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Date: Wed, 1 Sep 2010 12:41:24 +0100
Message-ID: <AANLkTimUDj5oaFLwDGHhjjjFLFLsNVAhjorRAi+zs1LT@mail.gmail.com>
From: Roger Lapthorn <rogerlapthorn@gmail.com>
To: rsgb_lf_group@blacksheep.org
DomainKey-Status: good (testing) 
Subject: LF: ERP calculation (revised)
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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
   possible 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 = *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*6.4uV/m
*.  Using the formula ERP = (E*d)^2/49 where E = 6.4*10E-6 and d=1.5*10E3
gives an *ERP = 1.9uW* giving an antenna efficiency of *-63dB* using the
earth electrode antenna with the elevated feed and 4W from the PA.

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*giving an antenna efficiency of
*-53dB* 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).

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 tests.

Great fun and I'm leaning as I go, which is the whole point of ham radio.

73s
Roger G3XBM

-- 
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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Today I managed, I believe, for the first time to <u>accurately</u> measur=
e 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=
 possible and a 10dB pad between the EFP and the FT817) and Spectran I wen=
t 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 confident this=
 is an accurate figure now and <i>not</i> effected by AGC and overload. As=
suming DCF39 is 1mV/m here (info from Alan Melia)=A0 then my FS at the tes=
t site is<b> 6.4uV/m</b>.=A0 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 an=
tenna efficiency of <b>-63dB</b> using the earth electrode antenna with th=
e elevated feed and 4W from the PA.=A0 <br>
<br>The test site is about 45 degrees off the main line of fire of the ant=
enna, 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 directio=
ns. Frankly I&#39;m amazed that anyone can copy this signal at any distanc=
e, 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 &quot;in the air&quot; loop and repeat=
ing these tests.<br><br>Great fun and I&#39;m leaning as I go, which is th=
e 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-qrp.blogspot.com/</a><br><a href=3D"h=
ttp://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=A0=A0 GQRP 1678=A0=A0=A0 ISWL G11088<br>

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