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Message-ID: <684332.41256.qm@web28505.mail.ukl.yahoo.com>
Date: Fri, 11 Mar 2011 13:05:49 +0000 (GMT)
From: Chris Osborn <g3xiz@yahoo.co.uk>
To: LF Group <rsgb_lf_group@blacksheep.org>
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Subject: LF: VLF G3XIZ - 12/13th March - Station Set UP - Advice Welcomed
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LF,

I shall be transmitting on VLF again over the weekend.

The main purpose will be to test (and=A0adjust) my new loading coil=A0ther=
efor the=20
transmitted frequency may vary.
I shall keep the reflector informed as to frequency and times that transmi=
ssions=20
occur should anyone wish to take a look for=A0my signals.

PRESENT STATION SET UP
=A0
TX

I=A0have the option to=A0use=A0either an internal OCXO or an external off-=
air standard=20
frequency, both=A0of 10.000 . . MHz which=A0is then passed through a progr=
ammable=20
divider=A0to give even divisions e.g.
10.000/1110 =3D 9.090 909 kHz=A0=A0=A0 10.000/1112 =3D 8.992 806 kHz etc.=
 . .

The=A0PA is capable of giving several hundreds of watts but it has a low=
 output=20
impedance and the aerial system has a high impedance (several kilohms).
To achieve reasonable matching I use a large laminated-core mains transfor=
mer=20
with a step up ratio of 1:24

LOADING COIL(S)

To tune out the aerial's capacitive reactance I use a series loading coil=
=20
(inductor).
The original coil was single-wound, about 600 mm diameter and has an induc=
tance=20
of ~ 1.25 H
With the above TX, loading coil and my 40m inverted 'L'=A0I can generate=
 an aerial=20
current of=A0 0.15 - 0.2A

The original coil's losses seemed high so to improve matters I have wound=
=20
another unit, this time using heavier gauge wire and of double-layer=20
construction.
Initial results have been disappointing as I generate less aerial current=
 than=20
with the old coil.

The inductance necessary to achieve resonance has also fallen: from ~=A01.=
25H to=A0~=20
0.75 H implying that the new coil has considerably more self-capacitance.
There are a few hundred turns on it which are not used and may be causing=
 the=20
problem so I intend slowly to remove these, checking the aerial current at=
=20
intervals.

AERIALS=20

I generally use my 40m inverted 'L' aerial, height 10m but have the facili=
ty=20
(wind conditions being suitable) to launch balloon or kite-assisted wires.
My property borders a public playing field so I need a wind direction SE=
 - S=A0 or=20
SW for kite operations and near still air conditions for balloons.

ADVICE
=A0
I should be much=A0obliged for information which will enable me to improve=
 the=20
station's ERP and detectability.
Can someone point me in the right direction to improve the matching system=
,=20
maybe using ferrite cores which are readily available ?
Link coupling to the loading coil may be an option but my early attempts=
 at this=20
merely shorted out the loading coil and damaged the PA, so I have avoided=
 it.

73=20
Chris G3XIZ


     =20

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<html><head><style type=3D"text/css"><!-- DIV {margin:0px;} --></style></h=
ead><body><div style=3D"font-family:arial, helvetica, sans-serif;font-size=
:10pt"><DIV>LF,</DIV>
<DIV>&nbsp;</DIV>
<DIV>I shall be transmitting on VLF again over the weekend.</DIV>
<DIV>&nbsp;</DIV>
<DIV>The main purpose will be to test (and&nbsp;adjust) my new loading coi=
l&nbsp;therefor the transmitted frequency may vary.</DIV>
<DIV>I shall keep the reflector informed as to frequency and times that tr=
ansmissions occur should anyone wish to take a look for&nbsp;my signals.</=
DIV>
<DIV>&nbsp;</DIV>
<DIV><U>PRESENT STATION SET UP</U></DIV>
<DIV><U></U>&nbsp;</DIV>
<DIV><U>TX</U></DIV>
<DIV>&nbsp;</DIV>
<DIV>I&nbsp;have the option to&nbsp;use&nbsp;either an internal OCXO or an=
 external off-air standard frequency, both&nbsp;of 10.000 . . MHz which&nb=
sp;is then passed through a programmable divider&nbsp;to give <U>even</U>=
 divisions e.g.</DIV>
<DIV>10.000/1110 =3D 9.090 909 kHz&nbsp;&nbsp;&nbsp; 10.000/1112 =3D 8.992=
 806 kHz etc. . .</DIV>
<DIV>&nbsp;</DIV>
<DIV>The&nbsp;PA is capable of giving several hundreds of watts but it has=
 a low output impedance and the aerial system has a high impedance (severa=
l kilohms).</DIV>
<DIV>To achieve reasonable matching I use a large laminated-core mains tra=
nsformer with a step up ratio of 1:24</DIV>
<DIV>&nbsp;</DIV>
<DIV><U>LOADING COIL(S)</U></DIV>
<DIV>&nbsp;</DIV>
<DIV>To tune out the aerial's capacitive reactance I use a series loading=
 coil (inductor).</DIV>
<DIV>The original coil was single-wound, about 600 mm diameter and has an=
 inductance of ~ 1.25 H</DIV>
<DIV>With the above TX, loading coil and my 40m inverted 'L'&nbsp;I can ge=
nerate an aerial current of&nbsp; 0.15 - 0.2A</DIV>
<DIV>&nbsp;</DIV>
<DIV>The original coil's losses seemed high so to improve matters I have=
 wound another unit, this time using heavier gauge wire and of double-laye=
r construction.</DIV>
<DIV>Initial results have been disappointing as I generate less aerial cur=
rent than with the old coil.</DIV>
<DIV>&nbsp;</DIV>
<DIV>The inductance necessary to achieve resonance has also fallen: from=
 ~&nbsp;1.25H to&nbsp;~ 0.75 H implying that the new coil has considerably=
 more self-capacitance.</DIV>
<DIV>There are a few hundred turns on it which are not used and may be cau=
sing the problem so I intend slowly to remove these, checking the aerial=
 current at intervals.</DIV>
<DIV>&nbsp;</DIV>
<DIV><U>AERIALS</U> </DIV>
<DIV>&nbsp;</DIV>
<DIV>I generally use my 40m inverted 'L' aerial, height 10m but have the=
 facility (wind conditions being suitable) to launch balloon or kite-assis=
ted wires.</DIV>
<DIV>My property borders a public playing field so I need a wind direction=
 SE - S&nbsp; or SW for kite operations and near still air conditions for=
 balloons.</DIV>
<DIV>&nbsp;</DIV>
<DIV><U>ADVICE</U></DIV>
<DIV><U></U>&nbsp;</DIV>
<DIV>I should be much&nbsp;obliged for information which will enable me to=
 improve the station's ERP and detectability.</DIV>
<DIV>Can someone point me in the right direction to improve the matching=
 system, maybe using ferrite cores which are readily available ?</DIV>
<DIV>Link coupling to the loading coil may be an option but my early attem=
pts at this merely shorted out the loading coil and damaged the PA, so I=
 have avoided it.</DIV>
<DIV>&nbsp;</DIV>
<DIV>73 </DIV>
<DIV>Chris G3XIZ</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV></div><br>



      </body></html>

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