Belar FMHD-1, Руководство оператора

Страница: 15 / 58

FMHD-1 Operator’s Manual
BELAR ELECTRONICS LABORATORY, INC. Page 7
monitoring at any distance from the station transmitting, the accuracy of FMHD-1 readings is dependent
on the radio transmission path between the transmitter and the receiving antenna. Also, readings may be
compromised in receiving locations off the main beam of the transmitting antenna.
Once the monitoring location is known, follow the set-up directions in the appropriate section following
below. Then, to minimize the chance of damaging the
FMHD-1 by excessive RF input levels, carefully
follow the procedures for adjusting the input level(s) following power-up.
3.3 FMHD-1 Installation at the Transmitter
Once the FMHD-1 is properly mounted in the rack (see “Operating Environment,” above), make sure the
level of both the analog and digital 50
Ω FM
RF samples to be supplied to the monitor are less than
10Vrms (28.3Vpk-pk). Operation above 10Vrms input may damage the unit. Simultaneously, for
separate-line facilities, a sufficient analog RF signal level must be provided so that a proportionally scaled
IBOC
digital RF signal sample does not fall below 1Vrms (2.8Vpk-pk). Otherwise, accuracy of the
monitor readings may be reduced. If there is any doubt about the output level of the RF feed, follow the
directions in the following paragraphs carefully.
Prepare, but do not connect, a good quality 50
Ω coaxial cable, such as RG-58, to carry the analog RF
sample from its source to the BNC jack labeled “ IN 1 ” on the rear of the FMHD-1 . (The jack is located
within the “ RF INPUTS ” demarcation on the rear panel.) Note that the RF sample source and the coaxial
cable feeding the FMHD-1 high-level inputs
must have an impedance of 50Ω. Otherwise, performance of
the unit will be degraded.
For separate-line facilities, similarly prepare, but do not connect, a second
50Ω coaxial cable to carry the
digital RF sample from its source to the BNC jack labeled “
IN 2
” on the rear of the FMHD-1 .
The FMHD-1 RF input level is displayed near the center of the “Main Tuning Screen”, directly under the
tuning frequency readout. When the RF “
Input Select
” is set to “
High
Level”, the RF level
indication is a bargraph indicating in percent, which is demarcated in 20% increments. One hundred
percent is the optimum value. The bar lights yellow for readings below 80%, green between 80% and
110% and red from 110% to 120%. Operation anywhere in the green region will provide adequate
performance.
Transmitter Installation Procedure—Separate-Line Facilities:
1.
Mount the FMHD-1 in a rack with the required AC power and sufficient cooling.
2. Obtain a 50Ω RF sample of less than 10Vrms from the analog antenna transmission line. Install, but do not
connect,
a 50Ω coaxial line to carry the RF sample to the rear panel of the FMHD-1.
3. Obtain a 50Ω RF sample of less than 10Vrms from the digital antenna transmission line. Run, but do not
connect, a 50Ω coaxial line to carry the RF sample to the rear panel of the FMHD-1.
4.
Apply power to the FMHD-1.
5.
After the Main Tuning Screen appears, tune the FMHD-1 to the carrier frequency using the encoder knob.
(Control of the FMHD-1 and use of the encoder knob are described under “Front Panel Operation”, on page
11.)
6.
Bring up the RF Popup Menu on the display by depressing the encoder knob. Enter the “Input Select”
sub-menu and set the input to “High Level”.
7.
Set the potentiometer adjacent to jack “IN 1” on the rear panel to roughly three-quarters fully clockwise. Set
the potentiometer adjacent to jack “IN 2” on the rear panel to roughly one-half full.
8.
With the analog transmitter on, connect the analog RF sample feed to the FMHD-1 “IN 1” BNC jack. If the
RF Level bargraph indicates red, immediately remove the RF feed and reduce the level of the analog RF
sample at its source.
9.
Adjust the FMHD-1 “IN 1” potentiometer setting to obtain approximately 100% RF Level.