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Date: Fri, 5 Dec 2008 20:02:36 +0000
From: "Andy Talbot" <andy.g4jnt@googlemail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: !!!Re: LF: Re: E field active antennas
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Simultaneous whole band Rx, flat response.  And yes, it must be
simultaneous 2 - 30MHz
By all means come down and sort it out for us if you like. But mine
does the job perfectly.
Was only speculating if the helical winding might make any difference.

Andy  G4JNT
www.scrbg.org/g4jnt



2008/12/5 mal hamilton <g3kevmal@talktalk.net>:
> A long piece of wire and an AUTO atu would do the job, and the right ATU
> would handle as much power as you require.
> Small active antennas and preamps although handy are not a patch on the real
> thing. I know I have tried them all.
> Plenty of DC/data enigneers about but RF experts scarce. Maybe I should come
> down and sort it out for you, if you want the right results !!!
> G3KEV
>
> ----- Original Message ----- From: "Andy Talbot" <andy.g4jnt@googlemail.com>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Friday, December 05, 2008 7:05 PM
> 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
>>>>
>>>
>>>
>>>
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>>>
>>>
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>>>
>>
>
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