Radio problems on ambulance.

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rydzewski
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Joined: Sat Apr 22, 2006 11:34 am

Radio problems on ambulance.

Post by rydzewski »

We have been having an ongoing issue with one of our ambulances radio's. some days its better, some days much worse. the issue is a humming noise its gotten to the point to on the "bad" days the dispatcher says we are unreadable. We have had the local radio shop out 3 or 4 times and they were unable to replicate the issue or find a problem...

Its an older 2007 Ford E chassis Ambulance. There are 2 VHF CDM1250's one sitting on top of the dash, the other in the back of the ambulance. Both radios have the same issue. I started doing some basic troubleshooting last night and here's what i found. The higher the RPM's of the engine the louder the noise. Our dispatcher states it sounds like a vacuum cleaner in the back round. I have requested him email me the sound clips from the recorder so i could post the noise on here but have not gotten them yet.

by all means i am not a professional at this stuff. i run fiber for a living. so here goes...

Here is what i found. the power and antenna cables for the front radio all run through the same plastic tubing. for about 5ft then the positive hooks up to a terminal in the electric cab where all the lights and relays are. then ground goes to a grounding block in the same box. If i was to re-run power right to the battery and bond ground to the frame could that help the noise? i am looking for the cheapest fix. the radio guys said its the truck and didn't do anything more but charge us another 300 bucks. Any advice would be appreciated. Thank you.
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n7maq
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Re: Radio problems on ambulance.

Post by n7maq »

If the noise is not present with the engine off the the tech was probably correct when he told you it was the vehicle, check your charging system.

"i am looking for the cheapest fix" If this is in an ambulance you need to look for the best fix.

Jim
rydzewski wrote:We have been having an ongoing issue with one of our ambulances radio's. some days its better, some days much worse. the issue is a humming noise its gotten to the point to on the "bad" days the dispatcher says we are unreadable. We have had the local radio shop out 3 or 4 times and they were unable to replicate the issue or find a problem...

Its an older 2007 Ford E chassis Ambulance. There are 2 VHF CDM1250's one sitting on top of the dash, the other in the back of the ambulance. Both radios have the same issue. I started doing some basic troubleshooting last night and here's what i found. The higher the RPM's of the engine the louder the noise. Our dispatcher states it sounds like a vacuum cleaner in the back round. I have requested him email me the sound clips from the recorder so i could post the noise on here but have not gotten them yet.

by all means i am not a professional at this stuff. i run fiber for a living. so here goes...

Here is what i found. the power and antenna cables for the front radio all run through the same plastic tubing. for about 5ft then the positive hooks up to a terminal in the electric cab where all the lights and relays are. then ground goes to a grounding block in the same box. If i was to re-run power right to the battery and bond ground to the frame could that help the noise? . the radio guys said its the truck and didn't do anything more but charge us another 300 bucks. Any advice would be appreciated. Thank you.
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Bill_G
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Re: Radio problems on ambulance.

Post by Bill_G »

No - don't go grounding the radios to the vehicle chassis when everything else returns to the ground block in the electrical box. You'll create a ground loop that could be disastrous for the radios. You need to go over the battery cables, alternator, and crimps to ensure everything is clean, tight, and secure. Then you need to turn off every accessory one at a time to see which is causing the problem.

In the past I have found loose nuts on power terminals, loose crimps on batt cables, bad batteries, bad alternators, bad engine block ground straps, and bad body ground straps. I have also found bad accessory battery chargers for the lifepak, the gurney, and portable tools putting hash on the power system. Likewise, I've found AC inverters that supply power to the back cab put hash on the power lines.

These can sometimes be devils to find, and a one hundred penny problem, not a buck (many problems together rather than a single cause).

Good luck!
rydzewski
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Re: Radio problems on ambulance.

Post by rydzewski »

thank you for the replies. I will test with the ambulance engine off. I will also try to minimize the electrical load in the back, and check the connections out.
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Bill_G
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Re: Radio problems on ambulance.

Post by Bill_G »

If push comes to shove, and you can't get rid of the noise, and you're sure it's noise on the power line - not radiated noise - you can buy a 12-12 converter that gives the radio beautiful crystal clean juice aka crap-b-gon box. You just have to buy one with a big enough butt to carry all three of your radios. 20A versions from Duracom are around $150.
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wx4cbh
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Re: Radio problems on ambulance.

Post by wx4cbh »

Bill G said a mouth full. A common problem with modular ambulances is that no matter how well the cab is grounded by the chassis manufacturer, the upfitter companies supplying the ambulance modules can't always get the ambulance module properly ground bonded to the chassis and to the cab. So, if the ground post in the panel of the module isn't at common ground potential in relation to the cab and the chassis, the result is dynamic device electrical noises running on the potential (voltage) differences between the ground points. This can happen to van ambulances also when the ground point in the panel in the ambulance portion is not properly bonded to the rest of the chassis and body. These problems show up sometimes simply because a good bond the chassis/cab/module had in the beginning has deteriorated due to wear, tear, corrosion, and lack of maintenance. People are aware of the positive side of the system requiring maintenance, but few ever think about the ground side of things. It needs love, too.

All the ground bond points are effected by electrical load, temperature, humidity/moisture, corrosion, and Murphy's Law, so it's absolutely necessary to make sure all these connections are clean and tight and protected from moisture and dirt for maximum corrosion resistance and best electrical conduction. This explains a lot of the good day/bad day symptoms. The more unequal the ground bonds are, the more likely you are to get ground loops and rogue dynamic noises on audio devices like radios, sirens, PA's, intercoms, supervisors (j/k :D), etc. This is why a common ground bonding point is the most desirable situation, but that's not always possible.
curmudgeon.....and I like it.
thebigphish
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Re: Radio problems on ambulance.

Post by thebigphish »

....fuel pump. Seen it many times personally. An appropriate cap across the power leads to the fuel pump can work wonders. I've tried those MCS2000 power line filters, with varying degrees of success, so YMMV.
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was jsikora
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Re: Radio problems on ambulance.

Post by KB2ZTX »

I happen to have the exact duplicate of your ambulance. I would almost bet when the rig is off there is no hum. We finally replaced our alternator and by gosh its dead quiet now. We also found our ground cables going to the ditribution panel to be loose on the far end. It was fine in the box, but under the hood you could move it all ovver on the bolt.
KB2ZTX
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Bill_G
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Re: Radio problems on ambulance.

Post by Bill_G »

jsikora wrote:I happen to have the exact duplicate of your ambulance. I would almost bet when the rig is off there is no hum. We finally replaced our alternator and by gosh its dead quiet now. We also found our ground cables going to the ditribution panel to be loose on the far end. It was fine in the box, but under the hood you could move it all ovver on the bolt.
When batt cables have been loose for a long time, they get blackened by arcing. I buff them as good as possible with a wire brush and/or a file. Then I apply some no-ox before tightening them down.
thebigphish
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Re: Radio problems on ambulance.

Post by thebigphish »

jsikora wrote:I happen to have the exact duplicate of your ambulance.
Who was the upfitter?
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" --Antonious Block
KE7JFF
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Re: Radio problems on ambulance.

Post by KE7JFF »

I deal with "temporary" radio installs in ambulances for special events; because of that, I've had to deal with noise from all sorts of devices inside the box and chassis using spit and duct tape pretty much.

Based upon what you said, I'm thinking the "vacuum sound" is the alternator. There's a few ways to fix that; you can make or build a simple filter, which would fall under your cheap fix qualifications...
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KB2ZTX
was jsikora
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Re: Radio problems on ambulance.

Post by KB2ZTX »

thebigphish wrote:
jsikora wrote:I happen to have the exact duplicate of your ambulance.
Who was the upfitter?
Ours was a Braun. We also have Medix and those have had similar issues.
KB2ZTX
rydzewski
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Re: Radio problems on ambulance.

Post by rydzewski »

The one mentioned above is a Demers Ambulance. Haven't had a chance to get into the electrical system yet. I will post an update with what I find within the week. Thanks again for all the help.
rydzewski
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Re: Radio problems on ambulance.

Post by rydzewski »

I know its been a few weeks but I was finally able to take a look at it. First thing I did was check the Ground. The ground is about 6Ft long and is grounded to the back of the Driver seat frame. I figured this wasn't the best ground so I unhooked it looking for another place to locate it. After I removed it I was still behind the seat when i heard a transmission on the radio, I looked up and saw that the radio was still on... With the ground unhooked. I do not have much experience in Radios but that didn't seem right. I unscrewed the antenna from the back of the radio and it powered down. Is this normal?

I also noticed this is the only ambulance out of 5 that has dual alternators. the other 4 have a single high output alternator. I am sure 2 alternators = more noise....

There are what look like noise suppressors on the positive line from the electrical box to the radio. one looks like some sort of transformer red in red out, the other has red in red out with a ground coming out of it to the ground bar.

I am still concerned about the radio staying on with the negative being removed. I swapped the radio with a spare and it did the same thing.

At this point i am stuck.... any and all suggestions would be appreciated.
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FireCpt809
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Re: Radio problems on ambulance.

Post by FireCpt809 »

The radio is pulling ground through the antenna lead. That is a good way to blow up the radio. ALWAYS make sure the radio is off or the battery is disconnected before servicing any two way equipment. The radio needs to be grounded to a Chassis ground, not a seat, not an aluminum box frame, solid steel of the vehicle body with a good connection of clean metal with a star washer and nut and bolt if possible or sheet metal screw.
KE7JFF
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Re: Radio problems on ambulance.

Post by KE7JFF »

If that ground was to the seat floor bolt, that would be much better than just the frame of the seat.
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Jim202
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Re: Radio problems on ambulance.

Post by Jim202 »

I don't think anyone has asked if you have done any testing with the charging system in the vehicle. As with most ambulances, they are required to have a dual battery system. You haven't mentioned just how you have the battery switch selected when your trying to resolve the noise problem.

My first question is about the batteries. Just how old are they? Anything about 3 years or older is like asking for problems. As batteries age, the internal resistance goes up and they don't act as good as a filter. The age also is in direct relation to just how much storage capacity they retain.

My second question is what position is the battery selector being used in. You have a choice of battery 1, battery 2 or both. It is not a good idea to run the switch in the both position with older batteries. Plus this position should be reserved for emergencies only. As batteries age, their capacities change. With old batteries, if you put the switch in the both position, you could cause a huge current flow from one battery to another while they try to equalize their voltage. This could cause an explosion in a battery if the plates warp enough to touch and short out. Plus there is a bunch of crap on the bottom of the batteries that collects over time. This can also help in causing this problem.

It might be worth the time to pull out a good digital voltmeter at this time and start to do some detective work. Take the vehicle out of service and let the electrical system sit idle over night. Make sure that there is not any shore charger connected. In the morning, measure the battery voltage at the battery terminals. Take a pad of paper and record your readings. Make sure you do this for both batteries.

Now start the vehicle and record the battery terminal voltage. Also put the meter in the AC scale and see just how much AC ripple there is. It should be down in the 10 to 50 millivolt range.

Next, turn on the headlights and repeat the meter readings in both DC and AC measurements. Write it down. make sure the vehicle stays at an idle. This should be between 600 and maybe 750 on the high side.

Now turn on the headlights to high beam and again make your measurements.

Next turn on the air conditioning system with the fan on high. Take your voltage measurements.

Start turning on the emergency lights one load at a time while doing your voltage measurements.

What your looking for is a drop off of voltage and a rise in the AC millivolts. The higher the AC reading, the closer your pointing the finger to a bad rectifier. This will cause the noise in your radio. You might also want to do a simple keying of the radio on a simplex channel while doing all these load tests.

The alternator has an output curve for voltage and current. You are trying to make sure that the alternator is putting out enough current to keep the load from dropping the voltage. Depending on where the voltage regulator is set, this may be 13.5, 13.8 or even 14.0 or slightly higher on the newer electrical systems. If you find a point where the electrical load causes a drop in voltage, you have found the output limit at that RPM of the engine. You can try to slightly increase the RPM and see if the voltage goes up or stays where it is.

My gut feeling is that you have either a grounding issue or a bad alternator. Problem here is pointing the finger in the right direction. You don't want to go replacing the expensive alternator unless you can prove there is an issue with it.

One item I haven't talked about is a diode isolator. These are normally installed on vehicles with a dual battery system. It keeps the batteries isolated form each other, but allows both batteries to be charged when the engine is running. It doesn't matter which selector position the battery selector is in. You should be able to locate the isolator with how the wiring is. There should be a heavy wire from the alternator to run directly to the center post of the isolator. Then each battery should be connected to the other 2 posts. The battery switch is independent of the battery to isolator connections.

Happy hunting.

Jim
Jim202
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Re: Radio problems on ambulance.

Post by Jim202 »

It has been over a week now an no comments back about what you found in the vehicle for the noise source.

How about letting the rest of us know what you found and what your next step was or is.

Jim
rydzewski
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Re: Radio problems on ambulance.

Post by rydzewski »

Jim,

Thank you for all your suggestions. Its been a busy week and I have not had much time to play around with the radio. I have been told that it sounds much better as of right now. The only thing that has changed from the last time I tinkered with it was we removed the portable refrigeration unit due to it not cooling correctly.

As for the battery's, Both were replaced about 3 months ago due to one being cracked.

I have scheduled this Thursday and Friday to pull the vehicle out of service. I will be checking everything listed above in your post and get back to you by the weekend.

Thanks again.

- Ben
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HLA
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Re: Radio problems on ambulance.

Post by HLA »

i'd unplug the antennaes and see if the radios still turn on? they might be getting their ground from the antennae and not from the ground terminal like needed. And what set of batteries are the radios connected to, the ones for the engine or the ones that run equipment in the back?
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Jim202
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Re: Radio problems on ambulance.

Post by Jim202 »

Did you ever find the time to play some more with the problem you were having on the ambulance?

Waiting to hear what you found. It would be of value to others that do service on this type of vehicle.

Jim
rydzewski
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Re: Radio problems on ambulance.

Post by rydzewski »

Sorry for abandoning this post... The problem was a blown head gasket. As soon as that was replaced the interference was eliminated.
Jim202
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Re: Radio problems on ambulance.

Post by Jim202 »

rydzewski wrote:Sorry for abandoning this post... The problem was a blown head gasket. As soon as that was replaced the interference was eliminated.



There is no way a blown head gasket on the engine was causing the noise problem. However, there is a very good chance that the ground from the engine to the battery and the vehicle frame was loose, missing or damaged. When the engine was worked over, the electrical ground was probably repaired and that solved your noise problem.

By any chance was there an issue with the engine cranking over slowly when trying to start it?
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Bill_G
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Re: Radio problems on ambulance.

Post by Bill_G »

Agree on the block ground probably getting fixed. They may have fixed an ignition problem too.
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