Return-Path: Received: from rly-me05.mx.aol.com (rly-me05.mail.aol.com [172.20.83.39]) by air-me07.mail.aol.com (v121.4) with ESMTP id MAILINME071-9bc4858e529328; Wed, 18 Jun 2008 06:36:42 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-me05.mx.aol.com (v121.5) with ESMTP id MAILRELAYINME058-9bc4858e529328; Wed, 18 Jun 2008 06:36:29 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1K8v0p-0001XM-FG for rs_out_1@blacksheep.org; Wed, 18 Jun 2008 11:35:35 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1K8v0o-0001XD-R7 for rsgb_lf_group@blacksheep.org; Wed, 18 Jun 2008 11:35:34 +0100 Received: from mailout09.t-online.de ([194.25.134.84]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1K8v0k-00083s-Qp for rsgb_lf_group@blacksheep.org; Wed, 18 Jun 2008 11:35:34 +0100 Received: from fwd24.aul.t-online.de by mailout09.sul.t-online.de with smtp id 1K8v0h-0003tK-00; Wed, 18 Jun 2008 12:35:27 +0200 Received: from [192.168.2.22] (EXcPf2ZHwht5yEPXUVwFKbk-vO9EnjPXmjkH88o3-1-1CBzgheO88A+yUj0Q0RdgBm@[217.95.86.111]) by fwd24.t-online.de with esmtp id 1K8v0T-1qhrtI0; Wed, 18 Jun 2008 12:35:13 +0200 MIME-Version: 1.0 From: hajo.brandt.dj1zb@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> <20080618082938.3733731E703@smtps01.kuleuven.be> In-Reply-To:<20080618082938.3733731E703@smtps01.kuleuven.be> To: X-Mailer: T-Online eMail 6.05.0004 Date: 18 Jun 2008 10:32 GMT Message-ID: <1K8v0T-1qhrtI0@fwd24.t-online.de> X-ID: EXcPf2ZHwht5yEPXUVwFKbk-vO9EnjPXmjkH88o3-1-1CBzgheO88A+yUj0Q0RdgBm X-TOI-MSGID: 18e2294a-6c04-4376-a6b9-fee7cd839034 X-Karma: 0: X-Spam-Score: 1.0 (+) X-Spam-Report: autolearn=disabled,HTML_FONT_FACE_BAD=0.452,HTML_MESSAGE=0.001,NO_REAL_NAME=0.55,UNPARSEABLE_RELAY=0.001 Subject: Re: LF: Finbar's Compact 500kHz Vertical Content-Type: Multipart/Alternative; Boundary="__Next_1213785127_Part56__" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=HTML_FONT_FACE_BAD, HTML_MESSAGE,NO_REAL_NAME autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-AOL-IP: 193.82.116.20 X-AOL-SCOLL-AUTHENTICATION: domain : post.thorcom.co ; SPF_helo = X-AOL-SCOLL-AUTHENTICATION: domain : t-online.d ; SPF_822_from = --__Next_1213785127_Part56__ Content-Type: Text/Plain; Charset="ISO-8859-1" Content-Transfer-Encoding: 8Bit Dear Rik, thank You for the internet address concerning the details of DI2AM. I have tried to find them again but without any success. But after sleeping on our discussion I came to the conclusion that we should regard the problem I have raised in a different way. When transmitting I concede that any losses in small antennas can be compensated by higher transmitter power. But when receiving such a compensation is not possible, and if a small antenna has losses weak signals may get lost. When recalculating the figuress I have mentioned of 7 meters and 10 meters antenna height respectively, related to 500 kHz this increase in height means that the radiation resistance (which is independent of the antenna being tuned or not) of the higher antenna has doubled, and as the antenna signal current may have remained equal the receiving power will have quadrupled! This would also mean than an OM using a small antenna for transmitting and receiving, as is common among radio amateurs, will have a reduced receiving range compared to a station using a higher antenna. Therefore I would like to repeat my statement that we should not disregard antenna height, unless we do not want to achieve anything else than just beaconing. HW? 73 Ha-Jo, DJ1ZB "Rik Strobbe" schrieb: 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" 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 for more information. Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm for more information. --__Next_1213785127_Part56__ Content-Type: Text/HTML; Charset="ISO-8859-1" Content-Transfer-Encoding: 8Bit T-Online eMail Dear Rik, 

thank You for the internet address concerning the details of DI2AM. I have tried to find them again but without any success.

But after sleeping on our discussion I came to the conclusion that we should regard the problem I have raised in a different way.

When transmitting I concede that any losses in small antennas can be compensated by higher transmitter power.

But when receiving such a compensation is not possible, and if a small antenna has losses weak signals may get lost.

When recalculating the figuress I have mentioned of 7 meters and 10 meters antenna height respectively, related to 500 kHz this increase in height means that the radiation resistance (which is independent of the antenna being tuned or not) of the higher antenna has doubled, and as the antenna signal current may have remained equal the receiving power will have quadrupled!

This would also mean than an OM using a small antenna for transmitting and receiving, as is common among radio amateurs, will have a reduced receiving range compared to a station using a higher antenna.

Therefore I would like to repeat my statement that we should not disregard antenna height, unless we do not want to achieve anything else than just beaconing.

HW?

73 Ha-Jo, DJ1ZB 

 
  "Rik Strobbe" <rik.strobbe@fys.kuleuven.be> schrieb:
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 for more information.

 


Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm for more information.

  --__Next_1213785127_Part56__--