How, To. Measure, Leakage' Nr - Wavetek SAM 3000 Operation Handbook

and the hum component being measured are displayed on the top line of the LCD.
You may scroll through 60 Hz, 120 Hz and <400 Hz by pressing the up or down
arrow key. The ability to discern which component (60 or 120 Hz) is contributing
the most to the hum modulation. A 60 Hz modulation component suggests a
possible corroded connector, a 120 Hz component tends to indicate a possible
failure related to the DC supply in the amplifier - possibly a capacitor going bad
and aggravating the ripple.
How To Measure Carrier-To-Noise
The SAM 3000 has a special Carrier-to-Noise measurement feature. This
measurement is simply a comparison in amplitude between the reference signal
and the noise. The reference carrier amplitude must be at least +20 dBmV at the
RF input of the SAM 3000 to provide an adequate measurement range for
measuring system noise as opposed to instrument noise. The noise measurement
automatically corrects to reflect a4 MHz bandwidth, peak detection vs. average
noise, and IF impulse bandwidth.
To make a C/N measurement, firstchoose a good frequency for the measurement.
The noise measurement must be made at least 2 to 2.5 MHz from any other carrier
on the system. The video carrier for channel 2 is commonly used for a reference
carrier, and the noise is then measured 2 to 2.5 MHz below this carrier. For the
purpose of this example, let's assume the measurement will be made at channel
2 and the video carrier frequency is 55.250 MHz. First, tune the meter to 55.250
MHz. Next, press "FCN" and then "C/N". The display will show the noise
measurement correction factor. Tune down to 53 MHz. Tune up and down using
the "T" and "\ "arrow keys to find the highest C/N reading, and to assure that you
are not measuring a beat (intermod) product.
How To Measure Leakage
Leakage signals may be measured using the SAM 3000, and a Wavetek RD-1
tunable dipole antenna. The RD-1 has a built-in 16 dB preamplifier to boost the
received signal for measurement on the SAM 3000. A loop-through provision
is made on the RD-1 to permit the use of a bandpass filter prior to the pre-
amplification of the leakage signal to limit intermod effects that result from
measuring a low level signal in the presence of other signals at much higher
levels.
The SAM 3000 should be tuned to the leakage measurement frequency, usually
a video carrier in the mid-band (108 - 140 MHz). The dipole antenna elements
should be adjusted to the correct length to correspond to the measurement
frequency (a chart is given on the back page of the RD-1 Manual). The FCC
prescribes a measurement procedure for leakage that should be followed. This
specifies that the leak should be measured at a distance of 10 feet, with the
antenna 10 feet off the ground, and 10 feet from any reflecting surface. Rotate
the antenna to obtain the peak measurement, and record the measurementin your
leakage log.
14