Interesting. I suspect I do not see these effects for one primary reason. My antenna is 140 feet from the house in the woods. The woods are on 22 acres. I own some of it and the rest is green space. So there just might be a few 600' or more length antennas running out there. Then again maybe not. ;-) Regards Paul. WB8TSL
On Sat, May 5, 2012 at 7:09 AM, Ulrich Bangert <[email protected]>wrote: > 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. > _______________________________________________ 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.
