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 <df...@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 > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.