Message-ID: <B29B0D3B57B04916899B26FFFFD7A580@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <fc7eccec0812050822x39e4cc98xc36b36cf0e73d6fa@mail.gmail.com> <007601c95709$acc95e50$0301a8c0@mal769a60aa920> <fc7eccec0812051105r36bfcc3cpea3dfa05030e53ee@mail.gmail.com>
In-Reply-To: <fc7eccec0812051105r36bfcc3cpea3dfa05030e53ee@mail.gmail.com>
Date: Sat, 6 Dec 2008 00:49:23 -0000
MIME-Version: 1.0
Importance: Normal
Subject: Re: LF: Re: E field active antennas
Content-Type: text/plain;
	format=flowed;
	charset="iso-8859-1";
	reply-type=original
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


Andy,

Have you ever tried a near filed array ?

I think you where at the hfc ,eggham where on the Sunday morning there where 
two lectures about loop type antennas, the first was quite fascinating, a 
near field array,  and the second was on contemporary loop arrays  ...

I made a near field   array based on the 'spirit' of the lecture .. and it 
worked very  well .. how it worked  ive no idea .. but work it did .. made 
from ? well

1 plastic dust bin as support ,
one standard alloy no-entry sign (round alloy)
3 feet vacuum cleaner plastic pipe (no spring) , as spiral former
1 sheet perspex as insulator
lenght of cotton covered 1.5 mm copper wire
earth tag and screw

wind wire on plastic pipe, bend into circle , place sine on top of bin , 
pespex on top of sine ,  place coil on plate, mount earth tap by coil end, 
connect -one- side of feeder (i used 450 ribbon) to  earth tag, connect 
other side to -one- end of coil 'only' take feeder to  tuner .. (1Kw racal 
auto)

place assembly in middle of lawn  ...  Retire to  safe distance

select frequency  tx on , await atu lock, increase power to  400w carrier 
and observe no flashover .. check from  1.8 > 30  mhz
find array  functions on all bands .. work south coast on 1.8 mhz  deep into 
eu on 3.8 and mid russia on 28 mhz

Await Howells  of laughter when you describe the antenna system ..

The step change to the  previously published system was the concept of a 
mirror .. so  the coil is not counter wound .. and dose not flash over..


I keep looking for a bigger round alloy disk to  try one on 500 .. i pass a 
few on the way  to  work each day hihi


73 G ..









--------------------------------------------------
From: "Andy Talbot" <andy.g4jnt@googlemail.com>
Sent: Friday, December 05, 2008 7:05 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Re: E field active antennas

>
> If you'd bothered to read the post, you'd have seen it was for a work
> related task where we want a broad band active Rx antenna for the
> whole HF band..
> Can you tell me how to get any other sort of antenna that will allow
> the whole HF band to be covered, in real time at high speed.?
> If you can, and it works on high power Tx as well, then you've solved
> the holy grail and stand to make millions of pounds!
>
> Contrary to Mal's all pervading wisdom in all things RF related, a
> long high tuned piece of wire is not the answer to all radio problems.
>
> Oh, and a loop is no good, any directionality is a definite no-no.
> If project funding permits, I may try an active horizontal loop in
> addition.  A 0.5m diameter loop into a broadband, balanced, common
> base amplifier with Zin < 0.5ohms ought to give a reasonably flat
> horizontally polarised omni directional HF band Rx coverage for
> skywave signals.
>
> Andy  G4JNT
> www.scrbg.org/g4jnt
>
>
>
> 2008/12/5 mal hamilton <g3kevmal@talktalk.net>:
>> Try a piece of wire as long and high as possible and an ATU this is 
>> superior
>> to any active antenna or loop for that matter, the loop only helps in a
>> noisy environment, and even then not always.
>> G3KEV
>>
>> ----- Original Message ----- From: "Andy Talbot" 
>> <andy.g4jnt@googlemail.com>
>> To: <rsgb_lf_group@blacksheep.org>
>> Sent: Friday, December 05, 2008 4:22 PM
>> Subject: LF: E field active antennas
>>
>>
>>> Having just had to make an active antenna for HF (for gainful
>>> employment-type work, not Am. radio purposes. The commercially made
>>> one we've ordered is on five weeks delivery and it was needed before
>>> yesterday) I was wondering about a helical element.
>>>
>>> As the thing had to be resonably lightweight, I made the antenna
>>> element from copper tape on 15mm plastic water pipe rather than use a
>>> solid copper tube.  Just for a bit of novelty I wound the tape in a
>>> helix, but then started wondering if doing that would make any
>>> difference to performance.    Normally, helically winding an antenna
>>> (rubber duck type at V/UHF) only serves to distribute loading
>>> inductance into a short antenna to make it resonate - unlikely to
>>> change improve the loss terms at all.  But I did wonder if the added
>>> extra inductance, or increased conductor length (not element length -
>>> that is 1.2m) would change the performance significantly from a
>>> straight tube.
>>>
>>> Does anyone have any ideas - food for thought if nothing else?  The
>>> base amplifier is one I've used several times before for V/LF up to HF
>>> based around a J310 source follower running at 20mA with bootstrapped
>>> input followed by a 2N5109 emiter follower at Ic = 80mA. I may have
>>> published it way-back-when in the amateur press in the 73kHz days.
>>> Not the best design judging by some of those published in more recent
>>> years, but did mean all the components were to hand for an instant
>>> job.
>>>
>>> Andy  G4JNT
>>> www.scrbg.org/g4jnt
>>>
>>
>>
>> --------------------------------------------------------------------------------
>>
>>
>>
>> No virus found in this incoming message.
>> Checked by AVG - http://www.avg.com
>> Version: 8.0.176 / Virus Database: 270.9.14/1831 - Release Date: 
>> 12/4/2008
>> 9:55 PM
>>
>>
>>
>
>



>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com
> Version: 8.0.176 / Virus Database: 270.9.14/1831 - Release Date: 12/4/2008 
> 21:55
>