Batboard

I have been asked to come up with a solution to improve radio coverage in a food processing plant. The building has been added onto four times and is a combination of wood and steel walls and ceilings with many many rooms. The communication system is an UHF 40 watt GR1225 using a duplexer with about 40' of hardline and a DB408 antenna mounted on the roof on one end of the building. After touring the place, we went up to roof and looked at the antenna. My first reaction was probably 80% of the signal was not being radiating into the building but above it due to the narrow beamwidth of the antenna. About 40 employees have 4 watt handheld Kenwoods so the system is very busy during plant operation. The problem is dead spots, drop outs, and spotty communication. Many people are walking around when using the radios so dropouts occur during transmissions. Checking the repeaters output measured 28 watts from the duplexer. That figured to be abourt right . The reflected power was .5 watt , So the equipment is working good.

My first idea is to get the antenna down inside the building preferrable a larger room with a higher ceiling somewhere central to the building.

Another idea is use radiating transmission line, end to end of the building BUT I have no experience using that or whether it works with UHF.
Also would you still use the duplexer or just use the radiating cable for RX or TX only but still use an internal antenna for the other. Even though I'm not an engineer I still try to engineer a job with all the knowledge I possess and if I still don't feel good about it I get help.

Due to the excess use of the system the owner now also wants a a second repeater so he can split the maint and operations of the plant. People that have the need can then scan both. Would like to have some help with this. Thanks.

Dave..

Hello Dave,

Although you checked the RF power output through the duplexers ... you didn't specify what the repeater's receiver sensitivity is for 20 dB Quieting or 12 dB SINAD. Is the GR1225 repeater's receiver using PL/DPL decode? I suspect the repeater's transmitter is penetrating the entire complex of buildings but with the combination of metal used throughout for buildings and food processing equipment, the 4 Watt Portable signals are not able to penetrate all the internal losses or are bouncing off of the metal objects with the buildings before the signal reaches the repeater's receiver. You also did not mention the required coverage outside of the plant ... away from the food processing facility?

Here's what I would suggest doing not knowing how the buildings are laid out, either ask the maintenance personnel to provide access the the building blueprints or walk & measure the entire lenght in feet as a continous run of 3/8" or 1/2" Andrews Radiax cable from the repeater room to the other end of the complex. I'm guessing it could be 300 to 500 FT or more of required Radiax cable but only you will know.

Most manufacturing facilities roofs are between 15 and 30 Feet in height depending on when the building was first constructed. As you have described the repeater's room could be located on the first floor or in a second level mechanical penthouse. You would disconnect the Heliax outside antenna, purchase and insert a SCALA PD2 50 Ohm RF Power Divider center N connector then connecting the Heliax cable outside antenna to one side N connector and the Radiax cable to the opposite N connector. SCALA builds 3 versions of the PD2 50 Ohm Antenna Power Dividers as follows: PD2-55 50%-50% Split, PD2-72 75%-25% Split and PD2-91 90%-10% Split.

http://www.kathrein-scala.com/error.htm RF Antenna Power Dividers

Now depending on how the buildings are constructed ... especially the roofs will determine how you or a subcontractor installs the cable near the inside of the roof. Keep the Radiax at least 1 to 1.5 Feet away from the roof itself and any parallel metal pipes. Try to install the cable through the center of each building allowing an even radiation pattern for the RF signal. Terminated the Radiax cable with a quarter wave antenna whip with a metal ground plane presenting a 50 Ohm load.

http://www.andrew.com/ Radiax Slotted Line Cable and Connectors. Use either RXL2-2 3/8" or RXL4-3 1/2" Radiax Cable and "N" Type connectors.

Since the owner would like an additional repeater to split the Maintenance and the Operations personnel, I would suggest getting a second repeater pair frequency at least 1 MHz higher or lower so there are less chances of problems to encountered between both repeater systems. This will also help when adding the additional hardware and combining both repeater systems on to the one antenna / radiax system.

Dave, Please PM me so I can supply the configuration information.

Dan

Before spending lots of money on a distributed antenna system, give the repeater a complete physical. Check for it's receive sensitivity by inserting a 30 dB coupler into the antenna line. Make sure this is tested with the transmitter operating. Ensure the radio is up to spec, and that there is no desense from the transmitter (ie. duplexer is working properly).

If talkback can only occur via a 4 watt portable with its quarter wave whip, or worse, "rubber duck" antenna, then you might try turning the repeater transmitter down to 4 watts to the antenna too. Have it transmit continously while you walk around the plant with a portable. With this balanced situation, how you hear the repeater is how it will hear you. If there are dead spots, you will know where they are and may be able to address these areas only. Perhaps positioning the repeater centrally may also help.

I've seen jails (lots of concrete, steel, multiple floors and bigger than your fish plant) work just fine with a centrally located 10W UHF repeater.

Good luck!

RF Dude