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 <[email protected]> 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 >> >> >> ______________________________**_________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/** >> mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> >> and follow the instructions there. >> > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
