Large inductors in GPS supply and data lines ?


Last week I attempted to reduce some of the noise that can be emitted out of a U3S.

Nothing specific to the U3, but as we know, just about any electronic device puts out some crap on
incoming or outgoing cabling. (GPS is in a remote separate box).

So I added some 470mh (MILLI-HENRY) chokes in the 1pps, data and 5v supply lines coming out of the
U3S. DC resistance is 7 ohms per choke.

Everything appeared normal I thought, but I have now observed some odd behaviour.

Occasionally I see the heartbeat give odd beats, strange time settings, the calibration whizzing off in only a few seconds.

Is it the chokes messing with the 9K6 data, and 1 PPS ?

Surely DC stuff, it shouldn't matter - but then I  might be wrong.

Has anyone ever seen the effects of inductance with data at a measly 9K6, or a simple 1PPS line ?

73 de Andy

Richard G4TGJ

At 9.6kHz 470mH is about 28k ohm.

Richard G4TGJ

And it will slow the rise time of the data.
What made you think 9k6 data was DC?


Its anything but DC!

The 1PPS signal is slow but the edges are square so any large inductance
or capacitance will distort the signal.

At 9600 that would be a killer.

Keep the chokes under 10-20uH (that's microhenry).

The DC lines that's ok but only the +V.  Ground for RF and Data
must be a solid ground within the circuit.


Graham, VE3GTC

In the uBlox hardware integration manuals a recommended practice is to use a ferrite bead, inductor, or small value resistor to help mitigate noise.

The idea is to slow down a bit the rising and falling edges of the digital signals.

quote: "On the other hand, noise generated at the I/O pins will emit from unshielded I/O lines. Receiver performance may be degraded when this noise is coupled into the GNSS antenna (see Figure 14). To avoid interference by improperly shielded lines, it is recommended to use resistors (e.g. R>20 Ω), ferrite beads (e.g. BLM15HD102SN1) or inductors (e.g. LQG15HS47NJ02) on the I/O lines in series. These components should be chosen with care because they will affect also the signal rise times"

LQG15HS47NJ02 is 47nH

cheers, Graham ve3gtc

On 2019-06-20 19:32, Richard G4TGJ wrote:
At 9.6kHz 470mH is about 28k ohm.

Jack <vhfplus@...>

The launcher shown on the web site is far more complex than the one obtained from the Joplin, MO, Amateur Radio Club, which performs quite nicely. The launcher used by my XYL and me may not have a vertical range of 150-feet but it does 50 to 55 feet easily and is very adequate for our needs. Rather than a tennis ball projectile it uses a PVC cylinder with an attachment eyelet on one end. It is ingenious and the price is certainly right.




Thanks everyone for your responses.

It appears I may have lapsed a bit in my thinking, and created a problem.

Hopefully this weekend I will try another way of reducing noise.

73 de Andy



I removed the huge r chokes and replaced them with some smaller ones.

I ordered some chokes, the type that are really just stiff wire with some ferrite moulded on to them

I measured the XL at HF, typically 40 ohms, and about 0.5 ohms down at 100Khz.

Presumably lower at the 1pps and 9k6 data, and the GPS now works properly ;-)

Lesson learnt.

For info, the symptoms of having too much inductance in the GPS leads was erratic 1 pps heartbeat showing.

For example, maybe every 10 beats there was a 2 pps or similar, the calibration windows whizzed by in a  few seconds ,
despite being told to do a calibration for 20 seconds, and occasionally times reported such 104:31:23 UTC !!

So now we know.

73 de Andy