osprey]

Many people in the GMRS community have spent some time trying to carve a bit more functionality out of the service, but the only place the FCC has relented is DOS. And even then they probably only did because of the ridiculous Garmin Rino ruling.

What happened with the Garmin thing? I don't really follow the GMRS world all that much, but I'm curious now that you bring it up.

-Alex

The shortish version is that the FCC granted a waiver for Garmin to use their GPS data exchange on GMRS, which was subsequently renewed, and only applied to the Garmin units, not the emission type or use of data transmission.

Later on, people queried the FCC for opinions on other devices and emission modes for transmitting data, and the only case I'm aware of the FCC giving the go-ahead was MDC1200.

[intermod]

Just stumbled over this June posting here in October. d119 noted:

.....you cannot interconnect to the PSTN (as you stated), you cannot link multiple repeaters together, and you cannot interconnect to other services. FHSS radios would likely be considered as operating in another service (ISM).

d119 is correct on the PSTN, but there is no restriction on linking repeaters, per se (if you think so, please specify the rule section). Using 902-928 ISM (FHSS, DSSS), 2.4 GHz, 5.8 GHz wifi bands (operating as a Part 15 device) is not prohibited. Another legal example is linking using a DSL or Cable internet service (there are not the PSTN; they are defined as an Iinformation Service). But - there are numerous other GMRS rules that are difficult to comply with when linking ("local service", pre-transmission monitoring, chanel sharing). We have been linking for over six years using 802.11B links and internet services.

I do agree that trying to use voter/comparators with anything but high-quality (and identical) audio links is a challenge as the devices can inproperly vote them. If you used all the same voice compression (ADPCM, etc.) on each link and controlled the latency within a few milliseconds it may be OK.

intermod

[Batman]

another question is can we use a split frequency ie 462.5625 as a control input?

say someone has hijacked your repeater can you use PSTN or an Aux RF input from another GMRS frequency to allow you as the control operator to disable the repeater from repeating?

[intermod]

Hi Robert:

Yes - you can use the PSTN or an alternate GMRS frequency for control (in fact, you *must* have some way to shutting it down when the input is tied up, although most licensees don't bother with it in reality). I would think you would want to use something up in the 467 MHz range for control - assuming the repeater receiver was on 467.600, you could use 467.6375, 467.5625 MHz; somthing that is not adjacent, but that is close to your receive ferquency so that you can just split the receive side of the duplexer to two separate receivers. But, you can likely use anything on 467 MHz side of GMRS as the duplexers will only attenuate and off-channel signal a small amount since tha band is only 200 kHz wide. I would just use another GMRS input since the FRS frequencies are often busy (especially when you have a high-elevation contorl receiver).

On linking, we simply used the hardware that the IRLP people sell for COS and PTT control, and modified their software to create a private network (separate from IRLP). We used a free product called Speak Freely to link the audio and create a voice bridge or reflector. But this all took *a lot* time....

intermod