RGO ONE Vairable band pass crystal filter (VBF) – understanding and using

RGO ONE has a neat option – 4 pole crystal filter which bandwith is controlled via varactor diodes. Firmware generates proper voltage bias and this manner realize 10 fixed filters – 3kHz down to 220Hz.

Variable bandwith function is activated with short press of FLT button on the front panel. Then rotating encoder 1 (PWR) controls receiver bandwith.

VBF is positioned in IF path right after first 9MHz (3kHz bandwith) roofing filter and first IF amplifier – board IF/AF, U1 GALI74. Since this is receive path it will act only on receive. If not engaged the signal passes thru 6db attenuator pad in order to equalize receiver gain in both cases (VBF-ON/VBF-OFF).

First roofing filter must always cover up and envelop the second crystal filter (VBF) in order to minimize the loss in VBF. Nevertheless a significant signal loss is observed when narrowing the filter bandwith. This is normal as the receiver AGC response depends on incoming signal which in crowded HF bands consist of heavy atmospheric and other (QRM and manmade) noises.

When choosing the bandwith from B01 to B10, RGO ONE firmware instantly reschedule LO/BFO frequencies in order to keep up current mode side band and CW settings and main frequency which is visualized on the display. Also selected pitch on CW remains unchanged. MENU functions 25 – 30 are intended to keep VBF characteristic and this way LO/BFO frequencies to be assigned when different filters are chosen by the operator.

 

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