[time-nuts] Active LORAN antenna

k4cle at aol.com k4cle at aol.com
Fri Aug 26 20:05:36 UTC 2011


Hey Brooke, 
How are you doing?  Are you still using that AMRAD antenna preamp I made for  
you several years ago?  It's been several years since we emailed each other  
and I have lost contact with you until now.  Last time I heard from you,  
your wife had run over the coax with the lawn mower and cut it into!  Just  
curious if that thing was still working.  73's.  Doug, k4cle.

Connected by DROID on Verizon Wireless

-----Original message-----
From: Brooke Clarke <brooke at pacific.net>
To: Discussion of precise time and frequency measurement  
<time-nuts at febo.com>
Sent: Fri, Aug 26, 2011 16:39:01 GMT+00:00
Subject: Re: [time-nuts] Active LORAN antenna

Hi Ulrich:

You might consider the AMRAD active antenna that they designed for the 
136 kHz ham band.
http://www.prc68.com/I/LF-Ant.shtml

or the McKay Dymec DA-100 active whip.
http://www.prc68.com/I/DR33.shtml#DA100

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.End2PartyGovernment.com/


Ulrich Bangert wrote:
> Gentlemen,
>
> my friend Frank and I both miss the matching actice antenna for our
> Standford Research FS700 Loran frequency standards. We also do not have a
> schematic of it. Nevertheless we have tried to re-engineer the circut from
> the part's list and the circuit description in the FS700 manual. Our  
result
> is shown in the accompanying schematic.pdf.
>
> The generator in the left in conjunction with the 10 k resistor represents
> the expected high footpoint impedance of the very short (3 m) antenna. The
> VDD in the right in conjunction with the 100 ohms resistor represents what
> it believed to be inside the FS700.
>
> Not shown here is a 100 k resistor that may be included between the filter
> output and the 7 k resistor to form a 30 dB divider together with it. Also
> not shown is a 390 micro henry inductance which's impact is not to be  
found
> in the circuit descripion. Also not shown is a small neon bulb for
> overvoltage protection.
>
> The ac analysis shows that the overall filter function is well around 100
> kHz. But it seems as if the fet (a 2N5991 in the original) would not have
> enough gain to counteract the overall damping included in the front end  
let
> alone to deliver some additional gain for the receiver's front end.
>
> We both feed the receiver currently with dipoles for 80 m ham radio and a
> resistor that makes the receiver think the active antenna is connected.  
The
> receiver has a possible total of 130 dB gain and my receiver says it uses  
94
> dB gain while Franks receiver says it uses 102 dB gain. The noise margin  
is
> also a bit better on my location. However, if one looks at the manual f.e.
> at page 17 one could get the impression as if a receiver gain of 75 dB may
> be considered much more normal as our values. Instead of improving the
> reception everything gets even worse if the active antenna is connected. I
> should also note that my qth is only 200 km away from SYLT (our German  
Loran
> station) while Frank is even 70 km nearer to it.
>
> Questions:
>
> 1) Anyone an idea what we are possibly doing wrong?
>
> 2) Anyone an idea for the 390 micro henry inductor?
>
> 3) Anyone own the original schematic?
>
> TIA for your help
>
> Ulrich Bangert
> www.ulrich-bangert.de
> Ortholzer Weg 1
> 27243 Gross Ippener
>    
>
>
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