The LP-1 FM Translator Preamplifier

DESCRIPTION:

    The LP-1 FM translator preamplifier has been specifically designed to select a weak FM signal in the presence of strong interfering signals.
    One of the more serious problems with FM translators is the loss of sensitivity due to strong RF signals other than the desired signal (referred to as "desense"). This is often caused by the translator's own output getting through the input RF section and finding its way to the first mixer. The result is an increased noise level which can degrade the desired signal especially if it's weak. In a worst case of only 400 kHz separation between input and output, a 1000 to 1 (30dB) improvement can be expected by using the LP-1.
    Another problem which often exists is caused by the presence of very strong undesired signals located close enough to the translator site to completely flood the front end of the translator. A preamplifier that can handle large signal levels without overloading along with a good filter is what's needed. The LP-1 fulfills this need.
    All of the above is accomplished by means of a high level preamplifier using a single VMOS transistor, followed by a very selective five section helical resonator filter. Because the preamplifier will accept large input signals without overloading, no intermodulation products are generated. The boosted signal at the preamplifier output contains both the desired signal and the undesired ones. This composite signal is then passed through the filter (FL100) which strongly attenuates the undesired signals. The result is a dramatic improvement in translator performance.

SPECIFICATIONS:

Frequency:	All FM channels (filter is tuned to a specific channel)
Overall Gain:	15dB Minimum, 20 dB typical (depends on desired filter bandwidth)
Noise Figure:	4dB Maximum
Intermodulation:	None appreciable under the following conditions:                                  2uV desired signal                                  10,000uV undesired signal with 400kHz separation
1dB Compression  (typical)	A typical amplifier with 20dB gain will have the gain compressed by 1dB with an input of -6dBm and an output of +13dBm (measured with a single tone input)
Rejection:	400kHz removed: 17dB  600kHz removed: 35dB  800kHz removed: 47dB  1MHz removed: 60dB
Impedance	50 Ohm or 75 Ohm
Connectors	UHF standard, others available
Power Requirements	+27 to +35 VDC, 150mA. This voltage is imposed on the receive coax through the voltage adapter. This makes it possible to use voltage from the translator power supply. RF connectors impedance normally match that of the preamplifier and filter but other combinations are available. The standard DC connector is a banana plug.
Mechanical	The preamplifier is mounted in a weather proof box intended for tower mounting. It will mount to 3/4" through 2 1/2" diameter pipe or angle, as well as any appropriate flat surface. The filter has provisions for mounting on a flat surface near the translator. The voltage adapter simply mounts in the transmission line between the filter and the preamplifier but nearest the filter. Construction is all aluminum except for the mounting hardware. Rack mount for filter is available.

For more information, email us at tepco@rapidnet.com .