If you have intermod problems with a vhf receiver, we may be able to help eliminate it!
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. In fact, the same preamp circuit is used as is in the popular LNY-( ) series of preamps. 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.
| MODEL | TUNES RANGE |
PEAKED AT |
TYP. NF |
NOM. GAIN |
TYP. 3DB BW | TYP. 20DB BW | TYP. 30DB BW | TYP. 40DB BW |
| LNP-146 | 140-155 MHz | 146 MHz | 0.6 dB |
18 dB | ±1 MHz | ±3.8 MHz |
±4.8 MHz |
±7 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 $10. |
||||||||
65 Moul Rd., Hilton, NY 14468-9535
www.hamtronics.com
Support and Orders: (585)-392-9430