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To: rsgb_lf_group@blacksheep.org
Date: Thu, 02 Sep 2010 13:07:22 -0400
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From: Markus Vester <markusvester@aol.com>
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Subject: Re: LF: ERP calculation (revised)
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Dear Roger,

thanks for sharing your results!=20

The directional dependence should be a simple cosine law, so going from 45=
=C2=B0 to 0=C2=B0 would give you another 3 dB, or 3.8 uW ERP. Thus your to=
tal radiated power was 2.0 uW (EMRP). At 62 km, this gives -14 dBuV/m, whi=
ch should indeed be well readable in QRSS 3 under quiet conditions.=20

Taking a loss resistance of 60 ohms, 4 watts would have given you an anten=
na current of 0.26 A. The radiation resistance is then=20
 Rrad =3D EMRP / Iq^2 =3D 30 microohms.=20
A standard formula for loops is=20
 Rrrad =3D 31171 ohm * A^2 / lambda^4,
resulting in an effective loop area
 A =3D 155m^2.

Note this is using the radiation resistance for a loop in free space, as=
 the effect of ground is already included in the earth antenna picture. Fo=
r an above-ground loop with a mirror image beneath it, radiation resistanc=
e would be doubled.=20

Best wishes,
Markus (DF6NM)





-----Urspr=C3=BCngliche Mitteilung-----=20
Von: Roger Lapthorn <rogerlapthorn@gmail.com>
An: rsgb_lf_group@blacksheep.org
Verschickt: Mi., 1. Sept. 2010, 13:41
Thema: LF: ERP calculation (revised)


Today I managed, I believe, for the first time to accurately measure the=
 ERP of my QRPp system on 137kHz.

This is the method used:

Using the E-field probe, FT817 (AGC off, gain backed off as far as possibl=
e and a 10dB pad between the EFP and the FT817) and Spectran I went to my=
 usual test site 1.5km away from the QTH, 45 degrees off the main lobe of=
 the TX loop/earth electrode antenna.
Measured the signal level of DCF39 on 138.83kHz

Measured the signal level of G3XBM on 137.675kHz

Repeated this three times to reduce errors.
Noted the difference in FS level.

Difference in signal level =3D 44dB . I feel pretty confident this is an=
 accurate figure now and not effected by AGC and overload. Assuming DCF39=
 is 1mV/m here (info from Alan Melia)  then my FS at the test site is 6.4u=
V/m.  Using the formula ERP =3D (E*d)^2/49 where E =3D 6.4*10E-6 and d=3D1=
.5*10E3 gives an ERP =3D 1.9uW giving an antenna efficiency of -63dB using=
 the earth electrode antenna with the elevated feed and 4W from the PA. =
=20

The test site is about 45 degrees off the main line of fire of the antenna=
, so in the best direction it could be 10dB (?) stronger, i.e. 20uW ERP gi=
ving an antenna efficiency of -53dB in the best directions. Frankly I'm am=
azed that anyone can copy this signal at any distance, so full marks to G3=
XIZ (48km) and G3XDV (62km).

Next stage is to try this arrangement for a few more days using QRSS3 and=
 WSPR before swapping to a full "in the air" loop and repeating these test=
s.

Great fun and I'm leaning as I go, which is the whole point of ham radio.

73s
Roger G3XBM

--=20
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM   GQRP 1678    ISWL G11088

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<font color=3D'black' size=3D'2' face=3D'arial'>
<div>Dear Roger,</div>


<div>&nbsp;</div>


<div>thanks for sharing your results! </div>


<div>&nbsp;</div>


<div>The directional dependence should be a simple cosine law, so going fr=
om 45=C2=B0 to 0=C2=B0 would give you another 3 dB, or 3.8 uW ERP. Thus yo=
ur total radiated power was 2.0 uW (EMRP). At 62 km, this gives -14 dBuV/m=
, which should indeed be well readable in QRSS 3 under quiet conditions.=
 </div>


<div>&nbsp;</div>


<div>Taking a loss resistance of 60 ohms, 4 watts would have given you an=
 antenna current of 0.26 A. The radiation resistance is then <br>
&nbsp;Rrad =3D EMRP / Iq^2 =3D 30 microohms. <br>
A standard formula for loops is <br>
&nbsp;Rrrad =3D 31171 ohm * A^2 / lambda^4,<br>
resulting in an effective loop area<br>
&nbsp;A =3D 155m^2.<br>
</div>


<div>Note this is using the radiation resistance for a loop in free space,=
 as the effect of ground is already included in the earth antenna picture.=
 For an above-ground loop with a mirror image beneath it, radiation resist=
ance would be doubled. </div>


<div>&nbsp;</div>


<div>Best wishes,<br>
Markus (DF6NM)</div>


<div>&nbsp;</div>


<div style=3D"CLEAR: both"></div>
<br>
<br>


<div style=3D"FONT-SIZE: 10pt; COLOR: black; FONT-FAMILY: arial,helvetica"=
>-----Urspr=C3=BCngliche Mitteilung----- <br>
Von: Roger Lapthorn &lt;rogerlapthorn@gmail.com&gt;<br>
An: rsgb_lf_group@blacksheep.org<br>
Verschickt: Mi., 1. Sept. 2010, 13:41<br>
Thema: LF: ERP calculation (revised)<br>
<br>


<div id=3DAOLMsgPart_2_50ca1a4a-e30f-4696-be2e-0f899db8bbb4>Today I manage=
d, I believe, for the first time to <U>accurately</U> measure the ERP of=
 my QRPp system on 137kHz.<br>
<br>
This is the method used:<br>

<UL>
<LI>Using the E-field probe, FT817 (AGC off, gain backed off as far as pos=
sible and a 10dB pad between the EFP and the FT817) and Spectran I went to=
 my usual test site 1.5km away from the QTH, 45 degrees off the main lobe=
 of the TX loop/earth electrode antenna.</LI>
<LI>Measured the signal level of DCF39 on 138.83kHz<br>
</LI>
<LI>Measured the signal level of G3XBM on 137.675kHz<br>
</LI>
<LI>Repeated this three times to reduce errors.</LI>
<LI>Noted the difference in FS level.<br>
</LI></UL>Difference in signal level =3D <B>44dB </B>. I feel pretty confi=
dent this is an accurate figure now and <I>not</I> effected by AGC and ove=
rload. Assuming DCF39 is 1mV/m here (info from Alan Melia)&nbsp; then my=
 FS at the test site is<B> 6.4uV/m</B>.&nbsp; Using the formula ERP =3D (E=
*d)^2/49 where E =3D 6.4*10E-6 and d=3D1.5*10E3 gives an <B>ERP =3D 1.9uW<=
/B> giving an antenna efficiency of <B>-63dB</B> using the earth electrode=
 antenna with the elevated feed and 4W from the PA.&nbsp; <br>
<br>
The test site is about 45 degrees off the main line of fire of the antenna=
, so in the best direction it could be 10dB (?) stronger, i.e. <B>20uW ERP=
</B> giving an antenna efficiency of <B>-53dB</B> in the best directions.=
 Frankly I'm amazed that anyone can copy this signal at any distance, so=
 full marks to G3XIZ (48km) and G3XDV (62km).<br>
<br>
Next stage is to try this arrangement for a few more days using QRSS3 and=
 WSPR before swapping to a full "in the air" loop and repeating these test=
s.<br>
<br>
Great fun and I'm leaning as I go, which is the whole point of ham radio.<=
br>
<br>
73s<br>
Roger G3XBM<br>
<br>
-- <br>
<A href=3D"http://g3xbm-qrp.blogspot.com/" target=3D_blank>http://g3xbm-qr=
p.blogspot.com/</A><br>
<A href=3D"http://www.g3xbm.co.uk/" target=3D_blank>http://www.g3xbm.co.uk=
</A><br>
<A href=3D"http://www.youtube.com/user/g3xbm" target=3D_blank>http://www.y=
outube.com/user/g3xbm</A><br>
G3XBM&nbsp;&nbsp; GQRP 1678&nbsp;&nbsp;&nbsp; ISWL G11088<br>
</div>
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