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Date: Fri, 5 Dec 2008 19:05:16 +0000
From: "Andy Talbot" <andy.g4jnt@googlemail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Re: E field active antennas
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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
>>
>
>
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