[time-nuts] Active LORAN antenna

paul swed paulswedb at gmail.com
Fri Aug 26 13:08:21 UTC 2011


Stan you beat me to it. This is the schematic I also have.
When LORAN C was active I was at 53 DB using a whip antenna 8' in length.
But I wound 24 guage wire on a 8 ft fiberglass pole hundreds of turns as a
single layer.
This feeds a loran c preamp that used to be common. Nothing magic about it.
The 99600 chain station was 90 miles from my location.
Very clearly the filter on the frontend helps.
Paul
WB8TSL

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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