Message-ID: <4B0B00EE.9050407@toya.net.pl>
Date: Mon, 23 Nov 2009 22:38:54 +0100
From: =?ISO-8859-2?Q?Piotr_M=B3ynarski?= <sq7mpj@toya.net.pl>
User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax)
MIME-Version: 1.0
To:  rsgb_lf_group@blacksheep.org
References: <4B09D502.8030200@toya.net.pl>,<006101ca6bd9$9ab3cb70$0900a8c0@lark> <BLU146-W27B621B125696A00C593C0CF9E0@phx.gbl> <7C21B1DD169746B0967307E2AB9E7FDD@JimPC>
In-Reply-To: <7C21B1DD169746B0967307E2AB9E7FDD@JimPC>
Subject: Re: LF: Re: N-turn TX Loop
Content-Type: text/plain; charset=ISO-8859-2; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


James Moritz wrote:

> Dear Piotr, LF Group,
>
> Considering only the conductor losses for the moment, in principle 
> increasing the number of turns of the loop by a factor N increases the 
> radiation resistance by approximately N^2, while the loss resistance 
> of the conductors increases by approximately N times, giving an 
> improvement in efficiency of a factor N. However, if you instead 
> connected the same N turns in parallel, you would have a single-turn 
> loop with N parallel conductors, with a loss resistance 1/N times that 
> of a single conductor loop, but with the same radiation resistance. 
> This would also give rise to the same N times efficiency improvement. 
> So from the conductor loss point of view, increasing the number of 
> conductors in the loop should improve efficiency by much the same 
> amount, it would not matter much whether the turns are connected in 
> series or parallel.
>
> However, the multi-turn loop inductance is also approximately 
> proportional to N^2, if the turns are fairly close together. The 
> current in the multi-turn loop will be reduced by a factor of N to 
> achieve the same radiated power. Most of the loop impedance is due to 
> its inductance, so the overall voltage across the loop will increase 
> by a factor of N for the same radiated power.This means a greater 
> electric field strength around the antenna, and so increased 
> environmental losses due to the multiple turns - dielectric loss 
> increases as the square of the applied electric field. So assuming a 
> constant value of environmental loss (1.5ohm in your calculation) is 
> not realistic, if a significant proportion of this resistance is due 
> to dielectric losses, which is probably the case for most practical 
> antennas. Probably the main virtue of the transmitting loop is the 
> reduced environmental loss due to it being a relatively low-impedance, 
> low-voltage device. so to maintain this advantage, it would seem to be 
> a better idea to have multiple parallel turns rather than series turns.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
   Dear Jim, LF Group
 I do thank you for your comprehensive answer. In particular,   I did  
like  your remarks concerning   the contribution of  increased 
dielectric losses  ( as  one increases the number of turns)   in the 
overall environmental loss. In some way it is still an open issue but 
as  you've said, from the point of view of  practical antenna
design , each tenth of Ohm  counts...  

                                                                                                              
73 de Piotr, sq7mpj
qth: Lodz /jo91rs/