Part 3 of 3 Parts

Notice: Restrictions on the use and distribution of this document appears on the first page.
Copyright 1996 - 2005 Jack Daniel Co. 800-NON-TOLL

SPECIAL APPLICATIONS:
There are some cases not covered by the more common Signal Booster configurations. TX RX Systems has a wide range of experience in solving unusual applications and will provide their assistance upon request if you have a special case. In fact, every TX RX Systems product is factory tested on operating frequencies and levels when the customer supplies operating parameters.

SIGNAL BOOSTERS IN SERIES:
In large facilities and long tunnels, Signal Boosters may be connected in series. The path between Signal Boosters may be either coaxial cables (both non-radiating or radiating) or antennas. It is general practice to set up one Signal Booster to 'talk to the outside world' and this is where the levels are adjusted so that the 'inside' portion has balanced levels of signal between the input and output paths. Balanced, in this case, usually means the following Signal Boosters will all have the same configuration of pads and gains. The greatest differential in signals are those over the air to and from the external repeater station. This technique becomes more apparent as the system design is developed.

MULTIPLE FREQUENCY BANDS:
It is sometimes desirable to operate the Signal Boosters on more than one RF frequency band in the same direction. This cases usually use one coaxial cable to reduce cable costs or due to other limitations at the installation site.

In these cases, there are several approaches;
1. Bandpass filters are paralleled to pass each band through the same amplifier sections. Four bandpass filters would be required for a two band two way Signal Booster.

2. Two or more single band Signal Boosters are operated in parallel using crossband coupler devices. This arrangement allows maximum signal level control for each frequency band and is the preferred method, as each band can be controlled independently.

There are some systems that operate with more than two bands through the same Signal Booster amplifiers. Specially engineered combinations are available.

Some two band combinations (UHF + 800, UHF + 900, 800 + 900) are becoming more common.

Some VHF or UHF combinations (152 MHz + 173 MHz or 450 MHz + 470 MHz for example) may also use parallel filters to reduce the number of undesired channels between the desired bands.

Another case would be to pass a paging channel one way while passing two way communications in another frequency band.

All of these possibilities require factory engineering assistance due to the unique operation of each combination. TX RX Systems will provide a prompt and free preliminary technical and cost evaluation of any requirement.

DOING YOUR OWN PRELIMINARY SYSTEM DESIGN:
Worksheets and examples are available to assist you in the preliminary design of a Signal Booster system in the Appendix. These worksheets allow you to organize and analyze the various system design factors and to get a better understanding of the principals used in Signal Booster system designs. Perhaps as important, the worksheet information will provide the basic information required by the TX RX Systems engineers to assist you in your requirement and establish common terminology.

DETERMINING SIGNAL LEVELS:
The primary objective of a signal level survey is to determine where the radios cannot communicate or the signal levels are too marginal to be reliable. Remember: If only one critical location in a building cannot get the signal, you will probably need a Signal Booster, regardless of any other higher signal levels in that same structure.

Test the most probable low signal areas first. Once it has been determined a Signal Booster is required, the layout can often be arranged to accommodate other areas of lesser priority.

System engineers can minimize initial measurements to those areas where Signal Boosters would probably be required in any case. Typical examples are;

- Second level or lower basements.

- Tunnels over 2000' or without end to end visibility.

- Windowless, thick walled structures. Especially stairwells and elevator areas.

It is not difficult to estimate the approximate signal strength that would be normally be present in the general vicinity surrounding an obstructed area using common 'over the air' propagation engineering methods, but it is more difficult to determine the signal strength inside an obstructed area by theoretical engineering models alone.

There are many variables in the nature of the materials causing the blockage and other obstacles within the area to be covered. For example, wall and floor construction attenuations can range from about 3 dB to over 90 dB. Even the type of glass used in a building window can have attenuation factors from near 0 dB to over 20 dB.

A Signal Booster system that is designed with little reserve and marginal signal levels limits the future flexibility of the system. The area to be covered can also be a dynamic and changing situation. What may be adequate today may not stay that way as station sites are changed, structures are altered and departments relocate.

Signal level measurements are more accurate when the test signal levels are relatively similar to those expected when the Signal Boosters are installed. Excessively low level testing measurements can be influenced by undesired signals and noise, especially when a high gain, wide bandwidth spectrum analyzer is used.

Measurements made with a high quality receiver (not a broadband scanner), which has had its RF signal level test point (i.e. RSSI) calibrated, is usually accurate enough for the tolerances required for a system design.

Sometimes, potential Signal Booster requirements for a proposed system can be based on simple 'walk-throughs' of areas using portables in the same band that communicate with an existing or similar radio system base station in the same frequency band located close to a proposed radio systems station site.

In critical "must talk" coverage areas, there is no good substitute for on-site signal measurements using close simulations of the anticipated distant base station facilities.

It is strongly recommended that the system design include considerable safety margin to accomodate future changes in the system. A 15 dB 'use factor' derating is commonly used.

Application Notes and Technical Addendums

CONCLUSION:
Thousands of TX RX Systems Signal Boosters are in use today solving coverage problems that were considered impossible just a few years ago.

TX RX Systems recognized the need for Signal Boosters several years ago and has continually designed and produced the most reliable and effective systems in the industry. TX RX Systems has the most experience and widest range of Signal Boosters and related support products available to you. They know when Signal Boosters are the best solution for your coverage problem and, more importantly, we know when they are NOT the best choice!

Please contact the TX RX Systems factory engineers or your local representative for additional information or applications assistance.

COPYRIGHT RELEASE: This document is copyrighted by The Jack Daniel Company and release to duplicate and distribute on a non-profit basis is granted to TX RX Systems and their factory authorized representatives for the sole purpose of promoting the use of TX RX Systems products only.

Use for any other purpose or removal of this notice or removal any other copyright notice is specifically prohibited!

Send us Your Comments, Information, Catalog Requests, etc.
Return to Home Page