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Radio Gremlins

Radio Gremlins

Postby iandvl » 28 Feb 2017 09:34

I'm posting this here as the issue is electric related. And hoping someone can give me some advice on where to start looking.

I've got an ORRA authorisation, and have a Kenwood TK7160 in my Patrol. Fantastic radio. The 1/4 wave antenna is installed above the right wheel arch. The radio has been installed for a year or two now, and I've had no issues with it at all until relatively recently.

My issue:

When the ignition is on on the vehicle (both when the motor is started and when it is off), I have started picking up interference on ORRA8 (steady static hiss). There is also interference on all channels using the same frequency as ORRA8 (ORRA1, and I *think* ORRA5). However, since the other two channels are toned, the radio does not make the general static noise. Well, generally wont, but something will generate the correct tone for ORRA1 when I hit about 2500 revs. Then I will get a burst of static, followed by silence again as I pass 2500 revs.

I've got no idea what is causing this. I have checked the following:

1: There are no breaks or issues with the antenna cables or radio power cables.
2: Radio power comes directly from the battery (properly fused on the battery side).
3: There is undefined ohm reading (ie: no connectivity whatsoever) between antenna centre and antenna outer cores.
4: There is zero ohm reading (ie: good connectivity) between radio-side centre core on antenna cable and the whip of the antenna.
5: There is zero ohm reading (ie: good connectivity) between radio-side outer core on antenna cable and the antenna base.
6: Likewise, there is zero ohm reading (ie: good connectivity) between radio-side outer core on antenna cable and Earth.

In other words, all seems to be perfect. But the problems persist.

The radio seems to be working well when there is no interference (ie: when ignition is off and similar), but I wonder about my range occasionally. On a few trips, it has seemed to be particularly short. On other occasions, it has seemed to be perfect. I regularly pick up radio traffic in Pretoria and Midrand from the R511 (depending on where I am, as the geography is a little weird there, and VHF is affected by line of sight).

In short: I believe there is some electric bit that is causing interference with the radio. This would be something which is on whenever the vehicle's ignition is in the on position (even though the motor is not running). This is something which is presumably affected by engine revolutions or alternator voltage (hence the correct "tones" being generated) when I hit 2500 revs.

I've checked the harness all over the place for breaks or shorts, but there is absolutely nothing. All looks perfect.

Oh - a final note: When the radio is picking up interference, and I open the driver side window about 5cm's, the interference stops. There is also no interference when I operate the driver's side window. This could indicate that the issue is voltage related, except that this is only when I operate the driver's side window. It's all very strange, and I cannot work out what is going on. It may be that the radio set is damaged in some way, but trying to work out cheaper.

In short: Anybody with any ideas on where to start, please let me know. Appreciate it.
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Re: Radio Gremlins

Postby ChristoSlang » 28 Feb 2017 20:04

Weird one :think:

I'd suggest that you disconnect the window motor in the right-hand door (whilst the window is closed!) to see if the problem persists. Easy enough to do by lifting up the console with the window buttons on it and disconnecting the plug underneath.

If your problem is gone, buy a generic electric window kit at Autostyle and replace the wonky motor in your door...
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Re: Radio Gremlins

Postby Peter Connan » 01 Mar 2017 05:52

I am not a radio expert at all, but as far as I know the only electrical system in a car that can routinely cause radio interference is the high-tension side of the ignition.

Thus:
1) Are you using "shielded" plugs (BPR5/6ES instead of BP5/6ES) (the R means it is shielded for radio)
2) What condition are your HT leads in?
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Re: Radio Gremlins

Postby SCUBA Patrol » 01 Mar 2017 07:36

I agree with Peter, also check the condition of the coil as that is where most of the noise is generated.

Also go on the Community forum and ask "Dirty Dog" the question if there are no answers further on this forum. (He is a radio fundi)
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Re: Radio Gremlins

Postby iandvl » 01 Mar 2017 07:42

ChristoSlang wrote:Weird one :think:

I'd suggest that you disconnect the window motor in the right-hand door (whilst the window is closed!) to see if the problem persists. Easy enough to do by lifting up the console with the window buttons on it and disconnecting the plug underneath.

If your problem is gone, buy a generic electric window kit at Autostyle and replace the wonky motor in your door...


Thanks Christo,

It's a thought.

Peter Connan wrote:I am not a radio expert at all, but as far as I know the only electrical system in a car that can routinely cause radio interference is the high-tension side of the ignition.

Thus:
1) Are you using "shielded" plugs (BPR5/6ES instead of BP5/6ES) (the R means it is shielded for radio)
2) What condition are your HT leads in?


The HT leads are in good nick. Also, I assume HT-side is only going to interfere when the engine is running. This does not explain the interference with the vehicle switched on (on - not ACC), but motor not running.

Any electrical system can interfere with the vehicle although HT is most common,

SCUBA Patrol wrote:I agree with Peter, also check the condition of the coil as that is where most of the noise is generated.

Also go on the Community forum and ask "Dirty Dog" the question if there are no answers further on this forum. (He is a radio fundi)


Thanks - although as my earlier comment, I don't see how this happens when the motor is not running. Will check it out though.

I chatted with Eric Skeen (ie: Family Dog) when the issue first cropped up. His idea was antenna / antenna cable faulty. Perhaps I should just get a temporary mag mount and test with that to make sure...

Antennas are cheap, but routing that cable through the firewall .... :(
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Re: Radio Gremlins

Postby iandvl » 01 Mar 2017 08:41

I must thank Tinus for putting me in touch with a radio guru. The issue in terms of interference would be one of two things.

1: Antenna.
2: Power.

Trouble-shoot by using mag-mount antenna with separate battery supply to isolate the system back to basics. And then mix and match from there until the problem is sorted.

I will be borrowing a mag-mount antenna from Tinus tomorrow (dankie mater). And will report back once I've got everything tested / similar - probably Sunday.

PS: A final tip from Andries (the guru) - and something I was not aware of. Reception can be vastly improved by trimming the antenna to 1/4 wave lengths (ie: feed cable MOD antenna whip length = 0).
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Re: Radio Gremlins

Postby offroadbiker » 01 Mar 2017 09:04

So what you are telling us is that Tinus knows a radio GURU, yet he has never organised a -radio day- where we can all get together and sort out all our radio problems and make sure that we can all talk to one another :surprised: :surprised: :surprised: :surprised:

Every single Forum trip we struggle to get everybody on the same channel - eish I am disappointed in the man :oldtimer: :naughty:
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Re: Radio Gremlins

Postby iandvl » 01 Mar 2017 09:11

offroadbiker wrote:So what you are telling us is that Tinus knows a radio GURU, yet he has never organised a -radio day- where we can all get together and sort out all our radio problems and make sure that we can all talk to one another :surprised: :surprised: :surprised: :surprised:

Every single Forum trip we struggle to get everybody on the same channel - eish I am disappointed in the man :oldtimer: :naughty:


For what it is worth, I took my laptop and programming cables along on river trip. People could just have asked. I only found out later that there were issues... :rolling: :rolling: :rolling:

Seriously, I think in the meantime, Jan (forget his surname - Tall Jan with the Toyota who was with) should just share his license-free configs as well.

ORRA VHF I know.
Hilux club VHF I know.
LFR UHF (default) I know.

But his configs were different. He was using tone 8 on channel 1 (the default is tone 10).

So, next time river trip, I'm happy to do a programming session *before* the trip. But just ask. :rolling: :rolling:
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Re: Radio Gremlins

Postby ChristoSlang » 03 Mar 2017 18:48

Ian, some reasoning behind disconnecting the window motor in the driver's door:

1. We know it has nothing to do with your ignition, since it also happens when the engine is not running. Forget about alternators, etc.
2. We also know that it has nothing to do with the antenna, because you have good reception when you wind the window down ever so slightly.
3. The window motor on the driver side has an auto-off function when it reaches the top or bottom. If this is not working properly, the motor will be stationary with the window at the top, but still supplied with current when the ignition is on. This may cause the brush contacts to arc & cause the interference you experience.
4. The fact that it goes away when the window is wound down slightly is further proof of point 3...

Some additional background:
ORRA 1, 3 & 8 share the same frequency (the latter has no tone)
ORRA 2, 4 and 9 share the same frequency (the latter has no tone)
ORRA 5, 6 and 7 share the same frequency (the latter has no tone)

Toned frequencies will be completely muted until the correct "tone" (actually a specific frequency) is superimposed on the base frequency. That explains why the "toned" channels are silent, and the "non-toned" ones are noisy...
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Re: Radio Gremlins

Postby ChristoSlang » 05 Mar 2017 12:43

iandvl wrote:PS: A final tip from Andries (the guru) - and something I was not aware of. Reception can be vastly improved by trimming the antenna to 1/4 wave lengths (ie: feed cable MOD antenna whip length = 0).


Ian, be careful... the 1/4 and 5/8 wave antennas are structurally different!

The 1/4 antenna we use is typically a ZARA 60 and does NOT have a bottom loaded coil. The 5/8 version is a ZARA 130, which as a bottom-loaded coil (BLC) antenna. Both have a stainless steel shock spring at the bottom for mechanical protection - do not confuse this with an electrical coil used the the BLC antenna.

The BLC changes the perceived electrical length of the antenna. Trimming a ZARA 130 to the same length does not make it a 1/4 wave antenna, unless you remove the BLC as well. At this point it's easier and safer just to spend the R500 for a 1/4 antenna. Think of it this way - removing every alternate tread block on an all-terrain tire does not turn it into a muddie!



But I agree - 1/4 antennas have a wider bandwidth (they can receive & transmit a wider range of frequencies) and perform better in hilly areas (i.e. 4x4 country!) than a 5/8 antenna and their short length creates less parking arcade issues. The only drawback is that they are somewhat down on transmission range, but this drawback is negated by the bad bandwidth characteristic of the 5/8 antenna that only really performs well in a very narrow frequency range.
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