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LF: Re: LA1BCN on 630m, earth dipole

To: [email protected], [email protected]
Subject: LF: Re: LA1BCN on 630m, earth dipole
From: DK1IS <[email protected]>
Date: Sun, 28 Aug 2016 15:13:20 +0200
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Hello John,

having installed the latest remote RX system only one week ago I´m still in a very early state of a learning process ;-). First of all the configuration used here:

Living in an urban region of Amberg I have to use whatever is possible. Please have a look to the satellite foto on my site with the highest resolution. I own the terrace house with the solar panel array on the roof. Moving the picture to the right you will see a row of 14 garages from ferroconcrete (thank Goodness without any utility mains!), the fourth from the top is mine having something on its roof. It´s an older picture with ony a small solar panel for the remote controlled door opener - meanwhile the roof is filled pretty good! The earth dipole is laid out on the ground parallel to the garage row at its lower rim, true bearing of the wire being 150°<>330° . It´s fed in my garage via a ferrite transfomer with 12 turns, the secondary having 4 turns for the Perseus RX which is a compromise for the earth dipole impedances measured on VLF, LF and MF. So the "dipole" looks HF-wise more like a Windom, the upper branch having about 11 m, the lower one about 31 m length. Each end has a grounding post (originally threaded metal hulls for parasols) which is 0.6 m long and screwed into the soil, connected to the dipole via a relay contact so that I can remotely define the grounding condition of each branch. In this way I can change between "earth dipole" (both ends grounded), "Windom on ground" (both ends free) and something like "Mini-Beverage with special feeding" (right side or left side grounded) - and all of them loaded capacitivey and inductively by 14 ferroconcrete garages ...
Each configuration has its own characteristic which in addition depends on frequency - it remains a lot to learn about it! Besides the earth dipole there a two more antennas on the garage roof: an Miniwhip from Bonito and a small fixed passive loop with 2 sqm winding area. Up to now I simply change the antennas via the remote control until the best SNR is achieved.

Concerning the directivity of the "real" earth dipole: it seems significant on VLF, LF and MF where it forms a large lossy loop throgh the ground. For example with the earth dipole I can´t see the Russian Alpha stations which are usually strong with the Miniwhip on the garage roof. On the other hand DHO38 is coming stronger with the earth dipole - and the very LA1BCN last night. On HF the directivity seems to be not very significant but up to now I have no general idea about this.

Sorry - it would be fine to have an additional earth dipole at right angles to the existing one but the satellite foto shows why this is nearly impossible! But perhaps there will follow another remote antanna on the garage roof with a ferrite rod turnable in azimuth and elevation - there are two more free channels on my 433 MHz remote control ;-)

73 and hpe to cuagn!

Tom, DK1IS

Am 28.08.2016 um 11:16 schrieb John Rabson [email protected] [rsgb_lf_group]:


Does your earth dipole antenna show significant directivity? Some years ago, a group of cave radio enthusiasts conducted measurements on a 50 m long earth dipole on frequencies from 87 to 648 kHz and with various orientations, on our local cricket pitch (with permission). The received field strength exhibited significant minima of as much as 25 dB.

Would another such dipole at right angles to the existing one show any difference on Geir’s signal?

73 John F5VLF/G3PAI
Cave Radio & Electronics Group and formerly underground communications specialist for Suffolk Radio Amateurs Emergency Network

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