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GTM21 traffic issues
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inspiredron
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Joined: Dec 17, 2006
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Location: Ellesmere UK

PostPosted: Sun Mar 09, 2008 1:20 am    Post subject: Re: GTM Traffic Issues Reply with quote

swing wrote:
I agree that the cause of the problem is the lower transmission strength of the UK radio transmitters, but I still hold that this makes it Garmin's problem.


I am not convinced. When I was in France and Spain last year I was getting signal strengths which were comparable with those I get in the UK - ie up to around 35 mainly. Just occasionally I would get 40 or a little over.
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CityArchitect
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PostPosted: Wed Mar 12, 2008 1:15 pm    Post subject: Reply with quote

Before viewing this forum (in fact before I spotted this site!) I went out last Saturday and bought a Garmin 660FM Traffic (includes the GTM 21) from Halfords. It includes a "Lifetime" subscription to the Trafficmaster system.

When I saw all these forum entries about the bad performance of Fm transmitters/GTM 21/or siting of the aerial (whichever this forum has decided is the problem) and, well, I panicked that the traffic feature wasn't going to work.

On my driveway out here in Ware, Herts I got nothing at all. The aerial was inside, horizontal across the windscreen at the bottom, behind the wipers.

Well, today I took it out on the way to Broxbourne station down the A10. Just going past Hertford, the thing burst into life, first giving me hazards in the North of England, and then all the hazards around London. Loads of them. So far so good! I'll let you know how it performs further afield, and in 2 weeks across France.
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Katabatics
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PostPosted: Sun Mar 16, 2008 9:28 pm    Post subject: Re: GTM21 service in the UK Reply with quote

Just terminate the outer coax wire mesh at the GAS end, it does not connect to anything, but keep it away from the cores soldered connection to the exposed end of the GAS. If you tightly coil the GAS at the point where it exits the plastic block close the the Sat Nav unit and tape it up, that will be fine. I did think of wrapping the coiled GAS with some of the outer mesh, which would protect the signal even more, but I have not needed to do this.

Let me know if it works




I'm quite happy to do this, but what do you do with the earth (outer) at the GAS end, do you just leave it floating, as I assume the aerial wire hanging out of the receiver is single core?

Keith.[/quote]
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Katabatics
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PostPosted: Sun Mar 16, 2008 9:40 pm    Post subject: Reply with quote

Yes, that's what Maplins advised, but I did not want to cut the GAS at the end as it invalidates the warranty and could cause problems when selling it. Cutting 1cm of to be able to re-instate the black plasitc cap, would, in my view, return the unit to its original state, unless the wire measurement is that exact.


The latter apporoach is what I have used in my car. The only drawback is that if my 660 isn't connected to the car power then the radio reception degrades a little - leaving me to suspect that the GARMIN radio is dependent upon the "ground" circuit being completed.[/quote]
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Katabatics
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PostPosted: Sun Mar 16, 2008 9:56 pm    Post subject: Reply with quote

Your test results are typical of my original problem and a number of others I have read in this forum. I would expect there is a local radio transmitter at Hertford that you pass close to and it boosts the signal strength (Just like Portsmouth in my area). It's not much use if your journey is in the opposite direction to Hertford. The solution is as the proposed in this forum and it should then work.

If you go on to the TMC web site they will list the radio channels they are outputting traffic data on.


When I saw all these forum entries about the bad performance of Fm transmitters/GTM 21/or siting of the aerial (whichever this forum has decided is the problem) and, well, I panicked that the traffic feature wasn't going to work.

On my driveway out here in Ware, Herts I got nothing at all. The aerial was inside, horizontal across the windscreen at the bottom, behind the wipers.

Well, today I took it out on the way to Broxbourne station down the A10. Just going past Hertford, the thing burst into life, first giving me hazards in the North of England, and then all the hazards around London. Loads of them. So far so good! I'll let you know how it performs further afield, and in 2 weeks across France.[/quote]
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Feek
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Joined: Mar 04, 2008
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Location: Englandshire.

PostPosted: Sun Mar 16, 2008 11:16 pm    Post subject: Reply with quote

Katabatics wrote:
If you go on to the TMC web site they will list the radio channels they are outputting traffic data on.


So if I'm reading it correctly here, it's just Classic FM that carries it?

Map of transmitters here.
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mikealder
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PostPosted: Mon Mar 17, 2008 5:29 am    Post subject: Reply with quote

It is not just Classic FM that is used for broadcasting the iTIS Holdings Traffic service, a number of other radio stations are also used to fill in gaps within the network. Are you sure the Garmin devices have switched over to iTIS yet though?

The map below shows the transmitter locations, red are existing (mostly Classic FM transmitter locations while the green ones are the new smaller radio stations that are being added to the network at the moment.



Mike
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DS_ROBB
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PostPosted: Fri Mar 21, 2008 6:20 pm    Post subject: GTM21 Reply with quote

Hi - I have brought a Nuvi 770 which came with a GTM21 traffic receiver and a lifetime usage of trafficmaster. I have spent ages trying to get any signal at all and nothing.

The LED on the lead flashes yellow but has never one gone green indicating a signal. The Nuvi says 'No Traffic Data' and when you go to the settings, you can try searching for FM signals and nothing.

It does show on the subscriptions page, Trafficmaster Lifetime, however then goes on about needing to have received a GPS and FM signal to have it activated.

Really fed up, only brought it for the traffic element.

I read some threads about connecting it to the car ariel, has anyone done this, has it worked and if so, how do you do it?

Many thanks
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mikealder
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PostPosted: Fri Mar 21, 2008 6:23 pm    Post subject: Reply with quote

A couple of points first, where in the country are you located and what vehicle have you got the device fitted to, do you know if the vehicle has an Athermic windscreen? - Mike
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DS_ROBB
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PostPosted: Fri Mar 21, 2008 7:36 pm    Post subject: Reply with quote

Hi Mike

I'm located in the UK and drive mostly round the M25/London area so would have thought there was reasonable reception. I drive a Mitsubishi Shogun Sport which is just a normal windscreen. I've even tried dangling the ariel lead out of the window whilst stationary to see if I could get any form of signal.

Thanks
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Katabatics
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PostPosted: Sat Mar 22, 2008 8:51 pm    Post subject: Reply with quote

Hi DS_ROBB

This is what I published in Sep 07 to get round the output signal strength limitations of UK radio stations. It works and I get traffic (Green Led on) in my drive (Chichester area West Sussex), in the downs. all the way to Southampton, about 90% on the time on a journey to London, on the M25 and very good coverage in most areas I have driven since then. It's not 100% and sometimes the traffic LED will go yellow and in areas where a signal is normally received, but this seems only to be temporary.

The solution is effectively replace the black Garmin string (GAS) and use screened coax cabling for the GTM21 airel (similar to car ariel cable but a thinner version). I have spliced this into the input run of the car ariel cable, close to the back of the radio, but I think any convenient point will do. This needs a good Stanley knife to separate the car's screening without breaking it so you can get at the core. I wrapped the inner cores together and then bound the inner splice with electrical tape, then with both screens are in contact taped up the whole splice. If you don't fancy cutting into the ariel cable, then you should be able to buy an ariel splitter on the web. The cable and coax plugs is available from Maplins

The important part is to run the new screened cable from the splice or splitter all the way up to where the GAS enters the black plastic block close to the satnav unit plug. This provides screening of the traffic signal as far as possible. Maplin suggested cutting the GAS close to the block, but I have not done this as it makes the GTM21 much less portable. I soldered the end of the inner core of the Coax cable to the exposed end of the GAS and then to closely coiled up the GAS, trimmed of the exposed outer mesh and placed the coil and the joined end of the screened cable close to the block, so as to provide screening almost to the back of the unit, and taped it together at the block. I also taped the two GTM21 cables together just to tidy up. I have inserted a co-ax m/f plug so I can separate the GTM21 from the car. The Volvo has a neat gap around the underside of the steering console that allows a feed back inside to the dash panels back to the ariel, so no need to drill any holes.

It will take at least minute, sometimes longer, to find a signal when you switch the unit on.
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DS_ROBB
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PostPosted: Sat Mar 22, 2008 9:40 pm    Post subject: Thanks Reply with quote

Many thanks for the advice and I will give this a go. You would have though Garmin might of thought of the same so they sold a product that would actually work, however I'd rather have a reliable trafiic signal and something I can use.

Once again, many thanks for the advice.
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DS_ROBB
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PostPosted: Sun Mar 23, 2008 7:00 pm    Post subject: Update Reply with quote

I haven't managed to get round to sorting the aerial out as yet, however I drove in to Oxford today and from around J6 (Chinnor) on the M40 I finally got a traffic signal which lasted all the way in to Oxford and all the way back to around J5 Stokenchurch on the M40 on the way back and then it reverted back to yellow LED occassionally flashing. Definately sounds like the reception problem.
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swing
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PostPosted: Tue Mar 25, 2008 5:46 pm    Post subject: Reply with quote

DS_ROBB wrote:
I'm located in the UK and drive mostly round the M25/London area so would have thought there was reasonable reception.
It sounds like you are using the Western section of the M25 - this is a large TMC blackspot for Trafficmaster, so you won't get a signal there.

You seem to have finally managed to get a signal on the M40, which would imply the unit itself is not faulty, so it's just (unfortunately) the "general" problems with TMC you are seeing.
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PaulB2005
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PostPosted: Wed Mar 26, 2008 12:36 am    Post subject: Reply with quote

Well I wish i understood what most of you are all talking about!!! I don't know my DIN from my ISO, or how to solder a 2.5mm jack....

I've read all 14 pages and i think i understood as much as i didn't. Certainly a lot of knowledge going round, just wish i could make use of it. Hopefully one day those that design and make TMC units will know as much as your lot!

edit: spelling
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