Splicing RG58

[Brian McVickers]

I think I figured out what the previoius owner attempted to do with the antenna setup --- http://www.firestik.com/Tech_Docs/SNGL-or-Dual.htm

There was one mount on the front bumper and one on the rear tire carrier. The vehicle is a mix of aluminum and steel, steel roof, steel passenger doors, aluminum front and rear quater panels, aluminum hood and rear door. So the ground plane is pretty bad!

Using the two mounts he may have been attempting to rig a co-phased antenna which requires RG-59 cable to be used. The front mount had RG-59 cable running to the radio wher it joined the other cable in a joiner plug that went to the radio. The problem I see was that the cable going to the rear mount was RG-58 and it had two very bad hand wound splices in it. This system would have requred him to have two antennas installed at all times!

One reason people try to splice coax is to feed two antennas from one source. There are probably correct ways to build a harness to do that, but other than truckers with their CBs I'm not personally aware of anyone who does that (other than commercial broadcasters, but that's a little more sophisticated). It's hard enough optimally tuning a single antenna, forget dealing with two radiators! With co-phased antennas you need to be super careful about the distance between the two whips and it'll really only works well at a relatively narrow bandwidth. The two whips probably should not be flopping around in the wind, either...

 

[Brian McVickers]

DUH! on me!
http://www.firestik.com/Tech_Docs/Mnt-Grnd.htmThe antenna mount is not grounded! :sport_box

SWR Readings:

Ok, the antenna is completely below the roofline and about three inches off the back door's vertical plane.

I just checked the SWR readings:

Ch-20 = 7
Ch-40 = 4.8
Ch-01 = 12.5

The % of reflected power is in the red on the meter. Red starts at SWR of 3 and is equal to 25% of power reflected, so my readings are over 50% reflected.

According to the directions: If reading is higher at ch40 than ch01 antenna needs to be shorter. If readingis lower at ch40 than ch01 antenna needs to be longer.

So I need a longer antenna. Is there more to it that I am missing?

Oh, and thanks by the way this is great help!

 

[Brian McVickers]

I think the answer here will be to properly ground the mount and then go with a taller antenna that will clear the roof line.

Considering the
FireStik 4' Fire Fly toploaded antenna or
Wilson 4' Flex toploaded antenna

I'm leaning towards the Wilson Flex

Since both are toploaded the majority of the TX power is emited in the top 1 foot of the antenna which will be above the roofline.

 

[crawler#976]

My best results for CB's have been with a whip type antenna. The Taco has a 1/2 wave base loaded whip, the trail beater a true 1/4 wave 108" with spring mount. Previous to that I used a roof mounted base loaded K40 quick detachable antenna. It worked the best of the three, but was a pain when trailing thru wooded areas. I quit spending large amounts of money on radios - they seem to get beat by trail use anyway, so I buy cheapys and use a good antenna. Seems to work out pretty well - rarely do I have problems w/ RX or TX (until the radios puke...)

The only disadvantage to the whips is having them flop around. I keep the 108" secured at the tip until needed, and when people are around on the trail, point it out and tell'm to stay clear...

As far as grounding goes, I run a seperate ground directly to the mount and connect it to the chassi at the same location the radio is grounded.

 

[k6uk]

A few points....

Just read through this thread and I have a few things to add:

1. I'm not sure about those SWR readings. Your swr should be below 2 on all channels. But I'm not sure where you are getting your numbers since most swr meters top-out at about 4 or 5. At any rate - you may have a problem if your SWR is that high.

2. Antenna Height. You definately want to get the antenna above the roof if possible - the more clearance the better. At least try to get 1/3 of the antenna up above the roofline.

3. Grounding.

As far as grounding goes, I run a seperate ground directly to the mount and connect it to the chassi at the same location the radio is grounded.

Grounding is super important when it comes to radio equipment. But it is also important to keep you ground runs as short as possible. You don't want the ground to be so long that it becomes an antenna itself - so always ground the antenna as close as possible to the mount.

4. A note about co-phasing and coax length. It is often talked about that coax legnth affects the swr of a given antenna, and there are certain "magical" lengths of coax that CBrs will sometimes swear you must use. This really isn't the case - properly sheilded and installed coax can be whatever length you want (see http://www.signalengineering.com/ultimate/coax_basics.html). BUT in the case of co-phased antennas you would need your runs to be exactly the same length and the same type of coax. In-fact, to do it right you would need to determine the velocity factor of the coax you are using, and cut specific legnths of coax. The reason has nothing to do with antenna length, but rather the speed at which the signals travel through the coax. If your antennas radiate "out of phase" they will cancel each other out instead of increase your gain. Here's a good link to an article on co-phasing (http://www.signalengineering.com/ultimate/co_phasing.html) but as you can see it is really most effective on large base-station antennas. Truckers co-phase their antennas to combat the huge trailer they are hauling which can cause dropouts in signal on one side of the vehicle.

-Mike

 

[k6uk]

A few points....

Just read through this thread and I have a few things to add:

1. I'm not sure about those SWR readings. Your swr should be below 2 on all channels. But I'm not sure where you are getting your numbers since most swr meters top-out at about 4 or 5. At any rate - you may have a problem if your SWR is that high.

2. Antenna Height. You definately want to get the antenna above the roof if possible - the more clearance the better. At least try to get 1/3 of the antenna up above the roofline.

3. Grounding.

As far as grounding goes, I run a seperate ground directly to the mount and connect it to the chassi at the same location the radio is grounded.

Grounding is super important when it comes to radio equipment. But it is also important to keep you ground runs as short as possible. You don't want the ground to be so long that it becomes an antenna itself - so always ground the antenna as close as possible to the mount.

4. A note about co-phasing and coax length. It is often talked about that coax legnth affects the swr of a given antenna, and there are certain "magical" lengths of coax that CBrs will sometimes swear you must use. This really isn't the case - properly sheilded and installed coax can be whatever length you want. BUT in the case of co-phased antennas you would need your runs to be exactly the same length and the same type of coax. In-fact, to do it right you would need to determine the velocity factor of the coax you are using, and cut specific legnths of coax. The reason has nothing to do with antenna length, but rather the speed at which the signals travel through the coax. If your antennas radiate "out of phase" they will cancel each other out instead of increase your gain. Here's a good link to an article on co-phasing (http://www.signalengineering.com/ultimate/co_phasing.html) but as you can see it is really most effective on large base-station antennas. Truckers co-phase their antennas to combat the huge trailer they are hauling which can cause dropouts in signal on one side of the vehicle.

-Mike

 

[Brian McVickers]

Thanks Mike.

I talked to the techs at FireStik and the guys at Apollo Communication CB shop in Phoenix and they wer not overly concerned with coax length either - more with grounding and obstruction clearance.

So I have gone with a Wilson "Flex" 4 foot with a quick disconnect. It clears the roofline about with maybe the top 30% but it is also a topload antenna which primarily uses the top one foot of the antenna.

I also ran a propper ground to the antenna mount from the vehicles frame whre I sanded down to bare metal.

It very well could be that I'm using the SWR meter wrong but the readings seem pretty straigt forward. Now with all I have done to improve things I get readings of 2.5 on ch40 and 3.5 on ch1. The Wilson has an adjustable tip and I have already maxed it out with little improvement to SWR. It should be good enought for the trail but it's not perfect - yet!

My biggest concern with the CB now is that I can faintly hear the WX band when on CB. I can hear the weather report very faintly in the background when close to the speaker. What is causing this - what to do?

 

[k6uk]

That SWR still is too high.
The Wilson comes with a little pigtail of wire attached at its base.
Did you leave this unattached, or did you ground it?

It's supposed to be left unattached, unless you have problems getting the SWR down low enough... then you ground it and see if it helps.

As for the bleed over from the weather band reciever - this is definately some problem in the radio. What model radio is it? Maybe there is a fix available online somewhere.

-Mike

 

[Brian McVickers]

:iagree: the SWR is still to high, but

I have that wire unattached but I did try it to see if it helps but the SWR just went higher!

The instructions on the Wilson suggest getting a longer piece of stainless steel rod to make a longer adjustable tip if you can't get the SWR down. But I'm not even sure I'm doing it right to begin with! The shop where I bought the antenna will tune it for another couple of bucks but I did not have the vehile with me when I was there, and no time this week.

The radio is a simple Radio Shack unit, a few years old.

 

[k6uk]

Well I notice on the Wilson website that they will provide you with a longer whip if necessary.
http://www.wilsonantenna.com/tsswrf.htm
(309) 756-4546

But I'm not even sure I'm doing it right to begin with!

Okay. Just so you're sure you're doing it right - here is the procedure.
I am assuming you are using a regular power/swr meter not built into the radio.

Of course the first thing is to attach the proper side of the meter to the Transmitter and the other side to the Antenna, the meter will be marked. This seem obvious, but I've seen people miss this step.

Now... first of all you will measure your forward power. There is probably a switch that let's you choose FWD/REV(or SWR)/CAL or something like that. This switch should be set on FWD for the moment. Now key down and you will see the power of you carrier. With a stock CB you should see about 2~4 watts at this point.

Now, you want to switch over to CAL or Calibrate. This can be the same switch or it can be somewhere else, but you want to use the knob on the meter to bring the needle to the CAL mark on the meter face. This should be around full scale.

Once it is calibrated for the channel you are on, flip the switch to REV or SWR, and read the SWR scale. This will give you your proper SWR.

I'm sure this is what you were doing, but better safe than sorry.

-Mike

 

[Brian McVickers]

Yep thats the procedure I did.
very basic SWR meter with one switch FWD/REV and a CAL knob
Switch to FWD then on ch20 key mike and adjust CAL to the infinity sign on the scal. Then switch to REV and key on CH40 and CH1 for readings.

 

[k6uk]

Okay.
Well then let me ask. What is the antenna attached to?
For example, if it's mounted on a swing out tire carrier, it may be necessary to ground the bumper/tire carrier with copper braid. Simply running a ground to the mount is sometimes not enough, since there is a difference between RF grounding and electrical ground. Oh, which brings up another question... what did you use to ground the mount? Did you use regular wire or copper strap?
Copper strap (or braid) is the preferred material.

-Mike

 

[Brian McVickers]

The rear door of the vehicle is aluminum, there is a steel tire carrier mounted just off center on the door, the antenna mount is bolted to the tire carrier.

I then have a 12ga copper strand wire running from one of the bolts attaching the antenna mount to the carrier to the frame of the vehicle attached to a spot where I sanded to expose bare metal.

The roof and 4 passenger doors are steel while the hood, four quarter panels and the rear door are aluminum.

 

[k6uk]

Here is a great article on Grounding, and in particular Bonding:
http://www.k0bg.com/bonding.html

There is a good chance that the door, and possibly the carrier are not grounded properly to the vehicle body. A couple of ground straps could magically solve your problem Take a quick read this may be your answer. Even if it's not, you can only improve things by bonding the rear door and the tire carrier (and all the other doors wouldn't hurt the situation any).

-Mike

 

[DaveInDenver]

Yep thats the procedure I did.
very basic SWR meter with one switch FWD/REV and a CAL knob
Switch to FWD then on ch20 key mike and adjust CAL to the infinity sign on the scal. Then switch to REV and key on CH40 and CH1 for readings.

One of my old meters is probably like what you're using, a single needle, switch and a knob. This is a pretty simple SWR bridge.

Set it to FWD and key the mic. When you do this, the needle should swing to the right and you adjust the knob until the needle is zero'd (or infinity). Switch to REF, key the mic again and is the SWR measurement. REF in this case means REFlected power.