Re: VLF: Carrier on 3675.005 Hz - fieldstrength

[Markus Vester <markusvester@aol.com>]

Comparing Stefan's carrier peak (-135 dB on the W cardioid) to my own 8270 Hz transmission from Aug 5 (-119 dB) shows a ~ 16 dB difference (assuming flat frequency response from the antennas). The distances are 226 km and 48 km, accounting for 13.5 dB using 1/r. Stefan's estimated ERP on 3675 is about 8 dB less than mine on 8270. So we can conclude that propagation from Stefan had about 13.5 + 8 - 16 = +5.5 dB propagation gain over 1/r groundwave. In other words, the fieldstrength has been approximately doubled by the presence of the ionosphere.

To me this is somewhat unexpected, as a simple geometric calculation for reflection at 70 km ionospheric height gives 41 km path difference, i.e. perfect antiphase at this wavelength and distance.

It will be interesting to look at simulation results.

All the best,
Markus (DF6NM) 

-----Ursprüngliche Mitteilung-----
Von: hvanesce <hvanesce@comcast.net>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: So, 13. Aug 2017 23:20
Betreff: RE: VLF: Carrier on 3675.005 Hz / EbNaut - YES again

Markus and Stefan,

 

Along with the FDTD diurnal phase simulation, I’ll include diurnal amplitude for comparison to the prospective path loss calculation that Markus mentioned.

 

73,

 

Jim AA5BW

 

 

From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Markus Vester
Sent: Sunday, August 13, 2017 4:49 PM
To: rsgb_lf_group@blacksheep.org
Subject: Re: VLF: Carrier on 3675.005 Hz / EbNaut - YES again

 

Hi Stefan, despite the 27% loss of signal, the message was decoded fine, even with a couple of dB to spare - not bad at all! Hope you can repair your coil and get back on air soon.

Jim, some simulation for the 226 km path might indeed be helpful. I suspect that the path difference between groundwave and first-hop skywave is close to a half-wavelength, possibly leading to partial cancellation and stronger diurnal variability. However the carrier SNR has not been strong enough to make a decently resolved measurement of diurnal amplitude and phase variations.

We could try to obtain a coarse estimate of absolute fieldstrength, using the received carrier level and e.g. DHO38 for reference. Knowing Stefan's radiated power, we could then try to derive propagation attenuation.

Best 73,
Markus (DF6NM)



-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: So, 13. Aug 2017 22:20
Betreff: Re: VLF: Carrier on 3675.005 Hz / EbNaut - YES

Hi VLF,

The repetition of yesterdays message failed. At 15:38 UTC the safety function tripped. I've just been on the roof, when re-starting the transmission i can see a spark in the center of one of the stacks. So now there is another one which has a flash over! :-(
It must be replaced, which is a lot of work. So the tranmissions on 3675 Hz will stopp for some time. At least we have some carrier detections and even EbNaut decodes.

I need to think about a different coil concept.... More current, more voltage, more power, more more more!

Am 13.08.2017 16:57, schrieb hvanesce@comcast.net:

Stephan wrote:

“The phase of that best decode is quite varying”

Is that observation based on the attached EbNaut Decoder window image from Markus?

It is just based on that decoder data. It is not really proof, just an idea.

Would it help to have an FDTD diurnal phase plot for this path at 3575Hz?

For sure it would be interesting! If you like, do it. I would be curious to see it.

73, Stefan