User's Manual

UtiliNet® Endpoint User Guide 1-5-2007

Page 26 of 30

• Power consumption versus dynamic range

• Size versus dynamic range

• Cost versus dynamic range

Currently, all UtiliNet products have a receive sensitivity of about -107 to -112 dBm, with an allowable

single-tone interference level of around -20 dBm before sensitivity reduction takes place. Thus, the

dynamic range is about 90 dB. For multi-tone interference, for example several strong paging transmitters

in the area, it is recommended that the maximum interference level be limited to -30 dBm. In general, price

increases exponentially with dynamic range. For example, specialized direct-sequence spread spectrum

transceivers with 130 dB dynamic range have been built, but they sell for $60,000 each. To make this type

of solarpowered radio with battery back-up would probably cost almost as much. The consequences of

interference to the radio system will be reduced RF connectivity. This is measurable as reduced tickle

success rate and data success rate to another radio. Interference problems can be classified as either in-band

or out-of-band. Each is treated differently.

In-Band Interference

This type of interference is from devices within the same frequency range as the desired radio system, and

therefore cannot be filtered out. This is encountered if, for example, two or more UtiliNet radios are placed

at the same site to increase data handling capacity. Another example would be a UtiliNet radio and another

unlicensed Part 15 radio such as a wireless LAN radio at the same site. Usually, this type of interference is

corrected by adjusting the antenna configuration of the radios at that site.

Out-of-Band Interference

Out-of-band interference is due to radio systems on other frequencies outside the desired radio system

frequency band. These can sometimes be strong enough to cause de-sensitization or generate an excess of

significant intermodulation products.

Cellular Base Station Interference

Cellular base stations are usually not a problem unless the radio is within approximately 500 feet line-of-

sight to a cellular base station site. If this is a problem, RF filters are available. If you are in doubt, use a

spectrum analyzer to check interference levels. A reasonable goal would be to have the highest cellular

base station interference signal be no more than -30 dBm. Levels between -20 and -30 dBm will probably

be noticeable, but still not a problem. Levels above -20 dBm, especially between 890 to 894 MHz, could

cause problems if there is not 10 to 20 dB Safety Factor in the link budget.

Paging System Interference

The Radio Frequency spectrum from approximately 929.5 to 931.5 is used for paging. This application

requires transmission of enormous amounts of RF energy to penetrate buildings and houses and still be

received by the relatively inefficient antenna of a pager shielded by a person’s body. In the frequency

domain, this activity takes place just above the highest frequency of UtiliNet operation. With the

proliferation of paging systems, these signals are getting more intense and increasing in quantity. Once

again, RF filters are available to solve this problem. As with cellular, you can use a spectrum analyzer to

check for allowable interference levels. The same limits and goals apply—paging signals should ideally be

no more than -30 dBm. Levels between -20 and -30 dBm will probably be noticeable, but not a problem.

Levels above -20 dBm could cause problems if there is not a 10 to 20 dB Safety Factor in the link budget.

Performing RF Field Studies

Field surveys are necessary to prove or disprove the path predictions, as well as to provide information as

to the potential of interference from other RF transmitters that may also be located at or near any of the