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TMC signal strength

 
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GPS_fan
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Joined: Jan 04, 2007
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Location: Hampshire, UK

PostPosted: Fri Mar 21, 2008 1:42 pm    Post subject: TMC signal strength Reply with quote

A bit of a numpty question, but in light of all the complaints about TMC reception, is there more to it than meets the eye?

There are places where the main radio signal is strong and can be happily blasting out of the speakers perfectly clearly, whilst the display is showing no RDS reception on the radio.

Is the RDS signal broadcast at the same strength as the main broadcast?

OK, so the RDS is a data signal which might be affected where the main signal isn't.

However, the main broadcast can usually be picked up outside the advertised coverage area for many radio stations (even with a non-amplified hand held radio), so it seems bizarre that the RDS-TMC signal can't even be detected and used by GPS well within the advertised coverage area of any radio station.

If the RDS signal is transmitted at a lower power, couldn't the likes of OfCom be leaned on to increase this signal strength to the same as the main broadcast signal?

Or am I being too much of a numpty and seeing things too simplistically?

I feel sorry for the guys from iTIS who came here with idealistic claims of great things to come, only to find that things weren't quite as rosie in the real world and they've faded away into obscurity.

TMC would be absolutely fantastic if it worked, but I back it up with a TrafficMaster Freeway and traffic bulletins on local radio - but this shouldn't be necessary if TMC worked as claimed.
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Scask
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Joined: Mar 31, 2006
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PostPosted: Fri Mar 28, 2008 2:11 pm    Post subject: Reply with quote

Just Started using the T1 TMC module for my Navman N20 and itís a real up and down journey (forgive the pun) I have been traveling between Brum and Hemel and the coverage down the M1 from M6 junc is very spasmodic. Just read about the issues with athermic windscreens (i have an Audi A4) but today had TMC aerial hanging out of window with unconfirmed benefits. Is there a map of Good/Bad TMC coverage anybody knows of?

Daz Aka Scask
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mikealder
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PostPosted: Fri Mar 28, 2008 2:26 pm    Post subject: Reply with quote

I am not too sure how accurate a map would be for signal reception as there are too many variables to consider:

Weather
Solar activity
Transmitter Power
Transmitter Location
Local Geography
Receiver Sensitivity
Vehicle attenuation
Athermic Glass
Actual location of the aerial

The would be much longer if I really thought about it, but I think you can get the picture, a map wouldn't show coverage taking into account the above.

What you can do is purchase a Mini-Scan Mag Mount aerial from Maplins (See Here), you will also need to make/ purchase an adaptor that connects the BNC on the mini-scan to the MCX aerial input on the T1, this will improve reception greatly and being mag mount it doesn't become a permanent addition to the vehicle - Mike
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Scask
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PostPosted: Fri Mar 28, 2008 3:33 pm    Post subject: Reply with quote

Thanks Mike I have also added this to Sticky: ITIS Traffic Information
Topic in this forum (FYI) The map I was thinking of was something like the GMS phone maps which are useful for letting you know where they won't work, but I understand the comments about the wide variety of factors affecting reception. I guess I am a bit disappointed that these things don't work straight out of the packet in this PnP world!!


Daz Smile
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Scask
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PostPosted: Fri Mar 28, 2008 3:45 pm    Post subject: Reply with quote

Just a thought, The connection to the T1 will be a challenge!!!
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mikealder
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PostPosted: Fri Mar 28, 2008 3:58 pm    Post subject: Reply with quote

There is a map of coverage shown on This page but in my opinion it is overly optimistic.

Having used a T1 receiver I have to say it is about the best of the bunch can that be bought at the moment, the fact it actually has an aerial connector is a rarity that opens the door to using an external aerial. It certainly outperformed any of the other types I have tried.

The connection to the T1 was easy via an adaptor cable I made, MCX plug on one end, 50 ohm BNC socket on the other, I made 5 of these and gave them away to forum users, but I no longer have any left, there is a stockist of the adaptor cables listed on This Thread, the ones I made can be seen on This Page, another often used technique to boost signal reception is to connect the T1 to the car radio aerial via a splitter - some food for thought - Mike
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mikealder
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PostPosted: Mon Mar 31, 2008 4:40 pm    Post subject: Reply with quote

Scask, if you are still after an mcx to BNC socket adapter I have found one in the car, PM or e-mail your name/ address and I will put it in the post - might save you the hastle of trying to make one - Mike
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