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Re: LF: Antennas

To: <[email protected]>
Subject: Re: LF: Antennas
From: "mal hamilton" <[email protected]>
Date: Wed, 4 Jan 2012 11:41:07 -0000
References: <008301ccc97c$51d9fcf0$0401a8c0@xphd97xgq27nyf>,<CABP+t7Zgr4iUWhCQzTKnqBQFcsK4_=zjuPWd5AHkvU5Tggu1EA@mail.gmail.com> <BF4A524700075746A6467658DFC7102CB0B489A6C5@ICTS-S-EXC2-CA.luna.kuleuven.be>,<003501ccca06$6bdef490$0401a8c0@xphd97xgq27nyf> <BF4A524700075746A6467658DFC7102CB0B489A6C6@ICTS-S-EXC2-CA.luna.kuleuven.be> <[email protected]> <004601ccca20$8aa7d1c0$0401a8c0@xphd97xgq27nyf> <00fc01ccca65$47277e60$1502a8c0@Clemens04> <00d901ccca69$1f897260$0401a8c0@xphd97xgq27nyf> <024c01cccad1$3c099ba0$1502a8c0@Clemens04>
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Clemens
It depends what you mean by a reasonable sized loop. A reasonable size might be say 3 metres x 3 metres or more and probably a good enough performer for size and optimised for the frequency of interest.  But the most used and talked about small antennas by the LF fraternity are small untuned loops, uProbes and ferrite sticks that hardly produce enough signal capture to enable AUDIO copy of DX long haul weak amateur stations. I emphasize Audible as opposed to visual QRSS screen displays.
73 de mal/g3kev
   
----- Original Message -----
Sent: Wednesday, January 04, 2012 11:08 AM
Subject: Re: LF: Antennas

>A tuned loop on a Battleship could be tricky with all the metal about.
 
Agreed.
OTOH I know from a retired Marconi antenna engineer that tuned loops (first shielded
later unshielded) in general have been used by the marine for DF.
From experience I also know that a Wellbrook *untuned* broadband receiving loop like the ALA1530
(diameter 1m) has a hard time when it is compared to a tuned dipole of only 2x15m on 160m
or 80m.
On 500kHz according to CCIR curves  external noise is around 13dB stronger than on 1,6Mhz,
i.e. about 63dB *at extremely quiet locations*, on 137kHz it's somewhere between 75dB and 80dB. 
So a receiving antenna could 'afford' an efficiency of say 70dB less than a fullsize dipole/monopole
without degrading the SNR on a decent MW/LW receiver having a reasonable noise figure.
Therefore it's obvious that a well made *tuned loop*  with reasonable dimensions would compare
favourably against any fullsize or near fullsize antenna (not talking of arrays).
Don't forget that the Wellbrook loop version you've tested against your wire antennas was a broadband
untuned design *and* not optimized for MW/LF.
 
73
Clemens
DL4RAJ   
 
 
----- Original Message -----
Sent: Tuesday, January 03, 2012 11:43 PM
Subject: Re: LF: Antennas

Merchant ships used inv L antennas slung between two masts and in some cases additional long whips for MF/HF. Aircraft also used inv L and long wire antennas strung between the cockpit and the top of the tail fin for MF/HF plus a trailing antenna that could be wound in/out as required.
No pocket micro or ferrite sticks used. Some early aircraft also had a small loop antenna for DF purposes.
I know why fixed services used large wire arrays,   for directivity and gain and switchable in direction in some cases but not so sure others did. 
A tuned loop on a Battleship could be tricky with all the metal about.
 
mal/g3kev
 
----- Original Message -----
Sent: Tuesday, January 03, 2012 10:15 PM
Subject: Re: LF: Antennas

Mal,
 
>Why do commercial receiving stations use large antenna farms out in the countryside ??
 
The reason is to get as much *directivity* gain as possible.
BTW british military vessels since decades used to use tuned loops with a preamp
for VFL/LW/MW operation.
And they operated also in CW in those days...
 
73
Clemens
DL4RAJ
----- Original Message -----
Sent: Tuesday, January 03, 2012 3:03 PM
Subject: Re: LF: Antennas

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