welland99 Posted November 9, 2018 Report Share Posted November 9, 2018 Hi all, another little long-standing issue on my cg4: When the heated rear screen is on, there is interference on AM radio from the engine ignition above about 1800rpm. Below this engine speed, there is no interference. Above this engine speed, there is an audible whistle that increases in frequency as the engine gets faster. I realise that the radio aerial is embedded in the rear screen (does it share the heating element?), but I can't work out how interference from the ignition is getting in? Anybody else get this, or have a solution? 2 Link to comment Share on other sites More sharing options...
Moderators PTR200S Posted November 10, 2018 Moderators Report Share Posted November 10, 2018 Yep, solution is to use an FM radio !!!!! Seriously, you are using AM ???? 2 Link to comment Share on other sites More sharing options...
Moderators Laird_Scooby Posted November 10, 2018 Moderators Report Share Posted November 10, 2018 Some radios use two aerial inputs from the heated screen amplifier/LNB, one for AM and the other for FM so you may find these have been swapped at some point on the back of your radio. If the radio only uses one aerial input and there is only one output from the heated screen amp (yes it does use the HRW element as an aerial) then first suspect for the culprit would be the amplifier. Remove, dismantle and check for dry joints, reflowing as necessary. Reassemble, refit and test. If that cures it, all good. If not, i'd suggest the alternator suppressor has failed or not been connected/has a broken wire. It could also be HT leads if yours has a distributor and/or spark plugs. If all else fails you could consider fitting a choke or even a pi filter in the supply to the radio. However, using AM invites interference because of the way it's transmitted. That's why FM is cleaner, comparing FM to AM is a bit like comparing broadband to dial up in that respect. A brief simple explanation is that on AM the carrier frequency (the one you tune the radio to) varies in size or amplitude (Amplitude Modulation) so louder passages of music/speech will be transmitted with a larger/stronger signal than quieter ones. On FM (hoping you're ahead of me now and have twigged it's Frequency Modulation), the carrier frequency is altered up/down to reflect the music/speech being transmitted so you'd get a bandwidth of say +/- 10kHz on the carrier frequency. At 98MHz, +/- 10kHz isn't going to alter the tuning but will allow the radio to "decode" these frequency variations into the music/speech that is being transmitted. The amplitude of the carrier frequency doesn't alter which results in a more consistent signal. 2 1 Link to comment Share on other sites More sharing options...
Moderators PTR200S Posted November 10, 2018 Moderators Report Share Posted November 10, 2018 So, get an fm signal then , Dave !!!!! 2 Link to comment Share on other sites More sharing options...
Moderators Laird_Scooby Posted November 10, 2018 Moderators Report Share Posted November 10, 2018 6 minutes ago, PTR200S said: So, get an fm signal then , Dave !!!!! I don't listen to anything on AM these days Pete, very rarely listen to the radio but have traffic reports set to come on which will over-ride the CD changer.... 3 Link to comment Share on other sites More sharing options...
welland99 Posted November 11, 2018 Author Report Share Posted November 11, 2018 17 hours ago, PTR200S said: Seriously, you are using AM ???? Well, yes, but only for 5live. ? 2 Link to comment Share on other sites More sharing options...
welland99 Posted November 11, 2018 Author Report Share Posted November 11, 2018 12 hours ago, Laird_Scooby said: Some radios use two aerial inputs from the heated screen amplifier/LNB, one for AM and the other for FM so you may find these have been swapped at some point on the back of your radio. If the radio only uses one aerial input and there is only one output from the heated screen amp (yes it does use the HRW element as an aerial) then first suspect for the culprit would be the amplifier. Remove, dismantle and check for dry joints, reflowing as necessary. Reassemble, refit and test. If that cures it, all good. As far as I can recall, there's only one aerial lead in the car, and the radio has only one aerial socket. Anybody know where the signal amplifier is located? 1 Link to comment Share on other sites More sharing options...
welland99 Posted November 11, 2018 Author Report Share Posted November 11, 2018 12 hours ago, Laird_Scooby said: If not, i'd suggest the alternator suppressor has failed or not been connected/has a broken wire. It could also be HT leads if yours has a distributor and/or spark plugs. If all else fails you could consider fitting a choke or even a pi filter in the supply to the radio. Where is the alternator suppressor - built into the alternator? Where would a pi filter go - somewhere inline with the radio aerial? Link to comment Share on other sites More sharing options...
Moderators Laird_Scooby Posted November 11, 2018 Moderators Report Share Posted November 11, 2018 8 hours ago, welland99 said: Where is the alternator suppressor - built into the alternator? No, mounted on or near the alternator, a small unit, about an inch or so long by about 3/4" diameter with a tab on one end to bolt to the engine/alternator mounting bracket and the other end, a wire with a terminal on the end to fit on the alternator + output terminal. 8 hours ago, welland99 said: Where would a pi filter go - somewhere inline with the radio aerial? 21 hours ago, Laird_Scooby said: a pi filter in the supply to the radio That's the power supply, the main + feed to the radio - not the memory line but the main, switched power feed. To be honest, a pi filter is a last-ditch attempt to cure interference, these days cars in general are so well suppressed there's virtually no need for it. Not even sure you can still get them to be honest! Also worth checking would be the coil suppressor, looks similar to the alternator suppressor but is mounted near the coil. Also check your plugs to make sure they're fairly new and of the resistor type. For example BK6E is non-resistor, BKR6E is the resistor type. 9 hours ago, welland99 said: Anybody know where the signal amplifier is located? Fairly certain it's #5 and it's probably mounted on the underside of the parcel shelf - also worth checking the HRW connections to the rear screen and to this module. 2 Link to comment Share on other sites More sharing options...
Administrators hughezee Posted November 11, 2018 Administrators Report Share Posted November 11, 2018 4 hours ago, Laird_Scooby said: Fairly certain it's #5 and it's probably mounted on the underside of the parcel shelf Correct Dave, two units labelled TDK 3 Link to comment Share on other sites More sharing options...
Lumpy Posted April 4, 2019 Report Share Posted April 4, 2019 Hi fellow coupeites. My radio reception seems poor on anything but BBC stations. The amp seems to be doing it's job though. Pioneer DEH-2100. Maybe just a crap area for it, and Cornwall was too 2 Link to comment Share on other sites More sharing options...
Moderators PTR200S Posted April 4, 2019 Moderators Report Share Posted April 4, 2019 I still have the original Bose unit in ( Stu, i know, i know !!! ) and it works great ! I have noticed that dab radios are particularly shit in my area but also my Elysion after market head unit doesn't work well in bad weather conditions. Do you notice a change to reception in relationship to the weather conditions .??? I would try another unit if you have access to one... Stu, radio guru, will be along to offer more useful advice soon , i suspect !! 1 Link to comment Share on other sites More sharing options...
Site Subscriber’s Kelvin Posted April 4, 2019 Site Subscriber’s Report Share Posted April 4, 2019 Mine's dreadful too - never had such bad reception. I just assumed it's the rear window Ariel that's poor. I have an aftermarket Pioneer unit in it that works fine in another motor. 🤔 1 1 Link to comment Share on other sites More sharing options...
Founding Member PaulS Posted April 4, 2019 Founding Member Report Share Posted April 4, 2019 I suppose it is worth checking that the aeriel is still connected all the way through and no rusty connections..... 3 Link to comment Share on other sites More sharing options...
Moderators PTR200S Posted April 4, 2019 Moderators Report Share Posted April 4, 2019 33 minutes ago, Kelvin said: Mine's dreadful too - never had such bad reception. I just assumed it's the rear window Ariel that's poor. I have an aftermarket Pioneer unit in it that works fine in another motor. 🤔 Maybe its the head unit not being compatible with the installed aerial ?? Not sure how though. 1 Link to comment Share on other sites More sharing options...
Moderators PTR200S Posted April 4, 2019 Moderators Report Share Posted April 4, 2019 36 minutes ago, PaulS said: I suppose it is worth checking that the aeriel is still connected all the way through and no rusty connections..... Good point and the place to start really, methodically checking every connection. I ended up installing a stick on window aerial on the tvr ...bit of a problem with the conductivity on that car !!! .....not that you can hear the radio 😲 1 Link to comment Share on other sites More sharing options...
Administrators hughezee Posted April 4, 2019 Administrators Report Share Posted April 4, 2019 My Odyssey is the same TBH, but when I had poor DAB signal in the coupe AM MW FM was perfectly fine, now its the opposite. Maybe a new aerial (sharkfin) would solve the issue as they're not actively maintaining things as they did, so built-in aerials become less effective now... 3 Link to comment Share on other sites More sharing options...
Site Subscriber’s Kelvin Posted April 5, 2019 Site Subscriber’s Report Share Posted April 5, 2019 18 hours ago, PaulS said: I suppose it is worth checking that the aeriel is still connected all the way through and no rusty connections..... Did that - well, Stu did and it's not any better sadly. 1 2 Link to comment Share on other sites More sharing options...
Moderators Laird_Scooby Posted April 7, 2019 Moderators Report Share Posted April 7, 2019 On 4/4/2019 at 8:34 PM, PTR200S said: Maybe its the head unit not being compatible with the installed aerial ?? That's about the size of it Pete. The OE head unit is designed to work with the OE aerial amplifier that uses the HRW elents as the antenna array. It "works" in reverse too, fit a head unit originally designed to run on an amp from an HRW and feed it with a normal aerial and recption isn't brilliant. I've never fathomed the why/how they've done this electronically but from a marketing point of view it restricts replacement to OE kit. A pain in the nuts but that's what i've found over the years. 2 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now