Magnus, on 26.8.2011 Stan has posted the Stanford Research circuitry of the original whip antenna belonging to the FS700. My friend Frank and I have both built this antenna from scratch and it works remarkably well.
However there is one caveat with whatever antenna for the FS700 which I had to learn the hard way: With several different kinds of active antennas that I have tried out with the FS700 a lot of them showed low receiver gains (indicating the antenna gain) and high noise margins (nice!) in the FS700's status display (only available after a lock). But when I looked to the FS700 some minutes to hours later it showed an error saying "Noise margin < 1dB" and was in a unlocked condition. Frank experienced absolutely the same 100 km away from me so it could not be a problem of the individual receivers and/or antennas but must have been a more principle effect. I have discussed this problem here in the group but there was no satisfying answer available. The effect stopped to appear from the very moment when the antenna was put out of the house in a distance of abt 20 m. While the effect is still not completely understood there are at least 2 possible reasons: 1) The FS700 has an BNC output on the front which delivers a higly amplified 100 kHz signal so that you can easily view the LORAN waveform on a scope or look to its spectrum on an analyser. If you have the antenna in the very near of the receiver (which I had before <5m) then there are chances that the antenna catches some of the amplified signal which can lead to unwanted oscillations of the complete system overdriving the receiver completely. 2) Despite the fact that the receiver reported high noise margins with the close in antennas there are a lot of noise sources (switching power supplies f.e.) which's aggregated effect on the noise margin may be small in general but may add up in some moments to make the FS700 unhappy. Moving the antenna away from the receiver naturally moved it away from these noise sources as well. 3) May also be a combination of 1) and 2): Say you are normally below the self-oscillation level then a sudden interfering signal may be large enough to start the self-oscillation with the same effect as in 1) For that reason > If I do a quick and dirty attempt, I probably won't go for out-door > operations. may not be the best idea. At least, if you see this message you know what to do. Best regards Ulrich Bangert > -----Ursprungliche Nachricht----- > Von: [email protected] > [mailto:[email protected]] Im Auftrag von Magnus Danielson > Gesendet: Freitag, 4. Mai 2012 21:00 > An: Time-Nuts > Betreff: [time-nuts] FS700 antenna > > > Fellow time-nuts, > > I just received an FS700 but with no antenna, a state I think many of > these receivers have. > > So, my options are: > > 1) Buy a FS700 antenna from SRS - it's just money > > 2) Buy a FS700 antenna from someone with a spare - if I find one... > > 3) Buy a random LORAN-C antenna on popular site - don't know what fits > > 4) Build a replica - probably possible > > 5) Build a quick and dirty - probably quickest > > Any comments and suggestions? > > If I do a quick and dirty attempt, I probably won't go for out-door > operations. > > Cheers, > Magnus > > _______________________________________________ > 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.
