User Manual Part 1

FSG 90F System
3. Installation
Page 18 November 2000
W. Dittel GmbH
e) Connect a 50 Ohm Wattmeter and a 20 or 30 dB throughline RF attenuator pad. Key
the transmitter and check RF output level (more than 6 Watts carrier, or more than
10 Watts carrier for FSG 90F-H1 model).
f) Adjust audio generator to 1,000 Hz (via attenuator for dynamic microphone or directly
via decoupling capacitor) connected to
Amplified/Carbon Microphone Input
With 100 mV rms input, the transmitter shall achieve more than 70% AM. Increase AF
input to 1.0 V rms, observe modulation envelope, no overmodulation shall occur; depth
of modulation must remain less than 95% AM.
Dynamic Microphone Input
With some 1 mV rms input, the transmitter shall achieve more than 70% AM (depending
on SET-UP presetting). Increase AF input to 10 mV rms and observe modulation
envelope. No overmodulation shall occur; depth of modulation must remain less than
95% AM.
3.3.1 Particular Remarks to FSG 90F(X) transmitter modulation
For the combined 8.33 kHz and 25 kHz channel spacing airband radio technology,
highly demanding, specific requirements shall be comprehensively considered as
follows:
1. Voice modulation with its typical dynamic peaks (fast and large level changes) shall
modulate the transmitter with peak AM depth of less than 85%.
2. Factory setting of the very specific FSG 90F(X) voice processor results in a
remarkable AVERAGE of approximately 80% AM depth (voice and sine
modulation!). Thus, optimized usage of the RF carrier is achieved.
3. Do not change this setting, otherwise the stringent Transmitter Spectrum Mask is no
longer maintained.
4. The Walter Dittel GmbH FSG 90F System incorporates a special Dittel VOICE
PROCESSOR, which is matched best to meet the requirements of the particular
environmental noise level situation.
a) This ensures always loud and clear transmitter modulation, under
consideration of specific test requirements.
b) Due to the voice processor voice signal transfer is IDENTICAL in both the
8.33 kHz and in the 25 kHz channel spacing mode.
c) Even under these very specific conditions, fulfillment of the critical, highly
demanding Spectrum Mask is achieved.
5. Although due to the specific voice processor compression of modulation peaks,
when tested with maximum sine wave modulation signal, a conventional testing of
"standard modulation distortion measurements" is possible. This does however refer
only to sine wave testing. It will be therefore higher than the usual 2% ... 10% sine
modulation distortion, but will stay far below the maximum allowed 25% modulation
distortion factor with sine modulation.
6. Therefore, judgement of the effectively occupied total transmitter band width
(spectrum mask) is the only true, real measurement method. Such measurements
can be made only with specific test setup.
7. For tests of the FSG 90F(X) modulation capability, a sine modulation signal is useful
only below some 70% AM depth, and is on the other hand helpful only in determining
of possible overmodulation, but is not applicable to judge "voice distortion" anymore.