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Commercial Radio Antennas - Please keep discussion related to professional, commercially used antennas and antenna systems for the two-way radio industry. Topics for the use of these antennas on amateur bands are accepted here.

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Old 09-20-2017, 12:08 AM
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Default Antenna Trouble ?

So here's the deal...
Kenwood TK-7360H radio's. Larsen NMO wideband antennas. One in the camper and one in the pickup. Camper has an aluminum roof and sides
Camper is loaded in the pickup box.

receiving VHF weather channels.
In the truck "one bar" in the camper "two bars" in the camper I receive one weather channel I don't in the truck.

Move the antenna and coil from the pickup to the camper, no change in the receive on the camper.
Move the radio from the truck to the camper, No change to the receive performance in the camper.

This leaves one of two options.

The antenna cable is somehow bad in the pickup, or that the receive just sucks that bad in the pickup. (drivers side fender mount '04 dodge)

Yes, the antenna is about 5 or so feet further in the air on the camper and I'm sure is enhanced a bit by the aluminum rood and sides, however driving around with the camper off has left me suspect something was wrong.
I was able to transmit, have the other party hear me but I couldn't hear them. (~20 miles?) over hilly terrain.
Distance was far enough it could be considered "normal"


Digital multimeter yields ~.4 ohms from center pin on the antenna mount to center pin for the radio.

No short or any resistance between center and ground. Good continuity on the cable shield as well.


What am I missing? other than continuity, how else can I test this cable with relatively simple tools?

Thanks,
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Old 09-20-2017, 1:27 AM
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Depending on how the NMO mount is installed, and depending on the base of the antenna, it's not unheard of for the center tab/pin/contact of the antenna to not make contact with the center button on the NMO mount.

Separate photos of the mount, antenna, antenna base, etc. would be really helpful.

The exact model number of the antenna would be helpful, too, however I think that's the one with the black base, spring (maybe) and thicker whip, 1/4 wave (about 18 inches long) Those probably have the spring tab on the underside of the base. Make sure that's bent down enough to make contact with the center of the NMO.

The continuity testing you did was good troubleshooting, that's usually what gets recommended, however far too many people don't know how to use one…
Anyway, what you can do is install the whip on the truck antenna mount, and check for continuity between the whip and the center of the coax connector at the radio end of the coax. There should be continuity. If there isn't, then the center tab isn't making contact.
Also, with the antenna installed, check for continuity again between the outer shield of the coax connector on the radio end of the cable and the center pin of the connector.

Other than that, having the antenna on the fender like that will add some additional loss. It's less than an ideal ground plane, and the cab can block the signal.

One thing not to rule out is interference from your truck. Some Dodges are notorious for VHF interference. If the interference is strong enough, it can overwhelm the receiver and make it seem like it's not hearing well. However, that would probably result in the radio working fine when the engine is off and not working well when the engine is running.
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Old 09-20-2017, 2:20 AM
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Thanks for the reply,
Hadn't considered checking with the whip in place.

The truck is a diesel, so no spark interference.

Larsen WB VHF, Black base, whip is about 34 inches, spring tab on underside of base...

Continuity between the ring (ground) and whip.
Center spring tab has no continuity with the whip (surprised me)
checked that against a second Larsen whip and some other no name brand. All check out the same.
I unscrewed the black base from the truck, placed the multimeter probe on the whip and the center spring tab - no continuity.
Touch the threaded ring, Continuity between the whip and the threaded ring.

Not having a way to check the center spring tab into the base is a pain.... Aside from that, if there was a problem with the whip/base it wouldn't have performed the same when screwed to the camper.
For giggles, I can take the whip from the camper and move it to the truck to see if there is a change.
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Old 09-20-2017, 6:17 AM
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You switched the radios and the problem stayed in the cab, correct?

If yes, did you switch the antennas? The WB-VHF is the most failure prone product Larsen makes in my experience.
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Old 09-20-2017, 12:59 PM
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Quote:
Originally Posted by westcoaster View Post
Thanks for the reply,
Hadn't considered checking with the whip in place.

The truck is a diesel, so no spark interference.
It's not just the ignition system on the gas trucks that cause the interference. There's enough electronics in modern vehicles and most generate some amount of noise.

Quote:
Originally Posted by westcoaster View Post
Larsen WB VHF, Black base, whip is about 34 inches, spring tab on underside of base…

Continuity between the ring (ground) and whip.
OK, I believe that's the half wave wide band antenna. Those will show a direct short from the whip to ground, that's normal.


Quote:
Originally Posted by westcoaster View Post
Center spring tab has no continuity with the whip (surprised me)
checked that against a second Larsen whip and some other no name brand. All check out the same.
I unscrewed the black base from the truck, placed the multimeter probe on the whip and the center spring tab - no continuity.
Touch the threaded ring, Continuity between the whip and the threaded ring.
Trying to recall, so I could be off here…

That sounds suspect. There's an impedance matching coil in the base that should show a DC short between the whip and ground. It should also show a connection between the whip and the center pin at the base.

I could be wrong, but that might indicate an issue, unless they are using a different base design.

It may be working better on your trailer due to enough signal leaking into the coax to act as an antenna. With the shorter cable run in your truck, coupled with possible RFI, it could be not getting enough usable signal to work.

Again, consider this coming from a guy on the internet that can't see your antennas, I could be wrong.


Quote:
Originally Posted by westcoaster View Post
Not having a way to check the center spring tab into the base is a pain.... Aside from that, if there was a problem with the whip/base it wouldn't have performed the same when screwed to the camper.
For giggles, I can take the whip from the camper and move it to the truck to see if there is a change.
It'd be worth picking up a simple quarter wave antenna to test with. Either that, or cut a length of wire to around 18 inches or longer, and remove the antenna from your truck. With your radio tuned to the local NOAA weather channel, touch that length of wire to the center pin on the base and see if it works better than the original antenna.
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Old 09-20-2017, 11:11 PM
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Figured I would check the antenna mount on the fender. Took things apart, ensured good continuity between the bracket and negative battery terminal. Reassembled and it had made things worse!
Now weather 1 doesn't come in at all on the 7360...


Alright figure this one out......
Took the TK-760HG out of the buggy (parked behind the camper. Larsen LM-150 base. Weather channels came in perfectly)

Plunked that in the truck. Weather 1 did not work. Left the radio on, got out to check the antenna, closed door, weather 1 starts receiving, open door, stops, get in close door, no receive, get out, close door, starts receiving.
I'm sure there is a comedy act out there based on this very thing....

On the bright side I think I am getting closer to narrowing down my problem....
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Old 09-20-2017, 11:42 PM
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OK, that's a bit odd.

Using an antenna analyzer, I've watched how some antennas mounted in particular locations, like yours, will show a difference with doors open vs. doors closed.
But sitting in the seat or not is an odd one.
Might be damaged coaxial cable, especially if you ran it through the door or somewhere else it gets pinched.

Other, maybe non related thing, grounding of the radio.
Simply relying on the DC ground connection through the negative power lead, or through the antenna base may not be enough. RF grounds and DC grounds can be totally different things.
If weirdness persists, install a short ground lead from the radio chassis to the vehicle body.
While not the same issue you are having, the first mobile radio I had would sometimes turn itself on and off when I got in my truck. Turned out it was static electricity built up by my butt sliding across the cloth seat. The radio was mounted to the front of the bench seat and only relied on the negative power lead and coax shield for ground. That wasn't enough. Installing a short jumper from the radio frame to the truck body (keep the wire short) fixed the issue.

Intermittent issues like this can be frustrating. About the only thing more I can offer is to systematically isolate the faults (like you are doing. Seems like you have it pretty well narrowed down. Run your hand along or visualize every single inch of the coax. Make sure there is no damage, no broken jacket, no pinched cable, etc. Make sure the radio frame is well grounded. Check all your power connections. Suspect any crimped connector. Give it a good hard tug to make sure it's tight. Might seem unlikely, but you need to check everything.
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Old 09-21-2017, 12:51 AM
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Well, now then that's the other oddity....

I *thought* I had run both positive and negative to the battery posts. But tonight when I was monkeying with the antenna I went looking for the fused negative from the battery post to the radio only to not locate it... Every other radio I have installed I have run two leads...
I can't discount some other "environmental" issue. I grabbed a mag mount antenna, screwed it in to the radio and dropped it on the hood, only to find minimal improvement.

Back to square one....

Since "04 I have had a TK-760H, 760HG, TK-7360H and now TK-7360HV
I thought the tk-7360H performed better than the 760HG
This really came to the fore front when I changed the non V tk-t360H for the current tk-7360HV. I paid little for the V radio and started suspecting it had issues.

The antenna has changed in that time from a Larsen LM-150 to the WB-VHF (sometime to the tail end of the 760HG)

Poor pictures due to the lack of light...
Attached Images
  
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Old 09-22-2017, 12:51 AM
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Solved! (sort of)

When Uncle mmckenna spins a yarn about grounds, pay attention kids....

It still isn't as good as the camper but I'm going to chalk some of that up to antenna position and the shadow cast by both the camper and the house.

The radio was grounded to a piece of sheet metal under the dash with a self tapping steel screw.
I noticed an improvement in the receive when I worked on a ground lug under the dash I mistakenly thought was the radio ground.

Changing this to the negative battery terminal improved the receive on two of the four weather channels from "one bar", to "two bars". The one channel that didn't come in before is a bit spotty and weather 1 is steady at one bar where it was scratchy to non existent before.

There is more work to be done however, I should replace the power lead. This one has been cut and spliced too much for my liking. Looks like they cut the power lead when I had the airbags replaced last year. There is a but splice in the line. I never use those. I always solder....
I think I'll try grounding the radio chassis to the same spot the radio negative lead was grounded to previously. I can't see it hurting anything...
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Old 09-22-2017, 1:13 AM
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Quote:
Originally Posted by westcoaster View Post
Solved!
Glad I could be of some assistance. Now if you could please explain to my wife that I'm not totally useless, that would be great.


Quote:
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I think I'll try grounding the radio chassis to the same spot the radio negative lead was grounded to previously. I can't see it hurting anything...
I've done that on my installs. Since long power wires can pick up noise, giving it a local ground connection can sometimes help. And, no, it won't hurt. Bad/lack of grounding can be a source of a lot of headaches.
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Old 09-22-2017, 1:33 AM
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Quote:
Originally Posted by mmckenna View Post
Bad/lack of grounding can be a source of a lot of headaches.

As I have just found out.....
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Old 09-22-2017, 6:37 AM
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Question based on your last photo. Can you reach underneath where the sheet metal screws go through the Lip? If so I would suggest you replace the sheet metal screws with machine screws with star washers under the head and nut. The star washers will help to bite through the paint, getting down to bare metal to improve the ground at the bracket. The sheet metal screws also tend to wallow out the holes over time allowing corrosion to build up further reducing the conductivity of to the body.
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Old 09-22-2017, 10:23 AM
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Sadly, no. No access to the underside. On the bright side the metal is fairly thick there so the screws are fairly secure.
It's been that way since 2004.

I hear you on the wallowing out. I had that happen on the samurai....
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Old 09-26-2017, 11:42 PM
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Help me wrap my head around grounding the radio chassis to the cab metal....


My radio chassis is DC electrically isolated in the plastic dash.
Only the (now fused) ground lead and antenna cable shield are the sources of ground for the radio.

I run a strap from the radio chassis to the cab metal, will I not then have the potential of having a shorter path to the negative battery post through the radio chassis and ground lead on the radio? (back to the possibility of a floating ground as transient voltage drains through the radio chassis)

What benefit is having the radio chassis and interior cab metal on the same DC ground plain?
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Old 09-27-2017, 12:03 AM
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DC grounds and RF grounds are different things.

On the DC power side, grounding the chassis of the radio won't hurt anything. Most electrical devices in your truck use the truck body as the return path. Some higher power radios don't come with long negative power leads to reach the battery. I've had some older ones that had (from the factory) a short negative lead and install instructions are to ground to the chassis.
Different radio manufacturers and installers will use different methods. Mine isn't necessarily right, although I believe it is -one- right way to do it. I also know it works and has solved issues for me in the past.

On the RF side, long power leads and even the coaxial cable jacket can radiate RF and pick up RF. That RF can go places you don't want. Unwanted RF energy, as in interference from vehicle electronics, can get back to the radio and cause issues. Ignition noise is one, alternator whine is another. Some RF can also leak out the radio using the power lead and/or the antenna. That can get into vehicle electronics and cause issues. Grounding the radio chassis gives everything a nice short path to ground.

As always, your results may vary. Each install can be a bit different. Plenty of people just use the negative lead as the ground and it works fine.
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Old 09-27-2017, 1:27 AM
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Thanks for that, I was getting wrapped up with ground loops etc...
The factory kenwood power leads are fairly generous with their length alright.

just looking for tips tricks and best practices that will improve transmit and receive performance.

Parking the antenna in the center of the roof would provide the best performance, however, sleeping with an antenna poking me in the backside isn't in the cards. (bunk is over the cab). I'm also sure the coil of antenna wire under the dash isn't doing me any favors either...

How much physical separation between power leads and antenna coax? although, it's sort of impossible to run coax out to a fender on the drivers side without crossing paths/running parallel with a bundle of wires somewhere along the line....
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Old 09-27-2017, 1:35 AM
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Cab over camper? Yeah, those are a challenge.

When it comes to coax, use just what you need. Keep a few extra inches in case you need to replace a connector, or to facilitate removing the radio.

Trick is, not everyone has the tools to terminate coaxial cable properly. It takes some skill, and in some cases, specific crimpers, strippers, etc.
Honestly, though, unless you have several feet coiled up under there, you probably won't notice the difference.

Coax should ideally cross other cables at 90º angle. Keeping a few inches separation between the coax and the vehicle wiring. Although, making sure you are using well shielded coax is important. Some cheap coax has a lot of gaps in the outer shield. Good coax will have 95% or better shield coverage, 100% coverage is really easy to get, though.
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Old 09-27-2017, 2:00 AM
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It's whatever coax Larsen sells as their NMO cable kit.

Larsen solder PL259 for the radio. I think I do ok with those...

It's a coil of about 2-3 foot. I didn't think at the time it would make much of a difference so just left it there.
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Old 09-27-2017, 3:03 AM
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Quote:
Originally Posted by westcoaster View Post
It's whatever coax Larsen sells as their NMO cable kit.
Even the basic Larsen NMO mounts is decent cable. No issues there, likely.

Quote:
Originally Posted by westcoaster View Post
Larsen solder PL259 for the radio. I think I do ok with those...
It tested out OK, so you are probably doing them right. As coaxial connectors go, PL259's are pretty straightforward.

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Originally Posted by westcoaster View Post
It's a coil of about 2-3 foot. I didn't think at the time it would make much of a difference so just left it there.
I agree, I wouldn't mess with that. 3 feet of decent RG-58 on VHF is going to be 0.149dB. You wouldn't be able to hear the difference.

I'd say go ahead and clean up the power and grounding, then call it good.
You don't really have much choice on where to mount the antenna. With it that close to the cab and with a slide in/over cab camper on board, you're probably doing pretty good.
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Old 09-27-2017, 9:48 PM
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Sounds like the coax is acting as part of the antenna

Given the location of the truck antenna mount, a 5\8 wave antenna isn't the best choice since 5\8 wave designs rely on an adequate ground plane which you don't have on a fender

I would be using a 1\2 wave Larsen instead

The NMO150HW would be a better choice

This lack of ground plane may be causing some of your issues
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