#8 KHZ BANDWIDTH CRYSTAL FILTER DESIGN SERIES#

I'll try and find a copy of the 1939 RSGB 'Amateur Radio Handbook' reference.ДЇirstly, the xtal will cause hysteresis with the regen setting. The M0AYF webpage referred to can be found here: I interpret some of the text as talking about Symmetry, but ignoring the notch. However, the notch is still there, it just moves a long way away.ДЄlso I think there is confusion between Symmetry, and whether or not the notch is present. So when the phasing caps is at zero, the response becomes almost symmetrical. By careful adjustment of this control a nearby interfering signal could be nulled out' As C2 is increased, a notch appears in the stop-band (Fig 9) and progressively rises in frequency towards the pass-band peak. If this is set to a minimum value, the filter has a form which is an almost symmetrical band-pass shape. In Fig 8, C2 is the so-called phasing control. They were made adjustable so that the desired cw signal could be received with minimal adjacent-channel interference. 'Filters of this type were originally developed for use in am receivers fitted with a bfo for cw reception. See Fig 8 in the reference (and my earlier post):

#8 KHZ BANDWIDTH CRYSTAL FILTER DESIGN SERIES#

The Peak is the Series resonance of the Crystal, while the notch is at the Parallel resonant point.Д«ut because the parallel resonance will be affected by the Crystal holder's holder's capacitance, an anti-phase signal from a centre-tapped coil can be used to move the Parallel resonance point (eg notch). There is a peak and a notch close together (plus over-tones). My understanding is that the basic crystal has a response as shown here: Probably a crazy and impractical idea, but that's the sort of thing that we radio hobbyists tend to investigate.ДЄny comments on the filter bandwidth of a single crystal at 2 MHz, and whether it would be usable in practice for AM SWBC? It is hoped that the super-regenerative detector's extreme sensitivity will not only compensate for the filter's insertion loss, but also will be so sensitive that it will remove the need for the 3 IF amplifier stages - as well as providing inherent AGC. Then, a super-regenerative IF stage at 2 MHz would pick up the filtered IF signal after the crystal. The idea is to achieve the IF selectivity with a single damped crystal immediately following the mixer. The ultimate (and possible unachievable) goal is to radically simplify my current receiver, which uses 4 IF transformers and 3 IF amplifiers ahead of a regenerative IF stage. Could a damped single crystal at 2 MHz achieve this? However, intuitively speaking, it seems that I could simply damp the crystal (with either a series or parallel resistance), which should theoretically physically inhibit the ability of the crystal to oscillate, therefore lowering its Q, and broadening the bandwidth enough for AM reception.ДЄny opinions on if this could work? I'm not expecting a perfect, flat-topped, 10 kHz-wide IF response, just a somewhat but not too-narrowly-peaked response that is somewhat akin to that of a 2 MHz LC regen that is set just below threshold. I expect the bandwidth to be too narrow for AM reception. I am considering adding a single-crystal filter using a 2 MHz crystal. The receiver is intended for AM SWBC reception and it works okay. A 2 MHz IF was chosen for better image rejection than with an IF of 455 kHz. I have built a shortwave superhet with a regenerative IF stage at 2 MHz.

8 khz bandwidth crystal filter design