Receiver Roofing Filter

Rodhe recent advances in receiver design qst nov 1992.

Receiver roofing filter.

O roofing filter width test tone spacing width o test tones are attenuated by roof o dr3 value is limited by upstream components includes the roof in band. Roofing filters installed in the main and sub receivers are the 12 khz 3 khz and 600 hz plus a 300 hz filter is installed in only the main receiver. The goal of a roofing filter is to limit the passband of the first intermediate frequency if stage. A roofing filter is a type of filter used in a hf radio receiver it is usually found after the first receiver mixer.

Strong signals outside the channel which may cause overloading and distortion by the following amplifier stages and mixers are blocked. Even though the dsp may be cranked down to hear only the desired signal the signal gets through to the dsp front end and will reduce the gain of the receiver because the hardware agc is being activated by the strongest signal within the passband of the roofing filter the result is agc pumping as a result of a signal that one may not. Now the elecraft k3 also offers multiple roofing filters of am ssb cw bandwidths. A roofing filter is one which is placed ahead of the main gain stages in a if stages of a superheterodyne receiver.

Best receiver possible especially for cw operation the sherwood 600 hz cw roofing filter fixed the r 4c in 1976 and the ten tec orion put that concept in a commercial design in 2003. The first if frequency is 9 mhz and a low noise figure dual gate mos fet d quad dbm double balanced mixer with excellent intermodulation characteristics is implemented in the mixer section. Three optional roofing filters are available the 300 hz ysu xf 129cn for the sub receiver and the 1 2 khz ysu xf 128sn for the main and ysu xf 129n for the sub receivers also only available by. Crystal roofing filters produce phenomenal multi signal characteristics.

Roofing filters installed in the main and sub receivers are the 12 khz 3 khz and 600 hz plus a 300 hz filter is installed in only the main receiver.