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Aerial recommendation for TMC

 
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ijhill
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Joined: 13/03/2003 14:39:30
Posts: 31
Location: United Kingdom

PostPosted: Mon Mar 10, 2008 12:32 pm    Post subject: Aerial recommendation for TMC Reply with quote

Hi,

I've got a Garmin 510T with the GTM21 TMC adapter.

The unit suffers from the typical poor reception although I had spliced the aerial into my car's fm aerial (rear windscreen aerial) on a trip up the M6 yesterday I got no traffic reception from Stafford all the way to Chester, when I got off the motorway and headed to Beeston Castle and finally got a signal at the top of some hills.

My unit seems to hunt the bands quite a lot until it find a signal with a level in excess of 35, typically on channel 96 in the Wolverhampton area (I presume this is Beacon radio who transmit the Trafficmaster stream)

I have looked at an external magnetic mount aerial and have found one that is good for 25-1300 Mhz (http://www.rocketradio.co.uk/discrete-miniature-car-scanner-antenna-96-p.asp). As this covers the FM band as well should I expect good traffic reception with on of these, I do not want to drill the car roof. The other suggestion seem to concentrate on Classic FM at 100.1 and aerials that are tailored to this frequency.
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mikealder
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Joined: Jan 14, 2005
Posts: 19638
Location: Blackpool , Lancs

PostPosted: Mon Mar 10, 2008 1:29 pm    Post subject: Reply with quote

Take a look at Maplins for the mini-scan or better still the sky-scan, they are both mag mounts and work very well, while you are at the shop get a 50 ohm BNC socket to solder to the end of your RDS-TMC aerial - the mini-scan works down to 100MHz, the sky-scan goes down to 25MHz so is more suitable but does look rather strange (I have both fitted to the Ovlov, and having compared them the sky-scan is slightly better) - Mike
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ijhill
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Joined: 13/03/2003 14:39:30
Posts: 31
Location: United Kingdom

PostPosted: Mon Mar 10, 2008 2:09 pm    Post subject: Thanks Reply with quote

I just had a look at the sky-scan in Birmingham, seems a little too much for me though, although I am fitting it to a large SUV.

I'm going to go for the discrete mini whip I linked to as it covers the same frequency as the sky-scan, I will let you know how it improves reception.

How much did your reception improve with the external aerial.
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mikealder
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Joined: Jan 14, 2005
Posts: 19638
Location: Blackpool , Lancs

PostPosted: Mon Mar 10, 2008 5:53 pm    Post subject: Reply with quote

I live in an area of poor radio signal strength for both iTIS and Traffic Master (who Garmin use) so its an ideal area for testing aerials, since a more local transmitter was re-enabled TM reception is somewhat easier these days.
The mini-scan does offer quite a decent improvement over the Garmin "string" the sky-scan is better though.
I can fully understand your reservations over the sky-scan though, it does look a liitle strange!! - Mike
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GPSinC3
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Joined: Dec 16, 2003
Posts: 135
Location: Nottingham

PostPosted: Wed May 21, 2008 7:42 pm    Post subject: Aerial TMC connector Reply with quote

I have just ordered a Garmin 760T, presently using a Navman 750 with T1 traffic addon, with that added an external aerial, ...Rocket radio, little mag one, works quite well, .............can anyone advise what the TMC aerial connection is on the Garmin so iIcan look at adaptors, at the moment I'm BNC socket to a MMCX for navman, or do I cannabilise the supplied aerial plug and connect to my BNC, unless of course things work without an extrenal aerial but I don't believe they will
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PaulB2005
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Joined: Jan 04, 2006
Posts: 9323
Location: Durham, UK

PostPosted: Thu May 22, 2008 10:41 am    Post subject: Reply with quote

The aerial on the 760T is part of the power lead and isn't detatchable. I've stripped a section off th end of the shoestring and soldered a BNC plug on the end. This connects to the BNC on my FM MagAntenna. Works ok. Not been used "in anger" yet....
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GPSinC3
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Joined: Dec 16, 2003
Posts: 135
Location: Nottingham

PostPosted: Fri May 23, 2008 3:08 pm    Post subject: Reply with quote

Got my Garmin and see what you mean....the aerial combined with power cable but..................surprise the attached wire seems to work, much better than Navman one, its now tucked quietly away up the side of the windscreen behind the rubber and it seems to work, takes about five minutes to get signal, so far, tried at home, Nottingham and elsewhere in East Midlands.

Coming back from Corby today, had signal had traffic alerts which existed and Garmnin reroutes so quite pleased.

Missing somethings about the Navman but Garmin seems Ok just different. I will sell of my Rocket radio aerial along with the 750
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ijhill
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Joined: 13/03/2003 14:39:30
Posts: 31
Location: United Kingdom

PostPosted: Fri May 23, 2008 4:48 pm    Post subject: keep the aerial Reply with quote

I would suggest that you keep the aerial as you may find you need it if you travel further afield, coverage with the supplied aerial is not ideal in fringe areas, especially if you travel up the north-west.

You can connect the end of the string aerial to the rocket one with an a adapter seach on the forum for the part if required.
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MCSE
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Joined: May 21, 2009
Posts: 2

PostPosted: Thu May 21, 2009 2:23 pm    Post subject: GTM21 and GTM12 mods to work with FM car antenna Reply with quote

I also posted this on GPSPASSION.com http://www.gpspassion.com/forumsen/pop_printer_friendly.asp?TOPIC_ID=61537 on a thread that's not been active lately. I repost it here as you may find it useful.

UPDATE - this excellent post http://www.pocketgpsworld.com/modules.php?name=Forums&file=viewtopic&t=75842 by mikealder shows in photographic detail how to achieve what I describe below... plus a warning about 12v antenna boosters. Recommended!

I chose the Nuvi 300T as my first foray into SatNav back in Dec 07. I was intensely frustrated with the extremely intermittent coverage I got with the GTM12. So much so that I complained to Garmin who firstly sent me this guide [which really didn't help at all but I include some of it for completeness].

"Dear

If you are experiencing problems with your GTM traffic receiver not receiving any traffic updates, then please find below a few things that you can try:

We have found when using the GTMs ourselves that where you mount the GTM traffic receiver can have a big effect on the reception of the traffic service
A few things to be aware of are 1) keep the GTM antenna away from any metal panels as these will work as a barrier and block the FM signals.
2) Some vehicles are fitted with UV reflective and heated front windscreens, again these will block the FM signals so you will not get traffic updates. If you have any of these screens then the best log term fix is the GTM10 which is wired into the radio antenna in your car.
3) You can also make sure that you unit is running with the latest unit software, and also the latest GTM traffic receiver firmware. The easiest way to keep your unit up to date is to download and install the Garmin WebUpdater. Once you have downloaded this connect your GPS unit and follow the onscreen prompts.

download and install the GTM update; you will get a screen to say that it has been successfully installed.

Once you have installed the update you then need to go out and use the device. Please keep in mind it will take a few minutes to gather the traffic information particularly as Traffic master update every 3 minutes. In weaker FM signal areas you may not be able to receive traffic information so please make sure you have used the device on a good route."

There was also a screenshot and URL related to WebUpdater but you guys know plenty enough about THAT already.

So I tried all that and it helped almost not at all. They sent me a new one via an RMA.... it was little different but also had a new fault! I changed the Garmin power adapter for a Pure Digital one I have for my Highway device. I tried Ferrite suppression on the charger cable and even round the short mini-USB cable from the Nuvi to the device. NONE OF THIS HELPED!

Anyway I bought myself a new Nuvi 860 on boxing day. It comes with a GTM21, which looked more impressive and indeed picked up a bit more often than the GTM12 did. For comparison:
Journey from Bracknell to East London - GTM12 got nothing while I was stuck for 45 minutes in a jam on the M4, only got a signal near Wycombe and again near Enfield, otherwise it was effectively dead - useful time getting traffic reports - 5-10% [I am aware that atmospherics have a small effect here so this isn't entirely scientific]
Journeys from East London to Hemel Hempstead and back - GTM21 would be "scanning" for 25-40 minutes at a time - useful time getting traffic reports - 25% or so.

So having read ijhill's post on what happened when he took off the end of the antenna lead and connected it to a real FM aerial, I decided to do the same. Except that I didn't want to permanently damage the GTM21 in case of warranty issues! I noted that on the rubber end cap there is a small pop-out cover, which I removed and pulled out a short section of the antenna, and stripped back a millimetre of insulation on one side only, very close to the end of the lead [so this can be retracted back inside the cover again and hidden should I ever need to]. I took some TV antenna cable and removed the outer housing, then separated the braided shielding and slid it over the length of the GTM21 "string" antenna - to prevent it adding stray signals to my FM reception. I then taped over that with insulating tape.

I then soldered a short length of wire to an F-series plug from the bared insulation of the string antenna, and connected the braided shield to the housing of the F-plug. I similarly attached a short length of insulated co-ax to the antenna cable attachment at the back of my car radio, and terminated this with an F-series socket.

I then mated the F-plug and F-Socket so that my car antenna was now supplying the FM feed into the Garmin string antenna on the GTM21. Surprise, surprise - now it only drops out for "scanning" for short moments - longest I have seen it off-the-air was 15 minutes on a journey to and from Bristol. The rest of the time it works very well!!

Now I know this forum is not about the 860 but the good news is - this process can be reproduced for users of the GTM12 as well. And another good thing... the antenna doesnt have to be mounted on the windscreen - I now have it discreetly tucked away out of sight.

Cost to resolve - pennies and a couple of hours.
One small drawback... the FM signal quality isn't quite as good on some radio stations. I put this down to the less than professional quality of my connections. However as I mostly listen on DAB these days that doesn't bother me so much as getting good traffic updates.
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