[time-nuts] FS700 antenna

paul swed paulswedb at gmail.com
Sat May 5 22:19:47 UTC 2012


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 <df6jb at ulrich-bangert.de>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: time-nuts-bounces at febo.com
> > [mailto:time-nuts-bounces at febo.com] 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
> >
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