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Message-ID: <526D75B9.4020203@t-online.de>
Date: Sun, 27 Oct 2013 21:21:13 +0100
From: Christoph Schumacher <chris-schum@t-online.de>
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Subject: Re: LF: air solenoids
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Hi Clemens,
thank you for the great idea. I will try to stimulate the lf coil 
without a galvanic contact and look what happens.

cu next weekend
73 Christoph, dl7saq


Am 27.10.2013 08:56, schrieb Clemens Paul:
> Hi Christoph,
>
> from the coil parameters you have given I would
> estimate an unloaded coil Q of roughly ~500  on 137kHz.
> I guess you've made your measurements with the measuring
> equipment galavanicaly connected to the coil.
> In this case *and at this quite high Q* it is very likely that every bit of conducting
> structure of your *whole* test setup is radiating.
> I would try the following procedure:
> Couple the test signal *very loosely* inductively into the coil by using a coupling coil.
> For measuring series resonance connect the ends of the coil together,
> for parallel resonance leave the ends open.
>
>
> 73
> Clemens
> DL4RAJ
>
>
>
>    
>> -----Original Message-----
>> From: owner-rsgb_lf_group@blacksheep.org
>> [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of
>> Christoph Schumacher
>> Sent: Saturday, October 26, 2013 11:43 PM
>> To: rsgb_lf_group@blacksheep.org
>> Subject: Re: LF: air solenoids
>>
>> Hi Graham, Warren, Bob, Rik, Jim
>> thanks for your comments. What I found (by chance) is a series
>> resonance in the impedance spectrum of solenoid air coils, a
>> little underneath the high impedance parallel resonance. The
>> series resonance could derive from the coils main inductance
>> and its capacity to the surrounded electric field. But it fits
>> only very vague. However on that frequency the coil is a very
>> efficient radiator especially related to its shape.
>> Stimulating the coil on the high impedance parallel resonance
>> does not effect any far field radiation.
>>
>> For instance: my lf coil for 135kHz has app. 5mH inductance,
>> 42cm (17 inch) diameter, 27cm (11 inch) length. The high
>> impedance parallel resonance is 600kHz and the low impedance
>> series resonance is 500kHz. The resistance on that frequency
>> is 180 Ohm and the SWR=2 bandwidth is 2kHz. On 500kHz the coil
>> is a very efficient radiator related to its mechanical length
>> of lambda/500ppm. Using an input of app. 7mW (DDS-gen.) into
>> that coil I could read cw code at 1km distance via active
>> antenna on my car roof (maybe 6dB SNR).
>>
>> I become suspicious on whether the radiation resistance model
>> is still valid for such a tiny radiator. It is not my
>> intention to introduce a new lf radiator because at that
>> resonance the voltage across the coil must be gigantic. I only
>> would like to understand the physics. Do you have an idea?
>>
>> Best regards
>> chris dl7saq
>>
>>      
>
>
>    


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<![endif]--><span
 style="font-size: 12pt; font-family: &quot;Times New Roman&quot;;" lang="EN-GB">Hi
Clemens, <br>
thank you for the great idea. I will try to stimulate the lf coil
without a galvanic
contact and look what happens. <br>
<br>
cu next weekend<br>
73 Christoph, dl7saq<br>
<br style="">
<br style="">
</span><br>
<br>
<br>
Am 27.10.2013 08:56, schrieb Clemens Paul:
<blockquote cite="mid:B0E07F33C9EA4C19A3076C496D9F17D9@Clemens0811"
 type="cite">
  <pre wrap="">Hi Christoph,

from the coil parameters you have given I would
estimate an unloaded coil Q of roughly ~500  on 137kHz.
I guess you've made your measurements with the measuring
equipment galavanicaly connected to the coil.
In this case *and at this quite high Q* it is very likely that every bit of conducting
structure of your *whole* test setup is radiating.
I would try the following procedure:
Couple the test signal *very loosely* inductively into the coil by using a coupling coil.
For measuring series resonance connect the ends of the coil together,
for parallel resonance leave the ends open.


73
Clemens
DL4RAJ 

  
  </pre>
  <blockquote type="cite">
    <pre wrap="">-----Original Message-----
From: <a class="moz-txt-link-abbreviated" href="mailto:owner-rsgb_lf_group@blacksheep.org">owner-rsgb_lf_group@blacksheep.org</a> 
[<a class="moz-txt-link-freetext" href="mailto:owner-rsgb_lf_group@blacksheep.org">mailto:owner-rsgb_lf_group@blacksheep.org</a>] On Behalf Of 
Christoph Schumacher
Sent: Saturday, October 26, 2013 11:43 PM
To: <a class="moz-txt-link-abbreviated" href="mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org</a>
Subject: Re: LF: air solenoids

Hi Graham, Warren, Bob, Rik, Jim
thanks for your comments. What I found (by chance) is a series 
resonance in the impedance spectrum of solenoid air coils, a 
little underneath the high impedance parallel resonance. The 
series resonance could derive from the coils main inductance 
and its capacity to the surrounded electric field. But it fits 
only very vague. However on that frequency the coil is a very 
efficient radiator especially related to its shape. 
Stimulating the coil on the high impedance parallel resonance 
does not effect any far field radiation.

For instance: my lf coil for 135kHz has app. 5mH inductance, 
42cm (17 inch) diameter, 27cm (11 inch) length. The high 
impedance parallel resonance is 600kHz and the low impedance 
series resonance is 500kHz. The resistance on that frequency 
is 180 Ohm and the SWR=2 bandwidth is 2kHz. On 500kHz the coil 
is a very efficient radiator related to its mechanical length 
of lambda/500ppm. Using an input of app. 7mW (DDS-gen.) into 
that coil I could read cw code at 1km distance via active 
antenna on my car roof (maybe 6dB SNR).

I become suspicious on whether the radiation resistance model 
is still valid for such a tiny radiator. It is not my 
intention to introduce a new lf radiator because at that 
resonance the voltage across the coil must be gigantic. I only 
would like to understand the physics. Do you have an idea?

Best regards
chris dl7saq

    </pre>
  </blockquote>
  <pre wrap="">


  </pre>
</blockquote>
<br>
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