[time-nuts] Active LORAN antenna

[Ulrich Bangert]

Hi George,

I appreciate your help a lot and the next week is surely early enough.

73s de Ulrich, DF6JB

Am 26.08.2011 um 14:15 schrieb George Dubovsky:

> I have the schematic of the active antenna, but I will not be able to get to
> it until Monday.
> 
> 73,
> 
> geo - n4ua
> 
> On Fri, Aug 26, 2011 at 6:00 AM, Ulrich Bangert <df6jb at ulrich-bangert.de>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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Ulrich Bangert
Ortholzer Weg1
27243 Gross Ippener
Deutschland
Tel   +49 (0)4224 95071
Fax  +49 (0)4224 95072
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www.ulrich-bangert.de