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Tomtom TMC antenna -- horizontal or vertical?
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alanwalne
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Joined: Apr 16, 2006
Posts: 28
Location: Kent

PostPosted: Tue Jan 22, 2008 11:05 pm    Post subject: Reply with quote

lazysod wrote:
I posted this problem before about the charger interfering with the Signal strength and tomtom have sent me 3 units to try,it,s absolutely brilliant when running on battery but almost as useless as the old one when charging in a low signal strength area. I gave the device to the instrument tech's at work and they performed a few tests, I'm not sure what they plugged it into (oscilloscope or something like it with wave forms on) and they said when connected to the charger sensitivity of the receiver dropped by some 40%. When I travel up the M1 it doesn't seem to make much difference but where I live in SE Kent we have a weak signal so it's rubbish.


Not working in Kent? - The only place mine(V.013) works reliably is between Sittingbourne and Basildon. Going upto Birmingham up M1 & M6 I get no more than 10 mins coverage after M25 J28.
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jparton
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Joined: May 12, 2007
Posts: 20

PostPosted: Wed Jan 23, 2008 1:41 pm    Post subject: Reply with quote

I've been reading this forum with interest.

I have no technical knowledge compared to many (on this thread in particular) but I'll share my view for what it's worth!

My main route to work (3+ times a week) is A1 Southbound from Sandy area to M25, then round to J16, M40, J2, drop into Slough - all major routes.

I've been using the TMC with my TT 920 since the first week of Jan.

In all that time I've had a green disc for about 5 minutes in total with one "incident" shown on the right hand bar.

I travelled through the Aspley guise / Woburn Sands area yesterday (where I believe there is a transmitter according to the POI file) and I had an instant and solid lock with an incident displayed on my route.

It went back to the familiar perminatly spinning circle about 5 miles outside of the area for the rest of my journey.

I've seen the debates about windscreens, aerial positioning, etc (i have a BMW 3 Series Coupe) - surely if I don't change the car or position of the antennae between getting a solid lock and nothing at all, it makes the positioning of the area / screen coatings a bit of red herring?

Isn't it simply proving it's down to signal strength?

I'm preparing to be shot down in well thought through flames!! Wink
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pcaouolte
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Joined: Dec 27, 2006
Posts: 998
Location: South Lincs, UK.

PostPosted: Wed Jan 23, 2008 1:56 pm    Post subject: Reply with quote

jparton wrote:
I've seen the debates about windscreens, aerial positioning, etc (i have a BMW 3 Series Coupe) - surely if I don't change the car or position of the antennae between getting a solid lock and nothing at all, it makes the positioning of the area / screen coatings a bit of red herring?

Isn't it simply proving it's down to signal strength?

It is down to signal strength, you currently appear to be able to receive the signal when it is very strong (when you are near the transmitter). All the fiddling with the aerial and the debates about windscreens etc is designed to give the receiver a better chance of receiving a weak signal.
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jparton
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Joined: May 12, 2007
Posts: 20

PostPosted: Wed Jan 23, 2008 5:28 pm    Post subject: Reply with quote

pcaouolte wrote:
jparton wrote:
I've seen the debates about windscreens, aerial positioning, etc (i have a BMW 3 Series Coupe) - surely if I don't change the car or position of the antennae between getting a solid lock and nothing at all, it makes the positioning of the area / screen coatings a bit of red herring?

Isn't it simply proving it's down to signal strength?

It is down to signal strength, you currently appear to be able to receive the signal when it is very strong (when you are near the transmitter). All the fiddling with the aerial and the debates about windscreens etc is designed to give the receiver a better chance of receiving a weak signal.


Yeah, I admire all the efforts people are going to, but isn't it all in vain for a really frustrating customer experience, and inaccurate data when it does actually work!
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othilla
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Joined: Jan 13, 2006
Posts: 57
Location: Kent

PostPosted: Wed Jan 23, 2008 9:29 pm    Post subject: Reply with quote

alanwalne wrote:
lazysod wrote:
I posted this problem before about the charger interfering with the Signal strength and tomtom have sent me 3 units to try,it,s absolutely brilliant when running on battery but almost as useless as the old one when charging in a low signal strength area. I gave the device to the instrument tech's at work and they performed a few tests, I'm not sure what they plugged it into (oscilloscope or something like it with wave forms on) and they said when connected to the charger sensitivity of the receiver dropped by some 40%. When I travel up the M1 it doesn't seem to make much difference but where I live in SE Kent we have a weak signal so it's rubbish.


Not working in Kent? - The only place mine(V.013) works reliably is between Sittingbourne and Basildon. Going upto Birmingham up M1 & M6 I get no more than 10 mins coverage after M25 J28.


Now I am using the Carcomm mount with TMC extension lead I am getting signals about 90% of the time now when charging.This has been the best bit of kit after the OneXL.
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quentinh
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Joined: Oct 15, 2007
Posts: 1

PostPosted: Wed Jan 23, 2008 11:05 pm    Post subject: FM polarisation Reply with quote

I know this is pedantic but all FM transmitters in the UK are either circular/mixed polarsation, or (very rarely) vertical only. 30 years ago, the BBC used horizontal polarisation but this was changed in the 80's to mixed (for example, Wrotham in Kent, Holme Moss, Wenvoe, etc. used to have 125KW radiated power only in the horizontal plane per FM service, but now each is 250KW mixed: 125kW horizontal and 125KW vertical. Mixed and vertical polarisation was introduced particularly to serve the motorist.
Classic FM shares the same antennae as BBC national networks at most of the main sites, and at the same power. There are some exceptions (e.g. Belmont in Lincolnshire, Blaen y Plyf near Aberystwyth) and a few smaller sites using a type of antenna which puts 75% of the power into the vertical plane and 25% horizontal. This type of antenna is also used by a number of local commercial stations too. In practice it makes lttle difference and performs much the same as equal power mixed polarisation.
In reality, by the time any FM signal has skipped across the rooftops and bounced off car bodies, it will be a jumble of polarisations with little semblence to the carefuly aligned polarisation that left the transmitter.

The biggest influence on reception in cars is the metalwork of the car itself and vehicle-induced interference. Windscreen mounted antennae are notoriously fickle and there is little rhyme, reason or logic as to what arrangement will deliver the best reception. I know this is of no comfort but trial and error of different TMC antenna layouts is really the only solution. This forum could help by assembling a database of users' experience of working TMC antenna layouts for each type of car (with photos).

Receiving TMC requires a pretty good FM signal - probably much stronger than would be necessary for acceptable audio in a car. TMC data is carried as part of the RDS digital carrier which sits on the edge of the FM carrier. A reasonable rule of thumb would be that if you get hiss-free stereo then you should be able to decode RDS (and TMC). If you tune a car radio manually but the RDS name won't display then the FM RDS signal is too weak and there's no hope of getting TMC data either, even less so on a loose-wire windscreen antenna.

Having just bought a TomTom720T, I too have found that interference is caused to ALL my FM reception from the TT cigar socket power supply - it is a stunningly obvious design shortcoming which kills my car radio on FM as well as undoubtedly affecting TMC reception. I will experiment with ferrite coils and report any success, otherwise Halfords can have it back (prepare for battle....)

Anorak now removed.
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carl_w
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Joined: Mar 13, 2004
Posts: 242

PostPosted: Thu Jan 24, 2008 9:01 am    Post subject: Reply with quote

lazysod wrote:
I posted this problem before about the charger interfering with the Signal strength and tomtom have sent me 3 units to try,it,s absolutely brilliant when running on battery but almost as useless as the old one when charging in a low signal strength area.
I tried some experiments in my house yesterday and I have exactly the same problem. With the aerial stickered to the patio doors, I get lock straight away. Plug in the charger (USB from PC) and within 1 minute it's back to th yellow 'searching' icon. Unplug the charger, and it locks on again. I tried it a number of times to make sure it wasn't just an anomaly.

What's to do? Should I get Tomtom to ship me another ONE XL? I see that you've had some success with the Carcomm mount -- I was also thinking of getting that but of course it means the charger will be plugged in all the time, so poor TMC reception.

Might I ask where you bought the Carcomm mount? Buybits.com are out of stock, and TotalPDA never replied to my query about whether the ones they were selling were the ones with the TMC connector (picture showed one without).
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Greenglide
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Joined: Apr 04, 2006
Posts: 295
Location: South East Northumberland, UK

PostPosted: Thu Jan 24, 2008 11:58 am    Post subject: Reply with quote

Quote:
I've seen the debates about windscreens, aerial positioning, etc (i have a BMW 3 Series Coupe) - surely if I don't change the car or position of the antennae between getting a solid lock and nothing at all, it makes the positioning of the area / screen coatings a bit of red herring?


The BMW 3 series is on the list of vehicles which have been fitted with athermic windscreens at some point ( http://www.tssltd.co.uk/traffic-faq_gps.html ).

From my experience with my Zafira the impact of having one of these is by no means obvious - having the vehicle stationary(!) seems to help - distance from the transmitter seems not to be a real issue - heading South on the A1 from Northumberland through Durham (where the Pontop Pike transmitter is located) doesnt help.

The only satisfactory solution (for me at least) is to use the external aerial - it does work.

The quality of TMC data and the TT unit's processing of it is a separate issue!
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DaveMatthews
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Joined: Dec 25, 2004
Posts: 221

PostPosted: Thu Jan 24, 2008 4:43 pm    Post subject: Re: FM polarisation Reply with quote

Quentinh - a very useful study - thanks. There's one point I'd take issue with, however...

quentinh wrote:
A reasonable rule of thumb would be that if you get hiss-free stereo then you should be able to decode RDS (and TMC).


Not in my experience - at least not at the moment. I think atmospheric conditions have a huge an impact on signal reception...

I rely on the Morecambe Bay transmitter (which is sited near Barrow-in-Furness), as I live in north Lancs. With one rather weird exception - which I'll detail below - despite using the car radio's own antenna (via a "Y-splitter") and getting crystal clear (ie no hiss) audio reception of Classc along with the accompanying RDS data dutifully posted to the radio's display, I simply cannot get a TMC signal anywhere in the Preston / Blackpool / Lancaster / Kendal / Grange-Over-Sands area. You'd think I should get something in Grange given that it's just a few miles from the transmitter!

... At the moment the only place in this area I consistently pick up TMC is the small town of Carnforth. Upon coming within half a mile of the town - from any direction - the TMC signal strength suddenly jumps from zero to 40 percent - it doesn't even "creep up".

There's a very narrow sidestreet in Carnforth (just off Stanley Street for anyone here who's familiar with the town) that is tightly covered on both sides by tall buildings... yet this is where I get the best signal strength - 60% !! Perhaps the buildings somehow prevent any negative effects of atmospherics?

As soon as I leave the town - or even if I drive past it on the M6 - I get absolutely no TMC signal. It's all very weird!

I suspect the general "black out" of north Lancs may be down to the poor weather we've had since December because in the past I've been able to pick up a reasonably consistent signal between Kendal and Preston. Not sure how this explains the current "Carnforth Phenomenon", though!

--

Cheers,


Dave
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othilla
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Joined: Jan 13, 2006
Posts: 57
Location: Kent

PostPosted: Thu Jan 24, 2008 5:15 pm    Post subject: Reply with quote

carl_w wrote:
lazysod wrote:
I posted this problem before about the charger interfering with the Signal strength and tomtom have sent me 3 units to try,it,s absolutely brilliant when running on battery but almost as useless as the old one when charging in a low signal strength area.
I tried some experiments in my house yesterday and I have exactly the same problem. With the aerial stickered to the patio doors, I get lock straight away. Plug in the charger (USB from PC) and within 1 minute it's back to th yellow 'searching' icon. Unplug the charger, and it locks on again. I tried it a number of times to make sure it wasn't just an anomaly.

What's to do? Should I get Tomtom to ship me another ONE XL? I see that you've had some success with the Carcomm mount -- I was also thinking of getting that but of course it means the charger will be plugged in all the time, so poor TMC reception.

Might I ask where you bought the Carcomm mount? Buybits.com are out of stock, and TotalPDA never replied to my query about whether the ones they were selling were the ones with the TMC connector (picture showed one without).


If you notice when the charger is plugged in it jumps quite a bit in the frequency search (ie from 88.9 to 102.5 and so on),when not charging it takes very small steps this is the sensitivity being altered by the charger.When attatched to the carcomm mount (even though it is charging) the steps are the same as when no charger is plugged in at all.It's not worth getting tomtom to send another OneXL,I have tried 3 and they are all the same.I bought my Carcomm from PDAplus.nl
http://www.pdaplus.nl/catalog/carcomm-cnm69-holder-p-2630.html

It was 66 including postage

I know it's a lot of money to risk but it got my one working?
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PicklesDad
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Joined: Jan 06, 2008
Posts: 35

PostPosted: Thu Jan 24, 2008 9:21 pm    Post subject: Reply with quote

I'm now getting a consistent green dot on my journey between Bury St. Edmunds and Ipswich on the A14, so the Aerial splitter has been a success. I've yet to have any problems on the route though, so can't comment on the quality of the information. For those having problems with the power, I'll try connecting mine up on my next trip and let you know, I usually use batteries and charge each night.
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carl_w
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Joined: Mar 13, 2004
Posts: 242

PostPosted: Thu Jan 24, 2008 9:56 pm    Post subject: Reply with quote

Hmm, the common thing with both of these solutions (splitter and Carcomm extender) is moving the receiver farther from the charging part. Maybe it's really leaky and could be solved by some ferrite toroids?
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mikealder
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Joined: Jan 14, 2005
Posts: 19638
Location: Blackpool , Lancs

PostPosted: Thu Jan 24, 2008 10:06 pm    Post subject: Reply with quote

I did try looping the aerial wire of one of the earlier RDS-TMC devices through a large ferrite and it improved the reception considerably, since the introduction of the -013 receiver I have not found this necessary although reception is better on some TomTom devices than others, by far the best is the TomTom One Third Edition for some strange reason perhaps the screen size and coresponding backlight inverter is causing EMI on the devices with larger screens? - Mike
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Scotty-uk
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Joined: Dec 24, 2006
Posts: 61
Location: J7 M11 (Essex)

PostPosted: Sat Jan 26, 2008 2:00 pm    Post subject: Reply with quote

I've had enough.

I had the very first verison of the aerial and after modding it, recently got a new version from TT. Yes it's better i.e. i get about 70% station lock and about 10% data compared with virtually 0% before.

I'm not having a device hanging in my windscreen looking like a washing line and distracting from my view to get a lock. I've tried all the positions I can and some are slightly better but not workable on a daily basis i.e. down the middle of the screen.

I'm asked TT to credit the full purchase amount against Traffic.
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othilla
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Joined: Jan 13, 2006
Posts: 57
Location: Kent

PostPosted: Sat Jan 26, 2008 2:11 pm    Post subject: Reply with quote

Well I have just finished off the install with the Carcomm unit.I wanted to tidy up the Aerial so I ran the extension through the back of the dash to the offside corner of the windscreen where it is connected to the aerial,then I ran the areial up behind the A pillar cover then up under the roof lining so it is completely out of sight.I drove out to all the bad spots where I never got a signal before and it picks a signal up 95% of the time,so you don't have to have an ugly wire dangling about.I think the answer has got to be getting the oval part away from the charging connection,didn't the old one have this on the end?
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