20-06-2012, 06:32 PM
Just another thought, would welcome any ideas/comments etc on this:
So far the tunable IF that has been selected is centered on 2.5 Mhz and tunes approx +- 500khz either side of that frequency, the anoe of the Mixer is connected in series with the primary winding of the tunable IF tank circuit (Regen det. tank), from a practical point of view the primary winding cannot be variably tuned because of loading effects on the high impedance secondary tank circuit, the point I am coming to is this:
So far as a harmonic generator for the local osc is concerned I originally thought of a tuned tank in that stage to select the harmonic of a 1 Mhz osc to set the band whilst rejecting the adjacent harmonics to a low enough level as not to be to noticible in any mixing process, I am also thinking now of another approach, it is nothing new, Racal use it but not entirely in the same context as the Regenerodyne. The idea is this, instead of selecting the required harmonic with a tank circuit in order to supply the mixer how about having no tunable tank and instead feed all the harmonics generated to the grid of the mixer ie a "comb" of frequencies ie: untuned and beef up the filtering in the Mixer anode circuit before the signal is coupled to the tunable regen detector by way of a bandpass filter?
Can anyone see any fundamental flaw in this (theory wise) The signal input to the mixer is preceeded at the moment by a double tuned RF tank (RF grid and Mixer grid) I realise that this would not prevent any spurious mixing by any of the harmonics presented to the mixer in combination with any signal that the double tuned RF tanks cannot reject down to a certain level, I also realise that this is more of a problem the higher up the shortwave spectrum I go. It is possible that I could use a triple ganged RF tank as triple gang second hand caps still seem to be available this would enable a double tuned tank to be used in the grid of the RF amp with top capacity coupling as well as a tank in the Mixer grid, I realise that the gain stakes are now going down but by using more modern valves than what I am presently using I feel sure it could be made up for.
Lawrence.
So far the tunable IF that has been selected is centered on 2.5 Mhz and tunes approx +- 500khz either side of that frequency, the anoe of the Mixer is connected in series with the primary winding of the tunable IF tank circuit (Regen det. tank), from a practical point of view the primary winding cannot be variably tuned because of loading effects on the high impedance secondary tank circuit, the point I am coming to is this:
So far as a harmonic generator for the local osc is concerned I originally thought of a tuned tank in that stage to select the harmonic of a 1 Mhz osc to set the band whilst rejecting the adjacent harmonics to a low enough level as not to be to noticible in any mixing process, I am also thinking now of another approach, it is nothing new, Racal use it but not entirely in the same context as the Regenerodyne. The idea is this, instead of selecting the required harmonic with a tank circuit in order to supply the mixer how about having no tunable tank and instead feed all the harmonics generated to the grid of the mixer ie a "comb" of frequencies ie: untuned and beef up the filtering in the Mixer anode circuit before the signal is coupled to the tunable regen detector by way of a bandpass filter?
Can anyone see any fundamental flaw in this (theory wise) The signal input to the mixer is preceeded at the moment by a double tuned RF tank (RF grid and Mixer grid) I realise that this would not prevent any spurious mixing by any of the harmonics presented to the mixer in combination with any signal that the double tuned RF tanks cannot reject down to a certain level, I also realise that this is more of a problem the higher up the shortwave spectrum I go. It is possible that I could use a triple ganged RF tank as triple gang second hand caps still seem to be available this would enable a double tuned tank to be used in the grid of the RF amp with top capacity coupling as well as a tank in the Mixer grid, I realise that the gain stakes are now going down but by using more modern valves than what I am presently using I feel sure it could be made up for.
Lawrence.
