[time-nuts] Thunderbolt - trouble locking with some types of antennas

[Didier Juges]

The Thunderbolt is well known for not having the best sensitivity among GPS
receivers. It seems that timing receivers in general, particularly those of
the same generation as the Thunderbolt are not as sensitive as navigation
(possibly newer) GPS receivers. It may be because they are expected to run
with amplified antennas?

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 and
the shingle roof, there are no other obstructions and they are doing OK not
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 in
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 but
> 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 using
> a small patch antenna with internal LNA placed near my window had satellite
> & PPL lock within a few seconds.  It requires 3-4 satellite locks for its
> PPL.  However, when I attached the patch antenna to my Thunderbolt –
> satellite signal strength were zero or minus for all satellites.  The specs
> 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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