Date: Thu, 25 Feb 2010 00:02:06 +0000 (GMT)
From: "Alexander S. Yurkov" <fitec@omskcity.com>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
In-Reply-To: <BF4A524700075746A6467658DFC7102C1286AD406E@ICTS-S-EXC2-CA.luna.kuleuven.be>
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Subject: RE: AW: LF: VLF_8.79 kHz_grounding systems
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> 
> if using a short vertical monopole antenna at 9kHz a ground loss of more than 1000 Ohm seems quite realistic to me.
> "Ground loss" at my QTH: 
> 500kHz = 35 Ohm
> 137kHz = 130 Ohm 

I don't think it is real ground stake loss. Mainly it is 'enviroment'
loss (due to trees, house e.t.c.). 

> The frequency ratio is 3.65, the resistance ratio is 0.27 = 1/3.7
> If this 1/f behaviour goes down to 9kHz (not sure) 

I don't think so. This behaviour should change. Good insulator (HF
frequency) or good conductor (VLF freqency) in enviroment does not yelds
losses. Trees are good conductors on VLF. And they are good insulators on
HF. MF is 'unfortunely case' :-)

> Regarding the parallel capacitor: you are right, it will not reduce the 
> losses. 

It will increse loss:-)

> But it is much easier (and cheaper) to make a 3mH coil than a
> 30mH coil and it will also transform the large loss resistance to a more
> convenient value.

True, true... But large coil will be much better anyway.

I heve perform very rough estimations. Seems real radiation (not
quasistatic near field) is posible on 9 kHz. Certanly with very small
radiated power. If TX is 1 kW (really) and antenna height is 30 m
(difficult, but reallly) and coil is abt 1 m in diameter then one can
achive about 0.1 mW radiation. This yelds about 1 uV/m in distanse of 100
km. Seems to be enough for QRSS (not CW i think, very strong noise).
Calculations was 'in mind' so i am not sure they are right.

But anyway 30m high good top loaded antenna has about 1 mOhm radiate
resistance on lamda=30km (10 kHz). Then 1 A in ant yelds 1 mW ERP (and
about 20 kvolts on ant if C=1 nF i.e. abt 200 m wire in horisontal part).
1 mW is not too low power:-) But one need 'clear' square for this without
trees, houses e.t.c. Seems it is a main problem:-( 


Regards,
Alexander/RA9MB