[time-nuts] Active LORAN antenna

[Brooke Clarke]

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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