[time-nuts] Active LORAN antenna

[George Dubovsky]

Ulrich,

I have the SRS active antenna schematic FS700-14, Revision B, and it is
identical to Stan's schematic except that my R3 is 1k and his is 100k. Don't
know which is the newer schematic.

73,

geo - n4ua

On Fri, Aug 26, 2011 at 9:02 AM, Stan, W1LE <stanw1le at verizon.net> wrote:

> Hello UL,
>
> My SRS active antenna is internally potted in resin, so tracing the circuit
> is difficult.
>
> I was able to chip away the PVC white housing and some of the black potting
> material to get at the antenna input terminal. Then I repackaged it with a
> new CB antenna.
> Living on Cape Cod, quite near to the former Nantucket Loran station, I can
> only rarely receive
> some of the European stations.
>
> The schematic in the manual shows a switch or a jumper for the gain
> reduction.
> So, the schematic is probably an old version, and "all bets are off" as to
> what
> the production models, we have, consist of.
>
> I did buy the manual form SRS and the active antenna schematic shows a
> 2N5951,
> not the 2N5991 you mention. My schematic is a rev B, Document Number
> FS700-14
> This document in not dated.
>
> The frequency selective L-C filter network is different, see attachment.
>
> If the attachment does not get thru, please send your direct e-mail
> address.
>
>
> Stan, W1LE     Cape Cod    FN41sr
>
>
>
>
>
> On 8/26/2011 6:00 AM, 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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