Re: Re: VLF: 8270.002

["Markus Vester" <markusvester@aol.com>]

Hi Domenico,

 

nothing special, no radials etc.. I've pasted a copy of a recent posting, describing my current LF / VLF antenna and grounding scheme in short words. 

All the best,

Markus (DF6NM)

 

PS a web archive for Blacksheep messages would come in handy ;-)

 

From: ing.lindo

Sent: Saturday, February 08, 2014 11:14 AM

To: rsgb_lf_group@blacksheep.org

Subject: Re: Re: VLF: 8270.002

Hello Markus and LF,

can we have some info on grounding arrangements on your vlf system?

Thanks. 

Domenico, iz7slz

-------- Original message --------
From: Markus Vester
Date:08/02/2014 00:08 (GMT+01:00)
To: rsgb_lf_group@blacksheep.org
Subject: Re: Re: VLF: 8270.002

Thanks Jim!

 

My antenna's effective height measured at LF is about 9 m. It will be slightly less at VLF due to increased shielding by trees, my guess is ~ 8 m, giving 77 microohms radiation resistance. Thus 0.3 amps would radiate 7 µW (EMRP) or 13 µW ERP.

 

Operating hours are a bit limited by politeness to the neighbours who have to bear the acoustical emission from the loading coil. The 8.3 kHz tone is not really loud but quite penetrant. Here are a couple of pics of the present setup, with the coil enclosed by two rubber bins and placed outside the window:

http://dl.dropboxusercontent.com/u/26404526/vlf_coil_at_window.jpg

http://dl.dropboxusercontent.com/u/26404526/vlf_coil_and_antenna.jpg

 

Good luck with your forthcoming experiments!

 

Best 73,

Markus (DF6NM)

 

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From: Markus Vester

Sent: Saturday, January 11, 2014 7:13 PM

To: rsgb_lf_group@blacksheep.org

Subject: Re: VLF: 8270 (antenna and grounding)

Yes. I sneaked a separate ground wire down the chimney to the basement, where PE and heating system are connected to the metal water inlet pipe. On a cold and dry winter day, the antenna resistance at LF (including the coil) is as low as 15 ohms. This probably is probably aided by a Faraday shielding effect from the thermal insulation under the roof, which is covered by a vapor-stop layer consisting of very thin aluminium foil strips - seems the roof is acting as a sort of ground screen.

 

The telescopic rod consists of several sliding sections separated by insulating plastic rings, which I thought was good. But I was plagued by erratic partial discharge problems between segments, which sometimes came and went away with wind-induced bending. Strong noise in my neighbour's FM radio, and strange krrrk krrrrrk sounds coming out of the chimney doorlet. In a recent rework, I have connected all segments with little bolts, and tied the bottom of the mast to ground potential.

 

73, Markus

From: Bob Raide

Sent: Saturday, January 11, 2014 6:44 PM

To: rsgb_lf_group@blacksheep.org

Subject: RE: VLF: 8270

Markus;
That is an amazing antenna!  That short to work so well at VLF.  Evan for LF but it really works for you.  I see no provision for ground system and would guess you use house plumbing for ground system?
 

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From: markusvester@aol.com
To: rsgb_lf_group@blacksheep.org
Date: Sat, 11 Jan 2014 18:26:30 +0100
Subject: Re: VLF: 8270

Bob,

 

it's the same antenna that I use for LF. The mast is a fishing rod on an aluminium telescopic pole, pushed out of an unused chimney. It carries three topload legs (N, W and S), about 42 m wire in total (230 pF). The apex is 20 m AGL or 11 m above the roof, but the effective height is only 9 m (calibrated at 138 kHz). On VLF frequencies this is probably even a bit lower due to increased shunting effect from trees. Assuming heff = 8 m, radiation resistance on 8.3 kHz would be 0.08 milliohm. With 60 Watts input, I got 0.3 A and 25 kV rms, and radiated power (EMRP) would be around 7 microwatts.

 

Here's a sketch of the wire layout and the auxiliary H- and E-field receive antennas:

http://dl.dropboxusercontent.com/u/26404526/Hans-Fallada-59_antennas.jpg 

 

One could actually see the antenna in Google Map's slant view, but the imagery may have changed since:

http://dl.dropboxusercontent.com/u/26404526/googlemaps_df6nm_antenna.jpg

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

 

Best 73,

Markus

From: Bob Raide

Sent: Saturday, January 11, 2014 5:37 PM

To: rsgb_lf_group@blacksheep.org

Subject: RE: VLF: 8270

Markus;
What are you using for antenna on 8270?
 

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