[time-nuts] Thunderbolt - trouble locking with some types of antennas
shalimr9 at gmail.com
Tue Aug 1 14:11:12 EDT 2017
"The newer the receiver, the more horsepower in the silicon. In the case of
gives you more correlators to do DSP. The sensitivity improvement is a
of that. If you take a look at the guts of a TBolt, they date to the late
a long time in silicon years …."
It seems that more correlators would speed up the time to first fix, not
necessarily the sensitivity, particularly I do not see how it would
directly affect the capability to stay locked when signal strength
On the other hand, more correlators may help when there is multipath and a
whole bunch of extraneous signals are fed into the receiver, so maybe the
apparent lack of sensitivity is really the inability to see the signal from
the chaff, not necessarily sensitivity in terms of noise figure.
On Mon, Jul 31, 2017 at 3:06 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
> > On Jul 31, 2017, at 3:32 PM, Didier Juges <shalimr9 at gmail.com> wrote:
> > The Thunderbolt is well known for not having the best sensitivity among
> > receivers. It seems that timing receivers in general, particularly those
> > the same generation as the Thunderbolt are not as sensitive as navigation
> > (possibly newer) GPS receivers. It may be because they are expected to
> > with amplified antennas?
> The newer the receiver, the more horsepower in the silicon. In the case of
> GPS, that
> gives you more correlators to do DSP. The sensitivity improvement is a
> direct result
> of that. If you take a look at the guts of a TBolt, they date to the late
> 1990’s. That’s
> a long time in silicon years ….
> > Based on the spec you wrote, it looks like your antenna has no gain, so
> > definitely I would expect less than good performance.
> > My 3 Thunderbolts have been running with inside antennas (2 pucks and one
> > Trimble Bullet) but my ham shack is upstairs and other than the ceiling
> > the shingle roof, there are no other obstructions and they are doing OK
> > great (all 3 go on holdover somewhat regularly). I am now running one
> > downstairs (while I work on the new software for the TB Monitor) with 50
> > feet of RG-58 going to a HP 58532A antenna somewhat in the clear but
> only 8
> > feet above ground with significant obstructions in pretty much all
> > directions due to the low height and the Thunderbolt is happy as a clam
> > spite of the significant losses in the cable. The HP antenna works much
> > better than the Trimble Bullet antenna.
> > On Mon, Jul 31, 2017 at 12:19 PM, Jerry <jsternmd at att.net> wrote:
> >> Due to access problems, I run my Thunderbolt with a Symmetricom 58532A
> >> antenna placed indoor near a window facing South… can’t get much worse
> >> most of the time it will be locked onto 3 or 4 satellites. I recently
> >> bought a www.leobodnar.com <http://www.leobodnar.com> GPSDO for my SDR
> >> ham
> >> radio setup. I was very surprised to find that this minimalist GPSDO
> >> a small patch antenna with internal LNA placed near my window had
> >> & PPL lock within a few seconds. It requires 3-4 satellite locks for
> >> PPL. However, when I attached the patch antenna to my Thunderbolt –
> >> satellite signal strength were zero or minus for all satellites. The
> >> for the patch antenna are listed below.
> >> I would appreciate any advice understanding this behavior.
> >> Jerry NY2KW
> >> Center Frequency 1575.42MHz±3 MHz
> >> V.S.W.R 1.5:1
> >> Band Width ±5 MHz
> >> Impendence 50 ohm
> >> Peak Gain >3dBic Based on 7×7cm ground plane
> >> Gain Coverage >-4dBic at –90°<0<+90°(over 75% Volume)
> >> Polarization RHCP
> >> LNA/Filter
> >> LNA Gain (Without cable) 28+/-3dB
> >> Noise Figure 1.5dB Typ.
> >> Filter Out Band Attenuation (f° =1575.42MHz)
> >> 7dB Min f0+/-20MHZ
> >> 20dB Min f0+/-50MHZ
> >> 30dB Min f0+/-100MHZ
> >> V.S.W.R <2.0
> >> DC Voltage 2.7V/3.0V/3.3V/5.0V/3.0V to 5.0V/other
> >> DC Current 5mA /11mA/15mA Max
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