SWR. going to yank the CB out by the wires.

[The DB]

By all means, if your step by step method works, use it. That being said, that does not mean all the steps are necessary all the time, and some of them may be useless all together. Because of this I urge caution in treating such a method as written in stone. If such a method is ever written in stone you stop learning and that is never a good thing. When it comes to antennas and how they work there is always something more to learn...

I personally prefer to set up the antenna then run a few low power tests, and if they check out and more power will be used I repeat at the higher power level. If there is a problem said tests will quickly narrow down the source of the issue for resolution, although typically there isn't any. Strangely the most common fix I do on mobile antenna systems is something the most people only ever consider doing on base antennas...

besides worrying about the antenna amperage draw is another thing to take into consideration

I'm assuming this is either a mistype or I misunderstood what it was you were trying to say, but in case it is not... Something to note, the antenna does not draw current from a battery in any form, and the negative terminal of the battery does not feed or draw any current directly to/from the antenna. The current types in question are completely different not only in function, but even where they exist in (and around) the wire carrying them. Square peg/round hole type thing...

Something you said I do like...

other factors at play

That is something that some people never learn. Its not just an antenna after all, it is called an "antenna system" for a reason...


The DB

 

[M0GVZ]

Never said it was required but it definitely eliminates a bunch of potential problems and by eliminating potential problems right at the beginning you're automatically taking a bunch of guesswork out of the equation simultaneously.

Step 1 for taking a bunch of guesswork out is to learn about the theory. Step 2 once step 1 is learnt is to use the right tool for the job.

Had you don'e that you would know that making sure you have DC conductivity to the battery does absolutely nothing for ascertaining whether you've got a good RF ground or not. That can only be done by putting a whip in the mount, getting an antenna analyser and measuring what the feedpoint impedance is at resonance, therefore removing a whole bunch of guesswork right there. A quarter wave over perfect ground is 36.8 Ohms when the antenna is at resonance ( X=0 ). Anything other than that and you've got losses and its usually in the ground for the antenna. You could stick a wire directly from the mount to the battery 3ft thick and it wouldn't improve the RF ground.

 

[rabbiporkchop]

explaining the difference between an RF ground and a DC ground to someone who does not understand the importance of either one would have been a waste of my time so I have a tendency to over simplify things without giving the reasons for doing what I do

 

[rabbiporkchop]

explaining the difference between an RF ground and a DC ground to someone who does not understand the importance of either one would have been a waste of my time so I have a tendency to over simplify things without giving the reasons for doing what I do. if he had said that he had a perfect DC ground I would have had him elaborate further to find out if it was a sufficient Rf ground

 

[BigKahuna]

In my experience lil wils, k30's etc don't like big ground planes. Seems weird but I always trouble getting good swrs on top of vans, minivans, suv's with these antennas. But stick them on a trunk of a small car and they worked fine. Maybe it was just me but I can recall running into that same prob lots of times.

On vans for mag mount I always useds a wilson 1000 or similar or ran a fender mount with a fiberglass or metal whip antenna (so I could take it into garages).

Big antennas on top of vans never gave me prob - coils, big whips always had good results.

 

[M0GVZ]

In my experience lil wils, k30's etc don't like big ground planes. Seems weird but I always trouble getting good swrs on top of vans, minivans, suv's with these antennas. But stick them on a trunk of a small car and they worked fine. Maybe it was just me but I can recall running into that same prob lots of times.

The Lil Wilsons, K30s etc are all designed to work out of the box on piss poor mobile installations because that is what the majority are. Stick them on a vehicle that presents a decent ground plane and the SWR will be too high on the CB band because the antenna is too long when used with a good ground. Putting it on the trunk of the car you're replacing a good ground with a piss poor one so it works exactly as the manufacturers designed it to work, with a poor ground. They would've worked on the vans etc but you would need an antenna analyser to see just how much below the CB band they were actually resonant at and get the cutters out to shorten the whips because they usually need shortening more than the adjustment in the antenna allows.

You shouldn't get too obsessed about trying to get a low SWR other than that needed to keep the transceiver finals happy. An analyser is better than a SWR meter because a SWR meter tells you very little. To quote K0BG,

A low SWR doesn't mean squat because we're dealing with a complex impedance which includes a resistive component, and a reactive component. A good example is a 2:1 SWR. It could mean that the input impedance is 25Ω or 50Ω non reactive, or it could mean the input impedance is 50Ω resistive, and either plus or minus 30Ω reactive (±j).That is something an SWR bridge can't tell you.

Trying to get 1:1 SWR is pointless. There's nothing to gain from it and you usually find antennas which can give a SWR of 1:1 quite easily tend to be because they're not very good performers and the low SWR is an indication of losses. As I've said elsewhere, the feedpoint impedance of a 1/4 wave over perfect ground is 36.8 Ohms at resonance. 36.8 Ohms doesn't give 1:1 SWR, it maybe gives around 1.5:1 depending on other factors. If you've got 50 Ohms at resonance you've got issues.

 

[Beetle]

Trying to get 1:1 SWR is pointless. There's nothing to gain from it and you usually find antennas which can give a SWR of 1:1 quite easily tend to be because they're not very good performers and the low SWR is an indication of losses. As I've said elsewhere, the feedpoint impedance of a 1/4 wave over perfect ground is 36.8 Ohms at resonance. 36.8 Ohms doesn't give 1:1 SWR, it maybe gives around 1.5:1 depending on other factors. If you've got 50 Ohms at resonance you've got issues.

And if you have a 1:1 SWR on one frequency, when you move 10 KHz or so up or down, things will have started to change, unless you're using a dummy load for your antenna.

 

[E412B]

RF flows on the surface of a conductor ....

So that is the reason the flatten brad of the coax is better than the 8 gauge wire.

I haven't had a lot of time to adjust the antenna. I have worked on the ground plane system a little.
I removed the bolt and ring connectors on the mount side and added a PL259 connector and a connector for the antenna mount. added the K40 antenna.

Went to an open area and checked the SWR. I now have

1.7 : 1 on channel 1
1.7 : 1 on channel 20
2.0 : 1 on channel 40

I need to work on the grounding strap from the ladder rack to rest of the van.

Don't know why though. On the way back from my last job Friday night. I KOed a 6 point buck. Driver side headlight is held in by zip ties. The passenger side is held in by zip ties because 3 weeks ago, a pickup with a 5th-wheel camper could pull around me at the gas station. Took out the right side of the van. I need a complete new front clip. Core support (plastic) that hold radiator on is broke on left and right side.

Once I get the SWR where it should they will take van and put me in a rental and I will have to start over. Practice makes perfect.

Have to leave in a few for Cincinnati, OH and Dayton, OH for the week.

 

[E412B]

... Strangely the most common fix I do on mobile antenna systems is something the most people only ever consider doing on base antennas...

What would that be?

 

[The DB]

What would that be?

A common mode choke. Most vehicles don't have enough of a groundplane to keep common mode currents from forming...


The DB

 

[M0GVZ]

A common mode choke. Most vehicles don't have enough of a groundplane to keep common mode currents from forming...


The DB

For 12/11/10m bands they have one sufficient that when all the bonding is done and you're using a fixed mount, not a lip or magmount, common mode RFI is almost non-existent to the point that one shouldn't be needed. Given that any choking should be done on the outside of the vehicle then you can only really do it on lip mounts and magmounts.

 

[The DB]

shouldn't

Should... Love that word... Anyway...

You are right, such a choke shouldn't be needed, but sometimes it still is, even after an antenna is properly bolted down in the middle of a roof and the vehicle is properly bonded. It depends on the vehicle, and some small vehicles are just to small... Especially some of these eco-boxes that exist today.

Further, some of these eco-boxes don't actually have a metal roof anymore, and in some cases the only metal is in the chassis and engine and they use plastic or fiberglass panals for the rest of the vehicle. Unfortunately (or otherwise) that is likely the wave of the future for vehicles. Plastic is cheaper, and often easier to repair/replace. Further, its lighter, and to a vehicle, being lighter makes almost everything better.

I prefer to use ferrite beads as a choke, and they can be put an inch or three inside the vehicle with no ill effects. On a magnet mount antenna the choke goes out by the mount, and I use two layers of a fairly thick wall heat shrink tubing to help protect the vehicle.

In my experience, lip mounts often produce the worst CMC's, and again, a ferrite based snap on choke a few inches after the feedline enters the vehicle works fine.

The bolt on solution you mention is not always the best solution for everyone. Not everyone is a hard core enthusiast. If someone in a mobile environment simply needs to communicate with someone else in a mobile environment no more than a few miles a way, say several vehicles traveling to and from the same places, and use CB radios to keep in contact and coordinate between themselves things like meal and bathroom stops, that perfect setup that "should" eliminate CMC's is serious overkill. I wouldn't think these groups are rare either, I know of several groups in this immediate area that goes on such trips, and many of them monthly if not more often.


The DB

 

[E412B]

Been a few and here is an update and a few questions.

I've removed the 3" spring and added a 3" folding adapter like this one


That has come in VERY handy.
Now my SWR is the following with the 3' K40 stick antenna.
2.0:1 on Channel 1
1.7:1 on Channel 20
2.1:1 on Channel 40
I know the antenna is still a bit long.

Questions. Why does SWR act this way in the examples below.
Example 1
When going over a bridge or overpass. Have only checked on channel 20,
but the SWR drops to around a steady 1.2:1 while on the bridge.

Example 2
When going over a bridge like the one below

or underpass.The SWR on channel 20 will bounce from 1:1 up to 2:1 depending on where I'm at on the bridge.

In example 1, is it because of the capacitive coupling of the van ground plane and the steel under the concrete of the bridge?

In example 2, same capacitive coupling but with the steel above the antenna and then the van's ground plane and the steel under the concrete?

Would a 4' (or longer) antenna get the SWR even lower?

 

[The DB]

Questions. Why does SWR act this way in the examples below.

As your vehicle moves, the SWR of your mobile antenna will change as well. To accurately gauge SWR while on the move you really need a 2 needle meter, as when the result changes for the reflect setting the forward also changes. The reason SWR changes when you move is environment around the antenna changes as you move. This changing environment thus changes the tuning of the antenna as you move through it. This is normal. Also, an SWR meter that doesn't take into account both forward and reflect (that is 99% of SWR meters in the world) overreport this change. It isn't something that you normally need to be concerned about.

Would a 4' (or longer) antenna get the SWR even lower?

That depends on the vehicle and the setup, but in general, a longer antenna in a mobile environment will generally get you a lower SWR, and often a wider bandwidth (lower SWR across the whole band) as well. As the vehicle is a large part of the equation in a mobile setup, it is possible that it may be as big of a limiting factor as your 3 foot antenna... If you haven't yet, you may look into RF Bonding as well, especially if you own a smaller vehicle.


The DB

 

[E412B]

Thanks for everybody's input and help.

2nd update today...
I've changed the coax from the SWR meter to the antenna. That was no help.
I changed to a new antenna see thumb below

It's a ROADPRO 54 Air Cooled Helical Coil Center Loaded CB Antenna 1000 Watts RP-2500S.
Had to cut about 4 inches off the base of the whip.
Now the SWR meter reports
1.2:1 on Channel 1
1.2:1 on Channel 20
1.3:1 on Channel 40

The watt meter on the SWR is only showing about 3.5 watts where before with the K40 3' stick it was showing about 4.3. I guessing it showed the return power.(?) When I couldn't get the SWR down with the K40 3' stick.

I have a 49" K40 Plus whip TR40PLUSBC. When I installed it the SWR went 3+:1 on all channels. (Just like the 54 Roadpro Heli). I didn't want to cut the whip for fear it was something else with my setup giving me trouble.
That is the reason I installed the Roadpro and then started to cut it down.

Now, I may try to install The K40 Plus.

Thanks again.