Burning Smell

[K5RFD]

This is a dualband Kenwood in the truck. When I key up - and only when I key up - I get a burning smell like wires are shorting out. I cannot find the wires that are shorting out. I recently installed a new Austin dualband antenna and had to solder the NMO mount onto the cable I already had. I also had to reattach a yellow wire to the battery due to battery change. Since the smell does not occur when I turn the radio on, I don't think the yellow wire is the issue.

Is it possible that something is crossed in the antenna where I soldered it together and causing this? Is it possible that dirt has gotten in the unit (which is under the back seat of the extend-cab) and is causing this problem?

Either way, I'll appreciate any advice or direction since I'm a little apprehensive about using the radio until I find out what the problem is.

Thanks and 73

 

[Ham4CW]

Hiya George (and welcome to the forum!)

The quickest way to rule out the antenna system would be to disconnect the antenna and use a dummy load. They may be boring, but 50 Ohm dummy loads can save a lot of headaches! If you did use a dummy load and the smell no longer occurred then we know that the fault is in the antenna system somewhere.

If you don't have a dummy load, maybe you have access to another antenna? Maybe you could use a mag-mount as a temporary measure while you rule out the main antenna as being the culprit.

If you find that the antenna is not to blame, then we come back to your 'mystery' yellow wire. Is the yellow wire anything to do with the Kenwood transceiver at all? Have you tried running the radio with the yellow wire disconnected to see if the same fault occurs?

Unfortunately automotive wiring colour coding is as varied as the stars in the sky, there is just no standardisation at all.

If the yellow wire is not connected to your Kenwood transceiver then perhaps it is part of the vehicles alarm system wiring, or maybe feeding some other accessory. If the yellow wire is a thin one it could be the memory backup supply feed for your car hi-fi system or broadcast radio.

What we really need to ask is: "What has changed to make your system fail?"

Well, we have four possibilities:

1) That the new antenna and/or mount are faulty

2) That the new battery has caused some change to the radio system

3) That your soldering has in some way affected the system

4) That the new antenna system, though not in itself faulty, has changed something causing your dilemma

Firstly then, as mentioned at the start of this post, try substituting the new antenna system with either another temporary antenna or a dummy load.

Secondly, check the voltage of the new battery and/or charging control circuitry. It could be that the voltage of your new battery is a lot higher than before and so possibly allowing the Kenwood transceiver to deliver a lot more power. Sometimes the silliest things are to blame.

Thirdly, when you soldered on the NMO connector did you solder your old lead directly to the NMO base, or did you splice in your old lead to the lead already connected to the mount? A direct connection to the base should be OK, but if you've spliced in to the lead from the NMO unit you could have significantly upset the SWR of the antenna system, causing the radio to overheat in the process. Also, if you did splice then it could be that whatever you have used to insulate the joint could be breaking down under load, or else flashing through, giving rise to your burning smell. Have you checked the SWR and/or continuity of the antenna system after you made the changeover?

Finally, it could be that the entire antenna system is perfectly fine, BUT, that by changing over to a different antenna mounting system you have either inadvertently created an earth loop (DC or RF), or else you may have removed an existing one.

If you have CREATED one, then it could be that DC current from the transceiver is passing through the antenna cable/mount, causing it to heat up on transmit and so giving rise to your smell.

If you have REMOVED one, then maybe the DC current that used to flow through the antenna system is now being forced to use the existing power wiring for the Kenwood transceiver, and is just not up to the job on transmit, so giving rise to heating etc. etc.

It could just as easily be a mixture of all of the above.

Hope my ramble helps!


Best 73, Mark.

 

[K5RFD]

Thanks - and the response is highly appreciated. I'll answer a few questions you brought up and we might be able to eliminate some problems that way.

If you don't have a dummy load, maybe you have access to another antenna? Maybe you could use a mag-mount as a temporary measure while you rule out the main antenna as being the culprit.

No dummy load, but do have an old 2 meter antenna that I was using before I got the dual band antenna. I'll pop it on and see what happens. More on that in a moment.

I seem to recall that the radio did not work with the wire detached. I'll double check that.

What we really need to ask is: "What has changed to make your system fail?"

Well, we have four possibilities:

2) That the new battery has caused some change to the radio system

The batteries are essentially identical to the old ones. In fact, I think they have slightly LESS cranking amps. Voltage is the same, however.

3) That your soldering has in some way affected the system

Since I'm no Solder Meister, that's a real possibility.

4) That the new antenna system, though not in itself faulty, has changed something causing your dilemma

This opens a whole new realm of possibilities. More on that momentarily.

when you soldered on the NMO connector did you solder your old lead directly to the NMO base, or did you splice in your old lead to the lead already connected to the mount? A direct connection to the base should be OK,

I soldered directly to the NMO fitting. I looked at the old one on a mag mount and basically followed that pattern - center wire to center and outer wire thing to outer stuff. I checked continuity to make sure I didn't accidentally solder everything into one unit and it was fine. I didn't think to check continuity between the plug at the radio and the mount. I'll put that on the list.

Finally, it could be that the entire antenna system is perfectly fine, BUT, that by changing over to a different antenna mounting system you have either inadvertently created an earth loop (DC or RF), or else you may have removed an existing one.

Its the same mounting system, just different stuff. I was using a mag mount on the top of the truck with a NMO mount, and switched to a fender mounted NMO arrangement with this dual band antenna. Which means that yes, I probably significantly changed some of the operating parameters. Which brings us to the rest of the questions. . .

If you have CREATED one, then it could be that DC current from the transceiver is passing through the antenna cable/mount, causing it to heat up on transmit and so giving rise to your smell.

If you have REMOVED one, then maybe the DC current that used to flow through the antenna system is now being forced to use the existing power wiring for the Kenwood transceiver, and is just not up to the job on transmit, so giving rise to heating etc. etc.

How do I know if I did either and what do I do about it?

It could just as easily be a mixture of all of the above.

as I've previously said "oh, joy."

Hope my ramble helps!


Best 73, Mark.

Helps greatly! Many thanks and 73!

George

 

[Ham4CW]

Hiya George

How do I know if I did either and what do I do about it?

You may have partially answered your own question...

I was using a mag-mount on the top of the truck with a NMO mount, and switched to a fender mounted NMO arrangement...

And also...

I seem to recall that the radio did not work with the wire detached. I'll double-check that.

So it looks as if you do need the yellow wire (for whatever reason), but my thoughts mainly go to the change of mount and antenna.

The mag-mount would most likely only have had a capacitive coupling to the vehicle body, it's very rare to get a DC path through a mag-mount if for no other reason than that the paint-work would act as an insulating layer. Also, a lot of mag-mounts tend to have either a rubber 'boot' or else some king of plastic protector on their bases to help prevent scratching paint-work.

With your new fender mount I'm guessing that it either clamps on, or perhaps bolts through, the vehicles fender, so either way you might now have a DC connection (assuming a metal fender), which you did not have before.

With a new path for the DC current to flow through it could be that the resistance back to the negative side of the battery is a lot lower than before, allowing the transceiver to 'suck' much more current through the existing positive power supply lead, causing it to heat up. If you can smell 'smoke' then something must be getting warm, so maybe you could just try transmitting while holding the power supply lead to the transceiver to see if it is heating up.

Sometimes too, you may find that any inline fuse holders or fuses can also start to heat up on transmit, not so much as to blow or burn out, but enough to produce a burning smell.

Alternatively, if you have fitted the mount on to a plastic fender it could be that you have now lost your RF 'earth' connection (before it would have been provided capacitively by the mag-mount), and when you transmit you may have high RF currents flowing back along the outside of the coaxial feeder, and then onwards through whatever path they can find.

A thought that did occur to me was that now you have moved the position of the antenna you may now be 'firing' lots of RF energy though the inside of the vehicle, so it might be that it's not the transceiver system itself that's producing the burning smell, but something else in the vehicle that's conductive and taking a 'hit' from your transmitted RF energy. Just a thought anyway...

If you can I would also check the SWR of the antenna system, even new antennas can be faulty or mis-tuned, and a high SWR could cause the insulation to break down on transmit giving rise to localised heating on the coaxial cable, and in turn produce a burning smell. Again, it's just a thought...


Best 73, Mark.

 

[K5RFD]

I think you may be on to something here!

If I put some sort of insulating element between the fitting and the metal fender, might that do the trick? I'm thinking of silicone or something.

Thanks

73

K5RFD

 

[K5RFD]

Some developments in this problem - and new questions.

First, I found out that the yellow wire mentioned earlier in this thread does NOT impact the radio. I don't know what it does, but it doesn't have anything to do with the radio - right now, its disconnected (it came off the negative post on the battery).

Second, I swapped out antennas with one I've used previous and I still detected the burning smell. I also think I spotted some bluish wisps coming out of the engine compartment on the passenger side. This is the same side as the antenna . . . interestingly, it is also the same side as the truck AM/FM radio antenna.

Is it possible that the Ham antenna is causing some sort of harmonics with the AM/FM antenna and causing this? I cannot find any wires to or from the ham radio which are heating up, nor is the smell coming from the ham unit. How far does the antenna need to be away from the other antenna (I should know this, but it has slipped my mind)?

I'm also trying to figure out the best location for this antenna. I want to get it off the top of the truck because of parking issues, but I have some concerns about RF inside the cab, particularly if I place it on the driver side fender. I'm pretty sure, however, that I need to get it away from that other antenna.

Does it sound plausible that the proximity to the AM/FM antenna (3" or less) is the root of this burning smell problem?

I really hope I can get this solved before severe weather rolls through on Thursday, but we'll have to see.

Thanks for any advice or suggestions!

73

K5RFD

 

[K5RFD]

Turns out, the yellow wire is attached to the radio. Its connected to the black wire, which is negative/neutral if I remember correctly. Oddly, the radio works even if its not attached, but some how, I suspect that that is bad.

Second, I swapped out antennas with one I've used previous and I still detected the burning smell. I also think I spotted some bluish wisps coming out of the engine compartment on the passenger side. This is the same side as the antenna . . . interestingly, it is also the same side as the truck AM/FM radio antenna.

Is it possible that the Ham antenna is causing some sort of harmonics with the AM/FM antenna and causing this? I cannot find any wires to or from the ham radio which are heating up, nor is the smell coming from the ham unit. How far does the antenna need to be away from the other antenna (I should know this, but it has slipped my mind)?

Apparently, this was the problem. I moved the ham antenna to the opposite side of the truck and moved it forward on the fender. It works with no burning aroma at all now. It does appear, however, that the Austin antenna is dead. I cannot hit any repeater at all with it. When I use the mono-band (145mhz) I can hit repeaters at 30 and 60 miles, but not with the dual-band Austin. So, now I'm looking for a new dual-band antenna. I also suspect I need a ground plane thing, so the search is now on.

At least I'm not worried about burning the truck up any more.

Thanks for all suggestions!

73!

K5RFD

 

[Ham4CW]

Hiya George

Sorry for not replying sooner... I've had 'issues' with my PC

As soon as I read your post about how close the ham radio antenna was to your broadcast antenna I thought "Yup, I bet that's it!", and behold you confirm it in your last post.

As you say, at least you don't have to worry about your truck going up in flames!

As for the yellow wire mystery, I'm pretty sure the radio is being earthed either via its mounting bracket, or perhaps via the new antenna mount you've fitted (or both).

Oh well... On to the next problem hi hi

Best 73, Mark.

 

[K5RFD]

I wrapped the bracket up with electrical tape before I bolted it back on the fender, so any grounding through the bracket should be eliminated.

I worked a couple stations last evening and today with the new setup, and no hint of undesirable aroma. Major plus. Also, previous whenever I keyed up I could hear a "thump" on the AM/FM radio. None of that any more. So it worked.

I'm now looking for a good dual band antenna for the NMO mount on the fender - currently considering the MFJ 1432 which is pretty tall, but has good gain . . . and a fold-over thing for low garage roofs. My only reservation is what drawbacks there are to having a 62" antenna mounted on the front driver side fender. . .

Maybe that's a different thread, however

Many thanks for your earlier suggestions and advice - much appreciated!

73

George K5RFD