Re: 150Khz Antenna question

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

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