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antenna for caterpillar excavator??

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radioguy32

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I need to put a Motorola mototrbo radio in a caterpillar excavator. There is a nice place to mount the radio. They even have an antenna for me. However all of that is for a AM/FM radio. My Motorola radio will fit into the AM/FM radio spot perfectly. There is power, ground, and ignition already up there but the gauge is too small so I will run new wires to the battery and ignition source. The problem is the antenna. I can't use the existing antenna and there is no spot to mount an antenna. The roof is 2 inches of fiberglass. I am assuming there is steel under the fiberglass and above the headliner. What is a good spot to mount an antenna and what mount should I use? The mounts I use for a regular Ford truck won't come close to working in this instance.
 

clbsquared

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I would imagine your best option would be something like a fender mount or trunk lip mount. What model excavator is it?

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RFI-EMI-GUY

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Could you post some pictures inside and outside to see what you are working with? Also, are you trying to hit a distant repeater, or is this an on site sort of communications?

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radioguy32

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I don't remember the model off the top of my head. I will post some pictures tomorrow. The communication radius will be about five miles.
 

madrabbitt

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all of our dozers use thick NMO mounts thru the center of the roof. The ones with fiberglass over steel dont get a separate ground plane, the new ones are plastic-fiberglass, and they get a ground plane made from thin gauge metal.
 
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One thing you have to be careful about when it comes to industrial equipment...they like to use 24 volt systems instead of 12 volt so check and makes sure you have 12V and not 24 volt sources. Last week I was digging around a loader because two 24-12V converters failed in a week's period. Basically, whoever installed the radio initially had tapped the 24V battery disconnect relay and an ignition based ground. However, something happened and when the ignition turned on, the ground began to be lifted. Grounded to chassis and it solved the issue...
 

RFI-EMI-GUY

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Ideally you want a center mounted 1/4 wave antenna whip with a ground plane. There are NMO mounts that are for thick fiberglass body vehicles like ambulances. If there is steel where the NMO mount will clamp on the inside, you can scrape the paint away and have an electrical connection. That should work OK. Check with a magnet through the headliner and see if the steel is right there.

If you cannot electrically ground the NMO mount I would suggest an aluminum disc equal to or greater than 1/4 wave in radius mounted and epoxied atop the fiberglass shell. You should predrill the disc and position it after drilling the roof. This will be an ideal ground plane. You can buy durable teflon aluminum pie pans at target or wall mart for a nice disc, though you might need to trim the lip, and rough up the Teflon on the side to be epoxied. I would attach a grounding wire to the underside of the NMO mount in this case and ground it to the frame as close as possible. This because you don't want lightning or a downed power line entering the cab by this "floating" antenna mount.

If the fiberglass is really two inches thick, and you are using UHF, an external ground plane still might be required for a good VSWR and pattern . It wouldn't hurt to go the extra step if it is really that thick.

There are antennas sold as not requiring a ground plane, they are 5/8 wave, but not ideal as the coax is likely to radiate RF into the cabin and other electronics. Also they are tall and and more likely to snag and break if you hit some tree limbs.


Then there is this, not same model, but another idea. However the signal will tend to be unidirectional, meaning it will be weaker on the corner it is mounted.

https://m.youtube.com/watch?v=YMm9eY-xgOQ

Whatever you do, before drilling, be sure you are not cutting structural members as that cab is your rollcage.

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lmrtek

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You can use a 3/8 inch hole NMO mount for thick roofs

Use a 1/2 wave antenna so that you won't need to worry about adequate ground plane
 

madrabbitt

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You can use a 3/8 inch hole NMO mount for thick roofs

Use a 1/2 wave antenna so that you won't need to worry about adequate ground plane
3 reasons not to use a half wave (or a 5/8 wave)

1. the coax line becomes a counterpoise, which increases RF leak into the cab, literally right on top of the operator. While its probably not a HUGE concern, its something to be avoided if possible.

2. Vibrations from a piece of heavy equipment will constantly cause the whip to vibrate. The longer the antenna, the more vibration. This causes premature failure due to metal fatigue, set screws vibrating out, the mount falling apart. Its weird, but its a thing. One of the reasons we use 1/4 wave on the fire dozers. Even though they dont have the range a good 5/8 whip will give them, they are also less likely to fall apart, and in a IDLH environment, thats critical.

3. The longer the antenna, especially a VHF whip, the more likely the antenna is to smack around on stuff. I realize on an excavator, the antenna will probably never be the tallest part of the unit while its moving around, but its still a concern.
 
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2. Vibrations from a piece of heavy equipment will constantly cause the whip to vibrate. The longer the antenna, the more vibration. This causes premature failure due to metal fatigue, set screws vibrating out, the mount falling apart. Its weird, but its a thing. One of the reasons we use 1/4 wave on the fire dozers. Even though they dont have the range a good 5/8 whip will give them, they are also less likely to fall apart, and in a IDLH environment, thats critical.
I actually have a theory based on the mas exodus to knob style antennas in UHF and 7/8/900 MHz...just a theory though. On the newer digital systems, frequency stability are much tighter than they were on the analog systems (for example, 300 Hz off frequency on analog is okay...on DMR it begin causing bit error). The theory is that vehicle/road vibration is causing the shorter antennas (which stay in the turbulent flow of the slip stream compared to the longer VHF whips which always will have drag from extending beyond the slip stream into areas of laminar flow) to oscillate and actually shift transmissions off frequency.

That being said, many of us have seen the waveforms form in 48" whips on vehicles which idle rough.
 

jonwienke

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Nope. The longer wavelength of VHF means that the antenna has to oscillate proportionally farther to cause the same phase shift. And 300Hz off-frequency is not an issue for digital or analog. If it was, none of the CCR DMR radios would work.
 
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Nope. The longer wavelength of VHF means that the antenna has to oscillate proportionally farther to cause the same phase shift. And 300Hz off-frequency is not an issue for digital or analog. If it was, none of the CCR DMR radios would work.
300 Hz off an XPR4580 will show out of range on both Capacity Plus and Connect Plus (40 Hz is the error Motorola actually specs for a SU).

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RFI-EMI-GUY

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300 Hz off an XPR4580 will show out of range on both Capacity Plus and Connect Plus (40 Hz is the error Motorola actually specs for a SU).

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That seems like a tight value, do those TDMA have an AFC tracking the base station carrier? I know that inbound TDMA has some ramping requirements and a short preamble bits for synch.

Something I have observed, if you have metal rattling around a radio antenna in either TX or RX mode, a noise will be created. Digital modes will have increased BER. The message, don't hang a key ring on your belt near the radio, or use the antenna to hook the antenna to.

I have seen another effect with portable radios where quickly changing the coupling of your hand and the antenna will cause RF current in the radio to change and cause the VCO to momentarily lose lock. I don't see that happening with a mobile antenna whipping around unless it is side mounted near the cab.

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That seems like a tight value, do those TDMA have an AFC tracking the base station carrier? I know that inbound TDMA has some ramping requirements and a short preamble bits for synch.

Something I have observed, if you have metal rattling around a radio antenna in either TX or RX mode, a noise will be created. Digital modes will have increased BER. The message, don't hang a key ring on your belt near the radio, or use the antenna to hook the antenna to.

I have seen another effect with portable radios where quickly changing the coupling of your hand and the antenna will cause RF current in the radio to change and cause the VCO to momentarily lose lock. I don't see that happening with a mobile antenna whipping around unless it is side mounted near the cab.

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These are all mobiles. Re-aligning the reference oscillator fixes the problem everytime. I actually have found XPR4x80's only hold alignment for roughly 18 months then they have to be aligned. I align roughly 150-200 of the 400 radios we have in service a year.
 
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You can use a 3/8 inch hole NMO mount for thick roofs

Use a 1/2 wave antenna so that you won't need to worry about adequate ground plane
Motex is right on. A quarter wave will not work. You need a "no ground plane" 1/2 wave antenna. You can use either a thick roof mt, 3/8 which is adjustable for thickness, or I have also used a 1/2 wave that mounts on the surface via a top ring with 3 screws. The 58a/u cable comes straight out of the bottom of the coil, so only a 1/4 inch hole is required. These are similar to a marine application, mount wise, but are available via Tessco. Keep in mind they are about 30 inches long, but tune nice and flat.
I'll see if I can find the part number.
 
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The Tessco sku # is 23888. It is made by Pulse/Larsen, 144-174mz Model # is OM150CK It shows in item description as adhesive mounting. Not true, it might have some double face tape but has 3 stainless screws. I used this on a firetruck with a fiberglass cab. This will solve both your cable and antenna in one piece. Works well
 
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A halfwave will be app twice the quarterwave antenna in length.. I believe he mentioned business band which would be in the 150's. Most I have cut and tuned are about 30-34 inches.
A halfwave at 50 inches equals 112mz
 
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3 reasons not to use a half wave (or a 5/8 wave)

1. the coax line becomes a counterpoise, which increases RF leak into the cab, literally right on top of the operator. While its probably not a HUGE concern, its something to be avoided if possible.

2. Vibrations from a piece of heavy equipment will constantly cause the whip to vibrate. The longer the antenna, the more vibration. This causes premature failure due to metal fatigue, set screws vibrating out, the mount falling apart. Its weird, but its a thing. One of the reasons we use 1/4 wave on the fire dozers. Even though they dont have the range a good 5/8 whip will give them, they are also less likely to fall apart, and in a IDLH environment, thats critical.

3. The longer the antenna, especially a VHF whip, the more likely the antenna is to smack around on stuff. I realize on an excavator, the antenna will probably never be the tallest part of the unit while its moving around, but its still a concern.
You can not use a quarterwave antenna mounted on a 2 inch thick fiberglass roof. Your reflected will be the same as your forward, not to mention the beating the finals will take. Will eventually eat up the radio.
 
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