GTM21 TMC Problem

RichDem · Posted: Mon Dec 04, 2006 12:38 pm Post subject: GTM21 TMC Problem

Hi,

I have just brought a Nuvi660 with a GTM21 TMC reciever, I used it this morning on a 35 mile journey into leeds to drop a relative off, the led on the charger was green for most of the journey but on the journey home I could net get a traffic signal at all.

Is there a way of improving the signal using this type of reciever, can it be connected to the car's FM ariel to improve things.

I have been a TomTom user for many years and so far love the Nuvi but the traffic is an important option for me,

Regards

Richard
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RichDem · Posted: Tue Dec 05, 2006 4:08 pm Post subject:

A few more thoughts on the above subject, have done a bit more driving around today and found the quality of the tmc signal to be fairly intermittent. I obviously understand remote locations & adverse weather could effect the quality of the signal. I was wondering if it is possible to extend the standard wire ariel or even stipping the end back and connecting it to the ariel lead of the car's hifi to help get better reception.

If anyone has done this any tips would be greatly appreciated.

Richard
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swing · Posted: Tue Dec 05, 2006 4:49 pm Post subject:

There are one or two people who have successfully connected their GTM12 / GTM21 to their car aerial and found improved signal reception. Searching the forums should highlight them - failing that, I'm sure one of them will comment in this thread soon.

JoshT · Posted: Tue Dec 05, 2006 7:15 pm Post subject:

Richdem

I've been trying to get Garmin to acknowledge their is a problem with the GTM 21.

TMC Reception is extremely limited round the NW of the M25, M4 junctions 1 to 11 and M40 Junction 1 to 5 (Haven't checked antwhere else). I can only pick up TMC on the M1 at Milton kenynes and the centre of Reading.

I didn't have as much problem on my old 310D with GTM12 and that was before Garmin modified the cigarette charger to overcome the noise problem.

I'd urge anyone with a reception problem to report it to Garmin - That way with enough problems reported or people taking the units back for a refund Garmin might acknowledge that the GTm 21 has an issue

swing · Posted: Tue Dec 05, 2006 8:23 pm Post subject:

Although you may not have had so many problems with your GTM12/310D - I personally feel even a GTM12 with the correct car charger won't pick up a signal on the NW M25 or the M4 J1 through 11 (I don't drive the M40 to be able to offer an opinion on that road). My personal feeling is that this is not down to a fault in the unit itself, but a limitation of the technology, which Garmin should offer a long term solution to (producing new units with an option for an external aerial connection would seem to offer a good solution to me).

JoshT · Posted: Wed Dec 06, 2006 10:57 am Post subject:

Swing

I used to pick up TMC reports ( Nuvi 310D)on the M4 between these junctions - The signal might not have been over level 7 in all areas but at least I got traffic reports.

On the Nuvi660 + GTM21 I pick up absolutely nothing! I can pick up signals in the centre of Reading (Not much use to me when I'm stuck in traffic between Junctions 10 & 12 on the M4) - but then I guess I'm right next to the transmitter when I'm in the centre of Reading!

I personnally feel the GTM21 is not fit for purpose especially when it does not recieve TMC on large sections of motorway - I wouldn't mind if Garmin accepted their was a problem or offered some sort of alternative solution.

swing · Posted: Wed Dec 06, 2006 4:22 pm Post subject:

JoshT · Posted: Wed Dec 06, 2006 5:10 pm Post subject:

At least you are receiving something on the M4. With the 660 and GTM21 I get nothing Sad

daps · Posted: Wed Dec 06, 2006 6:29 pm Post subject:

I used in parts of the M6 and M42 and got nothing last week-end.
Although it was displaying green on the charger unit.. Is this normal
to have it display Green with no info?
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Harveyc · Posted: Thu Dec 07, 2006 9:55 am Post subject:

I've had my 660 with GTM21 since mid-October and have noticed very few dropouts. My usual commute is Hampshire/Sussex south coast up either M3 or A3 , round the M25 and into London on J13/14/15. The furthest north I've been with it is up to Luton, then back down to Kent and then west to home with traffic reports all the way. The traffic has identified many real jams, successfully rerouted me and already in 2 months has saved me hours.

My experience thus far leads me to agree with swing that the unit performs perfectly subject to the reception of information, itself a function of antenna placement and the substandard UK TMC transmitter infrastructure. I have to drive up to Lancaster tomorrow morning and looking at the UK TMC transmitter map I fully expect the signal to drop out. When it does I'll want to scream at somebody but I can't really see what a Garmin or indeed any TMC unit can do without an adequate signal.

perussell · Frequent Visitor Joined: May 12, 2006 Posts: 292

Yes, got to agree with HarveyC; have been up the M4 J 17-4 on 3 return trips over the last 2 weeks and have had an apparent TMC signal on my 310D continuously albeit it did miss a major jam on the 1st occasion but as stated elsewhere I think this had more to do with a lack of transmitted info than the unit reception. Used in conjunction with my Trafficmaster Freeway it has been very helpful and some of the route planning has been way better than offered by my car's OEM fit satnav which I have now given up on!

JoshT · Posted: Thu Dec 07, 2006 7:25 pm Post subject:

What I'm getting at is the 660 + GTM21 is less sensitive than a 310D + GTM12. So whilst you are receiving TMC information on the M4 between J 17 & 4 with your Nuvi 310D, I'm getting absolutely Nothing Exclamation

I want Garmin to acknowledge the fact and make the GTM21 as sensitive (or better) than the GTM12.

portman · Posted: Thu Dec 07, 2006 8:01 pm Post subject:

Not so long ago people were discussing that the GTM21 with a different serial number to 10R-023487 was better, can't find it now. So is there any difference, do the ferrites make any difference?
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g6ens · Occasional Visitor Joined: Dec 08, 2006 Posts: 2

Well, having just bought a 660 in the US which comes with the GTS20 as well as a 610 in the UK for an xmas present for someone which i am checking out to make sure its ok.....

like everyone i also get poor TMC reception, even worse on the GTS20 (briefly had reception whilst on the M40) which does not have the little wire fly lead than the GTS21 (at times had reception near reading, but nothing on the a30/m3)

however, whilst i agree that signal strength is clearly better outside of the UK (in the US my 660 worked perfectly) i dont think we can just blame the UK.

mostly i bought my 660 for business travel for use in hire cars, but i use them in my main cars for speed camera detection as well. Both my cars have built in satnav with TMC and work 95%+ of the time.

I do also note that i think in the UK there are actually two different TMC providers, one which is broadcast by classic FM which i thought was free and i think the trafficmaster one which has a charge and is on a different channel.

I am additionally complaining to GARMIN that its expensive to get additional leads, the connector on the 610/660 is very week and i suspect it will fail quickly if i plug/unplug between cars when travelling (same problem compaq/hp have with the ipaq) so i really wanted spare cables but not at the price they charge !!!!

g6ens · Occasional Visitor Joined: Dec 08, 2006 Posts: 2

sorry for the double post.... the 610t i got for someones present has the 10R-023487 and does not seem any good either. it has a thin wire fly lead with a couple of suckers to try and help you get good reception.

GARMIN tried to blame my problem on heated/metalised windshields, one of my cars has these (only sirf3 gps work without retransmitter) but my other car is a soft top and has a plane glass windshield.

reption in the later is also pretty patchy !!! maybe i should drive round with the top down and hold the wire with one hand in the air ? shame its a manual gear change !!!

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