[propnut]

Hello all

I have recently installed an Android headset into my daughters 2009 1.0 Picanto but the FM reception is very poor. I have tried two other headsets as well one of which is a Kenwood and all three have the same issue. However when I put the original back in reception is perfect. As such my process of deduction is leading me to the possibility that the factory head unit has a built in amplifier.

Does anyone know if this is definitely the case and/or has anyone gone down this journey.

EDIT: Oh buy the way I have checked whether or not the actual antenna of the car is an amplified unit and I don't believe it is as there is no 12v at the centre pin of the factory headset antenna which would typically be the sign that it is.

Thanks

 

[Radiorail]

It is possible that the antenna is amplified but fed with power not from the co-ax but a separate pin on the radio unit. Some radio units have an ANT pin on the multiway connector which is used to raise an automatic extending antenna. Although these are not used much these days, with short roof mounted antennas being the norm, the ANT connection is an obvious candidate for supplying power to the antenna amplifier.

If you have a wiring diagram for the original installation it may indicate the presence of an ANT wire in the loom. Failing that is there any access to the antenna available to check?

 

[iuygoig]

Hello all

I have recently installed an Android headset into my daughters 2009 1.0 Picanto but the FM reception is very poor. I have tried two other headsets as well one of which is a Kenwood and all three have the same issue. However when I put the original back in reception is perfect. As such my process of deduction is leading me to the possibility that the factory head unit has a built in amplifier.

Does anyone know if this is definitely the case and/or has anyone gone down this journey.

EDIT: Oh buy the way I have checked whether or not the actual antenna of the car is an amplified unit and I don't believe it is as there is no 12v at the centre pin of the factory headset antenna which would typically be the sign that it is.

Thanks

Understand the reasoning but if the amplifer is near to the aerial then it might have a direct supply. Further thought: It used to be that car radios has an aerial tuner (tiny flat blade screw head) which needs to be adjusted to properly match to the aerial and cable. Dunno if they still do.

 

[Radiorail]

Understand the reasoning but if the amplifer is near to the aerial then it might have a direct supply. Further thought: It used to be that car radios has an aerial tuner (tiny flat blade screw head) which needs to be adjusted to properly match to the aerial and cable. Dunno if they still do.

If the car antenna is multipurpose (FM/AM/DAB/GPS) it will probably have active power at all times. Some head units I have seen have separate GPS antenna inputs which do have the voltage feed on the connector as GPS antennas are usually active at the antenna.

If the antenna is just AM/FM/DAB, and has an antenna amplifier, it may be wired as I suggested previously so that the amplifier is only active when the radio is ON.

The tuning cap was primarily to adjust the AM (MW) tuning. It matched the input circuits to the length of the antenna. On FM there is generally no tuning.

If it's any help to the OP I would plug in a separate antenna to test the head unit. As described it does look like the car antenna is not working with the new head unit.

 

[propnut]

Thanks guys, I will do some further digging. I have ordered an antenna to try and will tray and look behind the ceiling light and see if there is any obvious circuitry near the base of the antenna. I also have the Picanto workshop manual somewhere so will squirrel through the schematics. I will report back what I find for the benefit of any one else going down this journey.

 

[propnut]

Ok so I checked the pinouts of the ISO connector and there isn't even a wire in the Antenna port. The only wires used on the kia are reverse, key, aux, neg and VCC+ so if there is an external amp it is not being powered by the radio. Just to check I put the factory head unit back in and tested each pin for a positive feed and there only ones were AUX and Positive. I tried another aerial supposedly amplified from ebay it was rubbish, I got no signal whatsover and I tried one of those inline amps and it does nothing worthy of note either :-(

 

[propnut]

Ok so today I bought an old fashion long telescopic aerial and that worked beautifully so the aerial is the problem not the radio. Measuring resistance from the centre pin of the aerial plug inside the car to the actual aerial shows 100 ohms resistance which is clearly not right. It could be this is a base loaded antenna or there is an amplifier in line. I am going to pull down the headliner this weekend and see what is going on.

 

[Radiorail]

Base loading would not generally add 100 Ohms, the base loading is normally a coil (inductor) and would normally have low resistance. What do you measure across the co-ax (inner to outer) ? Another thing to look for is bad connections at the plug.

What does the antenna look like? Is it the sloped rod with a helix wound around it?

Previously you reported that the original head unit was good on FM is that still so?

 

[propnut]

So I took out the ceiling light and stripped back the roof liner and A pillar trim and followed the aerial through. There is definitely no amplifier anywhere in the circuit. There is an ISO plug join in the A pillar hidden by the cover. There is definitely 100 ohms in the base of the antenna and doing some research 75-100 ohms is apparently normal impedance for a car aerial. Any way in the course of my journey I noticed that the threads on the aerial (where the actual whip meets the base) was badly corroded. Cleaning this up with emery paper and contact cleaner has resolved the issue. Signal is now perfect. In the process I have also fitted a DAB adaptor so am well happy now. I have good FM and DAB.

In answer to your last question, the original head unit still worked fine before I cleaned the threads so it must just be more sensitive or as I suspect has an internal AMP

 

[Radiorail]

So I took out the ceiling light and stripped back the roof liner and A pillar trim and followed the aerial through. There is definitely no amplifier anywhere in the circuit. There is an ISO plug join in the A pillar hidden by the cover. There is definitely 100 ohms in the base of the antenna and doing some research 75-100 ohms is apparently normal impedance for a car aerial. Any way in the course of my journey I noticed that the threads on the aerial (where the actual whip meets the base) was badly corroded. Cleaning this up with emery paper and contact cleaner has resolved the issue. Signal is now perfect. In the process I have also fitted a DAB adaptor so am well happy now. I have good FM and DAB.

In answer to your last question, the original head unit still worked fine before I cleaned the threads so it must just be more sensitive or as I suspect has an internal AMP

Well done.

Although a car antenna has an impedance of 75-100 Ohms you would not normally see this with a mustimeter, it's an impedance (not resistance) at 100 ~ MHz, at DC you would usually see a resistive short or open circuit. It maybe that there is some matching in the antenna base to cater for the AM band.

 

[iuygoig]

Agree with radiorail. Impedance is not the same as resistance and there are no multimeters whoch will measure impedance. this being an AC phenomenon and it is frequency dependant. That Co-ax cable is also probably 75 ohms and you will not be able to measure that with a multimeter either

Glad you got it sorted though. Odd that the original head unit worked with that fault?

 

[propnut]

Ah well the story didn't end there. Whilst cleaning the corrosion off the threads certainly made a huge difference I decided I really wanted to find out where the 100ohms was coming from and so decided to take the aerial mount off the roof and strip it down. Turns out that the 100ohms was a phantom resistance and not an intended 100ohm impedance as you guys clearly articulated. The root cause was again oxidation but this time actually within the base itself. There is a spring that connects the external facing stud with a copper plate that in turn forms part of a socket into which the aerial cable plugs in. The copper plate was in a bad way. Moisture has been getting in via a crack around the periphery of the threaded stud, no doubt caused by stupidly long aerial flopping up and down over the years. Cleaning the copper plate has removed the resistance entirely and reception is an order of magnitude better again. See pics

 

[Radiorail]

Well done, that much corrosion would have been presenting all sorts of differing results depending on the frequency tuned to and the input impedance and circuity of the receiver head and probably the humidity - probaly explains the differences you saw between units.

Good pointers for others suffering reception problems.

You get the Agatha Christie RF mystery award.

 

[propnut]

The final result. Actually this is my second radio, the first one was also Android but rubbish.

 

[iuygoig]

Looking good - what head unit did you settle on?

 

[propnut]

Looking good - what head unit did you settle on?

Thanks, the one in the picture which can be found here

Android head Unit

 

[iuygoig]

Thanks.

 

[propnut]

Thanks.

There are loads available so do your research in terms of features, functions etc. I just wanted something cheap and functional. This one certainly doesn't have all the features of the one I fitted to my other car but then that one was £179 vs the £65 of this one.