Re: 150Khz Antenna question

christofire wrote:
> "Joerg" <notthisjoergsch@[EMAIL PROTECTED]
> wrote in message 
> news:PCRak.9391$89.2693@[EMAIL PROTECTED]
>> christofire wrote:
>>> "christofire" <christofire@[EMAIL PROTECTED]
> wrote in message 
>>> news:5sydnRVLb6_dU_bVnZ2dnUVZ8vSdnZ2d@[EMAIL PROTECTED]
>>>> "Joerg" <notthisjoergsch@[EMAIL PROTECTED]
> wrote in message 
>>>> news:r7Pak.8821$89.4911@[EMAIL PROTECTED]
>>>>> Tom Bruhns wrote:
>>>>>> On Jul 2, 7:29 am, "Jacques St-Pierre" <multe...@[EMAIL PROTECTED]
>
>>>>>> wrote:
>>>>>>> Anyone can help me with the design of a compact 150Khz antenna?
>>>>>>>
>>>> . . . snippity snip . . .
>>>>
>>>>> Back at the university I always wondered about that: Immature fields

>>>>> (near field), juvenile fields, adolescent fields? So where does an
EM 
>>>>> field reach puberty?
>>>>>
>>>>> :-)
>>>>>
>>>>> -- 
>>>>> SCNR, Joerg
>>>> John Kraus gave a workable definition in his book 'Antennas', that
the 
>>>> [appropriately] normalised magnitudes of the different field
components 
>>>> (reactive and radiation) are all equal to pi at a distance
lambda/2.pi 
>>>> away from the 'antenna' so, closer than that, the 1/r^2 and 1/r^3 
>>>> reactive terms dominate, and further away the 1/r radiation terms 
>>>> dominate.
>>>>
>>>> So the larger value of lambda/2.pi can be taken as the bare minimum 
>>>> separation of two simple antennas intended to operate independently. 
Of 
>>>> course, there will still be major coupling between them on account of

>>>> radiation (TX) or re-radiation (RX) and gainful antennas demand 
>>>> pro****tionately more separation in their line(s) of fire.
>>>>
>>>> Chris
>>> PS: That final statement is 'in practice' in respect of coupling, of 
>>> course. The mechanisms that give rise to directivity for the radiation

>>> field are likely to affect the reactive fields in a similar way at
small 
>>> distances.
>> In EMC the rule of thumb is usuallt (2*D^2)/wavelength, with D being
the 
>> antenna width. That's where you can begin to measure real radiation 
>> patterns.
>>
>> Of course Jacques seems to be well below that distance.
>>
>> -- 
>> Regards, Joerg
> 
> 
> Could've mentioned that, but it's more about arrays than fundamental 
> elements.  I guess with a stated frequency of 150 kHz, a wavelength of 2
km, 
> and a 'plastic case of 2" x 4" inches' there's not much chance of an
array!
> 

Yes, Jacques just has to decide on how much inductive coupling and how 
much capacitive coupling he wants. Or maybe just one of them. There is 
no real antenna.

And he needs to mind the law so that the mounties don't show up ;-)


> 2D^2/lambda, as you say, is a useful criterion for minimum measuring
radius 
> for dishes, for example.  I did the expt once at 11 GHz and the depth
and 
> shape of the first null was wrecked closer than 2D^2/lambda.  Beyond it,
the 
> pattern was essentially independent of the distance away.
> 

-- 
Regards, Joerg

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