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From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <4F209013.2030803@iup.uni-heidelberg.de> <4F219B7E.6090001@m0dts.co.uk> <4F22F36A.6090209@iup.uni-heidelberg.de> <4F230085.2060504@m0dts.co.uk> <00ec01ccdd51$41077900$4001a8c0@lark>
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Date: Sat, 28 Jan 2012 00:33:25 -0000
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Subject: Re: LF: Conds
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Good guide lines  Alan

I would  add , try a  top  loading coil  at the  end of the  vertical 
section , that  seems  to  increase  the  amps in the  vertical ,
I found  using a  U shaped  top  wire, one end of  the  U connected , the 
other  open,  gave better  gain  than  a parallel set up.

73 -G..

--------------------------------------------------
From: "Alan Melia" <alan.melia@btinternet.com>
Sent: Saturday, January 28, 2012 12:05 AM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Conds

> Hi Rob it sounds like you must have a loss resistance in excess of 
> 100ohms,
> it you can only get an amp with 90W. Unlike Top Band, putting ground rods
> under the vertical doesnt help much at LF. Most (55%)of the return current
> is collected from under the remote ends of the to wire.
>
> Think about it....this is where the maximum voltage is, and the current
> passes through the top capaxity to ground. The bigger the area of the
> top-wire/ground acapaitor the less loss in the ground "plate". If you have
> poor conductivity ground try running a wire back from the remote 
> groundstake
> to the TX ground.  If it doesnt make any difference you can remove it
> easily. The next step is to incease the top load capacitance. More wire in
> the air. The paralell wires should ideally be around 70cm apart minimum.
> They can be connected anyhow series, parallel, or meander. Dont worry 
> about
> current cancelling, these wires dont radiate anyway. Dont run the top wire
> into or close to or over bushes or foliage. I you terminate the top wire 
> on
> a tree make the end insulator as far from the tree and it is above the
> ground. Even if this shortens the antenna it will reduce the 
> "environmental
> loss" Dont run the top wire over roofs and keep the vertcal as far as
> possible away from walls. If necessary slope it out to the top wire. The 
> top
> wire only needs to be thick enough to support its own weight. Resistance 
> up
> there doesnt matter, this part of the aerial is above the effective Rrad 
> (in
> the vertical section) so doesnt add to "loss" (even though that sounds
> counter-intuitive).
>
> The best way to improve the aerial is to build a simple bridge, not a 
> noise
> bridge that wont work at LF, the aerial has to be a measured at the
> frequency of use, because the loss is frequency dependent. You require to
> use several volts of bridge source drive (to overcome the received signal
> pick up) and a tuned detector like a receiver. A good bridge null will be 
> of
> the order of 50dB deep or your bridge is not working properly. It will 
> tell
> you whether simple quick alterations are improving things before you spend 
> a
> lot of time and money "engineering them" properly. You measure the 
> untuned,
> (unloaded) wire so it saves risking you PA and keeps the qrm down too. It
> looks like a capacitance and resistance in series and the resistance is 
> "ALL
> LOSS" the radiation resistance is minimal. So try mods to increase the
> capacitance and reduce the resistance emasured.
>
> This is distilled from 15 years of experiments on the band by many of the
> pioneers (G3XDV G3LDO, G3AQC, EI0CF, MOBMU, Bill Ashwell US Lowfer, and 
> many
> other too) using normal domestic enviroments . Dont be diverted by what 
> the
> "professionals do" they dont operate from a domestic premises and use
> verticals or umbrellas.......they use earth mats because you need those
> under a vertical but they are not really any advantage under an "L" or "T"
> unless they are at least 1/8th wavelength in dimensions (300 m  square!!).
> Bill built an aerial over virgin rock, but he needed a lot of elevated
> isolated radials (counterpoise) to get it to work properly. On the very 
> poor
> ground, the radials couple to the lossy ground, increasing the loss over 
> the
> use of elevated wires.
>
> Some may disagree but what works will depend on your particular location 
> and
> ground conditions, and what works for someone else may not work for you. I
> sit on top of heathland, very sandy with the water table about 60 feet
> down....not exactly ideal. But I got an aerial loss down to around 40 
> ohms,
> in approximatly the same size as you have there (60m top "L")
>
> Good Luck with it
> Alan G3NYK
>
> ----- Original Message ----- 
> From: "Rob, M0DTS" <rob@m0dts.co.uk>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Friday, January 27, 2012 7:52 PM
> Subject: Re: LF: Conds
>
>
> My TX is now working all be it fairly QRP 90W ;-)
>
> Antenna is 53m horizontal at ~9m high.. a droopy 'T' single strand
> copper all the way.
> I'm also receiving on this antenna too with much better results than the
> loop i have.
>
> Problem is going to be getting enough routes to earth, my last attempts
> were getting ~1A antenna current with the same power but it looks much
> worse on G4WGT's grabber than last time so i guess it's less than 1A.
> Will do some more improvements over the weekend.
>
> Rob
> M0DTS
>
> On 27/01/2012 18:56, Stefan Schäfer wrote:
>> Hi Rob,
>>
>> Thanks for the report.
>> Oh yes, looking forward to see you on the band (or hear?).
>> What will you use as the TX antenna?
>>
>> 73, Stefan/DK7FC
>> PS: Conds (local) are excellent again this evening! Worth to come to
>> QSO mode ;-)
>>
>>
>> Am 26.01.2012 19:29, schrieb Rob, M0DTS:
>>> On 25/01/2012 23:28, Stefan Schäfer wrote:
>>>> LF,
>>>>
>>>> Excellent conds on 137 in a range of 2500km! Signals show up in RN,
>>>> 4X, TF, YO at good strength. Worth to try!
>>>>
>>>> 73, Stefan/DK7FC
>>>>
>>>>
>>>>
>>>>
>>> Stefan.. vy good tonight again too, you're 579 here.. best I've heard
>>> you!
>>>
>>> Still trying to get time to re-assemble the tx and make some
>>> transmissions.......
>>>
>>> Rob
>>> M0DTS
>>>
>>
>>
>
>
>