Path: ...!eternal-september.org!feeder3.eternal-september.org!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: Jeff Liebermann <jeffl@cruzio.com>
Newsgroups: rec.bicycles.tech
Subject: Re: Difference between GPS and measured distace.
Date: Mon, 26 Aug 2024 15:32:38 -0700
Lines: 40
Message-ID: <74vpcj5sv8cakvvr4gccd2dauar46mbqbs@4ax.com>
References: <ItvpO.115575$BYv6.6500@fx09.iad> <NDvpO.697397$zXH9.679428@fx01.ams4> <CCwpO.50105$5Mb7.8596@fx47.iad> <v865p1$2gfi$1@dont-email.me> <gBypO.1077484$VBH2.372545@fx16.ams4> <v86p6d$5kqb$1@dont-email.me> <xtHpO.700315$zXH9.686505@fx01.ams4> <P_2zO.143264$WT8.52019@fx45.iad> <3n6zO.385362$Ny_9.78320@fx03.ams4>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
X-Trace: individual.net VjDE5FXYkc31cLJxW0uhzwMbM2VYuId/uRmrkcSH9TXnMZ7DtZ
Cancel-Lock: sha1:izrbky3eU18u/0iKYau1yvdR4bA= sha256:O20d+aEM85AGtOKJOdeLV7pnoWJt6nA6e0TV41o2d7U=
User-Agent: ForteAgent/8.00.32.1272
Bytes: 2959

On Mon, 26 Aug 2024 21:23:11 GMT, Roger Merriman <roger@sarlet.com>
wrote:

>cyclintom <cyclintom@yahoo.com> wrote:
>> I've already said that it is probably a radio interference problem since
>> it only occurs on GPS near the Airport. Once I installed the speed sensot
>> on the wheels it disappeared. Do you suppose that's a "Tom thing"?

It is likely to be a "Tom Thing" when only Tom has the problem.

>Since I ride though almost certainly closer as Heathrow was built close to
>the various then villages and the roads many haven’t changed alignment, let
>alone it’s size and I use the same unit no problem nor does it seem to be a
>reported problem to the best of my knowledge.

Is your cycling computer setup to use the same Satellites as Tom's
computer?  Tom is using a Garmin 830, which offers the option of using
GPS and *EITHER* Galileo or GLONAS satellite constellations.  Each
constellation uses a different frequency range (or band).  The Garmin
830 doesn't have enough horsepower to use more than 2 constellations
at one time.

Meanwhile, you are in the UK where Galileo is the most commonly used
for navigation.  I don't know (or remember) which cycling computer you
have.  If it only does Galileo then interference from a US located GPS
pseudolite (ground based satellite) will act very different compared
to a UK based pseudolite operating on Galileo frequencies.  The
difference in pseudolite frequencies will make the two cycling
computers respond differently to ground based interference.
<https://en.wikipedia.org/wiki/Pseudolite>
The interference could be coming various communications equipment
located at the airport.  These will also likely be somewhat different
in the US and UK.


-- 
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558