Cables; Antenna Spacing - Motorola CDR500 Programming Manual

CDR500 & CDR700 Repeater Service Manual
Series radios, the power handling capability would
have to be increased to 100 Watts.
• Insertion loss: 3 dB maximum
Less insertion loss of the duplexer means the receive
radio will be able to discern weaker signals and the
transmit radio will deliver more power output to the
antenna. The 3 dB specification will result in coverage
range being reduced approximately 30%. Typical
insertion losses quoted in catalog sheets are 1.5 dB.
• Frequency spacing: Band dependent
Frequency spacing" is the frequency difference
between the operating frequencies of the receiver
and the transmitter. Frequency spacing less than
3 MHz can be achieved but the physical size of the
duplexer increases dramatically. If a VHF repeater is
being assembled, be aware of the minimum fre-
quency spacing that a duplexer can provide when
choosing the operating frequencies for the repeater.
The VHF duplexers available from Motorola stock
are specified at 4.5 MHz minimum spacing. In the
United States, the spacing in the 450 MHz to
470 MHz UHF band is 5 MHz and the spacing in the
470 MHz to 512 MHz band is 3 MHz.
If the proper equipment necessary to tune a duplexer is
not available, then the duplexer must be pretuned by
the manufacturer. Be ready to provide the exact
receiver and transmitter frequencies at the time of pur-
chase. Also indicate that the duplexer will be used in a
CDR500 or CDR700 repeater.
• Connector type-N
The type BNC connector may be used on the
receiver and transmitter inputs but must be avoided
for the antenna. The BNC is prone to mechanical
movement which can generate noise when the
transmitter is operating. Type UHF connectors will
suffice for VHF but should be avoided for UHF. The
mini-UHF connector, if available for the duplexer, is
very good. Other connectors, such as the SMA and
the TNC, are very good but may be more expensive,
fragile and rather difficult to assemble in the field.
The best general performance comes from the
type-N.
The cables provided with the CDR500 and CDR700
repeaters mate with a type-N at the duplexer end. Any
other type of connector will require you to assemble

cables.

Cables
The coaxial cables that connect the radios to the
duplexer are fabricated from RG58A/U (the cable that
is used with most of the mobile antenna kits). Since
RG58A/U does not have a perfect shield, the routing of
March, 2001
the cables should allow a physical separation of
approximately 1 inch.
Do not use RG58A/U as the coaxial cable that connects
the antenna connector of the repeater to the antenna.
The rather small size of RG58A/U can introduce exces-
sive losses in the system that will decrease the effective
range of the repeater.
Substitute RG400/U for short lengths and RG214/U or
1/2-inch "hardline" for the longer lengths. If the
"hardline" is used, connect the antenna connector of
the repeater to the end of the "hardline" with a flexible
jumper cable. This will avoid undue stress on the con-
nectors of the cables and the repeater.
In planning a system, make sure that the various con-
nectors found on the duplexer, feedlines, feedline
jumpers and antenna are the correct mating pairs.
Table 1-5 can be used to determine which feedline to
choose for a given frequency band and line length to
maintain 1.5 dB (approximately 30%) or less power
loss. Table 1-6 is a list of Motorola part numbers for the
various connectors and cables.
Table 1-5. Maximum Feedline Length in Feet (Meters)
Band
Low (50 MHz)
VHF (150 MHz)
UHF (450 MHz)
800 MHz
Table 1-6. Part Numbers for Connectors/Cables
Part
mini-UHF male connector
UHF male connector
type-N male connector
type-N 1/2" hardline male
type-N 1/2" hardline female
RG58A/U coaxial cable
RG400/U coaxial cable
RG214/U coaxial cable
1/2" hardline cable
8 ft. jumper cable
type-N f-f adapter
*Use of the type-N f-f adapter may be required to connect the jump-
er cable to the main feedline.

Antenna Spacing

Isolation between the output from the transmitter and
the input to the receiver may be obtained with physical
distance. Instead of using a duplexer, two antennas may
be spaced apart and connected to the receive radio and
6864110R66-O
Introduction to Repeaters and Components
Duplexers, Cables, and Antenna Spacing
RG400/U RG214/U
55 (17) 100 (30)
25 (7.5) 50 (15)
15 (4.5) 25 (7.5)
10 (3) 20 (6)
Motorola Part Number
2884606M01
2884579F04
2884476G01
TDN6677
TDN6678
3000475378
3084173E01
3015068A17
3080329A22
TDN8406A*
5882764A01*
Hardline
300 (90)
150 (45)
90 (27)
70 (21)
1-5