I decided to breadboard my tuning circuit so that
I don’t wind up wrecking my radio wiring!
To recap, here’s the schematic diagram:http://www.bignick.net/SimpleX/simpleX_Schematic.jpg
And, here’s a video of me trying in vain to get the
two peaks to coincide by using a variable L3
When I replicated the circuit on my bench-top, it
behaves in the same fashion as in the SimpleX
Here’s a photo of my bench top circuit:http://www.bignick.net/SimpleX/breadboard_1.jpg
And here’s what the Sweep Generator/Scope shows:http://www.bignick.net/SimpleX/breadboard_2.jpg
I tried adjusting L3, adjusting C1 and tried placing
C1 in series with C2 to reduce instead of add to the
capacitance, but none of those experiments fixed
So, then, I decided to try changing L2 to an adjustable
What I discovered in the process of replacing L2 with
an adjustable coil is that when L2 is opened (disconnected)
the peak becomes larger and single in shape!
From an earlier message from W8JI:
1.) You have a different slope of capacitance change
with rotation in C2a and b or the values are far
apart and you have not corrected for that. This
circuit was designed for C2a and b to be about equal.
(Even though that is NOT a requirement for tracking
if we dicked around with L1 and 3 and some shunt
fixed capacitance enough.)
KC9KEP: The bench top circuit is using a different
capacitor than the one in the
radio, i.e., the tuning capacitor has been replaced.
2.) You have C2a somehow connected to C2b.
KC9KEP: Checked the circuit several times: you can
see the wiring on my bench-top.
3.) You have something loading L1 or L3 heavily and
changing the reactance.
KC9KEP: Replaced the coils, they measure about 16 uH
4.) L2 has too many turns, or has an open circuit. L2
has to be set at the HIGHEST frequency to keep the
system out of critical coupling.
KC9KEP: Tried two different L2’s, one on a “form”
and one on a 100k 1W resistor
The circuit seems to work when L2 is open?
5.) You have the antenna port coupled far too tightly
into L1 from the link.
KC9KEP: I followed the instructions in the ARRL
handbook .. I have not tried using a coil
that is not as closely coupled yet.
6.) You have stray capacitance messing things up.
KC9KEP: Is that likely in two independent circuits?
You do have C2a and C2 isolated, and not tied
KC9KEP: Yes, isolated
If the tracking a double peak on the highest
frequency, as well as the lowest? C1 will not "mesh" the two peaks??
KC9KEP: Yes, two peaks for all frequencies.
I don’t get it L
--Tom Nickel KC9KEP