[ntp:hackers] u-blox reference clock driver

[Achim Gratz]

Udo van den Heuvel via devel writes:
> On 14-08-18 21:03, Achim Gratz via devel wrote:
>> If you have a GPS antenna with SMA connector then you'll want this
>> module instead:
>
> No antenna yet but SMA looks more robust...

Certainly, but it's still quite delicate.

> Question: So what antenna would we need?

I am using both patch antennas (the "mid-size" ones about 1"x1", there
are both larger and smaller ones) with fixed U.FL tail and GPS "puck"
(also patch antennas, slightly larger then the other ones) with fixed
SMA tail.  I have a few SMA to U.FL pigtails for when I need to bridge
the SMA to the smaller formfactor.

> One that covers multi GNSS, i.e.: GPS, Glonass, Galileo, Beidou, etc,
> etc.

I wouldn't worry about that unless you plan acentralized antenna
distribution system.

The ones I have are GPS/GLONASS, I just haven't found one that does the
other two at the same time at a Price I like.  Also, with most modules
timing accuracy actually deteriorates when activating more than one
GNSS.  I've configured all active modules to do GPS only.

> We have partial sky view due to indoor (window) use.

All my antennas are indoor, although I don't have reinforced
concrete walls / ceilings and I am at the top floor.

> We could provide a ground plane but it is not there yet.

Patch antennas need a ground plane to properly function in
not-quite-ideal reception conditions.  A square foot of aluminum foil on
a level surface under the antenna works good enough, the magnetic pucks
are better off when put on some steel surface (just because they stay
more easily where you put them, not because of some improved
performance).

> A 5 meter cable is OK, but 7 meters would be better.
> I have some (local) DVB-T and cell transmitters not too far away.
> The M8T can be in an RF-closed enclosure, but don't know yet how to do that.
> Power from USB. RS232 TTL converter and M8T need this power.
> Similar (without TTL) to how I run the GPS18X's.

If you must go RS232 (why?) you'd be better off putting all distance on
the serial link and shorten the RF cables as much as possible.  Most
antenna cables have pretty high damping and the ones that don't cost quite
the premium.  Easier on the noise (and money) budget if you keep the RF
runs short.

I myself am just putting another rasPi next to the GPS & antenna and
put it where it isn't in the way, so the only thing I have to worry
about is power and network cable.

> What antenna can cope with these requirements?

I'd start with a magnetic puck antenna with fixed cable if you go SMA
connector.  For longer cable length you should look out for slightly
higher amplification.  Avoid extremely high amplifications in the 40dB
range, these antennas are for less sensitive receivers.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

SD adaptation for Waldorf Blofeld V1.15B11:
http://Synth.Stromeko.net/Downloads.html#WaldorfSDada