Astro Ignition Noise - Desense

[4n6inv]

OK, I'm ready for some smart remarks, so load 'em up.

I have an Astro Spectra VHF, W-3 installed on a John Deere Gator as a search and rescue vehcle. The radio is installed in a Motorola motorcycle enclosure and mounted on the cargo bed with a 1/4 whip installed on the top. The radio has been powered down to 20 watts high / 10 watts low as to not overlad the system. I've installed am Optima gell cell automotive battery in it to handle the accessories, as well as the John Deere high output alternator for the Gator (55amps) I have all of the radio wires connected directly to the battery.

The problem is when the engine is running, it affects the TX and RX of the radio as to the point of them being nearly non-existant. From 1.5 miles away from my home, you can't hear the signal from the radio on the Gator. Nor, can I hear TX from the house to the Gator. When I cut the engine off; I can talk and hear for 10 miles simplex.

Any ideas? I know this is sort of a combination Astro / Install question, so feek free to reroute me to the appropriate forum if needed.

Thanks in advance.


Jim

[tvsjr]

I'd suspect the alternator making some nasty power. You really need an oscilloscope to look at the input power, and a spectrum analyzer to start doing diagnosis.

[wavetar]

You should be able to source a high-current DC power filter at your local auto parts store. Install that in-line and it should clear up your issues. Motorola offers them as standard issue with their dual-head MCS2000 radios, but I don't have the part number off hand.

Todd

[kj7xe]

TLN5277D. They work VERY well for filtering out the crap and are heavy-duty.

[Wowbagger]

First, you need to know if you are dealing with alternator whine or ignition noise - filters on the DC will do little for ignition, but will help greatly on alternator.

I'd try just disconnecting the field from the alternator (so as to disable it) then see if the radio shows the noise - if so, then it is NOT alternator noise (and thus is likely to be ignition noise).

[wavetar]

First, you need to know if you are dealing with alternator whine or ignition noise - filters on the DC will do little for ignition, but will help greatly on alternator.

I'd try just disconnecting the field from the alternator (so as to disable it) then see if the radio shows the noise - if so, then it is NOT alternator noise (and thus is likely to be ignition noise).

Good point, although in my experience the alternator noise is far more common. I've seen a write-up in older GE manuals on handling ignition noise, but am curious as to any tips you might have?

Todd

[Wowbagger]

Good point, although in my experience the alternator noise is far more common. I've seen a write-up in older GE manuals on handling ignition noise, but am curious as to any tips you might have?

Todd

I'm fighting my own S9+20 ignition noise on my Grand Marq - coil on plug ignition, and I *think* that the ground return for the HV side is through the wiring harness, so there is a HUGE area in the loop. I may see if it is possible to bond a ground braid from the COP assembly to the engine to reduce that, but....

Ferrites on the wiring didn't faze it.

[4n6inv]

What is the amp rating for the Motorola Filter?

I'm still not sure what my problem is, but I put it on a NOAA channel (while running) and it sputtered with crackling noises on RX that sounded like whips being cracked. As the engine speed increased. the radio RX disappeared.

Thanks for the info, so far!!!

Jim

[jim]

First, most ATV/bike radio installs that I've seen are using a 1/4 wave antenna on a non-grounded body panel, which doesn't work.
If it's on a metal panel, the panel still must be grounded with a braid strap. Get a 1/2 wave "no groundplane" antenna for UHF or 800 MHz. If on VHF, use a fiberglass whip/base loaded "motorcycle" antenna (which is also loaded for internal 1/2 wave) to tune properly.

Second, a Gator alternator is designed to run lights and the engine and has little or no EMI/RFI filtering since it does not have to meet any quality specs as a road-going vehicles' does. Add a GOOD filter as stated. I also add a 35,000 uf or higher filter capacitor on the output of the filter to further clean things up.

Third, the fuel system and ignition system also does not need to meet any spec of any sort since it is not DOT approved for road use. The fuel & ign systems may radiate tons of noise on these things. Bypass caps on the ignition system, fuel pumps and Diesel control will always help. Remember also that you may have to install resistor type plug wires since some off-road equipment uses solid-core wires. Don't forget to solder and shrinktube ALL connections since they'll definitely get wet.

Adding engine-to-frame, axle-to-frame, exhaust-to-frame braid straps may also help since you don't have the typical automotive sheet metal covering everything as a shield.

[n1pfc]

What is the amp rating for the Motorola Filter?

I'm still not sure what my problem is, but I put it on a NOAA channel (while running) and it sputtered with crackling noises on RX that sounded like whips being cracked. As the engine speed increased. the radio RX disappeared.

Thanks for the info, so far!!!

Jim

It's got to be at least 30A intermittent duty. We use em on the high power dual head MCS2000's and on high power Maratracs all the time. They almost always cure alternator related problems the first time (usually humming).

On the gator, check your spark plug wire(s) to make sure they are the suppressor type. These have pretty much been the standard for cars now for quite some time (1960's? ) but they may not be using them on the Gator.

I've had to do an install in one of these before as well, except the one I did also had a low band mobile in addition to the VHF one (Both CDM1250s). No motorocycle box so it was fun trying to find places for the radios. The customer hasn't had a single problem with it yet as far as range is concerned, so something must have changed with the design or it may be a slightly different model gator. You do hear the engine bog down when you key up on the low band though

Kurt

[jim]

For coil-over-plug ignition, get yourself a piece of brass door screen and cover the coil completely. Attach the screen with the coil mount bolts.

[4n6inv]

Aww; Piss!!! I ordered a Motorola power line filter, but didn't think about it NOT being waterproof! Anybody have any suggestions? It definitely won't fit inside the motorcycle housing.

I've tried completely lining the inside and underneath of the motorcycle box with copper tape, and that made absolutely NO difference. The copper/bronze mesh over the coils sounds good, but I'm afraid of moving parts nearby, as well as arcing.

Thanks for all of the input and suggestions. Once I solve the problem, I'll post the cure.

Jim

[4n6inv]

OK. I sealed the power filter and installed it last night. That made a substantial difference (50-60%), but I still have some crackling and desense while the engine is running. I have some brass screen on order for the ignition and will install it when it gets here. I'm also going to install ground straps from the dump bed, where the radio housing is located, to the chassis. The engine and everything else appear to be well grounded.

Any other ideas??

Thanks,

Jim