[time-nuts] Re: Effect of temperature on cheap puck style GNSS antennas?

[Joseph Gwinn]

On Fri, 13 May 2022 03:30:35 -0400, time-nuts-request at lists.febo.com 
wrote:
time-nuts Digest, Vol 217, Issue 25

> 
> Message: 2
> Date: Thu, 12 May 2022 07:01:11 -0600
> From: Bob kb8tq <kb8tq at n1k.org>
> Subject: [time-nuts] Re: Effect of temperature on cheap puck style
> 	GNSS antennas?
> To: Discussion of precise time and frequency measurement
> 	<time-nuts at lists.febo.com>
> Message-ID: <805C458D-7630-4CCB-8E40-D56254C452E2 at n1k.org>
> Content-Type: text/plain;       charset=utf-8
> 
> Hi
> 
> 
>> On May 12, 2022, at 3:21 AM, Lux, Jim <jim at luxfamily.com> wrote:
>> 
>> On 5/11/22 11:50 PM, Matthias Welwarsky wrote:
>>> Dear list members,
>>> 
>>> My DIY GPSDO has a rather well defined dependence to the environmental
>>> temperature, which correlates almost linearly with a frequency 
>>> shift of the
>>> OCXO. However, at times I see the error against the GNSS 
>>> reference increasing
>>> with its case temperature not warranting such effect.
>>> 
>>> My antenna is one of those cheap, magnetic, active antennas you'd 
>>> put on a car
>>> roof. It's facing south and has full exposure to the sun, obviously.
>>> 
>>> During sunrise I see the TIC error increasing 20ns-30ns over lets say 2000
>>> seconds. The GPSDO case temperature rises, too, during that time 
>>> as the room temperature increases, but it is only by 0.3°C.
>>> 
>>> I'm wondering if the temperature of the antenna, which of course 
>>> rises much
>>> faster than the room temperature, can have an effect of this magnitude?
>> 
>> 
>> Very possible. I've seen fairly large changes (nanoseconds over a 
>> 0-40C temp range) in delay in the LNA and bandpass filter for GNSS 
>> receivers with temperature. If they're using any sort of ceramic 
>> filter or ceramic antenna, then that can have a fairly large 
>> tempco in the time delay.
> 
> The ceramic typically used for antennas is unlikely to have that 
> much change 
> over any reasonable temperature range. The ceramic filters are very 
> different
> beasts …. The impact of the antenna should be down in the “couple 
> of ns” range at most. 
> 
> Since this is a “who knows what” antenna, there is no way to be 
> *sure* of what it’s 
> doing. A properly designed small / low cost antenna should do pretty well. 

Before doing anything fancy, I'd be tempted to enclose the GPS puck 
in a cheap small polystyrene foam beer cooler, to reduce and slow 
down temperature changes at the puck due to sun and wind, and see how 
much effect this has.

Joe Gwinn