The second graph shows 4 kHz as the worst. This is the dip between Mode 0 and 
Mode 1 in the waveguide.

15 kHz range is the best for Mode 1 Earth Ionosphere Waveguide Propagation. The 
antenna efficiency is the main reason navy transmitters have all moved up to 19 
- 25 kHz. It is a trade off between antenna efficiency and frequency of best 
propagation.

Naval communications use VLF Mode 1 and ELF Mode 0 at around 80Hz. Not much use 
in between because it doesn't really work. Poor antenna efficiency combined 
with high propagation loss. 

73 John VA3VVV 


--------------------------------------------
On Mon, 10/23/17, DK7FC <[email protected]> wrote:

 Subject: Re: VLF: Using resonance effects of earth-ionosphere for radio 
experiments
 To: [email protected]
 Received: Monday, October 23, 2017, 10:50 AM
 
 PS: I don't want to say that
 15 kHz is trivial, not at all. It is all 
 interesting (except skype!!), 20m, 80, 630m,
 2200m, 36km, 46km, 58km, 
 101km, 309 km and
 of course also 20 km! :-)
 
 73 and good luck on the mid VLF!!!!!
 Stefan
 
 Am
 23.10.2017 16:40, schrieb DK7FC:
 > Hi
 John,
 >
 > Yes, like on
 HF it is a different league to work on 15 kHz or 8.27 kHz
 
 > or 2.97 kHz. Working VK from DL in SSB
 is usually easier on 20m than 
 > on 80m,
 same for WSPR of course. So one may ask "Why are you
 trying to 
 > work VK on 80m, 20m is much
 easier?!"
 > Some youngsters may even
 ask "Why are you using radio at all, there is 
 > skype!!?!" :-)
 >
 > 73, Stefan
 >
 > Am 23.10.2017 16:17,
 schrieb John Fisher:
 >> Hi Stefan,
 >>
 >> Actually, 1 -
 4 kHz is the worst frequency range as it is right 
 >> between the two waveguide Modes 0 and
 1.
 >>
 >> ELF
 around 100 Hz is good for Mode 0 and Mode 1 peaks around 15
 kHz.
 >>
 >> 73
 John VA3VVV
 >>
 >>
 >>
 --------------------------------------------
 >> On Mon, 10/23/17, DK7FC<[email protected]> 
 wrote:
 >>
 >>  
 Subject: Re: VLF: Using resonance effects of
 earth-ionosphere for 
 >> radio
 experiments
 >>   To: "[email protected]"<[email protected]>
 >>   Received: Monday, October 23, 2017,
 9:05 AM
 >>
 >>  
 Hi John,
 >>
 >> 
  Thank you.
 >>   The large image
 is
 >>   well known meanwhile but i
 did see the other one so
 >>   far.
 Where did you take it from and are there
 >>   more informations?
 >>   What means ||Tn| ? I
 >>   guess n is the numer of hops. But T
 = Tesla? Not
 >>   really. It should
 be |B(n)|. So maybe something
 >>  
 else. But it would make
 >>   sense
 that is is
 >>   something that has to
 do with the field strength. Odd...
 >>   Assuming it is actually the
 fieldstrength, then
 >>   1 kHz looks
 most
 >>   interesting again. I
 need
 >>   to continue to work in that
 range!!
 >>
 >>  
 73, Stefan
 >>
 >>   Am
 >>  
 23.10.2017 14:21, schrieb John Fisher:
 >> >
 >>   Hi
 Stefan,
 >> >
 >> >
 >>  
 Attached re two graphs on this subject you might find
 >>   interesting.
 >> >
 >> > 
 73
 >>   John VA3VVV
 >> >
 >> >
 >> >
 >> >
 >>  
 --------------------------------------------
 >> >  On Mon, 10/23/17, DK7FC<[email protected]> 
   wrote:
 >> >
 >> >    Subject:
 >>   VLF: Using resonance effects of
 earth-ionosphere for radio
 >>  
 experiments
 >> >    To: [email protected]
 >> >    Received: Monday, October
 23, 2017,
 >>   7:15 AM
 >> >
 >> > 
   Paul,
 >>   Markus, VLF,
 >> >
 >> > 
   Some days ago there have been
 >>
 >    local
 >>   thunderstorms
 near DL0AO in JN59.
 >> >   
 Two
 >> >    images in
 attachemnt.
 >> >    The distance
 is about
 >> >    225 km. The
 thunderstorms were on a
 >>   small
 spot only.
 >> >
 >> >     The sferics are clearly
 >> >    pronounced
 >>   with an SNR increase of 10 dB
 and
 >> >    more, quite a sharp
 peak/trace. That's not
 >> > 
   a new observation but now we
 >>
 >    are operating
 >> >   
 just in that frequency range!
 >>
 >    The
 >>   effect
 >> >    seems to appear in
 integer
 >>   multiples of about 1.7
 kHz, which
 >> >
 >> >    is roughly a wavelength of a
 180 km,
 >>   and
 >> >    the earth-ionosphere
 height
 >>   is
 >> >    just
 >> >    lambda/2.
 >> >
 >> > 
   It
 >>   would be most
 >> >    interesting to see how
 >>   a similar spectrogram looks from
 >> >    Pauls site (time and date
 given in the images).
 >> >    Is
 the effect still
 >> >    there in
 881 km? How
 >> >    strong is it
 expressed. Are the
 >>   frequencies
 the same?
 >> >    If so, we
 >>   should try to find that region
 of
 >> >    enhanced propagation,
 by
 >> >    using a
 >>   2-tone or
 >>
 >    3-tone carrier signal. No
 >>   problem to provide that from
 >> >    here.
 >> >
 >> > 
   The
 >> >    effect is less
 expressed on 3.4 kHz in
 >>   this
 event. Recently
 >> >    we
 >> >    discussed about a
 geometric
 >>   single-hop
 >> >    path difference between
 >>   DK7FC and
 >>
 >    DL0AO
 >> >    (Markus
 calculated 63.3 km difference
 >>  
 between groundwave and
 >> >
 >> >    skywave). 5.17 is at a 1.09
 lambda
 >> >    difference on that
 path, so
 >> >    groundwave
 and
 >> >    skywave will add
 constructively. The 3rd order trace of
 >> >    the sferic resonance effect
 is also at
 >>   5.1
 >> >    kHz!
 >> >    3.4
 >>   kHz, or the 88.2 km wave, is
 then
 >> >    at
 >>   1.4 lambda difference, so
 >> >    skyway
 >>   and
 >> > 
   groundwave do not add so
 >>  
 constructive. Maybe this explains
 >>
 >
 >> >    the lower expressed
 resonance
 >>   effect?
 >> >
 >> > 
   It
 >>   looks like there can be
 SNR
 >> >    difference of several
 dB when changing
 >> >    the
 >> >    frequency
 >>   by just a few 10 Hz, at least
 arround 5.1 kHz and
 >> >    on
 the
 >> >    path to
 >>   DL0AO. We should try to
 >> >    check
 >>   that!
 >>
 >
 >> >    Could
 >>   there be
 >>
 >    a frequency with an
 >>  
 advantage on the way to RN3AUS? On a
 >> >    2000 km path the effects
 will be less
 >> >     expressed.
 But worth to think about...
 >> >
 >> >    73, Stefan
 >>
 >>
 >>
 >