[time-nuts] Active LORAN antenna

Ulrich Bangert df6jb at ulrich-bangert.de
Wed Aug 31 10:53:51 UTC 2011


Gentlemen,

I would like to thank you all for your help in this affair. In the meantime
we have both built the antenna according Stan's circuit and it seems to
perform well. It seems however that the antenna needs to be put a bit away
from the receiver itself because otherwise some kind of self-oscillation is
observed.

While 1 k and 100 k are indeed far away from each other: I tried the circuit
with 0 k (!) and with 100 k without seeing a difference in performance.

BTW: Since a few of you have the antenna circuit, do you have perhaps the
scchematics of the receiver itself too?

Best regrads
Ulrich Bangert

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von George Dubovsky
> Gesendet: Montag, 29. August 2011 17:22
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Active LORAN antenna
> 
> 
> 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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> >
> >
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