28-05-2012, 08:52 PM
Hi Lawrence. Right! Working day over - time to play radios!
O.K., so we are now looking at a tunable regenerative detector that tunes from
2 → 3 MHz, and an R.F. signal range 5 → 15 MHz.
For the oscillator on the high side, we have:
Osc. minus R.F. = I.F., where "I.F." is 3 → 2 MHz.
For R.F = 5 → 6, Osc. = 8
up to
for R.F. = 14 → 15, Osc = 17
So the required osc. freqs. are from 8 → 17 MHz: 10 in total.
For the oscillator on the low side, we have:
R.F. minus Osc. = I.F., where "I.F." is 2 → 3 MHz.
For R.F = 5 → 6, Osc. = 3
up to
for R.F. = 14 → 15, Osc = 12
So the required osc. freqs. are from 3 → 12 MHz: 10 in total.
For the moment, setting aside the harmonic generator concept, I've had a think about alternative ways of producing the required discrete freqs. in either of those two ranges. I can see a method of doing this involving one crystal oscillator, a L/C oscillator with 5 switched L/C ccts., one mixer, and a 3-bank, 10-way rotary switch. I can also see a method using 3 or 4 crystal oscillators, a number of frequency multipliers, two mixers and a single-pole, 10-way rotary switch. Both of these methods produce discrete freqs. in either of the required ranges, but the circuitry is quite complex in either method.
So, setting those approaches aside (at least as maths. exercises, they were entertaining 
), it will almost certainly be a lot easier simply to build a stable manually-tuned L/C oscillator that covers the required range (8 ~ 17 MHz, or 3 ~ 12 MHz) and simply tune to the freq. as required. That osc. could have any number of switched ranges: a trade-off between circuitry complexity and ease of tuning to the correct freq.
As for the H.G. approach, (a-la the Racal RA-17), the one real difficulty I foresee is in trying to reproduce the low-pass filter that follows the H.G. stage. (I must study the cct. in some depth
) Possibly a salvaged one from a scrapped RA-17 could be acquired?
As for the 6AS6 valve, the distinguishing feature of that valve is its unusual suppressor grid control over the cathode - anode electron stream. I believe that the 6AS6 is still readily available.
All said (for now).
Al.
O.K., so we are now looking at a tunable regenerative detector that tunes from
2 → 3 MHz, and an R.F. signal range 5 → 15 MHz.
For the oscillator on the high side, we have:
Osc. minus R.F. = I.F., where "I.F." is 3 → 2 MHz.
For R.F = 5 → 6, Osc. = 8
up to
for R.F. = 14 → 15, Osc = 17
So the required osc. freqs. are from 8 → 17 MHz: 10 in total.
For the oscillator on the low side, we have:
R.F. minus Osc. = I.F., where "I.F." is 2 → 3 MHz.
For R.F = 5 → 6, Osc. = 3
up to
for R.F. = 14 → 15, Osc = 12
So the required osc. freqs. are from 3 → 12 MHz: 10 in total.
For the moment, setting aside the harmonic generator concept, I've had a think about alternative ways of producing the required discrete freqs. in either of those two ranges. I can see a method of doing this involving one crystal oscillator, a L/C oscillator with 5 switched L/C ccts., one mixer, and a 3-bank, 10-way rotary switch. I can also see a method using 3 or 4 crystal oscillators, a number of frequency multipliers, two mixers and a single-pole, 10-way rotary switch. Both of these methods produce discrete freqs. in either of the required ranges, but the circuitry is quite complex in either method.
So, setting those approaches aside (at least as maths. exercises, they were entertaining ), it will almost certainly be a lot easier simply to build a stable manually-tuned L/C oscillator that covers the required range (8 ~ 17 MHz, or 3 ~ 12 MHz) and simply tune to the freq. as required. That osc. could have any number of switched ranges: a trade-off between circuitry complexity and ease of tuning to the correct freq.As for the H.G. approach, (a-la the Racal RA-17), the one real difficulty I foresee is in trying to reproduce the low-pass filter that follows the H.G. stage. (I must study the cct. in some depth
) Possibly a salvaged one from a scrapped RA-17 could be acquired? As for the 6AS6 valve, the distinguishing feature of that valve is its unusual suppressor grid control over the cathode - anode electron stream. I believe that the 6AS6 is still readily available.
All said (for now).
Al.
Mind you, that doesn't necessarily mean I'll get permission to use it, let alone bring even 
