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+--- Thread: Propagation... why do I miss some signals? (/showthread.php?tid=2749)
RE: Propagation... why do I miss some signals? - cutty - 2018-11-06
There is another reason you might miss strokes... even if its recognized as a 'stroke', you might "lose out" as being a 'locator'...
for sure, it can affect the overall network 'location' accuracy...
Observe:
![[Image: gps%20errW.png]](https://frankfortweather.us/blitzblitz/gps%20errW.png)
(Graphic should refer to the "third DECIMAL digit")
....with that much error, the server may even discard the signal...
Yet...
![[Image: gps%20init.png]](https://frankfortweather.us/blitzblitz/gps%20init.png)
More in depth explanation in the INTERNAL forum for Operators: HERE
Not posting more explanation here...
RE: Propagation... why do I miss some signals? - cutty - 2018-11-07
There are some 'Hidden' "Gotchas" that may result in 'missed signals'... when looking at your stats..
The 'trigger' threshold level must be at least twice your noise level... any triggered channel signal failing that will be ignored by the server. That sometimes may change, but most of the time the baseline is 'twice the noise level'. The 'best' channel for any given station, for any given impulse, will be selected, and compared with others, beginning with the timestamp and trigger point... (TOA) then such tricky things as 'Zero Crossings' i, etc...(TOGA)
Both H channels and E channels have KNOWN inherent time delays. Each Filter setting has KNOWN time delays. Each antennas type has expected or computed time delays.... This is why it is extremely important to configure your station properly on your owner's page on BT... especially as regards antenna type, and dimensions.
as an example,
We are going to use the RED's E channels to illustrate delays, because they're much more obvious than H channel Antenna differences... :
Here would be the KNOWN and EXPECTED time delays and frequency responses of a System RED which has three E channels available:
Filters:
The coax and it's shielding is effectively part of a High Pass filter network >5 KHz System RED)
(preamp, coax, amp combined) (This is also true for system BLUE expect ± 8 KHz )
These numbers are specific to RED, but basic principle is similar for Blue:
First stage HP filter is in Pre-Amp, third stage in amp.
50,100,150,200,250 Hz is effectively attenuated
Similar with 60Hz and harmonics
This is specific to RED channel design:
18 KHz cutoff
44 KHz cutoff
>50 KHz
± effective channel selectivity
A = 5KHz ± —— 23KHz ±
B = 18KHz ± —— 44KHz ±
C = 5KHz ± —— > 50KHz ±
Again the below is a RED's E channels signal.
![[Image: REDEChannelExpecteddelays.png]](http://frankfortweather.us/blitzblitz/REDEChannelExpecteddelays.png)
On E channels, the 'Probe delay' is virtually 'zero', but the surface area of the probe (from dimensions) affects both the 'type of charge' content, it's amplitude, and the 'capacitance' value of the 'circuit'... In effect, a primary component of the above mentioned 'high pass' filter. Therefore it's 'response' can affect both BW and delay, especially in the TOGA chain computations. The Server Knows this 'designed' delay, for each selected channel, and that is factored into the 'TOA and TOGA computations.
The exact same thing is true for BLUE, except there is only ONE wide band E channel with optional filtering variations.... The delays in the designed and optional filter settings are KNOWN by the server. And computed 'surface area' of the probe can be factored in if the station's configuration data is correct
APPLY SIMILAR LOGIC to H channels on either system, RED or BLUE... but equate the E Channels Above to different antenna types and construction, That info must be entered correctly in your station configuration,... otherwise you may 'miss out' on best effectivity and efficiency.
example: Here are two identical FERRITE core antennas... with one difference: the faster response has an experimental core wrap modification...
(which I now use as my 'standard' H antenna, in two build designs.)![[Image: csstSigTimeDif.png]](http://frankfortweather.us/blitzblitz/csstSigTimeDif.png)
A 2 to 4 Microsecond time difference can refine a 'deviation' error by 0.5 to 1.2 kilometers!
(600-1200 meters)
So ensure your station antenna and probe configurations are correct... Yes, the 'dimensions' should be metric.
System BLUE.. and tick the shielded, or transformer boxes as appropriate. E SHOULD HAVE NO Ticks..
![[Image: AntennConfigBlue.png]](http://frankfortweather.us/blitzblitz/AntennConfigBlue.png)
0-2 are for H field antennas
The server and the rest of us
would expect HA=0, HB=1 If using HC = 2, if not, undefined, skip it...
E Field ALWAYS begins at 3 regardless of system - undefined if NO E connected
4,5 ALWAYS undefined for BLUE's single channel. Red has 3 channels which should be defined if E is utilized.
RE: Propagation... why do I miss some signals? - mwaters - 2018-11-08
Which layer of the ionosphere do 16 kHz signals bounce off of?
Also, the idea of a skip zone at such low frequencies is new to me! They are almost unheard of at 2 MHz, and more common as you go up in frequency, depending on the time of day and solar activity.
RE: Propagation... why do I miss some signals? - cutty - 2018-11-08
(2018-11-08, 05:23)mwaters Wrote: Which layer of the ionosphere do 16 kHz signals bounce off of?
Also, the idea of a skip zone at such low frequencies is new to me! They are almost unheard of at 2 MHz, and more common as you go up in frequency, depending on the time of day and solar activity.
Any layer or height it wants to.. I suppose.. what does your research show? Lower freqs bounce. Higher Freqs escape.
You could assume D layer... E maybe at times... I'm an operator, Jim, .. not a physicist.... but, conditionally, the others also have some say about it. maybe 40-80 miles, whichever is currently 'in charge'... pun intended.
Also do NOT forget: THE EARTH is the other 'wall' of the wave guide! It makes stuff bounce too.
Unheard of? You've never listened to a distant am radio station fade in and out?
RE: Propagation... why do I miss some signals? - mwaters - 2018-11-08
Fair enough.
As for an AM station fading in and out, that most often called selective fading. Remove the carrier (SSB) and it's greatly reduced.See https://en.m.wikipedia.org/wiki/Fading
RE: Propagation... why do I miss some signals? - readbueno - 2018-11-08
Hi Mike and Cutty, During the night time there is no "D or E Layer," only "F" Layer.
During the Daytime it is possible, due to ionisation density variations, to have Sky wave signals at VLF and ELF from all three and possibly four ionised layers ("D, E, F, or F1 and/or F2,) simultaneously or at varying intervals.
Theoretically it is possible to have Sky wave propagation without contact with the ground for considerable distances, especially where there is a transition from day to night, night to day, Chordal Hop and Grey line effects.
Neither the Ionosphere nor the Earth are smooth flat surfaces, nor perfect curves, so there are various forms of Diffraction, Refraction, Absorption and Scattering etc., and other natural phenomenon, (Aurora? Non Great circle paths, due to ground wave becoming sky wave or vice-versa) that may account for fading or enhanced propagation at varying distances and for the different frequencies in the bandwidth of a stroke of lightning.
There possibly could also be considerable time differences for the same stroke, if there is long path and short path propagation, at the same time, or multiple around the world paths, as in near antipodal situations.
While this probably does not make things much clearer in regards to our case, there have been many studies done with ELF propagation for submarines.
Kindest regards,
Brian.
RE: Propagation... why do I miss some signals? - mwaters - 2018-11-08
I found this ELF propagation link from sferics.com and plan on studying it a little. The goal is to find out whether a skip zone exists at ~16 kHz.
https://www.semanticscholar.org/paper/Modeling-Electromagnetic-Propagation-in-the-Cummer/9bb42933311b65ebd9075e1c070dc60ac651cd46
RE: Propagation... why do I miss some signals? - cutty - 2018-11-09
(2018-11-08, 17:47)mwaters Wrote: I found this ELF propagation link from sferics.com and plan on studying it a little. The goal is to find out whether a skip zone exists at ~16 kHz.
https://www.semanticscholar.org/paper/Modeling-Electromagnetic-Propagation-in-the-Cummer/9bb42933311b65ebd9075e1c070dc60ac651cd46
While you're absorbing the link you posted...
(here's direct link to paper: WAVE GUIDE }
You might add these two additional factors... as 'starter' papers....
Impulse Earth Surface
Coupling Mechanism
![[Image: smallprobe.png]](https://frankfortweather.us/blitzblitz/smallprobe.png)
There's a point where I become very enamored with the basic 'light switch' theory... throw the switch, stuff happens... hopefully.
RE: Propagation... why do I miss some signals? - mwaters - 2018-11-09
Thanks, Mike. I've studied the first one and did brief searches through the other two just now.
One thing to consider is that diagrams imply that there is a single takeoff angle from a strike. The reality is different.
RE: Propagation... why do I miss some signals? - mwaters - 2018-11-09
Right or wrong, https://en.m.wikipedia.org/wiki/Skip_zone seems to imply that there is no skip zone at LF.
"A method of decreasing the skip zone is by decreasing the frequency of the radio waves. Decreasing the frequency is akin to increasing the ionospheric width. A point is eventually reached when decreasing the frequency results in a zero distance skip zone. In other words, a frequency exists for which vertically incident radio waves will always be refracted back to the Earth. This frequency is equivalent to the ionospheric plasma frequency and is also known as the ionospheric critical frequency, or foF2."