RE: VLF: 8270 (antenna and grounding)

[Bob Raide <rjraide@hotmail.com>]

Markus;
Proves you don't need an exotic ground system and 40 meter tall antenna!  Works well for you. 73, Bob
 

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From: markusvester@aol.com
To: rsgb_lf_group@blacksheep.org
Date: Sat, 11 Jan 2014 19:13:04 +0100
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 = 0.8 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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From: bvgbob@hotmail.com
To: rsgb_lf_group@blacksheep.org
Date: Sat, 11 Jan 2014 14:28:32 +0100
Subject: RE: VLF: 8270

Hello Markus!

Nice signal here, congratulations!

Lubos, OK2BVG

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From: markusvester@aol.com
To: rsgb_lf_group@blacksheep.org
CC: paul@abelian.netcom.co.uk
Date: Sat, 11 Jan 2014 13:59:58 +0100
Subject: Re: VLF: 8270

Took the carrier off air at 12:48. Looks like a good trace at OK2BVG, and a dash with marginal SNR in Todmorden UK.

 

73, Markus

 

From: Markus Vester

Sent: Saturday, January 11, 2014 11:33 AM

To: rsgb_lf_group@blacksheep.org

Subject: VLF: 8270

At 10:23 I have started to transmit a straight carrier on 8270.000 Hz, estimated ERP around 14 uW. If all stays well, I'll leave it on for a couple of hours, trying to leave a dash on Lubos' and perhaps Paul's spectrograms.

 

73, Markus (DF6NM)