Cross Band Repeaters Standard Repeater Operation Operate on one - - PowerPoint PPT Presentation

Cross Band Repeaters

Standard Repeater Operation

• Operate on one band with specific shift

between receive and transmit frequencies. —Two meter shift is 600 KHz —70 CM shift is 5 MHz

Repeater Block Diagram

Duplexer* Receiver Transmitter Controller *Duplexer typically has cavity filter(s)

Why a Cavity Filter?

• Cavity filters have high Q and can

provide better filtering than LC filters.

• Cavity filters also offer opportunity for

very narrow trap to isolate the transmit frequency from the receive frequency.

• Without the sharp filters, the transmitter

would de-sense the receiver.

What is a Cross-Band Repeater?

• A cross-band repeater is a repeater that

utilizes two bands. In our case, 70CM and 2 meters.

Why Use a Cross-Band Repeater?

• It allows use of standard radios such as a

mobile radio to be used as a repeater (so long as the radio has cross-band capability).

• Cross-band operation works because the

frequency difference between the transmit and receive frequencies are sufficiently distant in frequency to eliminate receiver de- sensing.

Why Would MIRO Need a Cross- Band Repeater?

• In the event of a loss of our standard

repeaters, a cross-band repeater would give us better geographical coverage than simplex frequencies.

How Would MIRO Use the Cross Band Repeater?

• Net control would operate on 70 CM.
• Field operators would operate on 2 M.
• Both frequencies would be operated as

simplex frequencies.

What Frequencies Will MIRO Use?

• 70 CM—440.350 MHz
• 2 M—147.160 MHz
• 440.350 is a frequency that MIRO currently

does not use.

• 147.160 is our 2 M receive frequency. We

can use that frequency because we assume that the repeater is not operational when we need to use a cross band repeater..

Frequencies (cont.)

• To use the 2 M frequency, it will be

necessary to set up a memory position in your HT to operate on 147.160 MHz

• simplex. You can’t use the repeater

memory because while you would receive on 147.160 MHz you would transmit on 147.760 MHz.

How Does it Function?

• NC makes a call on 440.350 MHz.
• The cross-band repeater in a mobile

unit receives the 440.350 MHz signal and repeats it at 147.160 MHz.

• Field communicators receive it on

147.160 MHz and answer on the same frequency.

How Does it Function? (cont.)

• The mobile cross-band repeater

receives the 2 M frequency and retransmits it on 70 CM.

• NC receives the signal on 70 CM.
• Note: No CTCSS tone is needed.

Mobile Unit

• The mobile unit will be located in some

advantageous location that will allow the best coverage possible on Mercer Island.

• The mobile unit can use an enhanced

antenna that will result in better coverage than a mag-mount antenna.

Enhanced Antenna

I built a copy of the Vashon Island J-Pole antennas (with modifications) for use as the enhanced antenna.

Antenna Modification

The modification was to increase the mast mounting area on the angle bracket.

Then I modified a trailer hitch adapter by adding a 1” diameter aluminum rod to allow for antenna mounting.

Trailer hitch adapter mounted to vehicle.

The antenna mast has two pieces. One mounts to the antenna and the other (smaller) is a long mast to provide additional height. The two pieces slip together and are held With bolts and thumb nuts.

I added two support pieces that temporarily clamp to the rack

• n my vehicle when the antenna is in place.

Enhance antenna installed on vehicle.

Questions or Comments