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They are electrically connected and thus short the antenna. They are not connected to any antenna connections on the small PCB either.
Interesting Mark. I hadn't checked this (OK, OK - mainly because I'm lazy, but also because I'm a digital man - RF always seemed like black magic to me at college :D).
Clearly you've done what I didn't and checked. When you were looking at it, did you see where the antenna actually is? I presume they've built one into the PCB somehow, although given that a quarter wave is 75cm it seems unlikely, unless once again my understanding of RF theory has failed me yet again!
If there is a 'proper' connection point for an antenna, let's try that as well - we may all get even better reception......
I may be biased as I wrote the original "How To" in the first place, but it is certainly working for me of course. There may be a short between the two pins at DC but from my testing, this definetely not the case at RF frequencies. This is probably not the right forum to go into the details, but there are some valid explanations for this. Feel free to PM me if you want to discuss it further.
It's not that I don't believe you, indeed I have connected a length of wire to one of the points tonight and got a signal for the first time, be it only briefly. The point is is that there must be a better connection point than the ground plane. It's not a question of their being no RF connection between the two points or anything similar, it's just that the points you are using are not RF connection points. They are fixing points for a SMD connector. There must be a better point to use, which may mean that you don't need an amplifier at all. There must already be an antenna on the PCB already, we just need to find it. I suspect one of the wires in the connection cable as TomTom tell you to string this out along the dash or maybe the connection point labeled J3.
Joined: Dec 27, 2006 Posts: 37 Location: Cambs, UK
Posted: Sat Jan 06, 2007 10:45 pm Post subject:
vicky wrote:
Here are 2 Photos of the Unit
Vicky
Thanks Vicky, that should do hopefully.
pepperm - I am all up to discuss this if you want but I think it would be hijacking this thread. The original TMC antenna is built-in to the cable that plugs into the TomTom. They proably use the power connection and decouple the signal from that wire. I suspect that the two pads that I have use are probably for testing purposes (post production) the two larger pads being for the antenna and the smaller pads nearby for the data testing. The board is lowered onto spring loaded test pins and connected to the test rig. I have seen stuff like this before, but I am just speculating on this, I don't know for sure. I believe the two antenna pads are inductively coupled together for impedence matching onto an antenna. This is commpn practice. I haven't tested the connection to other items on the board as I don't have the kit, but a straight DC check from a DMM will prove very little as these pads could also be capacitively coupled onto the main board to allow RF and block DC.
Bottom line, it does work. The pad nearest the 4 connectors is common to the negative of the cigarette adapter and hence the ground plane (if not via DC, certainly via RF). The furtherst pad equates to the actual car antenna.
Perhaps we should start a new thread or PM if you want to discuss this more? :D
It's OK with me to start a new thread especially as this thread is for coverage discussions, but you are mistaken in thinking that this is an antenna connection, I am sure. The pads are definatelly for a SMD connector that for some reason is not fitted to the finished product. I have several and the PCB location is labeled J2 which is a give away. They are not test pads. There are other test pads around the board (round gold pads).
By the way I have found that a single length of wire 27.7 inches (or there abouts) connected to either of the pads works for me. 27.7inches is a quater wavelength at 101.1MHz.
At the radio end of the car antenna lead I have soldered in the Preamp unit I took out of the £9 preamped Antenna and it picks up a +12v feed from a splice into the Car Radio Red Wire
The output from the preamp then feeds to a homemade splitter unit that feeds
a) The Car Radio
b) The Core Pad on the TMC Unit
Since fitting the preamp the signal meter on my car radio reports much stronger and stable reception, before Classic was fluctuating 3 or 4 bars out of 5. now its an almost constant solid 5
So if you are confident enough to do the basic solder mod to the antenna then I would strongly recommend the addition of the Preamp unit for £9 it has made the TMC unit a viable unit...
Cheers
Vicky
Vicky,
Could I ask which wire goes where with this Halfords antenna?
(1) I'm okay with the red wire going to a switched live.
(2) Do I solder the core coax from the TMC unit directly onto the PCB of the Halfords antenna where it's core is connected?
(3) Where do I introduce the input from my car aerial? Do I extend the short black wire that is between the Halfords aerial and its PCB and then tap this into my car aerial coax?
Joined: 06/05/2003 18:01:04 Posts: 83 Location: United Kingdom
Posted: Sun Jan 07, 2007 12:20 am Post subject:
Its definatly something to do with the tuning stage of the reciever, you can see the voltage alter as it scans the frequency. Whether or not its to do with testing, I don't know or care, all I know is it now works bob on and I've not been anywhere in Warwickshire that hasn't given me TMC.
Joined: Dec 27, 2006 Posts: 37 Location: Cambs, UK
Posted: Sun Jan 07, 2007 9:36 am Post subject:
I have found coverage a bit patchy along the M4 between J15 and J5 and there was also a big hole in the coverage on the A45 starting between Wellinghborough and Northampton and in my case ending on the A43 at Silverstone.
I was hoping to never see the orange indicator again, but on reflection this is unrealistic as it will obviously need to tune from one transmitter to another as you drive around. It would be nice of TomTom included a signal strength indicator for the TMC receiver, it would certainly help people find the best position to route the cable on the un-modified units.
Hopefully with the addition of a signal booster, the few remaining blackspots might be eliminated.
Joined: 12/08/2003 19:53:08 Posts: 264 Location: Secret Base in the Nevada Desert
Posted: Sun Jan 07, 2007 10:50 am Post subject:
Quote:
1) I'm okay with the red wire going to a switched live.
(2) Do I solder the core coax from the TMC unit directly onto the PCB of the Halfords antenna where it's core is connected?
(3) Where do I introduce the input from my car aerial? Do I extend the short black wire that is between the Halfords aerial and its PCB and then tap this into my car aerial coax?
Hi
The Way I have done it is to
Solder the Preamp unit taken from the Halfords antenna in line between the Car Aerial and the Signal splitter that sents the signal to the car radio and the TMC unit
So basically I have soldered a standard socket onto the black core and ground braind goin into the Preamp, plugged this into the car aerial at its plug, then plugged the preamp plug into the splitter, and then the car radio and the TMC unit into the splitter to get the signals.
As noted on the TMC unit I have disconected the screen braid as I found I had problems with getting a signal once the charger was connected on my unit if the screeining was connected.
I have not experimented with the reason for this yet, I am begining to wonder if it is because I also have a stereo aux lead running for the TomTom Mount to my Car Radio.
But as all is working I cannot really be bothered to try resoldering the braid unless it gives me problems in the future,.
I will add some photos a little later as I have to pull the unit out of the dash to tidy up
Joined: 12/08/2003 19:53:08 Posts: 264 Location: Secret Base in the Nevada Desert
Posted: Sun Jan 07, 2007 11:14 am Post subject:
OK Here are some photos of my install
First off let me say its a bit heath robinson, so could be improved, its just that I had a bag of Standard Audio Coax Connectors around and no car connectors so I decided to use standard audio DIN connectors for the splitter,
You can off course get standard car cable splitters from places like Halfords or Maplins, but I could not be bothered when I had an abundance of the others sitting around already.
PHOTO 1 - THe General Wiring Spagetti
PHOTOS 2 - My Home Made Splitter and the TMC Unit
PHOTO 3 - THe Disected Preamp PCM in position
PHOTO 4 - 910 Now locks instantly in a non reception area
PHOTO 5 - Improved Signal Reception on Radio
Sorry if the photos are not very clear, just this was an aftertought after all was already sealled and working,
So as I said
Preamp wired beween car aerial and splitter, then powered from radio +12v, TMC Unit and Radio wired to splitter,
Nice and simple job, all and all about 30mins work,
Like everyone else I agree we should not have to do this , and the unit should work out of the box, but the plain fact it does not, and I cannot see it ever doing so.
Posted: Sun Jan 07, 2007 8:36 pm Post subject: Traffic
All, I had TMC for a week covered nearly 900 miles and did not get one signal. Thinking it was faulty I took it back for a refund and signed up for the Tom Tom plus Traffic service instead. It is instant and in most cases spot on. It seems we get what we pay for!
M
Joined: Dec 24, 2006 Posts: 61 Location: J7 M11 (Essex)
Posted: Sun Jan 07, 2007 9:28 pm Post subject:
So I'm another unhappy with the TMC so I thought I might as well give the modification a go.
My car's factory fit aerial is already amplified (it's in the rear screen and workd really well) and Classic FM comes through loud and strong. The first check was since I was splitting the aerial feed whether the radio suffered any signal desgredation. It wasn't, as least not that could notice.
For the TMC, three little taps with my hammer opened the case nicely and I soldered on the centre core of my coax onto the pad furthest from the wires. This pad appears to be labelled C2 as opposed to the one near the wires being labelled J2.
I didn't connect the shield to the J2 pad, as like Vicki, I also have my 910 connected to my head unit for music and instruction playback and I wanted to avoid any possible earthing issues.
Well the result of the mod was no different to before for me. It just wouldn't lock on even though I left it for a few hours. I don't get a lock at home despite the clear radio reception of Classic.
I also found that if I plugged the power into the cradle I instantly got a lot of interferance on the radio.
I've since checked all my cables and they all appear fine i.e. no shorts.
Any ideas?
Whilst buzzing the wires out I also buzzed out the TMC. The results were puzzling :
J4 (red) - Doesn't seem to be wired to the connector
J5 (green) - Doesn't seem to be wired to the connector
J6 (orange) - Appears to be the shield i.e. the outer on the connector
J7 (black) - Appears to be the 3rd part of the pin i.e. furthest in side the plug
Has anyone else buzzed it out? Did you get the same results?
Joined: Jan 14, 2005 Posts: 19638 Location: Blackpool , Lancs
Posted: Sun Jan 07, 2007 9:37 pm Post subject:
It has been suggested before in this thread to at least indicate where in the UK you actually are encountering the problem, turning on your location in your profile might help!
I am not too sure about the aerials fitted into the rear window of a vehicle but I do know they are not the best type of aerial, and quite often require an amplifier just to attain the reception quality of a normal aerial - perhaps this is the issue you are having - Mike
p.s. I didn't subscribe for TomTom Traffic as my mobile is work supplied and they watch the bills!
I've got the same problem Scotty, which is doubly embarassing considering who I work for, mentioning no names
Was going to tap out the wires myself, so you've saved me the hassle. However unlike you, I got a much better result in the house.
One thing I did though was to put the screen and the core the other way around to gizmo's original PDF. Given the other musings that these pads are both grounded it may be just coincidence, but when I had them the original way and plugged the coax into my house distribution amp, I got nothing, whereas with them the opposite way around I get a lock pretty much straight away.....
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and I've not been anywhere in Warwickshire that hasn't given me TMC.
