Re: LF: 74.5493 instead...(1of2)

[Markus Vester <markusvester@aol.com>]

Dex,

 

antennas are getting on in years, and so are we ;-) The one good thing about tree supports is that they grow taller with age: The pine tree supporting my southern top load leg has grown from 6 to 11 meters since I first attached a string in 1999.

http://maps.google.de/maps?ll=49.4158,11.1350&z=21

Recently one of my neighbours has given hints about shading and possible pruning, which I hope to be able to divert for a while.

 

Regarding ERP on 74 kHz: For a voltage limited E-field antenna, at half frequency you have to reduce input power until you have halved the current. In conjunction with the quarter radiation resistance, ERP would go down by a factor of 16! At VLF this is very severe: My small Marconi antenna, which can barely radiate 1 W ERP at 136 kHz, drops to 10 microwatts at 9 kHz. A similar same scaling also applies to loops driven at constant current.

 

In addition, at lower frequencies trees around an E-field antenna shunt a larger portion of the displacement current to ground, due to the ratio of capacitive versus ohmic impedances. From my experience, this degradation disappears only during deep frost when trunks apparently become completely dry.

 

Still hope to catch your 74 kHz beacon one of these days. However I suspect that the DCF77 noise may not be completely neglegible here, even between 1 Hz maxima. This might explain some of the perceived reception deficits in Germany, versus England and Holland.

 

Best wishes,
Markus (DF6NM)

 

-----Ursprüngliche Mitteilung-----
Von: Dexter McIntyre W4DEX <dexter.mc@gmail.com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mo, 21 Okt 2013 10:52 pm
Betreff: Re: LF: 74.5493 instead...(1of2)

I've been running /5 from sundown to sunup.  200 watts leaving the  

 shack.  Perhaps the signal will improve when the oak trees under the top  

 hat wires are bare.  The leaves are just now beginning to fall.   Most  

 of the several hundred feet of top hat wires run over a combination of  

 oak and pine trees.  I've often wondered if my antenna would be more  

 efficient with more loading instead of having the top hat.  I'll  

 probably never know because it would be way to much work to find out.   

 The antenna has been in use for 8 years.  I may find out when the top  

 hat wire fails because I doubt I'm now able to replace them. 

  

 Nice to at least see those traces Mike. 

  

 Dex 

  

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