To estimate the capacitance, although you could easily measure it:
Start with this handy transmission line formula:
C = td/Zo, which is capacitance equals time delay divided by the
characteristic impedance.
What is the td of 1 inch of wire? 1"/300,000,000 m/s = 85 ps
What is the Zo? Around 300 ohms.
The capacitance is then 0.3 pf, give or take some
Another handy formula I would not be without:
L = tdZo
Dave Cuthbert
Micron Technology
From: [email protected] [mailto:[email protected]] On Behalf
Of Ken Javor
Sent: Tuesday, July 12, 2005 11:59 AM
To: [email protected]
Subject: Re: Radiated emission measurement below 30MHz
You are vastly OVERESTIMATING the load at 10 pF. A 41" rod over a
ground
plane is a 10 pF load.
I find this thread interesting. I can buy an audio input device
transmitting in the FM band for the purpose of playing an audio device
through my automobile stereo system. Clearly this device was designed
to
intentionally transmit in the FM band, and further it must transmit with
the
same modulation and at the same center frequencies as stipulated by law
for
the FM band.
So it is not as simple as saying you can't transmit in a broadcast band.
There is the issue of control. If I am using the above described
device, I
will choose an FM channel not currently being broadcast on, and the
power
level is low enough it only reaches a few feet.
> From: "Robert A. Macy" <[email protected]>
> Date: Tue, 12 Jul 2005 08:52:23 -0700
> To: John Woodgate <[email protected]>
> Cc: [email protected]
> Subject: Re: Radiated emission measurement below 30MHz
>
> It radiated an ELECTROSTATIC field. We're talking voltage
> field of 100V at 150KHz. A little 1 inch wire poked out
> with 100 V on it. Current was the load of the parasitic
> capacitance around 10pF. You can't even see that 10 m away
>
> Yet, not allowed, go figure.
>
> - Robert -
>
> On Tue, 12 Jul 2005 05:33:29 +0100
> John Woodgate <[email protected]> wrote:
>> Robert A. Macy <[email protected]> wrote (in
>> <[email protected]>) about 'Radiated emission
>> measurement below 30MHz', on Mon, 11 Jul 2005:
>>> Is this allowed?
>>>
>>> It was my understanding that one of my clients tried to
>> get a *very* low power intentianal "radiator" [at these
>> frequencies, radiator is a euphemism] through Europe and
>> due to some application there, couldn't even start
>> although the power could not even be measured within 10
>> meters.
>>> Seriously, there was NOTHING at 10 m. They saw
>> "intentional radiator"
>>> 150KHz, and said NO.
>>>
>>> Did we use the wrong people?
>>
>> It's difficult to tell. Was 150 kHz the actual operating
>> frequency or did it just emit (marginally) at that
>> frequency? 150 kHz is just above the lower end of the LF
>> broadcast band (lower end 148.5 kHz) and it could be
>> argued that no intentional radiator can be accepted whose
>> operating frequency is in a broadcast band.
>> --
>> Regards, John Woodgate, OOO - Own Opinions Only.
>> Deadlines are 90% of deadliness.
>> http://www.jmwa.demon.co.uk Also see
>> http://www.isce.org.uk
>>
>>
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