29-06-2012, 10:57 AM
Hi Al, you've been busy, well thought out, all this mixing stuff is certainly a challenge, on my "simple" receiver I initially thought a 500 Khz or a 1 Mhz xtal osc as a basis to drive a harmonic generator, principaly for stability reasons, however that concept throws up an interesting problem:
The tunable regen det tunes from 2 to 3 Mhz therefore the harmonics are going to pop up when tuning to any exact Mhz frtequency ie: it is not possible to tune center zero to WWV on 5,10 or 15 Mhz and resolve that signal, similar issues occur at the start of some of the amature bands so far as the begining of the CW section is concerned, the quick fix solution is to offset the 1 Mhz osc by about 10 Khz or so when trying to receive frequencies that run very close to a Mhz interval.
As you can probably guess the Xtal will have to be pulled, I have no idea how far you can pull a 1 Mhz xtal, if I could find one I would give it a go but 1 Mhz xtals are are bit thin on the ground these days, with this in mind I have decided for the moment that any on board 1 Mhz osc will be L/C derived and it would be simple to fit an offset capacitor in the tuned circuit. I have simulated this with the donor 1 Mhz osc on the B40D, shifting the tuning knob slightly on that enables the Regenerodyne to be tuned right up to an exact 1 Mhz multiple ie: I can resove WWV time signals no problem.
Anyone reading this might get the impression that this receiver is complicated to use when in fact it is very simple as band setting is achieved by tuning non oscillatory circuits and the tunable regen det has a constant tuning rate and a constant performance no matter which band is being tuned.
Initially I had in mind that the frequency stability (once warmed up) should be as good as an old time comms set such as Hallicrafters, HRO etc to that end I think I am more or less there, constructing a stable 1 Mhz osc should not be too difficult, the critical thing is component selection/quality and the general practical layout used in its construction.
The Osc in the B40D is pretty solid at 1 Mhz.
It might even be possible to design it so that any drift in the1 Mhz osc. opposes any drift (from a temperature point of view) in the tunable regen det when it is set to oscillate for SSB/CW etc.
If the 1 Mhz osc is built the same as the Local Osc in the B40 then I have the option of Xtal or L/C as the tuning elements as that switchable facility exists on that receiver.
Interesting stuff, when we switch on a radio and tune it it is easy to take for granted what the poor radio designer had to go through, no doubt a series of trade offs and compromises and frustrations...
Lawrence.
The tunable regen det tunes from 2 to 3 Mhz therefore the harmonics are going to pop up when tuning to any exact Mhz frtequency ie: it is not possible to tune center zero to WWV on 5,10 or 15 Mhz and resolve that signal, similar issues occur at the start of some of the amature bands so far as the begining of the CW section is concerned, the quick fix solution is to offset the 1 Mhz osc by about 10 Khz or so when trying to receive frequencies that run very close to a Mhz interval.
As you can probably guess the Xtal will have to be pulled, I have no idea how far you can pull a 1 Mhz xtal, if I could find one I would give it a go but 1 Mhz xtals are are bit thin on the ground these days, with this in mind I have decided for the moment that any on board 1 Mhz osc will be L/C derived and it would be simple to fit an offset capacitor in the tuned circuit. I have simulated this with the donor 1 Mhz osc on the B40D, shifting the tuning knob slightly on that enables the Regenerodyne to be tuned right up to an exact 1 Mhz multiple ie: I can resove WWV time signals no problem.
Anyone reading this might get the impression that this receiver is complicated to use when in fact it is very simple as band setting is achieved by tuning non oscillatory circuits and the tunable regen det has a constant tuning rate and a constant performance no matter which band is being tuned.
Initially I had in mind that the frequency stability (once warmed up) should be as good as an old time comms set such as Hallicrafters, HRO etc to that end I think I am more or less there, constructing a stable 1 Mhz osc should not be too difficult, the critical thing is component selection/quality and the general practical layout used in its construction.
The Osc in the B40D is pretty solid at 1 Mhz.
It might even be possible to design it so that any drift in the1 Mhz osc. opposes any drift (from a temperature point of view) in the tunable regen det when it is set to oscillate for SSB/CW etc.
If the 1 Mhz osc is built the same as the Local Osc in the B40 then I have the option of Xtal or L/C as the tuning elements as that switchable facility exists on that receiver.
Interesting stuff, when we switch on a radio and tune it it is easy to take for granted what the poor radio designer had to go through, no doubt a series of trade offs and compromises and frustrations...
Lawrence.
