Garmins with Built-in Traffic Receiver

jonial · Posted: Sat Aug 30, 2014 9:29 am Post subject:

Even deeper.....

The acknowledged optimum length for a quarter wave FM Broadcast Antenna is between 70 and 86 cm depending on the frequeny of the transmission.

For DAB Radio he optimum length is between 31 and 43cm, again depending on the frequency of the transmission.

Assuming that the device is using DAB Radio I find it hard to believe that an antenna of sufficient length can be built into the unit.

Hence my asking if there any provision for an external antenna on the device
_________________
Jonial

Garmin Nuvi 2547LM
CamerAlert
PGPS Speed Cameras

M8TJT · Posted: Sat Aug 30, 2014 9:45 am Post subject:

One could consider how they build in antennas into transistor radios et. al. for the BBC broadcast at 1500m long wave, where a 1/4 wave aerial would be a bit less than 375m? Very Happy

jonial · Posted: Sat Aug 30, 2014 9:59 am Post subject:

Ah but the antennas within Medium Wave and Long Wave transistor receivers consist of coils wound on a ferrite core - this is not suitable for Very High Freqency use.
_________________
Jonial

Garmin Nuvi 2547LM
CamerAlert
PGPS Speed Cameras

sussamb · Posted: Sat Aug 30, 2014 10:50 am Post subject:

M8TJT · Posted: Sat Aug 30, 2014 11:44 am Post subject:

Ignoring the stuff over GSM or 3G (which?), is the stuff transmitted on DAB at about 200MHz or FM radio at about 100MHz, or both?

sussamb · Posted: Sat Aug 30, 2014 11:53 am Post subject:

Digital traffic is sent over DAB

http://static.garmincdn.com/shared/emea/custom/traffic/_downloads/traffic-faq-EN.pdf

Here is the INRIX/Garmin original news release:

http://www.inrix.com/pressrelease.asp?ID=174

M8TJT · Posted: Sat Aug 30, 2014 12:18 pm Post subject:

@John
RE:ferrite. Didn't think of that, which is quite a surprise as I spent 26 years in the RAF and 15 years with BAE Systems working on both radio, from HF to VHF and radar systems so don't usually make silly errors like that. 0/10 for clear thinking. Embarassed

BigJohnD · Posted: Sat Aug 30, 2014 3:39 pm Post subject:

DAB signals are quite different from FM. They're multi-plexed, summative (i.e. two weak signals can make a stronger one) and where there is only a single local transmitter, prone to shadowing from tall buildings.

DAB receiving aerials generally need to be higher off the ground than FM aerials, and ideally mounted on the roof of a car. Some athermic windscreens can attenuate the DAB signal picked up by internal aerials.

So I guess that Garmin do use what can be considered an over-size power cable for DAB signals to try to combat some of the shortcomings of an internal aerial.

Having said all that, it seems to work well, and is only as good as the info available.

INRIX is a major provider of traffic data, and there's the usual app which can be downloaded from http://www.inrixtraffic.com/ Adding info while driving along should be done by a passenger as it only seems link info to the current location - it can't added retrospectively from another location.

INRIX: http://en.wikipedia.org/wiki/INRIX
INRIX: http://www.inrix.com/whatwedo.asp

"Currently more than 200 customers and industry partners worldwide choose INRIX, including the MapQuest, Microsoft, NAVIGON AG, TeleNav, I-95 Corridor Coalition, Tele Atlas, deCarta, TCS, Telmap, ANWB and ADAC."

jonial · Posted: Sun Aug 31, 2014 8:13 am Post subject:

Perhaps its time to bring this interesting subject to a close.
I do thank all who responded to my query and know that I have learned a lot from the responses.
_________________
Jonial

Garmin Nuvi 2547LM
CamerAlert
PGPS Speed Cameras

	PocketGPS
	Web