From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Date: Thu, 6 Jan 2011 18:42:25 +0100
Thread-Topic: adding a L into a 300m LF vertical?
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References: <4D25EC9A.6030201@iup.uni-heidelberg.de>
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Subject: LF: RE: adding a L into a 300m LF vertical?
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Hello Stefan,

your calculations seems very resaonable to me. But if I compare it to the=
 "classic" antenna with loading coil at ground level, I am not sure that=
 it is worth the effort.

Using MMana-Gal a 300m vertical gives almost identical values as EZNEC (8-=
j604 Ohm).
The wire loss (1mm Cu wire) it about 2 Ohm, so the overall resistance rise=
s to 10 Ohm.
Assuming you use a good loading coil (Q =3D 350) the coil loss is 1 ohm an=
d the antenna impedance is 11 Ohm.
Plus 25 Ohm ground loss =3D 36 Ohm overall loss.
Overall efficiency =3D 8/36 =3D 22%

Adding a (lossless) 1mH inductance at 100m height gives 13-j20 Ohm (no wir=
e loss).
When including wire loss the resistance rises to 15 Ohm.
Further assuming that the elevated coil has a Q=3D 100 it's loss is about=
 8 Ohm and the overall loss  is 23 Ohm.
Plus 25 Ohm ground loss the resistive part rises to about 48 Ohm (very con=
venient), the small variometer (about 23uH) will hardly contribute to the=
 overall loss (at Q =3D 350 the loss is less than 0.1 Ohm).
So the overall efficiency is 13/48 =3D 27%.

The "flying coil" will improve the antenna by 27/22 =3D 1.23 or 0.9dB. May=
be the extra sag will cause more loss than that.

But at the other hand, I have good experience with elevated coils, that ca=
n not be explained by improved current distribution (larger effective heig=
ht).
So if it is not too much trouble making the elevated coil I would say: try=
 it and you will know.

73, Rik  ON7YD - OR7T

________________________________
Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or=
g] namens Stefan Sch=E4fer [schaefer@iup.uni-heidelberg.de]
Verzonden: donderdag 6 januari 2011 17:23
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: LF: adding a L into a 300m LF vertical?

LF,

I've just done some simulations in EZNEC. The model is my 300m vertical th=
at will be used on 137 kHz, probably this weekend.

When choosing a lossless gound and no wire losses i get the radiation resi=
stance of that antenna. It is 8.37 Ohm at 137.7 kHz. The reactance is -j58=
8 Ohm, so 680 uH is needed to compensate that. Assuming 25 Ohm earth losse=
s and 5 Ohm coil losses, the antenna efficiency is about 17 % (!).


If i choose copper losses for the wire and keep the ground lossless  AND=
 add a L of 1 mH (plus 3 Ohm assumed coil losses) in a height of 100m (whe=
re i add the 100m wire to the 200m vertical wire, so no cut is needed), i=
 am getting R(rad+wire)=3D22 Ohm and a reactance of j17 Ohm. Since the gro=
und will add some capacity in this series circuit the actual reactance wil=
l be slightly capacitive again i assume. Assuming 25 Ohm earth losses will=
 achieve about R=3D50 Ohm :-) and maybe almost no reactive part, so no coi=
l is needed at the ground and the antenna can directly be connected to the=
 RG58 cable (i would spend 10 kOhm against ground due to static voltages).=
 The radiation resistance would be 13 Ohm (calculated by assuming lossless=
 coil/wire/ground). So the antenna efficiency would be 26%.

Probably the effective height would be reduced due to stronger sagging of=
 the antenna wire. This will reduce the efficiency a bit, depending on the=
 wind.

Questions: Is my calculation reasonably useful? Would YOU add that coil in=
 a height of 100m above GND?

I tend to let it be since the improvement isn't that much and the effort=
 is high. Furthermore the coil losses could be higher since i have to use=
 a thin wire to keep the weight small...

About the weekend: WX forecast says there will be strong wind but rain as=
 well (not such a problem on LF).
I already have the permission of the German air traffic control for that=
 300m antenna... :-)

73, Stefan/DK7FC

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<div>Hello Stefan,</div>
<div>&nbsp;</div>
<div>your calculations seems very resaonable to me. But if I compare it to=
 the &quot;classic&quot; antenna with loading coil at ground level, I am=
 not sure that it is worth the effort.</div>
<div>&nbsp;</div>
<div>Using MMana-Gal a 300m vertical gives almost identical values as EZNE=
C (8-j604 Ohm).</div>
<div>The wire loss (1mm Cu wire) it&nbsp;about 2 Ohm, so the overall resis=
tance rises to&nbsp;10 Ohm.</div>
<div>Assuming you use a good loading coil (Q =3D 350) the coil loss is&nbs=
p;1 ohm and the antenna impedance is 11 Ohm.</div>
<div>Plus 25 Ohm ground loss =3D 36 Ohm overall loss.</div>
<div>Overall efficiency =3D 8/36 =3D 22%</div>
<div>&nbsp;</div>
<div>Adding a (lossless) 1mH inductance at 100m height gives 13-j20 Ohm (n=
o wire loss).
</div>
<div>When including wire loss the&nbsp;resistance rises to 15 Ohm. </div>
<div>Further assuming that the elevated coil has a Q=3D 100 it's loss is=
 about 8 Ohm and the&nbsp;overall loss&nbsp;&nbsp;is&nbsp;23 Ohm.</div>
<div>Plus 25 Ohm ground loss the resistive part rises to about 48 Ohm (ver=
y convenient), the small variometer (about 23uH) will hardly contribute to=
 the overall loss (at Q =3D 350 the loss is less than 0.1 Ohm).</div>
<div>So the overall efficiency is 13/48 =3D 27%.</div>
<div>&nbsp;</div>
<div>The &quot;flying coil&quot; will improve the antenna by 27/22 =3D 1.2=
3 or 0.9dB. Maybe the extra sag will cause more loss than that.</div>
<div>&nbsp;</div>
<div>But at the other hand, I have good experience with elevated coils, th=
at can not be explained by improved current distribution (larger effective=
 height).
</div>
<div>So if it is not too much trouble&nbsp;making the elevated coil I woul=
d say: try it and you will know.</div>
<div>&nbsp;</div>
<div>73, Rik&nbsp; ON7YD - OR7T</div>
<div dir=3D"ltr"><font color=3D"#000000" size=3D"2" face=3D"Tahoma"></font=
>&nbsp;</div>
<div style=3D"DIRECTION: ltr" id=3D"divRpF755464">
<hr tabindex=3D"-1">
<font color=3D"#000000" size=3D"2" face=3D"Tahoma"><b>Van:</b> owner-rsgb_=
lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Stefan=
 Sch=E4fer [schaefer@iup.uni-heidelberg.de]<br>
<b>Verzonden:</b> donderdag 6 januari 2011 17:23<br>
<b>Aan:</b> rsgb_lf_group@blacksheep.org<br>
<b>Onderwerp:</b> LF: adding a L into a 300m LF vertical?<br>
</font><br>
</div>
<div></div>
<div>LF, <br>
<br>
I've just done some simulations in EZNEC. The model is my 300m vertical th=
at will be used on 137 kHz, probably this weekend.
<br>
<br>
When choosing a lossless gound and no wire losses i get the radiation resi=
stance of that antenna. It is 8.37 Ohm at 137.7 kHz. The reactance is -j58=
8 Ohm, so 680 uH is needed to compensate that. Assuming 25 Ohm earth losse=
s and 5 Ohm coil losses, the antenna
 efficiency is about 17 % (!).<br>
<br>
<br>
If i choose copper losses for the wire and keep the ground lossless&nbsp;=
 AND add a L of 1 mH (plus 3 Ohm assumed coil losses) in a height of 100m=
 (where i add the 100m wire to the 200m vertical wire, so no cut is needed=
), i am getting R(rad&#43;wire)=3D22 Ohm and a reactance
 of j17 Ohm. Since the ground will add some capacity in this series circui=
t the actual reactance will be slightly capacitive again i assume. Assumin=
g 25 Ohm earth losses will achieve about R=3D50 Ohm :-) and maybe almost=
 no reactive part, so no coil is needed
 at the ground and the antenna can directly be connected to the RG58 cable=
 (i would spend 10 kOhm against ground due to static voltages). The radiat=
ion resistance would be 13 Ohm (calculated by assuming lossless coil/wire/=
ground). So the antenna efficiency
 would be 26%.<br>
<br>
Probably the effective height would be reduced due to stronger sagging of=
 the antenna wire. This will reduce the efficiency a bit, depending on the=
 wind.
<br>
<br>
<u>Questions:</u> Is my calculation reasonably useful? Would YOU add that=
 coil in a height of 100m above GND?<br>
<br>
I tend to let it be since the improvement isn't that much and the effort=
 is high. Furthermore the coil losses could be higher since i have to use=
 a thin wire to keep the weight small...<br>
<br>
About the weekend: WX forecast says there will be strong wind but rain as=
 well (not such a problem on LF).
<br>
I already have the permission of the German air traffic control for that=
 300m antenna... :-)<br>
<br>
73, Stefan/DK7FC<br>
</div>
</div>
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