Date: Wed, 18 Jun 2008 10:34:59 +0200
To: rsgb_lf_group@blacksheep.org
From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
In-Reply-To: <1K8k27-03I2I00@fwd24.t-online.de>
References: <57a24ca70806131827p690673d0kb0b8c0d76d85fddc@mail.gmail.com>
 <1K7Y7g-1RYRXM0@fwd31.t-online.de>
 <20080617131417.C7BE4F3863@smtps02.kuleuven.be>
 <1K8k27-03I2I00@fwd24.t-online.de>
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Subject: Re: LF: Finbar's Compact 500kHz Vertical
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Dear HaJo,

I can not find any reason to believe that the same ERP radiated from 
2 antennas with the same radiation pattern could produce different 
field strengths.
But I am far from an antenna specialist or propagation specialist, so 
maybe others can come up with these reasons.

Another thing:
At the moment we talk about skywave (ionospheric) propagation there 
might be no such thing as "the best antenna". An antenna that has a 
high takeoff angle may be superior to an antenna with a low takeoff 
angle at shorter distances (let's say less than 1000...1500km) while 
the low angle antenna will do better at long distances.

Regarding DI2AM:
http://www.seefunk-fx-intern.de/radiobeacon/radiobeacon_en.htm 
provides some figures:
- The TX has 18W input, at 75% efficiency this means about 13 W output.
- The antenna current is +/- 1.7 A, assuming 13W output the total 
resistance (Rrad + Rloss) is only 5 Ohm.
- The antenna top is 35m asl. Based on the picture I estimate that 
the antenna bottom is +/- 10m asl, so antenna hight is +/- 25m. 
The  topload seems about twice as long as the antenna height so let's 
estimate 50m. According to "mmana-ga"l Rrad is 2.3 Ohm, the antenna 
capacitance is 840pF (the website notes +/- 800pF, so thta's pretty 
close) and the gain is 4.64dBi (2.5dBd).
- Putting 1.7A into 2.3 Ohm means 6.65 Watt radiated or +/- 12 Watt ERP.
No wonder they are putting out such strong signal.

73, Rik  ON7YD - OR7T

At 00:51 18/06/2008, you wrote:
>Dear Rik,
>
>thank You for your contribution. Especially your last sentence is 
>interesting for me because this may explain the success of 
>MF-stations operating close to the coast.
>
>Another example for exceptionally high antennas on MF for me is 
>DI2AM, located on a museum ship in the harbour of Rostock. I have 
>been informed that the antenna has been put up between two masts of 
>30 meter in height. Other favourable conditions are the low ground 
>loss onboard of a ship and also the vicinity of water, of course.
>
>In general I do not have any objections to Finbar's setup; it shows 
>that effective MF antennas can be built up on a rather small area.
>
>But I am not yet convinced that height of MF antennas should not 
>matter, and I will continue to observe the scenery.
>
>OK?
>
>73 Ha-Jo, DJ1ZB
>
>
>   "Rik Strobbe" <rik.strobbe@fys.kuleuven.be> schrieb:
>Dear HaJo,
>
>>But in general I feel that antenna height should not be 
>>disregarded. Even with equal ERP sky waves may develop better from 
>>higher aerials.
>>
>>HW?
>
>I guess that the only cause that 2 antennas fed with the same ERP 
>produce different signals is a difference in the (vertical) 
>radiation pattern, ie. the takeoff angle.
>I simulated a 30m, 10m and 3m vertical (at 502kHz) with mmana_gal 
>and found only very small differences: from 18.2 degrees for the 30m 
>vertical to 18.6 degrees for the 3m vertical. This for a uniform 
>ground with a conductivity of 10mS/m.
>Making the ground poor (1mS/m) results in a takeoff angle of about 
>26 degrees (+/- a few tenths depending on the height).
>Increasing the conductivity to 100mS/m reduces the takeoff angle to 
>12-13 degrees.
>
>73, Rik  ON7YD - OR7T
>
>Disclaimer: 
><http://www.kuleuven.be/cwis/email_disclaimer.htm>http://www.kuleuven.be/cwis/email_disclaimer.htm 
>for more information.
>
>


Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm


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Dear HaJo,<br><br>
I can not find any reason to believe that the same ERP radiated from 2
antennas with the same radiation pattern could produce different field
strengths.<br>
But I am far from an antenna specialist or propagation specialist, so
maybe others can come up with these reasons.<br><br>
Another thing:<br>
At the moment we talk about skywave (ionospheric) propagation there might
be no such thing as &quot;the best antenna&quot;. An antenna that has a
high takeoff angle may be superior to an antenna with a low takeoff angle
at shorter distances (let's say less than 1000...1500km) while the low
angle antenna will do better at long distances.<br><br>
Regarding DI2AM: <br>
<a href="http://www.seefunk-fx-intern.de/radiobeacon/radiobeacon_en.htm" eudora="autourl">
http://www.seefunk-fx-intern.de/radiobeacon/radiobeacon_en.htm</a>
provides some figures:<br>
- The TX has 18W input, at 75% efficiency this means about 13 W output.
<br>
- The antenna current is +/- 1.7 A, assuming 13W output the total
resistance (Rrad + Rloss) is only 5 Ohm.<br>
- The antenna top is 35m asl. Based on the picture I estimate that the
antenna bottom is +/- 10m asl, so antenna hight is +/- 25m. The&nbsp;
topload seems about twice as long as the antenna height so let's estimate
50m. According to &quot;mmana-ga&quot;l Rrad is 2.3 Ohm, the antenna
capacitance is 840pF (the website notes +/- 800pF, so thta's pretty
close) and the gain is 4.64dBi (2.5dBd).<br>
- Putting 1.7A into 2.3 Ohm means 6.65 Watt radiated or +/- 12 Watt
ERP.<br>
No wonder they are putting out such strong signal.<br><br>
73, Rik&nbsp; ON7YD - OR7T<br><br>
At 00:51 18/06/2008, you wrote:<br>
<blockquote type=cite class=cite cite="">
<font face="Arial Black, Helvetica" size=2>Dear Rik,<br><br>
thank You for your contribution. Especially your last sentence is
interesting for me because this may explain the success of MF-stations
operating close to the coast.<br><br>
Another example for exceptionally high antennas on MF for me is DI2AM,
located on a museum ship in the harbour of Rostock. I have been informed
that the antenna has been put up between two masts of 30 meter in height.
Other favourable conditions are the low ground loss onboard of a ship and
also the vicinity of water, of course.&nbsp; <br><br>
In general I do not have any objections to Finbar's setup; it shows that
effective MF antennas can be built up on a rather small area. <br><br>
But I am not yet convinced that height of MF antennas should not matter,
and I will continue to observe the scenery.<br><br>
OK?<br><br>
73 Ha-Jo, DJ1ZB<br>
</font><font face="Arial Black, Helvetica"><br><br>
</font>&nbsp; &quot;Rik Strobbe&quot; &lt;rik.strobbe@fys.kuleuven.be&gt;
schrieb: <br>

<dl>
<dd><font face="Courier New, Courier">Dear HaJo,<br><br>
<blockquote type=cite class=cite cite="">
<dd>But in general I feel that antenna height should not be disregarded.
Even with equal ERP sky waves may develop better from higher
aerials.<br><br>

<dd>HW?</blockquote><br>

<dd>I guess that the only cause that 2 antennas fed with the same ERP
produce different signals is a difference in the (vertical) radiation
pattern, ie. the takeoff angle.<br>

<dd>I simulated a 30m, 10m and 3m vertical (at 502kHz) with mmana_gal and
found only very small differences: from 18.2 degrees for the 30m vertical
to 18.6 degrees for the 3m vertical. This for a uniform ground with a
conductivity of 10mS/m.<br>

<dd>Making the ground poor (1mS/m) results in a takeoff angle of about 26
degrees (+/- a few tenths depending on the height).<br>

<dd>Increasing the conductivity to 100mS/m reduces the takeoff angle to
12-13 degrees.<br><br>

<dd>73, Rik&nbsp; ON7YD - OR7T</font><br><br>

<dd>Disclaimer:
<a href="http://www.kuleuven.be/cwis/email_disclaimer.htm">
http://www.kuleuven.be/cwis/email_disclaimer.htm</a> for more
information. <br><br>

</dl><font face="Times New Roman, Times">&nbsp;</font>
</blockquote><BR>
<BR>
<FONT FACE=3D"Arial" SIZE=3D2>Disclaimer: <A HREF=  "http://www.kuleuven.be/cwis/email_disclaimer.htm">http://www.kuleuven.be/cwis/email_disclaimer.htm</A> for more information.</FONT>
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