Poor Radio And Gps Reception - Antenna/aerial Problem?

[aspire_helen]

I am suffering very poor radio reception and poor gps positioning. The gps is only picking up one satellite. The radio is only picking up the very strongest fm local stations. The symptoms would point to a defective antenna feed, that is assuming the radio and gps share the same feed. Ive unscrewed the roof aerial which made no difference either way. Before i start pulling the car appart to trace the coax cables, can anyone point me to anything specific?

[coastline taxis]

Im sure thers a booster type circut board just under the headlinging were the ariel is. clean the contacts on this and retry it

[aspire_helen]

Thanks coastline.

I understand the "aerial base" contains a pre-amp and signal splitter -  probably accounts for its £108 pricetag from Citroen.  Another forum says that water ingress can corrode the circuitry in time, so I have removed the base (see below) but have yet to remove the cover plate as it is retained by 5 very small torx screws (< T10).  It may be that the circuitry can be cleaned .  There are no external contacts.  In the meantime, I connected the aerial direct to the radio coax (circular) feed, ie bypassing the pre-amp, and the signal improved significantly but still nowhere near as good as it should be.  With this jury rig I can now receive most medium strength VHF stations, though certainly not all those I uesd to, and not always with RDS, but still no AM stations.  There is no improvement in the GPS accuracy which continues to find only one satellite.

 

There are 4 leads from the aerial base: 3 coax and one single wire.  The single wire I assume to be power for the pre-amp with return via the body earth (the special nut appears to be designed to provide an earth to the car roof structure).  The 3 coax connectors are colour coded and different styles: one black circular (radio?), green square and grey square.  I assume they feed different high frequency signals for radio, GPS, telephone, Trafficmaster - though it would be nice to know which is which.  My C5 is pre-wired for phone and Trafficmaster but I dont use them and can do without them.  The part no for my specific RPO is 6561P1, but 6561H1 is also listed against other RPOs.  I have seen 2-lead versions on ebay - I wonder if these are for radio only (ie exc GPS, phone, Trafficmaster).

 

Regarding access to the aerial base.  The retaining nut is under the headlining just infront of the rear interior lights.  The nut can be accessed by removal of the light assembly but I found that there was insufficient play in the 4 cables to disconnect them. Hence, I had to pull down the rear edge of the headlining.  Actually, I would recommed starting with that. Once the lining is free from the rear window trim it is easy to work from the boot and remove the light assembly from the inside of the headlining.  It is also much easier to get an open spanner on the base retaining nut (which is not tight) and undo the 4 connectors.

 

Just a note on the Citroen parts diagram.  It is innacurate. It shows the 4 leads connected to a the nut ("radio aerial fixing nut" 6561G3).  However, the 4 leads are permanently connected to the radio base - the nut is a separate item. 

 

As I write, tomorrow I think I will try connecting the aerial direct to each of the other 2 coax connectors and see if the GPS signal improves - hears hoping!

 

If anyone has any further technical knowledge please let me know.  Specifically, would the 2 cable aerial base variant be OK for radio and GPS only? There seems to be more of them around, or any cross referencing to other Citroen, Peugeot, PSA fitments.  The base has the number PSA 9638989980 - theres a 2nd hand one on ebay but still a bit pricey at £50

[coastline taxis]

Its that long ago that i done one but dry joints in the solder keep comming into my mind. im sure it was due to the inside being hot and the outside being cold then car going over bumps.   Sure we just resoldered the joints and it worked a treat. medium wave is a must for me as i love listening to dutch radio 747 mw and i have no problems listening to it in a c5

[aspire_helen]

Update - lucky to get a c5 aerial base from the local scrappy for £5 but only 3 leads, not 4. Opened it up, brushed away corrosion deposits and fitted. Success - perfect radio reception. Missing 3rd coax (grey connector) is clearly for gps. The 3-lead base has no gps antenna. It is also apparent that the gps antenna in my aerial base is not connected to any power or circuitry, nor the aerial wire, just to the coax. Hence, any compatible after market antenna for a few £s should do the job. Does anyone have an idea of compatible characteristics?

[paul.h]

If you just need an aftermarket aerial they do not work as well as Citroen ones and the proper ones are only around £3 from a dealer, so I would not even bother trying an aftermarket one which could well be more expensive. Our latest C3 had an aftermarket one and the radio reception was poor but once the correct one was on the reception was good. On the C3 section there is a current similar topic on the aerial where an aftermarket one is not working.

[aspire_helen]

Thanks Paul, but radio reception is no longer the issue -  its perfect now.  The circuitry of the scrapped aerial base  is nowhere near as corroded as my original.    I still have inadequate GPS reception. The GPS antenna is completely independent of the screw-in bee-sting aerial (wire) - but  is housed on the same base (earthing) plate under the black plastic cover . 

 

I attach a photo comparing the 2 aerial bases with GPS (my original) and without GPS (from scrappy). The 2 green micro circuit boards receive and amplify the FM/AM radio and moble phone signals.  This accounts for the power cable in and 2 of the coax cables out, one radio the other mobile phone/Trafficmaster.  Re Trafficmaster, I understand Citroen was the first car manufactur to fit Trafficmaster as standard.  That may explain why many (all?) are equipped for radio-telephone (RT) (ie aerial and cabling with green coax connector) whether they actually have a phone or not.

 

Note the corrosion at the bottom of the circuit boards - clear sign of water ingress.  The build up of corrosion deposits over time would cause a gradual degredation of radio/mobile/Trafficmaster degredation until failure, especially when the damp.  Considering the vulnerability of the micro circuit boards the waterproofing of the unit is pitiful.  I will be cleaning mine in an ultrasonic bath and then smothering with laquer, followed by sealing the unit with silicon sealant.

 

However, the GPS antenna looks in good shape so the poor GPS reception fault may lie elsewhere.

The GPS (1575.42 MHz) antenna, forward of the circuit boards, is an "embedded patch mounted" type.   It has only a coax, no separate power supply, hence may be passive.  Most modern antennas (remembering MK1s are 1990s technology) are active requiring a power supply.  So, I am enquiring of J2 Antennae whether a modern replacement may be more effective. I will let you know how I get on.

 

 

 

[aspire_helen]

Update - gps reception fixed.   J2 Antennas were very helpful.  The GPS antenna (in the antenna base  on the roof) is "active" having an integrated Low Noise Amplifier (LNA) powered with +5V from the satnav receiver (a Trimble receiver in the satnav unit under the dashboard) via its coax connector .  NB modern satnavs tend to be 3V but antenna often accommodate 3 to 5V.  As I measured +5v on the centre pin of the coax, chances were that the antenna was at fault not the gps receiver nor the cabling between them.  So, I bought an  external antenna advertised on Ebay as an old  but unused  Mercedes part for £2 (lucky  -- it was a old stock and came with the correct connector and 3m of cable).  When I received it, the packaging was  in fact labelled as a J2 product in addition to its Mercedes part no, so I was able to double-check its compatibility against J2's data sheet.     Plugging it directly into the back of the satnav unit  instantly brought up enough satellites to get a fix.  It has a magnetic base for attachment to the roof but my next task is to permanently fit the new  antenna, hopefully by tapping into the existing antenna base.

 

It would appear that many OE satnav antennas are broadly compatible with all others of similar age - just make sure they come with the right connector - there are at least 4 or 5 types in common use.  Indeed, there are 3 completely different types on my C5 alone!!

 

So, both radio and gps fixed for less than £5 - happy me!  The Citroen remedy would have been to replace the faulty antenna base for £108 plus labour, and probably damaged the roof lining in the process.  I wonder what next months fault will be - you've gotta luv C5s!!!!

[aspire_helen]

Final update. I acquired a replacemant gps patch antenna (thats the pink and silver 25mm x 25mm square component on the right) made by 2J Antennae - part no 2j850gps. In order to reuse the existing GT5 connector (not a common type) I had to cut off my existing gps coax, thread it through the antenna baseplate and resolder to the new patch - very fiddly. Radio and gps now back to normal. Nice successful repair project!

 

Recommendation. For those so minded and able - remove your antenna base, unscrew the cover and reseal with silicon sealant before corrosion gets a hold.

[paul.h]

To seal it as a precaution measure, could you get away with just putting some around the base on the roof ?

[aspire_helen]

Paul

Yes but the sealant would need to be forced between the base cover and the plastic cup gasket it sits in, not between the gasket and roof. The gasket is a softer plastic than the cover so i think a fine nozzle could be forced between the two to inject the sealant.

I think the corrosion problem arises from the cup gasket chanelling water to the metal baseplate, so the method above should prevent that.

I suspect another problem with age is that the gasket hardens and compromises the seal between the gasket and roof. That could let water into the roof lining through the cable hole. This can be corrected by tightening the antenna base attachment nut inside the rear edge of the roof lining. Sticking the lining back up is proving difficult!