BruceM Posted February 16, 2018 Share Posted February 16, 2018 I need some electrical diagnostic help. The issue My FM van radio used to work just fine. Now, it has good reception whilst the ignition is turned off, but turning the ignition on it looses reception on the weaker stations and instead introduces the fuzzy sound of interference. The reception of strong stations is also degraded. The aerial is a through window type. Diagnostics To minimise variables I’ve ensured that all cab devices are turned off or disconnected. My initial thought is that something has become disconnected but I’m at a loss at the moment to know where to start looking. I've verified the aeriel connection to the radio and it's good. An internet search turned up another motorhome forum with someone having an identical issue on their van – but no solution was posted. Looking at the cables coming out of the aerial I think that it may be 12v powered so I’m wondering if something might be going on there. I’ve yet to disassemble the dashboard to get at the cabling to check it – I’d rather rule out other causes before going to that effort. All advice gratefully received. Link to comment Share on other sites More sharing options...
Keithl Posted February 16, 2018 Share Posted February 16, 2018 I will agree that it is most likely 12 V powered so test the connection at the aerial for 12 V with the radio on. Failing that pull the radio and identify the aerial feed and see if it is still working. Keith. Link to comment Share on other sites More sharing options...
BruceM Posted February 16, 2018 Author Share Posted February 16, 2018 Although I posted that everything in the cab was turned off, I discovered through some experimental disconnections that the interference appears to be connected in some way to the van’s Snooper satnav charger unit – which remains powered up when the ignition is on and the satnav is turned off. So, with ignition on, connect the satnav charger unit to the satnav and interference appears, disconnect the charger unit from the satnav and the interference disappears. Any thoughts on what to infer from this.? Does it imply that the charger unit has developed a fault? Alternatively, might the battery circuitry in the Snooper satnav be the cause of the interference and consequently have developed a fault? Incidentally, the through glass aerial does not appear to be 12v powered – it just has two wires that go to the aerial input of the radio and an earth strap that I’ve checked is earthed. Also, removing the aeriel feed from the back of the radio looses all channels so I guess it's working correctly. Link to comment Share on other sites More sharing options...
747 Posted February 16, 2018 Share Posted February 16, 2018 The same thing sometimes happens when you have a dash cam. You need a suppressor on the 12 power cord. There is a new name for suppressors these days and I cannot remember what it is called but somebody will. Link to comment Share on other sites More sharing options...
Keithl Posted February 16, 2018 Share Posted February 16, 2018 747 - 2018-02-16 5:28 PM The same thing sometimes happens when you have a dash cam. You need a suppressor on the 12 power cord. There is a new name for suppressors these days and I cannot remember what it is called but somebody will. I think you mean a 'Ferrite Core'. Something like this... http://www.ebay.co.uk/bhp/ferrite-core Keith. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted February 16, 2018 Share Posted February 16, 2018 Try connecting the sat-nav to its charger (presumably it is plugged into a dashboard 12V socket) and then move the sat-nav so that the cable connecting it to the charger is as far from the radio as possible. My last motorhome had the charger-to-sat-nav cable crossing the dashboard above the radio and, when the sat-nav was being powered from the charger, the radio reception was zero. Link to comment Share on other sites More sharing options...
747 Posted February 16, 2018 Share Posted February 16, 2018 Keithl - 2018-02-16 6:40 PM 747 - 2018-02-16 5:28 PM The same thing sometimes happens when you have a dash cam. You need a suppressor on the 12 power cord. There is a new name for suppressors these days and I cannot remember what it is called but somebody will. I think you mean a 'Ferrite Core'. Something like this... http://www.ebay.co.uk/bhp/ferrite-core Keith. That's the fella. :D Link to comment Share on other sites More sharing options...
BruceM Posted February 16, 2018 Author Share Posted February 16, 2018 Thanks for the suggestions. The satnav is hard wired in but I’ll look to see if I can relocate the cabling to see if it makes a difference. What concerns me is that this was not originally an issue. So logically, if the satnav is the prime source of the interference (which seems to be the case) then something has changed which I assume implies something failing within the satnav or its charger? The satnav is probably about ten years old. Might the satnav charger electronics be failing? Is it time to change the satnav? Link to comment Share on other sites More sharing options...
Derek Uzzell Posted February 17, 2018 Share Posted February 17, 2018 The first thing to do is to correctly diagnose the cause of the interference. If the culprit is the sat-nav charger itself, or the charger ’s cable, then the cure would be to replace the charger/cable. If it’s the sat-nav that’s the culprit when the sat-nav is receiving charge, then the cure would be to replace the sat-nav. (Presumably the sat-nav running off its internal battery (rather than being charged) does not affect the radio?) I have two Garmin sat-navs, one about 10 years old and the other about 2 years old. The former is less able to acquire satellite signals and less able to hold on to those signals; it also lacks many of the younger sat-nav’s useful features and updating its mapping would not be financially sensible. It performs no worse now than it ever did - it’s just outdated tech and it shows. If you are happy with your elderly Snooper’s performance and can stop the interference without HAVING to replace the sat-nav, it’s up to you whether you opt for a replacement. Even though my older Garmin sat-nav still works, I would not choose to use it nowadays. Link to comment Share on other sites More sharing options...
BruceM Posted February 17, 2018 Author Share Posted February 17, 2018 Thanks all. I’ve ordered a 20 amp noise suppressor in an attempt to clean up the radio supply line. Once that’s fitted I’ll have an idea of where I stand. I’ll post the result here. Although the Snooper sat nav works well and when not on charge does not cause interference, the combination of its out-dated maps and it’s resistive screen technology was leading me in the direction of replacing it with an Xgody satnav. Something I’ll look at once the suppressor is fitted. Link to comment Share on other sites More sharing options...
Alanb Posted February 17, 2018 Share Posted February 17, 2018 Unless your radio is an anti-social ghetto blaster, I would have thought that a 20A suppressor was seriously overrated and possibly over sold. The radio fuses in my PVC are 7.5A. Filtering the radio supply may not be effective against radiated interference. The filter will need to be inserted into the supply cable close to the radio. I would have thought that suppression at source, by fitting the previously suggested ferrite core close to the satnav charger output would be a simpler and less expensive solution. If possible a second ferrite core close to the charger input may help.. Alan Link to comment Share on other sites More sharing options...
tonyg3nwl Posted February 17, 2018 Share Posted February 17, 2018 2 suggestions 1 turn the satnav off when parked up listening to radio. 2 turn radio off when driving being guided by satnav one or both will cure problem at minimum cost. The old satnav charger seem to me to be what is referred to as a switch mode controller, ie it is turning on and off at high speed causing electric pulses on the 12 volt supply. Modern plugin usb chargers are unlikely to cause interference, so throw the old charger away and buy a replacement. if that doesnt fix it, then replacee the old snooper device.. my old snooper ventura never caused a problem, but it is now confined to the cupboard, and modern garmin devices takes over the job. tonyg3nwl Link to comment Share on other sites More sharing options...
BruceM Posted February 17, 2018 Author Share Posted February 17, 2018 The car radio (a JVC) has a 15 amp fuse hence the selection of the 20 amp suppressor. The suppressor is just over £6 delivered and I’ll be fitting it just where the positive feed enters the radio. I think I’ve got some spare ferrite cores which I’ll dig out of a box somewhere to experiment with – they may be a little large for the cable size but worth a try regardless. Link to comment Share on other sites More sharing options...
BruceM Posted February 17, 2018 Author Share Posted February 17, 2018 2 suggestions 1 turn the satnav off when parked up listening to radio. 2 turn radio off when driving being guided by satnav one or both will cure problem at minimum cost. An eminently pragmatic solution and one that I shall raise a malt whisky to tonight. Link to comment Share on other sites More sharing options...
BruceM Posted February 22, 2018 Author Share Posted February 22, 2018 An update as promised. I wired in a suppressor in line with the radio and the interference continued as before. I upgraded the satnav and the interference symptoms didn’t change. So I’m thinking that either interference must be reaching the radio wirelessly – probably via the aerial, the radio is faulty in some way, or maybe there’s an inherent source of interference from the ignition system and attaching additional devices to the 12v circuit somehow amplifies it. I’ll carry on researching and experimenting and if I come up with a definitive cause/solution I’ll post the result. Link to comment Share on other sites More sharing options...
plwsm2000 Posted February 22, 2018 Share Posted February 22, 2018 Electrical interference can get into your radio by two different coupling mechanisms - conduction through cables and radiation from/to "antennas". You need to identify which one dominates to come up with the best solution. The inline filters you mentioned tend to help with conducted interference whereas the "ferrite clamp" mentioned in an earlier post tend to help with radiated interference (they change the antenna characteristics of the cable) The inline filter works best close to the source of interference and it is grounded properly. The ferrite clamp may work better at different positions along the cable. If you find it does help a bit and If the center hole is large enough, you can try to loop the cable back through the ferritre core to increase its effectiveness. Repositioning / reorientating plus the length of cables can also have big effects so you could try altering these too. Link to comment Share on other sites More sharing options...
BruceM Posted November 8, 2019 Author Share Posted November 8, 2019 I’ve reignited this thread because I’ve just inadvertently resolved the issue so the solution may help others that have the same problem. Our van is an A Class so the cab is not the Fiat original. Consequently there is a great expanse of space between the driver/passenger and the windscreen. This expanse is covered by a large fibre glass engine cover. This cover was lined with a foam core plastic faced sound deadening material . I’d noted that the lining was starting to disintegrate with small pieces hanging down into the engine bay so I removed the cover and replaced the lining with 10 mm aluminium faced vehicle sound proofing sheet. On reassembly the radio interference has disappeared. My suspicion is that the aluminium facing material, being earthed against the chassis, is shielding the cab and radio from engine generated radio interference although I’m open to other suggestions from those with more technical expertise. Link to comment Share on other sites More sharing options...
plwsm2000 Posted November 8, 2019 Share Posted November 8, 2019 Bruce, That is an interesting observation. Although you may have reduced the interference slightly, I think it is more likely you have improved the effectiveness of your antenna. What is important for good reception is the actual signal to noise ratio (SNR). Reception can be improved by either increasing the wanted signal level OR reducing the noise/interference. A simple monopole antenna needs a decent ground plane to work effectively (which is a bit difficult to get on an A class with a non-metallic body). With a poor ground plane, the antenna will have a low gain and will not be tuned correctly. This is a double whammy as it will also pick up lots of out of band noise and so compound the problem. I think you have probably now made a half decent ground plane for the antenna so it gets a much stronger signal. Link to comment Share on other sites More sharing options...
Charles Posted November 9, 2019 Share Posted November 9, 2019 Reminds me of AGC (automatic gain control) on an FM radio. When the signal is weak the tuner gain is turned up so it picks up any local interference. Remember when you used to drive under a bridge and all you can hear is engine interference. That's the gain going right up. https://en.m.wikipedia.org/wiki/Automatic_gain_control Link to comment Share on other sites More sharing options...
BruceM Posted November 9, 2019 Author Share Posted November 9, 2019 Thanks all for the comments. Turning the volume up and sticking my ear close to a speaker I can still determine a little interference that decreases if I disconnect the power supply from the sat nav so I think you might be correct regarding the ground plane and AGC. The change in reception since the change has though been remarkable. I’ve now got a perfectly usable radio whereas previously I had none. Drinks all round! Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.