Errata for "The Hybrid Cascode--A General Purpose AGC IF Amplifier"
Page 31, middle column, four lines down from the top.
The memory capacitor is described as C3. It should
be C16. (10Nov07)
Page 32, Fig 4 Caption. There are nine diodes in the circuit,
so the bill of materials should list D1-D9. (13Nov07)
Page 32, Fig 4 Caption. The bill of materials neglected
to list U1, which is a LM317L programmable regulator. Also
missing are the three JFETs, Q2, Q4, and Q6. These are all type J310.
Page 31, right hand column, 3.0 inches up from the bottom. We
made the comment that "If necessary, R5 may be increased to slow the attack."
The was a poor choice of words. If R5 is increased,
it will decrease the rate that charge is changed across the capacitor, but
it will actually make the attack faster.
In the extreme it could lead to a severe overshoot.
This problem can be fixed with addition of another capacitor from
the cathode of D6 to ground. (The "ditter" pulse modulator
[EMRFD, Chapter 7] that was used to test the design is really a useful tool
for this sort of circuit.) (23Nov07)
Page 33, Fig 4. Add a resistor, R37, from the AGC line to a
pad at the edge of the board. The value is 10K, but is not terribly
critical. This is a point that will drive the S-meter circuit described
on the applications page. Also add a pad at the board edge and
connect it to the 9 volt regulated output from U1. This voltage is
used in the S-Meter driver circuit. (2Dec07)
Pages 32 & 33, Fig 4. Several component changes are suggested
to enhance overall stability and to enhance the buildability of a PC board
version of the design. Technical details
are found by clicking here. (1) Replace L2, L3,
and L4 with 47 uH RF chokes. We use Mouser part number 542-77F470-RC.
(2) Change R1 from 2.2 K to 1K. (3) Add an 18 or
22 Ohm resistor, R38, in series with C12. There is no slot
for this resistor on the boards from KA7EXM, so it will be necessary to stand
C12 and the R38 on a single lead in the holes formerly used by C12.
The two components are then soldered together in mid air. Keep the
leads short and you will never notice it. (3Dec07)
Page 32, Fig 4. This is a modification to simplify the buildability
and does not relate to a problem. Replace L1, a 7.1 uH toroid
inductor, with a 6.8 uH RF Choke with a Q of 50 or more. The
choke we picked has a Mouser part number of 434-22-6R8. I measured
Q at 9 MHz of over 70. The self resonant frequency for this choke was
111 MHz. Also, change R7 from 3.3 to 3.0 K to improve the input
impedance match. (2Dec07)
Page 32, Fig 4. R15 can change to a 3.0 K. (It was 3.3K and
this change will have minimal impact on performance, but it keeps the cost
down on the kitlet offered by KA7EXM.) (3Dec07)