I suppose many variations are possible. People like regens where there are no additional windings on the turning inductor. That allows very simple band switching.
You could copy the "noisy regen" configuration and connect the tuned circuit directly to the collector of Q1 in the negative resistance circuit. Technically that is not the best solution as the tuned circuit will be damped down by poor impedance matching and linked directly to the semiconductor junction capacitances.
A Vackar arragement might be a better solution but I haven't tried it yet.
You could try reducing C8 to 33pF to increase the tuning range. C8 parallel C3 and L3 form the resonant circuit.
Even though the transistors are biased in an odd way, they are still operated within the datasheet defined operating region for most transistors. Of course there is some cost, the collector base capacitance is higher than normal, the gain is a little lower and the collector impedance is somewhat lower than normal.
Anyway the circuit is very similar to the "noisy regen" circuit which is well known.
The advantages of the Armstrong configuration are better matching of the base and collector impedances to the tuned circuit and the low phase shift of the transistor. Allowing the inductor to keep most of its natural Q.
You can also take a buffered output from the collector of Q2 which you cannot do with the noisy regen circuit without adding a third transistor. Removing R2 and selecting a nice value for R1 you could make a buffered output oscillator with very few components.
Where is the blog post?, and where should I pick off the link to the 455kc IF
Details about the T3
I am just about to launch into building a Q multiplier for a Drake 2B
Thanks
You can post what you want, it's all great
I suppose many variations are possible. People like regens where there are no additional windings on the turning inductor. That allows very simple band switching.
You could copy the "noisy regen" configuration and connect the tuned circuit directly to the collector of Q1 in the negative resistance circuit. Technically that is not the best solution as the tuned circuit will be damped down by poor impedance matching and linked directly to the semiconductor junction capacitances.
A Vackar arragement might be a better solution but I haven't tried it yet.
You could try reducing C8 to 33pF to increase the tuning range. C8 parallel C3 and L3 form the resonant circuit.
And the Armstrong topology based receiver:
Here is a receiver refinement for the Negative Resistance topology.
Even though the transistors are biased in an odd way, they are still operated within the datasheet defined operating region for most transistors. Of course there is some cost, the collector base capacitance is higher than normal, the gain is a little lower and the collector impedance is somewhat lower than normal.
Anyway the circuit is very similar to the "noisy regen" circuit which is well known.
The advantages of the Armstrong configuration are better matching of the base and collector impedances to the tuned circuit and the low phase shift of the transistor. Allowing the inductor to keep most of its natural Q.
You can also take a buffered output from the collector of Q2 which you cannot do with the noisy regen circuit without adding a third transistor. Removing R2 and selecting a nice value for R1 you could make a buffered output oscillator with very few components.