uhf interference

Submitted: Tuesday, Feb 24, 2015 at 16:29
ThreadID: 111228 Views:2512 Replies:6 FollowUps:21
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Hi guys,

I've been getting a strange kind of interference in my tx4200. Basically the interference will start on around channel 20, block the channel for maybe 5 minutes with static and then drop one channel and do the same thing, until it reaches channel .

It only happens when I've got the dual battery and the engle fridge running in the tray and only after a night of not running. The noise is only present while the car is running. As soon as you turn the key off it stops. My guess is that the second battery is becoming discharged overnight, and as the alternator charges it up the frequency emitted interferes with a uhf channel. As the battery becomes more charged the frequency drops until it's no longer in the uhf range.

Am I on the right track?

Any suggested fixes?

2.8d hilux, recently rebuilt alternator, dual battery in the tray with dedicated positive and ground to chassis, uhf wired with dedicated positive and earth to chassis.

Thanks!
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Reply By: TomH - Tuesday, Feb 24, 2015 at 17:24

Tuesday, Feb 24, 2015 at 17:24
Disconnect the second battery and see if it still does it
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Follow Up By: Jack W1 - Tuesday, Feb 24, 2015 at 22:43

Tuesday, Feb 24, 2015 at 22:43
I have tried removing the dual battery and the interference does stop, but there's no interference if I turn the fridge off for the night either, so that got me thinking it's got something to do with the second battery voltage being drawn down over night, or the power the alternator regulator is spitting out to recharge the battery?
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Reply By: Allan B (Member, SunCoast) - Tuesday, Feb 24, 2015 at 17:35

Tuesday, Feb 24, 2015 at 17:35
Hi Jack,

Where is your UHF antenna positioned?
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Feb 24, 2015 at 17:51

Tuesday, Feb 24, 2015 at 17:51
And is the interference a howl which rises and falls in frequency as the engine speed rises and falls?
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Follow Up By: Jack W1 - Tuesday, Feb 24, 2015 at 22:40

Tuesday, Feb 24, 2015 at 22:40
Hi Allen,

antenna is a whip type and it's mounted on the bulbar in the stock mounting tab. The noise is exactly the same as when you turn the squelch too far - just plain static. There's no change in pitch with engine revs, just a gradual shift in static through each station over time. The channel strength indicator remains at 0, and any transmission from another radio will be heard as normal and static free, however once the transmission is finished it's back to static.
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Feb 24, 2015 at 23:43

Tuesday, Feb 24, 2015 at 23:43
Jack, my questions above were to determine two possibilities.......
1) If the antenna was near the tray and maybe getting interference from body return current from the auxiliary battery whilst charging.
2) If superimposed whine from the alternator was a factor.
It would seem neither of these are likely. The fact that you hear a clear reception signal from another radio suggests that the interference is not entering through the antenna or its cable. Of course, with an incoming signal the receiver gain is automatically reduced and any interference is reduced with it. I take it that setting the squelch higher is not an acceptable solution?

As the problem only exists whilst charging current is flowing to the auxiliary battery it suggests that there is an issue there. Having your negative return current travelling by the chassis is not a good idea. Chassis return is only OK for small currents and vehicle manufacturers use this method to save on cabling. Higher currents can produce voltage drop at joints in the bodywork. You would do better to return your auxiliary negative via a well sized cable (as per the positive) from the auxiliary battery to the main earth stud where the cranking battery negative is connected. Returning the radio negative with a cable to the main earth stud may also eliminate interference.

Using suppressors to overcome interference is a last resort. It is somewhat like hitting your head with a hammer then taking Panadol to overcome the pain. Better to eliminate the interference at its source.
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Allan

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Follow Up By: Nomadic Navara - Saturday, Feb 28, 2015 at 12:57

Saturday, Feb 28, 2015 at 12:57
Quote "Chassis return is only OK for small currents and vehicle manufacturers use this method to save on cabling. Higher currents can produce voltage drop at joints in the bodywork."

That only applies to pre unitary construction vehicles. The older vehicles had bodies that were screwed or bolted together. Corrosion was a problem between the panels. Modern vehicles are spot welded together with good mechanical and electrical bonding. I would suggest that if you are getting resistance paths through the body then the vehicle should have been put off the road many years ago.

The only potential earthing problems you will experience in modern vehicles is the connections between the battery and the body (or chassis) and ten between the body (or the chassis) and the equipment.
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Feb 28, 2015 at 14:59

Saturday, Feb 28, 2015 at 14:59
Peter, What you have said is misleading.

The OP's vehicle is a Hilux. He has said.. "I've got the dual battery and the engle fridge running in the tray". He also said... "dual battery in the tray with dedicated positive and ground to chassis, uhf wired with dedicated positive and earth to chassis." When he says "chassis" he may well mean 'body'.
The tray is not "spot welded" to the chassis. In fact the whole bodywork is bolted to the chassis.
Then there are body panels such as mudguards that are attached to the adjacent body by bolting, not welding. There is no deliberate electrical path provided in the bodywork.
There are numerous places in current vehicles where there is no constructive electrical bonding and electrical resistance can and does develop. On top of that the steel body and chassis have significant electrical resistance.

My reference to "chassis return" was a generalisation to include chassis, body or any other path than an intentional copper cable for return of the load current.

I would be surprised if you were not aware of such problems as "earth loops" where the "grounded" ends in signal cables were at differing potentials introducing unintended current paths and interference in the signal. This is normally eliminated by astute grounding of shields and effective bonding of components to avoid IR voltdrops in the structure.

For many reasons, it is not good practice to employ body and chassis returns of significant currents.
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Follow Up By: Jack W1 - Saturday, Feb 28, 2015 at 15:39

Saturday, Feb 28, 2015 at 15:39
Hi Allan, Peter,

Just to clear up any confusion, the dual battery is earthed directly to the chassis while the UHF is earthed to the body (as in the center console - where it is mounted, just below the radio). The main battery is earthed directly to the chassis also, albeit at the front end of the car. I have checked and cleaned both connections.

Before emptying my wallet for a properly sized direct main-dual battery earth lead i might try battery-earthing the radio first?
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Feb 28, 2015 at 16:07

Saturday, Feb 28, 2015 at 16:07
Jack,

Generally, despite all I have said about body earthing issues, low current accessories such as radios (including UHF) are earthed direct to the body near the the accessory, and work OK. It is only when issues arise that a direct return to the battery negative may solve the problem. You could try a temporary wire from the UHF to the battery negative.

However, from what you have said, the problem only arises when the auxiliary battery in the tray is receiving a charge current. Therefore I suspect that the problem lies there. Or in the return path.

How is the charge delivered to the auxiliary battery?
Do you have a 'battery isolator' and what type is it?
Are you using a dc-dc charger/isolator and if so what model?
Is there anything else in the charge path?
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Reply By: Member - Rosco from way back - Tuesday, Feb 24, 2015 at 18:47

Tuesday, Feb 24, 2015 at 18:47
Sounds like you need a suppressor somewhere in the system (possibly the alternator). Was very common in the old days with coil ignitions etc. You can still get electrical interference with a diesel.

May need the expertise of an auto sparky.
AnswerID: 546505

Follow Up By: Jack W1 - Tuesday, Feb 24, 2015 at 22:46

Tuesday, Feb 24, 2015 at 22:46
I was thinking of fitting a suppressor, but because the static drops through the channels it must mean the interference is at the same frequency as each channel, so I don't see how a suppressor could let legitimate channel traffic through but stop this interference... Could be something I'm missing though... Maybe I need to pay a visit to an auto elec...
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Follow Up By: Nomadic Navara - Saturday, Feb 28, 2015 at 12:45

Saturday, Feb 28, 2015 at 12:45
"so I don't see how a suppressor could let legitimate channel traffic through but stop this interference."

The suppressor is in the DC side of things, not in the aerial lead. The problem is to find out where a suppressor would be fitted to fix he problem.
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Follow Up By: Member - Rosco from way back - Saturday, Feb 28, 2015 at 14:32

Saturday, Feb 28, 2015 at 14:32
I defer to you Peter as you've no doubt forgotten more than I ever learnt about radios etc.

I was merely equating it to radio interference in the old days, when a suppressor solved the problem.
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Follow Up By: Jack W1 - Saturday, Feb 28, 2015 at 15:50

Saturday, Feb 28, 2015 at 15:50
Hi Peter,

Based on the symptoms would you recommend a suppressor on the UHF? My understanding is that they are great for smoothing out incoming power to remove alternator whine, but do you think they would work in this instance?
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Follow Up By: Nomadic Navara - Saturday, Feb 28, 2015 at 16:41

Saturday, Feb 28, 2015 at 16:41
Jack, locating the source of the interference is nearly in the black magic area. Way back when a goodly percentage of vehicles required suppression the techos that chased it came armed with their suppression devices (chokes, condensers and filters) and then went around the usual suspects until they found the source and then permanently installed the in that spot. In your case the two suspects that would have been on he top of the list are not the most probable in this instance. As your motor has compression ignition (diesel injection) and not Kettering ignition that is a non event. The second suspect, the alternator whine, has been eliminated as you say the interference is not motor speed related. Your problem is not one I have encountered, I'm not sure exactly here to start.

Regarding the earthing of the battery in the tub, just check the connection from your battery to the chassis. There will be no resistance problems within your chassis as alluded to in a reply above.

One thing that has no been mentioned amongst the suggestions is static charges in the exhaust system. Exhaust pipes are all rubber suspended these days. Way back we had problems with two way radios in Falcons, Kingswoods and P76s. Earthing the ends of the exhausts completely eliminated the interference.
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Feb 28, 2015 at 17:02

Saturday, Feb 28, 2015 at 17:02
Peter,

You are misquoting me re "resistance problems within the chassis".

What I said was "Having your negative return current travelling by the chassis is not a good idea." and it is well recommended that return from remote batteries is best by copper cable.

In using "chassis" I include bodywork and sure enough, Jack then advised that the UHF was grounded to the "body in the centre console" even though he had earlier said to "the chassis" thus validating my generalisation.

Grounding "to the body" may well be to a frame component such as dashboard elements that may or may not be positively well connected right back to the battery. In circumstances such as this it is appropriate to consider all possibilities. As you say "black magic"!
Mind you an oscilloscope in the right hands will usually find it most times.



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Follow Up By: Nomadic Navara - Saturday, Feb 28, 2015 at 17:59

Saturday, Feb 28, 2015 at 17:59
"I was merely equating it to radio interference in the old days, when a suppressor solved the problem."

Rosco, I was not having a crack at what you said. Jack was worried about a suppressor attenuating the received signal. I was just telling him that the suppressors were in the DC circuitry and not the aerial circuitry. I supposed I should have also added that because there was nothing added to the antenna circuitry there will be no attenuation of the received signal, I thought he should have gathered that from the little I said.
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Follow Up By: Member - Rosco from way back - Sunday, Mar 01, 2015 at 00:07

Sunday, Mar 01, 2015 at 00:07
No offence taken old son.
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Reply By: Gronk - Tuesday, Feb 24, 2015 at 20:01

Tuesday, Feb 24, 2015 at 20:01
I get interference on my GME 3450 when I put the phone on charge in the carcomm cradle...but only on channel 16 ??

At least it's an easy fix...switch channels !
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Follow Up By: Jack W1 - Tuesday, Feb 24, 2015 at 23:01

Tuesday, Feb 24, 2015 at 23:01
Yep gronk I can also fix it by going up a channel, but I'd rather figure out why it's doing it. Just in case something goes wrong when I really need it!
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Reply By: Bob Y. - Qld - Tuesday, Feb 24, 2015 at 20:56

Tuesday, Feb 24, 2015 at 20:56
Jack,

The only time I've ever had interference like you have is when I temporarily wired a uhf to fuse box under the dash. Had a lot of alternator whine.......

Otherwise I've always wired direct to battery, for both pos & neg. In case of Landcruisers there is a black box adjacent to the the battery where you can pick up an earth and a positive, with either ACC or IGN. Easy peasy......

Suppose your antenna is good, and well earthed?

You can buy, at Jaycar or Altronics, ferrite cores that you might attach to leads to dual battery or fridge. Might help, or reduce the interference?

Bob



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Follow Up By: Jack W1 - Tuesday, Feb 24, 2015 at 22:55

Tuesday, Feb 24, 2015 at 22:55
Hi bob, the antenna is good. It's a whip type and mounted on the bulbar like normal.

The uhf is wired with positive direct to battery and earth to chassis. From what I've read on here and elsewhere the chassis should pick up less noise than if I ran an earth lead direct to the battery?

So the suppressor would still work to stop interference if It was on the fridge power lead and/or the positive lead connecting the dual battery? I'm not really sure how they work but I thought most people put them on the radio power lead?
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Reply By: HKB Electronics - Wednesday, Feb 25, 2015 at 12:20

Wednesday, Feb 25, 2015 at 12:20
It could be the alternators voltage regulator that is causing the interference, the alternator itself is not likely to cause RF interference due to the low speed and inductance of the windings which would make it impossible for it to generate UHF.

The same would apply to the regulator with regards to driving the rotor field current but it may be be possible for the regulator itself to generate UHF if it is unstable. So if the noise has only developed since the new alternator was installed I'd opt for the voltage regulator being the culprit.

Also worth consider is what type of dual battery you have installed, if it is a DCDC charger then it could quite possibly be the charger that is the culprit.

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Follow Up By: Bob Y. - Qld - Thursday, Feb 26, 2015 at 10:26

Thursday, Feb 26, 2015 at 10:26
Your mention of the voltage regulator got the memory cells working, HKB. Back in the '80's we had a Hilux dual cab that I'd fitted with a Codan HF, and the reception when travelling was atrocious, and at best non existent.

There were a number of other blokes with the same interference problems in both Landcruisers and Hiluxs, and as a number used the HF as part of their business, they were keen to see an improvement.

As it turned out, one of the local auto electricians in the Isa was selling electronic regulators made by Ingram, and replacing the OE reg with one of these pretty much cured most of the Rx problems. The only other "fix" in most cases was a piggy tail capacitor on the oil pressure sender.

The switch by many from HF to UHF usually cancelled any need for suppression, because there virtually wasn't any noticeable interference. That's why the OP's problem seems to point to an add on accessory.

Bob

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Follow Up By: Jack W1 - Saturday, Feb 28, 2015 at 16:01

Saturday, Feb 28, 2015 at 16:01
HKB,

The alternator is the stock unit, although it was rebuilt about a year ago as the bearing was on the way out, but i assume they also replaced the reg.

Is there any way to test a regulator for instability?

Nailing down a start time for the interference noise is a problem, as i installed the dual battery, bought the fridge and fitted the rebuilt alternator at the same time (in preparation for a trip over the Canning Stockroute). Although the interference wasn't noticed prior to this trip, the main battery would never have been drained to the same level as the dual battery currently is, and so if higher alternator charging load is (and was always) the problem i never would have noticed it.
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Feb 28, 2015 at 16:42

Saturday, Feb 28, 2015 at 16:42
Jack,

As you made several changes just before noticing the interference, any one of them may be a culprit.
You have eliminated the fridge.
That leaves the 'dual battery' and the alternator.
Whilst I have concerns about your charging return path, Leigh (HKB) could well be right about the alternator regulator. Such devices can produce r.f. interference if faulty. Certainly it can be tested, the easiest way is inspecting its output with an oscilloscope. I have one but I guess you are not in my Sunshine Coast region.
Substitution of the regulator is another option.

Possibly the cheapest trial is a suppressor capacitor connected to the output stud of the alternator and to its housing. A suitable one is Jaycar Cat. AA-3060 at $3.95 or similar from an auto electrician. Even if it only reduced the interference without fully eliminating it, this would identify the interference source as the alternator.
Cheers
Allan

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