If you have intermod from paging transmitters, fm broadcast stations, or other out-of-band signals, adding a preselector ahead of your vhf receiver may help eliminate the interference. Receivers with very low noise figures, such as the ones we manufacture, often have minimal selectivity ahead of the first amplifier stage in order to obtain the superior sensitivity. However, when used in a high rf field, receivers can suffer from front-end overload due to strong signals on adjacent bands.
Adding just a filter ahead of a receiver will degrade the sensitivity of the receiver because of its insertion loss. However, the LNP-( ) series of preselectors has been designed with a low-noise preamp ahead of the filter to establish a low noise figure before the signal reaches the filter.Surface mount technology is used in the preamp circuit to take advantage of the latest low-noise fet's and the excellent rf properties of smt capacitors and resistors.
The filter circuit comprises a sharp three-pole L-C filter which is optimized for the particular band of interest. This is in addition to the input filter in the preamp circuit. The table below indicates the sharp response of the filter. The preamp circuit provides enough gain to override the insertion loss of the filter circuit with enough additional gain to help overcome poor noise figure of older receivers. The LNP-( ) Preselector uses a pc board with RCA style jacks. Normally, the preselector is installed in the enclosure with the receiver, inserting it in the 50-ohm signal path between the antenna and the receiver input.
The appropriate LNP-( ) Preselector added in line before the receiver can help attenuate signals causing intermod and cross-band interference. A preselector will not replace a duplexer, though, and it will not help prevent desense from your own transmitter in a repeater. Also, a preselector is not the answer to problems caused by insufficient i-f selectivity in a poorly designed receiver.
LNP-( ) Preselector, wired/tested.... $99.00 (specify model from chart below)
Tuning charge if you want it tuned to custom frequency ...$20
Tuning Tool. Hex tool used for alignment. $6.00
RF plug & cable to connect to board.
A40 115VAC/12Vdc Power Adapter to power this unit ...$10.00
PF-1 Phantom Power Kit option (see above) ...$5.00
|120-130 MHz||121.5 MHz||0.6 dB||13 dB|
|216-226 MHz||223 MHz||0.6 dB||15 dB||±2 MHz|
|Note: Units are stocked tuned to center frequency indicated above. They are easily repeaked at your operating frequency if necessary. If you prefer, we can custom tune to your frequency at an additional charge of $20.|
PF-1 PHANTOM POWER KIT $5
Often, we are asked if the +12Vdc power for a preamp can be fed up the coax cable from the receiver for installations where the preamp is mounted at the antenna. We have long resisted the temptation to try to save a few cents on some light-weight hookup wire by using this trick, feeling that chances of messing up the rf performance are too great.
We now offer a kit for those who want to try this anyway. It consists of the rf chokes and dc-blocking capacitors needed for both ends of the cable, at the receiver and the preamp or preselector, along with general instructions.
See what our customers say:
It has been over 10 years since I first set up a low orbit receiving set up. I purchased an LNP-137 from you folks in the past two weeks. It removed much intermod from satellite receiver IF leakage. There are four such dishes within 30ft of (my antenna). Thought I would never get rid of the noise. The LNP-137 did away with all visible interference and there was a great deal of it to lose. The downloaded pics were trashed with vertical lines. They are no more with the simple addition of the LNP. I cannot recommend this unit too much. The gain of the unit just takes out the intermod and signal loss of the post processing. Very happy camper. Thanks much for everything including the fast order filling and delivery. ... Gerry Rolle