|
Hello Paul,
thank you for your post! Enclosed please find my comments:
Am 05.02.2018 um 10:35 schrieb Paul Nicholson:
Thank
you Tom, that was a most interesting post with much food
for thought.
Nice construction and good to see an alternative to air-cored
loading coils. The increase of inductance with current is
curious. An artifact of the test setup?
No, certainly not. Increasing the AC current from 0 to 600 mA in a
preliminary test with only two layers of inductors increased their
total inductance degressively by 3.8 % with positive resp. 3,7 %
with negative mutual coupling. Meanwhile Markus (DF6NM) told me he
often saw this: driving a ferrite inductor with DC decreases the
inductance (as well known) but driving it with AC first increases
the inductance until you go well into saturation when it decreases
again. He explained it with the different slope of the initial
magnetisation curve at low vs. medium drive levels, resulting in a
more complanate hysteresis loop and a lower inductance at low drive
levels. Additional there is a minor influence by the positive mutual
coupling, rising more than proportional with higher drive levels.
Interesting point
about the audio channels being out of phase.
Having made the bad experience with the bridged mode I tested the
stereo mode with two identical input signals in phase opposition via
a good quality 4 windings audio transformer. No better result, that
means at least the problems don´t come from the PAs internal
inverter stage. I have to stay with one-channel stereo but that´s
ok.
Do you
have any feedback from an E-field probe to stabilise
the phase?
With the synthesizer exciter now in use it´s impossible. Later on
with a PC and appropriate software it could be done, but see your
next item.
Perhaps that's not necessary with the relatively
low Q system.
Losses do have their adventages ...
The
antenna wires spaced one 1 metre - I assume 1 metre between
each wire.
Yes, that´s the situation - see picture below.
The
160 ohms antenna resistance, that must be
mostly ground resistance?
Yes, it is. I measured the Marconi without loading coil against
ground at 8,27 kHz. C was 660 pF then, including the open antenna
disconnection switch.
>
It´s always a little bit frustrating that I can´t hear my own
> signal even at the VLF RX site at our club station DL0AO only
> 6 km away in a forest.
Sometimes they become audible when a long transmission is
played back time compressed. I tried that with your 28th
carrier but even with x20000 compression it was still not
audible.
OK - meanwhile I´m accustomed to it.
The
ferrite chokes look a lot like RS components 715-6857,
which happen to be the same ones I use for filtering in
my 48V rx power supply. 10mH, Rdc = 3.394 Ohms.
RS No.715-6857 is the 500 mA version - I´m using the 600 mA version
715-6850 resp. Murata No. 1410606C.
73,
Tom, DK1IS
Marconi´s end on a frosty
winter morning:
![]()
|
|
