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

[Bob kb8tq]

Hi

> 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 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?

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 ….

Bob


> 
> 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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