One of Armstrong Regenerative Receiver
Credit Line: Thermionic Tubes in Radio Telegraphy
and Telephony, by: John Scott- Taggart, The Wireless Press LTD,
· Effectively increases the "Q" of the tuned
circuit by the
concept of "negative resistance." Any circuit that accomplishes
this will do the trick. Typically, an oscillator circuit, such
as a Hartley, Colpitts, or the like is chosen. One then sets the
loop gain of the oscillator circuit by some means to be just below
the point of oscillation. Later, it will be seen that there are
some clear design advantages to some circuits over the others.
· Runs in "oscillation" mode, if desired, to
act as a direct conversion or autodyne detector for CW or Single
Sideband signals. The oscillation mode provides the BFO, or course.
The workings are not dependent on vacuum tubes versus
transistors. The real problems in any design at least, are:
1. Interaction with the antenna, and QRM generated
by the receiver itself. "Grounded Grid" or equivalent
isolation amplifier does the trick here. An un-tuned grounded
gate FET amplifier seems to be the modern choice.
2. There is massive interaction with tuning as a function
of regeneration setting. If there is a way to separate detection
from regeneration, this problem can be addressed. One typical
vacuum tube design uses a Colpitts oscillator in parallel with
a plate or grid leak detector (my favorite for vacuum tube designs).
Another alternative (my Senior EE project in 1960!) was to insert
a cathode follower between the tuned circuit and the detector/feedback
Edwin H. Colpitts, “Oscillation Generator,”
U.S. patent 1,624,537
(filed: 1 February 1918: issued: 12 April 1927)
Figure Credit Line: Wiki