CB Bad???

[justfun1]

Hi all, I'm a bit stumped. :confused24:

 

I recently upgraded my '86 to an '89 and am working through the bike making sure all is alright. The bike was missing the tip of the antenna so I'm trying to "fit" a new tip. I cut an antenna about 20" thinking I can step it down until I get the SWR correct. Hooking up the SWR I found that the reading is pegged past infinity. I started troubleshooting but have not found any obvious issues. I'm now stumped as to what to check next???

 

Items done:

1) SWR : it is pegged off the scale on ch1, ch40 and ch19 :confused:

2) Antenna mount has continuity to the negative on the battery.

3) The antenna when removed form the mount it has continuity from base to tip

4) the cable has continuity for the center conductor to the antenna mount post

5) the cable shield has continuity to the antenna mount body

6) there is no continuity between the center wire and the shield

7) tested with the matching box both connected and bypassed

 

After this effort I was thinking on buying the stuff for the Marshal Mod but I'd like tofigure out if the CB is good or not prior to sinking the $$ into a new antenna setup.

 

Any help or thoughts would be greatly appreciated.

 

Thanks, Mike

[BOO]

Hi all, I'm a bit stumped. :confused24:

 

I recently upgraded my '86 to an '89 and am working through the bike making sure all is alright. The bike was missing the tip of the antenna so I'm trying to "fit" a new tip. I cut an antenna about 20" thinking I can step it down until I get the SWR correct. Hooking up the SWR I found that the reading is pegged past infinity. I started troubleshooting but have not found any obvious issues. I'm now stumped as to what to check next???

 

Items done:

1) SWR : it is pegged off the scale on ch1, ch40 and ch19 :confused:

2) Antenna mount has continuity to the negative on the battery.

3) The antenna when removed form the mount it has continuity from base to tip

4) the cable has continuity for the center conductor to the antenna mount post

5) the cable shield has continuity to the antenna mount body

6) there is no continuity between the center wire and the shield

7) tested with the matching box both connected and bypassed

 

After this effort I was thinking on buying the stuff for the Marshal Mod but I'd like tofigure out if the CB is good or not prior to sinking the $$ into a new antenna setup.

 

Any help or thoughts would be greatly appreciated.

 

Thanks, Mike

 

Just a couple of thoughts. You could be so far off with the length of the antenna that it would give you that kind of reading. I'm not sure what the length of the stinger part of the antenna is suppose to be. You could just use some with scrap wire to cut down or add to the length to try and find the proper length.

If I understand the readings you took, the mechanical part of the antenna is good.

I'm not sure buying another antenna is going to correct your problem.

Just a side note here the "electrical" length of a CB antenna is somewhere around 108 inches.

Good Luck

Boo

[frankd]

The tip on my 89 is 18 7/8" from the ball to about 3/8" below the set screw. Are you checking the swr in the garage? You need to be over a 1/4 wave (108" @ 27 MHZ) away from everything, so take the bike outside. Also, on mine, the matchbox doesn't work that great. Mine has a low swr on channel 1, but it's over 3:1 on channel 40, and I can't get the matchbox to adjust. I'd shorten the top section a bit, but the setscrew is frozen. I just leave it alone because it works good enough this way.

 

That brings up something.....Because the antenna works for AM, FM and CB, it isn't resonant at 27MHZ. That means that Yammie had to use a matchbox to get it to work. That matchbox is in the coax that connects to the CB. Have you been adjusting the matchbox OR just checking the SWR with the temporary antenna top section?

 

Cut a wire to 18 7/8" and install it. Take the bike outside and check the SWR on channels 1, 20, and 40. If the antenna loads at all (less than infinite swr) anywhere in the CB band, that should let you know what to do next. With the original length top section, I'd probably try to adjust the matchbox next.

 

Frank D.

[Bob Myers]

Long drawn out procedure but,, I rolled my bike out in the drive, unhooked the CB cable from the match box and by using a different CB and SWR meter I set the stinger(my disappeared too so I started out waaaay long with a new one) for as low SWR as I could on channel20,checked channel 1 and was somewhat higher but not bad, checked 40 and it was the same as 1. Hooked the antenna back to the matchbox and sat the SWR meter(it also is a Field Strength meter as far away as I could where I could still be able to see the needle wiggle. Then while keyed I adjusted the matchbox for maximum needle deflection. May not be easiest method but I do know the antenna is as resonant as possible.

[justfun1]

Thanks for the feedback!

 

My iniitial reading were with the bike about 20 yards from any building in the driveway. I am trying to use a piece of scrap wire that I was playing with to try to figure out what the antenna height should be. I just can't seem to get a reasonalbe SWR at any length.

 

I have also not adjusted the matching box . . . Is it even possible for the stock ones? In an attempt to rule it out I did remove it from the SWR setup a couple times and it did not change the result.

 

If I understand what I've read on the net about the SWR readings . . . my results indicate that basically all ofthe power is being reflected back to the radio & virtually nothing is being transmitted. Is this correct?

 

Thanks again for your help!

Mike

[Bob Myers]

Thanks for the feedback!

 

My iniitial reading were with the bike about 20 yards from any building in the driveway. I am trying to use a piece of scrap wire that I was playing with to try to figure out what the antenna height should be. I just can't seem to get a reasonalbe SWR at any length.

 

I have also not adjusted the matching box . . . Is it even possible for the stock ones? In an attempt to rule it out I did remove it from the SWR setup a couple times and it did not change the result.

 

If I understand what I've read on the net about the SWR readings . . . my results indicate that basically all ofthe power is being reflected back to the radio & virtually nothing is being transmitted. Is this correct?

 

Thanks again for your help!

Mike

Yes, the SWR reading is reflected power, higher the reading, the more reflected power(less radiated output)

 

In your continuity experiment, did you probe from center conductor of the coax after unscrewing it from matchbox, to the antenna mast itself? This should be an electrical connection between the two. If not the coax is open somewhere

Edited September 21, 2012 by Bob Myers

[justfun1]

Hey Bob,

Yes I did the motorola tip at the matching box to the tip of the antenna and had continuity . . . I did not measure the ohms though, if I understand it correctly it should be about 50 ohms resistance correct?

 

A friend at work suggested that the SWR meter may be faulty too, so he'll bring in one on Monday for me to verify with.

 

Thanks

[utadventure]

Mike-

 

When I first got my '86, other riders could hardly hear anything I was saying. I could hear just fine. It had a stock antenna and I started test things just like you have. The antenna length includes the cable, splitter in this case, and the actual antenna. Still didn't work. I replaced it with another stock antenna....same problem. Usually, off the chart SWR readings, means a ground in the system.

 

I finally did the marshall mod, kind of.

 

FYI, the radio itself has resistance. Be sure to disconnect the radio before testing.

Also, the antenna system length is mostly relevant when transmitting.

 

I eliminated the splitter and installed an aftermarket antenna with a cable directly to the radio. Better, but still the same basic issues.

 

Next, I swapped out the antenna for the Firestik with the adjustable tip....not an issue since. I have a 6' cable from the antenna to the radio. Getting the antenna, mounting lug and making or buying a short cable isn't overly expensive and most can be returned if it just won't work.

 

Good luck!

[Bob Myers]

You know, I hadn't thought about the swr meter being Kaput. I have one of those, looks pretty sitting on the shelf.

As Dave said, do a real antenna and obtain another CB mount for the other side and put a better quality antenna there for the AM/FM

[frankd]

Hey Bob,

Yes I did the motorola tip at the matching box to the tip of the antenna and had continuity . . . I did not measure the ohms though, if I understand it correctly it should be about 50 ohms resistance correct?

 

A friend at work suggested that the SWR meter may be faulty too, so he'll bring in one on Monday for me to verify with.

 

Thanks

 

 

No, 50 ohms is the impedance (similiar to resistance) to the CB ouput power, so 50 ohms is only to a 27 MHZ signal. With an ohmeter, you should measure very low resistance to the bottom section of the antenna from the coax that attaches to the output of the matchbox. The loading coil will have some dc resistance, so if you measure to the top section, you will measure a little more. I'd expect you to measure less than 5 ohms. Actually the 50 ohms impedance you were referring to is at the coax that connects to the CB. Because the antenna itself is non-resonant and a matchbox is used, the coax between the matchbox and the antenna will have a different impedance. The cb is designed to have that 50 ohm load connected to it. The swr meter measures the difference between what is actually connected to the cb and that 50 ohm value.

 

To use the swr bridge correctly, disconnect the coax at the cb itself. Connect this coax to the jack on the swr bridge that is marked antenna or output. Using a short coax jumper (made with RG-58, RG-8X, or RG-8 coax) connect it between the cb and the jack on the SWR bridge marked transmitter or input. You could take your ohmeter and make sure you have a good jumper===from the center of one connector to the other you should have very low resistance. The same for the outside of each connector to the other outside. And from the center to the outside (shield) you should NOT have continuity. Put the CB on a center channel, and with the switch on the swr bridge in the FORWARD position, key the CB and adjust the control on the SWR bridge so that the meter indicates full scale. Turn the switch to REVERSE and key the transmitter. Now you can read your SWR. If you get an swr of less than infinity, repeat at channel 1 and channel 40.

 

To adjust the matchbox, install a top section in the antenna, and with the swr bridge connected as above, adjust the trimmer that you can get to through the hole in the matchbox. Look in the hole and you can see a small screwdriver slot. Probably the best way for you would be to mark where the trimmer is now. Then turn it slightly and measure the swr. Then repeat that until you get the lowest swr available.

 

Frank D.

[justfun1]

Thanks for all the help with my "Issue", it is great to have such a great group to share knowledge with.

 

Well . . . As it turns out the problem was the operator of the SWR meter.

 

I had understood from the person I borowed the SWR from that the REF was the referance setting rather than the reflected setting. Seems that I had been setting the initial reading on the REF rather that the FOR so when I switched it to check the SWR it was always off the scale to the infinity.

 

Another embarassing lesson learned that won't be forgotten soon . . . .

 

Thanks again,

Mike

[Bob Myers]

Trust me Mike, you are not the only person who has ever operated it backwards, I'd bet if the truth be told, several people here could admit to hooking one up with the patch cord on the antenna and the antenna to the tx side of the meter too.

 

So, when operating as should what is your SWR reading?

[justfun1]

With my initial scrap test wire antenna, I was reading a bit over 3. Tonight I hope to start tuning in on the target height with my test wire & then fit my good antenna wire to the antenna.

[Bob Myers]

what are you using for test wire? Coat hanger? If so, make sure you strip the coating off where it goes into the load coil so it has a solid electrical connection with the setscrew.

I used a piece of stainless filler wire from my Tig welder. with much difficulty I removed the ball from a car antenna and press fitted it onto my stainless rod. It'll do until I find a CB donor rod in one of the flea markets.

[justfun1]

yeah I'm using a coat hanger to start with. I did have to grind down the dia. to fit it into the .082" hole so I should be OK with the electrical connection. I have a friend that is into HAM radio and he picked me up a treated SST antenna whip for $1 at a show he was at. Unfortunately it does not have a corona ball on it. I have been playing with a concept that my friend thinks should work well.

 

Initially I took a piece of oak and drilled about a 1/8" hole about 1/8" deep using a drill press. I then sanded the end of a test wire to expose the raw metal. Using a soldering iron I filled the hole up with solder and then put the tip of the test wire into the monten pool & let it cool. I was able to work the resulting plug out of the mold and clean it up a bit with a file.

 

I'm planning on trying a smaller dia. tip tonight that would have less mass. I also will play with different matierials to make the "Mold" from that might yield a better finnish. We'll see I guess, but it is fun tinkering with new ideas.

[dacheedah]

I like two antennas and eliminating the box, that mod will serve you well

[justfun1]

Just wanted to share how it all ended up.

 

The solder tip seems to have worked out well. Attached is a picture of tip.

 

After tuning in the height with the test piece of coat hanger I cut the good antenna 1/4" longer thinking I could walk in the Tuning. Upon installation I found that the new antenna was a bit too short! So it seems that the electrical properties of the metal used for testing will impact the final height too.

 

Thanks to the great responses on this thread, I learned that there was also a matching knob on the antenna splitter box. I was able to finish getting the antenna tuned in by using this matching adjustment.

 

SWR Results: 1:3.5 on Ch1, 1:3 on Ch20, 1:4 Ch40

 

Thanks again for the help!

Mike

[Bob Myers]

Metal properties effect the RF less than diameter and the coating on the steel wire. RF travels around the outside of the conducting element, so if it is larger in diameter there can be a minimal effect there, but I would never thought an additional ¼ would still end up short. Try a cheap car antenna, they too are hardened stainless and plenty cheap with static/corona ball already on