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Car AM/FM aerials


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#1 Nich...

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Posted 11 October 2017 - 10:08 AM

I'm looking at why my car has awful AM reception, and thinking it may be an issue with the aerial or the active amp attached to it.

It's an '06 Kia Rio, but I'm struggling to find anything about the specs of it, like what kind of power it should be running on, in order to diagnose if it's dead, before ordering a new unit.

I know a few people on here are gearheads - any thoughts on places I can look?
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#2 Rybags

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Posted 11 October 2017 - 10:57 AM

How's FM - the aerial is way more important for FM reception and it'll drop off way before local AM stations.

 

Amp functionality easy enough to test, try some other media - CD, USB, BT, whatever.

 

Is the aerial a traditional long type coming from bonnet, a shorter type mounted on a pillar or a barely visible integrated type similar to a demister?

 

Likely the connection to the radio is the traditional crappy banana type plug.  They aren't secured very well and could come loose or lose good conductivity without too much convincing.

 

You'll probably need to pull the radio out to properly diagnose.  Not sure if checking resistance between antenna and ground would give any enlightenment.

Getting the radio out will involve first removing surrounding console trim pieces.  If it's a higher end radio then it might have shaped keys that have to be inserted either side to get it out of the slide.

 

Before doing anything, make sure you have the required enable code for it if it uses one (probably does).  It's unique per unit and dealers will usually charge a fee for the simple task of looking it up in their database (tied to VIN) - though re-entering the code is only needed if the unit loses power.

 

Another thing that comes to mind - if extra accessories have been added, routing of power might be such that interference is occurring.

One diagnostic idea - you could try one of those transmitters that allow using media players via 3.5mm plug although they're pretty weak transmitters with maybe a few metres of range.

 

Ideally once you get the radio out it'd be nice to have another antenna to compare reception.


Edited by Rybags, 11 October 2017 - 10:59 AM.


#3 Nich...

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Posted 11 October 2017 - 11:34 AM

FM is flawless. Now I've remounted the digital aerial, DAB+ is flawless, too. ABC's News Radio only broadcasts Federal Parliament on it's AM broadcast, not digital - that's basically my usecase.

Aerial is a small whip mounted on the roof, near the rear hatch. There's a cable running from the back of the radio up along the passenger front A pillar, along the left side of the roof, and then over to the mount.

Tried the multimeter on the cabling on the A pillar at a plug, and it showed 0 with the radio on AM. If there's a power cable running up to the aerial, then I assume it's an active amp on it, but also should be returning some kind of load on the aerial cable.

The radio itself is an aftermarket unit, so no codes to worry about. I was a little concerned that the aerial and power cable for it are routed side-by-side, but it's like that from factory.
 


Oh, and I've tried two different external whip attachments, a shorter and a longer one.  The longer one provides slightly better reception, but it's still more static than anything else.


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#4 Rybags

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Posted 11 October 2017 - 12:05 PM

Most AM radios for the home just use an internal aerial for AM.  Not sure if that'd be the case here.  ABC also generally use stronger transmission than commercials which isn't a good sign.  Maybe it's just that they developed that stereo and didn't give a crap about it's AM performance.



#5 smadge1

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Posted 11 October 2017 - 01:10 PM

if you have the data to spare, consider using an app like TuneIn Radio Pro. I use it all the time, you get access to radio stations all over the country.


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#6 Nich...

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Posted 11 October 2017 - 02:32 PM

Most AM radios for the home just use an internal aerial for AM.  Not sure if that'd be the case here.  ABC also generally use stronger transmission than commercials which isn't a good sign.  Maybe it's just that they developed that stereo and didn't give a crap about it's AM performance.

I'd wondered that, too - if you're buying a DAB+ radio, surely AM is a place you could safely cut some costs - but it has shortwave bands.  Multiple.  That just screams overkill, but surely SW and not MW would be the first to suffer :\


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#7 Rybags

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Posted 11 October 2017 - 04:17 PM

I've got an old portable with AM/FM/SW - pretty sure only the AM uses the internal ferrite rod, for SW they usually recommend fully extended antenna, FM is usually directional so you rotate to best reception.



#8 stadl

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Posted 11 October 2017 - 05:26 PM

Antennas are generally an interesting subject, and many times consumer 'good enough' cuts many corners that you would think are necessary - simply because the commercial transmitters pump out that much power.

 

The old AM ferrite and coil still works well but they are generally too pricey (and big) to include in modern consumer electronics, so they leave them out. And for car units i'm not sure how well they would work when it's in the metal box of a head unit, buried in the dash of a car with all the other junk.

 

The telescopic mud-guard antenna is for the VHF FM stations. The MF/AM antennas are usually many metres long (electrically) - physically they may be a coil (which is why they used the ferrites in times gone past), and on a car this may be located as part of the FM antenna - either in the base, or as a second winding (for those cars with a fixed fibreglass/wirewrap antenna), so it is possible that the amp or coax connection back to the head unit is a source of problem.

 

First question would be to find out if there is a problem with the car design in the first place - do you know someone with a similar generation Kia that can check how good the AM reception is on their car - it could be a bad design because they figure few people care...

As suggested, checking for a disconnected cable would be a good option. I wouldn't have expected they'd need an active amp at MF frequencies, so the amp may be able to be bypassed or ignored for AM reception.


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#9 Nich...

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Posted 11 October 2017 - 06:37 PM

I don't think it's a design issue with the car per se, but the new head unit may be causing some issues.  When I first got it, AM wasn't great but it was listenable.  When I got the new radio unit, I stopped listening to AM for a fair while because DAB+.  But at some point I noticed that AM was just... awful.  I get it's never going to be great with how far I am from the transmitter, but even driving through urban Melbourne and it'd be awful.  I hadn't thought to wire the old unit back into the car to make sure it's definitely not something being mismatched between the new unit and the aerial.

 

If this weekend is dry I might try that, and pull the roof lining out to check the cabling right up to the aerial mount.


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#10 Dasa

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Posted 12 October 2017 - 07:46 AM

i believe the am signal is more prone to interference it may be worth comparing with a portable am radio sat in the car with the car on vs off

 

if you unplug the antenna and fm reception drops but am doesn't change i think its safe to assume that your head unit uses a internal antenna for am

in which case the best option may be to try out all the head units in store and see which one finds the most am radio stations


Edited by Dasa, 12 October 2017 - 07:48 AM.

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#11 ReapermanRS

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Posted 13 October 2017 - 08:04 PM

First things first. I can't remember if those looms you got had the Power Antennae wire connected from default. Pull it out and check that first.


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#12 merlin13

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Posted 21 October 2017 - 07:32 PM

FM and DAB+ is 100% fine? Doesn't sound like bad electrical connection 'tween the antenna and the input stage, although worth checking all the earth connections and antenna wiring shield integrity (Ohms measure from antenna end to plug) juuuuust to be sure on that Trap For Young Players. Oh, and checked you haven't kinked the coax antenna cable anywhere either.

 

After that, ongoing thoughts would be:

 

 - AM reception in the area is basically shite, my brother down in the Blue Mountains NSW keeps bleating his Alan Jones shit drops out once he crests over the top of the hills. Low ambient RF receive levels is a relatively standard symptom of either local AM stations aren't punching out enough RF power any more, low RF levels due to surrounding structure/topography etc and/or some radio-emitting source splattering the selected band and drowning out the desired signal in the radio input stage (more on this further down).

 

 - or the radio input stage hasn't been tuned to match the antenna and antenna cabling characteristics. Back In The Goode Olde Days you had a hidden trimmer that either lurked inside the cassette deck slot (I did say Goode Olde Days...) or on some units lurked on the back of the radio itself, and you had to fiddle the adjustment to tune the radio to the antenna. Time To RTFM on the radio itself.

 

 - or you've now got either a broken/damaged or basically shite radio. If this is the case then nowadays it'd be cheaper to paint it bright green, throw it into the long grass or nearby compost heap and look around for a betterer one.

 

 

Further Down bit - any electrical interference actually on AM (eg the good old days and RFI from a dirty alternator) "should" come up as noise or static on the band, but as mumbled above if you've got a loud RFI source in the district on a nearby freq it can deaden the receive stage on your radio. Think of this like you're sitting at the pub trying to to your mate across the table and there's a dickhead sitting at the table nearby shouting away in German or Greek  -  you effectively go deaf to your mate's words until the dickhead quietens down enough.   


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