5
Frequency Agile UHF Belt-Pack Transmitter
Rio Rancho, NM – USA
A/D CONVERTER AND DSP PROCESSOR
The processed audio signal enters the A/D converter to generate a digital signal for the modulator. A proprietary
algorithm is used for sampling and compression to minimize noise and distortion, and provide a wide, flat frequency
response. The signal then enters the modulator to generate a digitally modulated radio signal.
OUTPUT SECTION
Intermodulation (IM) occurs in the final amplifier stages of conventional transmitters when the transmitters are within
a few feet of each other. This can create serious problems in multi-channel wireless systems when an IM signal falls
on the carriers, IF frequencies, etc. of the systems being operated. To eliminate this problem in the UM700, the
modulated radio signal passes through a circular isolator before entering the antenna. The circular isolator functions
like a “one-way check valve” to allow the RF signal to pass through to the antenna, but not to pass backwards into
the amplifier stage. RF signals from other nearby transmitters cannot reach the output amplifier in the UM700. This
provides excellent stability and eliminates IM in the output stage of the transmitter.
LONG BATTERY LIFE
High efficiency circuits and switching power supplies throughout the design allow over 4.5 hours of operation using a
single 9 Volt alkaline battery. (A 9V lithium battery will provide over 14 hours of operation.) The battery compartment
is a unique mechanical design which automatically adjusts to fit any brand of battery. The battery contacts are spring
loaded to prevent “rattle” as the unit is handled.
FREQUENCY AGILITY
700 Series wireless systems are available on eight different “blocks” of 256 frequencies, from 537.600 to 767.900
MHz. Each of these blocks provides 256 selectable frequencies in 100 kHz steps over a 25.6 MHz bandwidth. This
wide variety of selectable frequencies alleviates carrier interference problems in mobile or traveling applications. Two
16-position rotary switches on the side panel of the unit are used to select the frequency.
The UM700 transmitter section uses a synthesized, frequency selectable main oscillator The frequency is extremely
stable over a wide temperature range and over time.
ANTENNA
At UHF frequencies, where wavelengths and antennas are shorter than at VHF frequencies, a resonant length wire is
preferred over using the microphone cable as the antenna. The antenna on the UM700 consists of a flexible 1/4
wavelength bronze cable, detachable via an SMA connector. The impedance of this connector is 50 Ohms.