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

Didier Juges shalimr9 at gmail.com
Tue Aug 1 14:13:10 EDT 2017


" having around 20 dB of gain at the antenna greatly decreases the effect
of feed line loss on noise figure."

And that would be consistent with usage for a timing receiver which is
expected to have a well exposed antenna and a significant line length, as
opposed to navigation receivers where the antenna is expected to have a
short feed line.

On Mon, Jul 31, 2017 at 4:17 PM, Brooke Clarke <brooke at pacific.net> wrote:

> Hi Jerry:
>
> The Trimble is the oldest mass produced GPS receiver I know of and because
> the early receivers used high gain antennas it seems that Trimble kept that
> idea for the newer designs. They like about 41 dB gain between the antenna
> and the input to the receiver.
> http://www.prc68.com/I/Trimpack.shtml#Ant
> Newer designs probably place that gain in the front end rather than at the
> antenna.  But having around 20 dB of gain at the antenna gretly decreases
> the effect of feed line loss on noise figure.
>
> --
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com
> http://www.end2partygovernment.com/2012Issues.html
>
>
> -------- Original Message --------
>
>> 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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>>
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