[time-nuts] EMI and CE certification

[Bob Camp]

Hi

On most of these “buried” systems, the *intended* output is an audio (< 15 KHz) 
signal. Since the carrier is below the bottom end of the regulations, you are in “who
cares” territory. That’s the intent. 

The problem comes from the fact that they modulate the carrier in ways the reg’s 
never envisioned (back in 1926). On top of that, there is a “it’s not RF, it’s audio” design
approach that ignores the need for filtering or EMI protection. 

As we bemoan the death of the various low frequency services. EMI from all these 
systems is what is really killing them. You may be able to pick stuff up out in the middle
of nowhere. If it’s jammed to death where 95% of the population lives, the service is
dead. 

You may not *like* the political process that shuts down a service when < 5% of the population
can access it. That does not make it any less real. Without some sort of push to get the
EMI situation under control, it will happen to all of these systems. 

Bob

> On May 11, 2015, at 3:52 PM, Adrian Godwin <artgodwin at gmail.com> wrote:
> 
> Is it driven as  an inductive loop? That might put it under different
> regulations.
> On 11 May 2015 17:47, "Chuck Harris" <cfharris at erols.com> wrote:
> 
>> Yes, but in the case of the lawnmower fence, and the
>> invisible dog fence, the transmitter drives the fence
>> as an antenna.
>> 
>> In the US, the antenna size for "free bands" is seriously
>> limited.  As an example, the so called "Lowfer" band at
>> 136KHz is limited to antennas no larger than 15m in length.
>> 
>> And, that is one of the larger limitations.
>> 
>> 15m would encircle only a very small lawn.
>> 
>> OBTW, I realized on reading my post below, that I was very
>> unclear on what could "be foiled."  I meant that the
>> operating permission for the lawnmower system could probably
>> be foiled by looking into the maximum antenna lengths for
>> unlicensed services of this sort, in this frequency range.
>> 
>> I would quite imagine that any certification they may have
>> is for the transmitter and receiver, without an antenna.
>> 
>> -Chuck Harris
>> 
>> Alex Pummer wrote:
>> 
>>> 
>>> 
>>> yes for transmitter  antennas, but not for receiver antennas in Austria
>>> Germany
>>> Switzerland France Hungary one could have receiver antenna as long as he
>>> want, but
>>> the height is limited similarly as in the US
>>> 73
>>> KJ6UHN
>>> Alex
>>>   On 5/10/2015 7:15 AM, Chuck Harris wrote:
>>> 
>>>> My recollection is that in the US, certain requirements
>>>> exist for antenna length on the so called "free bands".
>>>> 
>>>> I have no idea what the European requirements might be,
>>>> but, perhaps they can be foiled by their allowing their
>>>> minuscule amounts of power to flow into an over length
>>>> antenna?
>>>> 
>>>> -Chuck Harris
>>>> 
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