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From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <365C02722DD64F70B7C17A3A18F5978E@JimPC> <38F4A9873A5B474DB6FB337B1B69ABA11CEAA58849@HERMES8.ds.leeds.ac.uk> <6B7581263D6B4D85A5C256B7DB2DB385@JimPC>
In-Reply-To: <6B7581263D6B4D85A5C256B7DB2DB385@JimPC>
Date: Wed, 3 Jun 2009 20:43:54 +0100
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Subject: Re: LF: Re: 136k/500k Grounding experiments
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Jim,

An interesting  investigation,

Last  year i bonded everything  that conducted in the  back garden to the 
main earth bus bar in the shed, from short 6 ft alloy 2 inch scaffold pipes 
that hold  the  plants in ,  5 feet in the ground, to a 6 ft I section 
girder  that holds the mast and 2 10 foot  poles flush  in the ground

All of the pipes are connected with  insulated 35 amp 7 stranded wire , 
using a rf  ammeter it was possible to observe each earth 'working' .

Out of all, the  I section beam ( 10 inch x 6)  gave the  biggest reading , 
odd as the ground in that place is actually  covered and is quite dry, but 
this has the greater surface area , the pipes all gave  similar  results, 
but  round only  50 to  75% of the beam

Even though the  mains earth had 'always been connected , this re-work did 
improve the radiated signal on 500 and with a feed round 20 watts on 160 
mtrs an increase of 4 watts could be measured on the power meter

I would  assume this to be mainly  due to  reduced  local  I sqr R losses , 
in end feeding the top loaded vertical , but did show a positive result ,

Ive only  worked Hf portable , to  date, but I have  all ways made use of a 
handy  wire fence !

Tnx- G ..



--------------------------------------------------
From: "James Moritz" <james.moritz@btopenworld.com>
Sent: Tuesday, June 02, 2009 10:47 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: LF: Re: 136k/500k Grounding experiments

>
> Dear Chris, Laurie, Richard, LF Group,
>
> Thanks for the replies. Re the comments:
>
> G4OKW wrote:
>>...The mesh might not be as good on a rocky hilltop. There is probably
>>conductive soil under only 10cm or so of concrete drive, whereas a 
>>mountain
>>may be insulating rock all the way down to Old Nick....
>
> I agree - I don't think the wire mesh would neccessarily improve the 
> ground
> losses, but compared to the radial wires it gives similar performance in a
> quite compact form, which could well be an advantage in itself.
>
>>... Have you tried arrays of tent pegs?
>
> No, I limited myself to one per radial. My thought was that for portable
> operation with a vertical antenna, it would probably be easier just to add
> some more radials, while for fixed station use full-length ground rods 
> work
> better, and are probably less affected by the surface soil drying out. For
> the ground-loop type of antenna used for cave radio, I can see the array 
> of
> tent pegs would be a good idea.
>
> G3AQC wrote:
> ...> does seem to support my findings that the Mains/water pipes take most
> of the current,
> making all the work on radials earth rods etc a bit of a waste of time...
>
> The ground systems I tried are more-or-less insulated from the ground, so
> are coupled to the ground mainly by their capacitance, which has a
> relatively high reactance compared to their resistance. A ground rod on 
> the
> end of a considerable length of wire probably has a substantial inductive
> reactance compared to its resistance, due to the inductance of the wire.
> Either way, even though they may have low resistance, the overall 
> impedance
> of these grounds will be relatively high compared to a ground with a short
> connection to the return terminal of the TX or ATU, and so little current
> will flow in them.
>
>>...I would need to series resonate with a capacitor, value depending of
>>course on my particular system..... but did you say that the reactance was
>>capacitive ?
>
> The insulated radials, etc. have a capacitive reactance - the individual
> wires on the ground were roughly equivalent to 28pF/m. So these would
> require a tuning inductance to neutralise their reactance. For ground 
> rods,
> or buried bare-wire radials, I expect the reactance would be more 
> inductive,
> so a tuning capacitance would be required. Since we are talking about
> nanofarads of capacitance, or perhaps 10s of uH of inductance for the 
> ground
> systems, the tuning components required would be fairly small
> inductance/large capacitance.
>
> G3CWI wrote:
>>...I am intrigued about loaded radials in that the loading is effectively
>>supplied by the inductor in the ATU circuit. There was no sign that such 
>>an
>>approach worked on my last trip but possibly the inductance was
>>insufficient...
>
> The reactance of the radials adds to the total capacitive reactance of the
> antenna, so more inductance is needed to resonate the antenna. According 
> to
> your previous mail, you had somewhere around 60m of radials, giving an
> additional reactance of roughly 200ohms on top of perhaps 900 ohms for the
> 200ft long antenna. So the increase in overall tuning inductance required
> would have been quite large.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>
>
>



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