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LF: Ionospheric VLF propagation

To: <[email protected]>
Subject: LF: Ionospheric VLF propagation
From: "Markus Vester" <[email protected]>
Date: Tue, 16 Mar 2010 00:12:14 +0100
In-reply-to: <[email protected]>
References: <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Dear LF,
 
on the phone, Stefan mentioned that he was running about 0.4 A into the nearly vertical (70°), 100 m long kite antenna. Thus radiated power would be
 
 EMRP = 1579 ohm * (0.4 A * sin(70°) * 50 m / 33 km)^2 = 0.5 mW = -3 dBm.
 
Using 1/distance field decay above lossless flat earth, at 830 km we would expect a field strength
 
 E = -3 + 49.5 - 20 log (830) dBuV/m = -12 dBuV/m.
 
However Paul's calibrated spectrum at 14:38 UT showed a peak B = 3.1 fT at 8970 Hz, equivalent to an electrical field
 
 E = c * B = 0.93 uV/m = - 0.5 dBuV/m.
 
Taking into account a couple of dB's for measurement uncertainties, we are still left with an observed signal very significantly stronger than expected. This seems to support Alexander's statement about a slower than inverse distance decay in the two-dimensional ionosphere-earth waveguide.
 
On http://freenet-homepage.de/df6nm/vlf/vlf_DHO_dualfreq.htm , I have another observation pointing out an ionospheric effect on VLF. In 2006, the German naval transmitter DHO38, normally on 23.4 kHz, was simultaneously transmitting on 18.5 kHz as well. Surprisingly the fieldstrengths and the diurnal patterns for the two frequencies appeared to be completely different, presumably due to different phaseshifts between ground and skywave component.
 
Best regards,
MArkus (DF6NM)
 
----- Original Message -----
Sent: Thursday, February 25, 2010 6:53 PM
Subject: Re: LF: AW: 9 Dreamers

Hellow, Stefan.

> If that calculation is reasonably correct, what distance could be
> reached with 1,4mW @ 8,9 kHz

With such a condition you'll get about 2.5 uV/m at 100 km. Seems it can be
recievid. If there is no atmospheric and industrial noise it should be
very strong signal. But all depends on noise on 9 kHz. I have no ideas
about noise on 9 kHz. I neglet ionosphere in estimations. But at D=100 km
it should be approximately right.

Anyway if you can use 100 m high antenna then few of 100's km you should
reach. May be substantionally more. For large distances dependance of E
on D changes. On the distances more then ~100 km field should have
behaviour E ~ sqrt(1/D). This yelds only 10 dB attenuation if distance
became 10 times more. Thus if you'll have 20 dB over noise at 100 km (if
noise is 0.25 uV/m for example) then you'll have ~10 dB over noise at 1000
km. 

Do it if you have such an oportunity! It is very interesting.

Regards,
Alexander
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