3 questions. Using pass through on cab and RF Grounding??

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camoit

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OK guys, I'm just getting my first radio setup. It's a mobile Kenwood TS-480 and I have a question about using a pass through on the cab and a couple of other questions.
Background on the truck you might need to better understand the full set up.
The hole installation is a little unique because it's not a normal pick up with a bed or hitch where I can just set the Scorpion onto a Breedlove mount. The truck is a flat bed, dump bed with a headache rack and a tool box in the rear. In talking to Scorpion he suggest that the hole antenna be mounted at least 8 inches back / away from the headache rack since that is the tallest part and the strongest thing to build and weld a mount onto. The top coil of the antenna (MIGHT) be above it when retracted. The tip of the whip will be somewhere around 14 foot above the ground. That is as tall as a semi truck trailer.
Then just to add some more problems there is going to be a 5th wheel all aluminum horse trailer behind it.
The antenna will be controlled by a TuneMatic TM-1
Onto the main questions.
SO I'm looking at using a pass through instead of punching a big hole and finding something to use as a seal or grommet around the coax.
Q #1: Do you see and issue with using the pass through?
Q #2: Where do you suggest I place chokes on the coax? The coax run will be about 23 to 25 foot just along the bed and frame to the antenna from the back of the cab so I can still dump junk after removing the antenna and tool box when needed.
Q #3: RF Grounding. Currently the bed is grounded to the frame and electrical DC ground with large high strand welding cable. The frame is bonded to the cab with bonding strap in several locations and the hood is bonded to the cab. Should I add more bonding straps and where to bond them to?

Thanks in advance.
K6OEF


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mmckenna

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Q #1: Do you see and issue with using the pass through?

UHF connectors are not waterproof/weather proof. Only issue I see is that you'll need to do a proper job sealing the connection when you are done. Standard industry practice is to torque the connector to manufacturer specs (in this case, tight, but not white knuckle'd).
Wrap the connector with a layer of electrical tape. "Half lap and back", start near the cab, wrap out past the end of the connector and up the coax a few inches. Each wrap of tape should overlap the previous half way. When you get to the end, reverse direction back towards the cab. Cut the electrical tape, do not stretch it to break it.
Follow up with a layer of self fusing butyl tape sealant. Mold it around the connector and make sure everything is well sealed.
Finish up with a layer of electrical tape, half lapped and back.


Q #2: Where do you suggest I place chokes on the coax? The coax run will be about 23 to 25 foot just along the bed and frame to the antenna from the back of the cab so I can still dump junk after removing the antenna and tool box when needed.

I'll leave this to the HF guys, I'm primarily VHF and up.

Q #3: RF Grounding. Currently the bed is grounded to the frame and electrical DC ground with large high strand welding cable. The frame is bonded to the cab with bonding strap in several locations and the hood is bonded to the cab. Should I add more bonding straps and where to bond them to?

DC ground and RF ground are different things. You want to make sure the antenna mount is well grounded to the dump body. Don't rely on a couple of sheet metal screws.
Make sure your radio is well bonded to the truck body wherever you mount it. Do not rely on just the negative power lead.
Make sure the headache rack is either welded to the body, or grounded with braid. Same with the tool box.

As for the rest of it, you'll need to install it and see how it works. RF grounding might need to be added based on how well it all works. No point in running a bunch of ground straps until you know what you need.
 

prcguy

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I'm not picturing how or where the antenna will be mounted, are you considering the floor of the bed behind the forward bulkhead thing? Is the headache rack at the top of the bed bulkhead?

I've done lots of successful HF installations and my current pickup truck has a medium large screwdriver mounted to the drivers bed wall less than a foot behind the cab. Much of the lower mast runs parallel with the bed wall and the feed point is just a few inches above the bed. At HF frequencies a truck cab is a tiny bump as its very small in wavelengths at HF. It may look like the cab is blocking it but the radiated wave off the antenna is much bigger than the cab or entire vehicle.

With all that said it radiates a fantastic signal in all directions and parked in my driveway with 500W its about 3dB better than my 133ft 80-10m OCFD 30ft above it fed with 100w. That's not bad meaning its only about 4dB down from my big home antenna on 40m.

Using a grounded RF feedthrough connection can help keep RF out of the cab and avoid RF on the mic, etc. I would still use an effective RF choke between the antenna and RF feedthrough connector and another between the connector and radio or amplifier. I also run an RF choke on the motor/control leads at the radio and also near the antenna controller inside the cab.

I had lots of problems running 500w and it turns out there was a lot of RF on the power leads of the amp. It was so bad the engine would almost die and all the dash light would go off including the air bag warning lights when I transmitted at 500w. Using a 100AH deep cycle battery at the amp cured the problem and I later replaced that with a 15 Farad capacitor right at the amp. Now everything runs nice and my mobile signal is usually the loudest station on any HF net I join.
 
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camoit

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UHF connectors are not waterproof/weather proof. Only Thing .

I had herd that they should not be sealed as this can cause moisture to stay there. It's best to let it let it dry naturally. BUT it is open to the inside of the cab. As for me I have always been a seal it guy. I have shrink tube that has underwater rating for up to 600KV,

I'm not picturing how or where the antenna will be mounted, are you considering the floor of the bed behind the forward bulkhead thing? Is the headache rack at the top of the bed bulkhead?.

The mount will be welded to the right side vertical upright (see bad drawing LOL) about 1 foot from the outside. So it should make a solid ground. It will be to the inside of the bed as I don't have enough room between the bed and cab when down. I have chokes on order with the antenna. 6 of them so I should have enough to choke it where necessary. I had "seen" people choking it at just the antenna only. Including the motor control and reed switch wires. BUT I have herd of people choking everything before the cab.
I just want to make sure this thing works out of the box like it should when it's done. The wife and I are going full time mobile so it will become a main source of coms in case of emergency (or when she kicks me out of the living quarters). Next to having PLB that will be all we have for communications. The PLB is a life or death thing since once you send out the SOS there is no turning it off and a helo along with cavalry should be on site in about an hour. So someone had better be close to death at $10,000+ per hour.

This is a fresh install so I have time to make sure it's 100% because I will not be able to have the luxury of Amazon next day.
I'm also looking at a 500W Amp but I'm holding back at the moment because people have given mixed signals about the mobile ones.
Think of this as your chance to make the setup you wanted with out paying for it.
So any suggestions will be used.

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Storage and radio mounting.

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Center console with laptop mount. I'm in the process of building the Kenwood head mounting system.

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Thanks for the help.

This is the trailer we are getting just 10 times longer and no horses in the back.
 
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mmckenna

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I had herd that they should not be sealed as this can cause moisture to stay there. It's best to let it let it dry naturally. BUT it is open to the inside of the cab. As for me I have always been a seal it guy. I have shrink tube that has underwater rating for up to 600KV,

Yeah, no. These sorts of things are said by amateur radio operators and CB'ers (I'm a ham and I've done a lot of CB in my earlier years, so not slamming them) You want to keep the water out of the connector. Water can wick up the braid and cause issues. If you are using a stranded center conductor coax, same thing. The water isn't going to drain out of the connector. It's going to collect in there and corrode the heck out of everything, including your coaxial cable.

Some hobbyists will try and make up a valid sounding excuse for being lazy. Don't put all that work into this setup and skip the waterproofing. You're on the right track with wanting to seal it.
 

prcguy

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I don't think your mounting location will work all that well. The antenna wants to be mounted on something conductive right below it with lots of horizontal metal surface area around it. You would be mounting well away from a horizontal surface which will raise the feedpoint impedance and incur some ground loss.

One of the worst places you can mount an HF whip is a trailer hitch. Another bad spot is a roll bar or headache rack, which sits well above and away from a sheet metal roof. You can take an HF whip that is mounted on a van roof and working great, then raise it 6" above the roof with a bracket and you will loose an amount of performance due to the ground loss. Looks like you would be mounting to a vertical bulkhead on the opposite side of the flat bed which would otherwise make a good ground plane. I think the antenna will be unhappy and will complain.
 

camoit

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I don't think your mounting location will work all that well. The antenna wants to be mounted on something conductive right below it with lots of horizontal metal surface area around it. You would be mounting well away from a horizontal surface which will raise the feedpoint impedance and incur some ground loss..

Ok. so here is a better drawing and a picture of the back.
The fuel tank is not in place at the moment.
The base would be mounted to a solid plate just above the solid steel plate or close to it, and below the expanded metal.
My biggest problem is room. I'm trying to pack a hole house on wheels.
On the left side you can see the trailer plugs and fuel tank power next to a D Ring.
There is some room on the Right side but not much. The space is where the D Ring is. I had to move them over to the right and left when the tank is there to be able to use them. . There is just enough room for them to be used. You can see the vertical uprights through the expanded metal. I would make a mount that would go on the right side one.


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prcguy

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You mentioned Scorpion, so I assume you have a Scorpion HF screwdriver which in my opinion is the best screwdriver on the market and not cheap. The bottom line here is if you install as described, someone with a simple cheap Hamstick mounted in a good location will put out a much better signal than your expensive antenna. If you want your mobile station signal to be on par with the quality of its components please find a better place to mount the antenna.

You can usually get an idea of insufficient ground plane or high ground loss by measuring the feedpoint impedance of the antenna. Without any shunt matching coil on the antenna, and mounted in a good location, I would expect to see a feedpoint impedance probably well under 10 ohms on 80m and under 15 ohms on 40m. Your antenna mounted as described should have a much higher feedpoint impedance like 25 ohms on 80m or 40 ohms on 40m indicating lots of loss.

I would rather not hear you had to mount your antenna as described to find this out and look forward to hearing about a super nice setup in a different location on the truck, wherever that might be.....

A possible location might be to the back of the cab where the truck roof is right under the antenna.



Ok. so here is a better drawing and a picture of the back.
The fuel tank is not in place at the moment.
The base would be mounted to a solid plate just above the solid steel plate or close to it, and below the expanded metal.
My biggest problem is room. I'm trying to pack a hole house on wheels.
On the left side you can see the trailer plugs and fuel tank power next to a D Ring.
There is some room on the Right side but not much. The space is where the D Ring is. I had to move them over to the right and left when the tank is there to be able to use them. . There is just enough room for them to be used. You can see the vertical uprights through the expanded metal. I would make a mount that would go on the right side one.


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camoit

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The antenna is on order and about 10 weeks out. So I'm making sure I will get all the bang for the buck I can get.
So I should just go for a direct mount to the flat bed it's self? I'm thing I might be going that way since the amount of limited space I have. I will grab some better picts now that it's light again.
Avoid the headache rack all together.
Do you think the antenna would have a preference on where it wants to sit?
Right, or left?
The center is kind of a no go since it will have the trailer would run into it during turning.
I do have a couple of extra inches more room on the right side.
 

prcguy

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If it were mine I would consider mounting to the bed as far back from the front wall (bulkhead?) and centered as much as possible. The bulkhead wall thing is not that much of a reflector at HF and its not the size of the antenna up against it that matters but more the frequency you are on. At VHF it would be a major blockage but at HF not so much.

If you mount to the right front side of the bed it should have a lobe that prefers the rear left for best reception.


The antenna is on order and about 10 weeks out. So I'm making sure I will get all the bang for the buck I can get.
So I should just go for a direct mount to the flat bed it's self? I'm thing I might be going that way since the amount of limited space I have. I will grab some better picts now that it's light again.
Avoid the headache rack all together.
Do you think the antenna would have a preference on where it wants to sit?
Right, or left?
The center is kind of a no go since it will have the trailer would run into it during turning.
I do have a couple of extra inches more room on the right side.
 

camoit

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Alright. Thanks for the advice so far it's going to be used and noted in the memory banks.
40 meter is what I'm after most of the time but I will use all of what it and the radio can do as best I can.
Now here are some day light picts.
I would love to go smack dab in the middle of the bed but I need to give most of the room to the trailer for making a jack knife with out snapping it off.
I'm open to all suggestions on locations. Front of truck, under the hood, replace the wife with the antenna, you name it, I will look at it. I just need to make darn sure things clear. I only get one shot at this. So I'm using you guys as the problem solver and I'm just tossing out any interference I might have.
Looking at the back. The tape measure is how high the box and 50 gallon fuel tank is. The hand is reference for distance from the side of the box to the side of the truck.
I'm open to all points of location except the ones that have already been used for the load out.

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Right side below
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Left side below
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camoit

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Now the com center is starting to look more like it should.
Just waiting on the antenna. Then after mounting I need to order the coax.
Ram mounts are used to hold the Kenwood head.

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prcguy

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I would still target the bed as far back from the barrier thing with the lights and centered as much as possible. Even 2ft back from the barrier and 2ft in from the edge should work fine. The barrier thing looks to be about 3 1/2ft tall and an antenna tuned to 40m would not really know its there. Even on 10m it would not skew the pattern that much.

With all that flat surface area in the bed area a large HF screwdriver should work really nice and better than what I have.
 

camoit

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I would still target the bed as far back from the barrier thing with the lights and centered as much as possible. Even 2ft back from the barrier and 2ft in from the edge should work fine. The barrier thing looks to be about 3 1/2ft tall and an antenna tuned to 40m would not really know its there. Even on 10m it would not skew the pattern that much.

With all that flat surface area in the bed area a large HF screwdriver should work really nice and better than what I have.


It will be as far back as I can go with out interfering with the trailer turning.
It would be a bad day to snap the antenna off. (insert cussing face here)
Here is the pass through for the entrance to the bed area. Looks so much better then just a big old ugly hole.
Once the antenna comes in I can order the coax to the proper length. I was # 7 in the build line about a week ago.
Do you think it the antenna cares how thick of mounting surface it has under it?
The bed is made of 14 gauge. It will be well grounded when all said and done.

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prcguy

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RF wise there would be no difference in performance between tin foil and 2" thick solid steel. However if your getting a big HF screwdriver it will need some special mounting consideration due to their size and weight. They usually have a large bracket that mounts to a vertical surface. Some can mount to a vertical pipe and you may have to go wiht a custom bracket or pipe flange mounted to the bed with a short pipe sticking out.

I've hit underground parking structures three times with my Tarheel 100HP. Twice it ripped the mount out and the antenna was ok and once it bent the antenna shaft which cost $168 for the repairs.

Do you think it the antenna cares how thick of mounting surface it has under it?
The bed is made of 14 gauge. It will be well grounded when all said and done.

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camoit

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They usually have a large bracket that mounts to a vertical surface. Some can mount to a vertical pipe and you may have to go wiht a custom bracket or pipe flange mounted to the bed with a short pipe sticking out.


They just do a 3/4 inch bolt now. They were having problems with people forgetting to lube the two parts so they were sticking. If I have an issue with bed flex I can add a plate under it and sandwich the bed between the plate and antenna.
But it looks like I will only be able to get it around 8 inches away from the headache rack.
The trailer is 7 foot wide in the front so I will only get 6 inches of clearance when the truck and trailer are jack knifed hard. No matter it's all a give and take. Once I'm stopped I have a 36 foot portable mast I can stick together and rope down. It's made from 7 foot aluminum concrete bull float handles that will store in the back of the truck between the Aux fuel tank and headache rack. I have tested to 25 foot so far and it felt good going up. But there are over head power lines so going any further would have been a bad idea. At a full 36 foot I might use a back support that will pull from about 2/3 up like a crane uses back tension cables.
 

prcguy

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What will you use on the 36ft mast?

They just do a 3/4 inch bolt now. They were having problems with people forgetting to lube the two parts so they were sticking. If I have an issue with bed flex I can add a plate under it and sandwich the bed between the plate and antenna.
But it looks like I will only be able to get it around 8 inches away from the headache rack.
The trailer is 7 foot wide in the front so I will only get 6 inches of clearance when the truck and trailer are jack knifed hard. No matter it's all a give and take. Once I'm stopped I have a 36 foot portable mast I can stick together and rope down. It's made from 7 foot aluminum concrete bull float handles that will store in the back of the truck between the Aux fuel tank and headache rack. I have tested to 25 foot so far and it felt good going up. But there are over head power lines so going any further would have been a bad idea. At a full 36 foot I might use a back support that will pull from about 2/3 up like a crane uses back tension cables.
 

camoit

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OK. So I had to work between rain storms. I called Scorpion and went over the install.
What they recommend is to get the top at least 12 inches over the cab or any metal surface.
The reason is since the top is where the coil is it will produce a large magnetic field in a doughnut shape around the top.
The higher the better but that will also cause problems going down the road if you have the whip on it.
At the top of the whip I'm now at 14 foot in the retracted position. That is the same as a semi trailer. Look out for low bridge.

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