Fairhaven RD500 User Manual - page 26

comparators,  pretuning and 3 individual  FET VCO’s at HF and 3 VCO’s at 

VHF and UHF. 

Filters 

In ssb mode it uses a narrow 2.4 kHz Murata CFJ455K5 filter with a 

CFW455IT tail filter. The ssb filter is also used in AM narrow, and in AM 

wide, a 6kHz CFW455IT is used. In sync AM wide, both CFW455IT’s are 

used.   

Signal path  

A sensitive FET  HF pre amp (selectable), is followed by a bipolar 

mixer which provides good sensitivity and a high 3

rd

 order intercept, This is 

followed by a 45MHz roofing filter and a low noise second mixer and IF, 

which provide a wide dynamic range. The full wave, balanced detector has 

very low distortion over a wide dynamic range, and the AGC is delayed to 

maximise the signal to noise ratio of small signals while the two stage AGC 

decay shape is tailored to suit SSB speech. At VHF, three tuned RF filters are 

provided for preselection in the ranges of 48 to 175MHz, 175 to 460MHz and 

460 to 860MHz, a high pass section and an additional Shotkey diode mixer is 

used above 860MHz. These preselection stages are followed by low noise 

mosfet amplifiers and a high IP3 bipolar mixer.  

All mode reception is catered for by the HF receiver section except 

WBFM and video. The Video section uses a SAW filter, followed by a true-

synchronous vision IF demodulator (PLL) IC, to provide high vision quality. 

The demodulation of the TV sound and FM radio is provided by a PLL 

demodulation circuit, followed by a stereo decoder IC which is switchable to 

mono to improve audio under low signal conditions. 

8.

  Filter shapes for CW reception.