CB won't tune

Discussion in 'Electronic Toys' started by Miescha, Nov 2, 2007.

  1. Miescha

    Miescha

    Messages:
    1,096
    Location:
    St. Louis, MO
    OK, so I'm sure I'm goofing up something, but I can't figure it out.

    I have a Cobra 75 wxst and a brand-spanking-new Firestick Firefly 4ft with tuneable tip. I also ordered the hood groove-mount kit with 18ft of Firestick cable and mounting stud. I also ordered the Firestick quick disconnect and an SWR meter with cable.

    I mounted the antenna, ran the cable into the cab, connected the coax connector including soldering the wire tip, then made the connection at the radio box and powered it up. I can hear others just fine and I can get out just fine (tested a few times with StlCruiser and we could talk a mile or two away), so I know it will work for trail use, but here is the problem.

    When I hook up the SWR meter and test following the procedure in the Firestick SWR book CoxCB sent me, I get readings WAY in the red. Channel 1 is about 3.2 / channel 19 is about 4 and channel 40 is about 4.8

    I played with the antenna tip extension but no amount of screw in/out seems to matter. The SWR book states that a reading higher on 40 than on 1 indicates a 'short' antenna and I should lengthen it. Alternatively, it says a very high reading (in the red as I have) indicates a very poor ground plane or cable fault. I've checked my cable connections for continuity and everything checks out fine. I"m just wondering if I did something wrong putting the cable connector on the end.

    Any thoughts (other than ditch the CB and move to Ham)?
  2. FJ40_owner

    FJ40_owner  

    Messages:
    818
    Location:
    El Dorado County CA
    Ohm meter the cable with the antenna and radio disconnected. There should be no resistance between the shield and center conductor.

    Ohm the tip of the PL259 to the shield at the antenna. There should be no resistance.

    The higher the frequency ie channel 40 @ 27.405 Mhz the shorter the antenna. So assuming your coax is good as well as your PL259 solder job with a high SWR I would shorten or turn down the screw.

    If you have all new equipment and the SWR is not reacting properly and the coax is good you may need to look at your installation. Is there continuity from the shield at the PL259 to the chassis and all the way to the antenna mount? Try installing the antenna in a different location, have a good bond between the car frame and antenna mounting hardware.

    Same frustrations apply to Ham radio as well.

    Good luck
  3. Jerry D.

    Jerry D. SILVER Star

    Messages:
    519
    Location:
    Citrus Springs, Florida
    Yes, check the cable first. Only I believe you should have infinite resistance between the PL259 tip and shield. A “no resistance” to me is zero ohms which would show a short in the coax or connector.

    You should make sure the small metal box where the coax/power and mic are connected is also well grounded.

    How is the antenna mounted??? Pics???

    Jerry D.
  4. Miescha

    Miescha

    Messages:
    1,096
    Location:
    St. Louis, MO
    I'll try to get a pic of the mount install, but it is dark now so may not work. The mount is a hood groove mount by Firestick. It is the MK-174 as shown here:

    http://www.walcottcb.com/firestik-mk174-hood-groove-mini-kit-p-311.html

    I've checked (and triple checked) that the antenna side 'fire ring' and assorted stud, washer, lock washer, etc... is in the correct order and the ridge of the ring is facing the correct direction. I've also made sure all connections are tight.


    It is mounted using a factory nut/bolt on the PS just forward of the power am/fm antenna - as recommended by Toyota 4WD Owner Magazine and shown (partly) in the pic below. I did not remove the cruiser's paint at the mount point (and would rather not). I'll try to get a pic of my install given the darkness and post later.

    I didn't think about the ground at the metal box - I'm currently testing with it loose inside the cab (easier to make connections for SWR meter without it mounted). If this is a likely cause, I may have found the problem. I'll have to reconsider my planned mounting location as I'm not sure it will provide much ground for the metal box. I'll start looking for a good mounting location in the DS under-dash / footwell area.

    I think the only possible causes (outside the highly unlikely bad antenna or bad SWR meter) are

    1) Bad/incorrect conection of cable connector at radio side (bad solder, short, etc . . .). I'll go through all the continuity / ohm tests again.

    2) Lack of good ground at antenna mount (I could try running a 12 guage wire to the frame).

    3) Lack of good ground at the radio's metal box (I'll find a better mounting location and bolt the sucker down tight).
    Toy 4WD Owner Mag.jpg
  5. Miescha

    Miescha

    Messages:
    1,096
    Location:
    St. Louis, MO
    OK, I froze my hands but I managed to check everything noted. First, I found this from Firestick regarding continuity:

    There is a minimum of four priorities with every GP antenna installation.
    1. No continuity from the coax connector center pin to the coax connector housing while disconnected from the radio.
    2. No resistance continuity from the coax connector center pin (disconnected at the radio end) to the base of the antenna.
    3. No resistance continuity from the coax connector housing (disconnected at the radio end) to the antenna mount.
    4. Final SWR reading below 3.0:1 on any channel that you use.
    Upon testing, I have NO CONTINUITY from the PL259 center pin to the threaded housing. Ohm reading was 00.4

    I also have NO CONTINUITY from the PL 259 center pin to the MK174 base of the antenna. Ohm reading was also 00.4

    I also have NO CONTINUITY from the PL259 threaded housing to the antenna stud mount (or anywhere else on the antenna).

    There IS continuity from the PL259 center pin to the antenna stud and everywhere else on the antenna except the the MK174 base, as noted above.

    There IS continuity from the PL259 threaded housing to the MK174 base.

    There IS continuity from the MK174 base to the chasis ground (I used the battery negative terminal as a test point, as it has a direct ground to the engine block and chasis).

    There IS continuity from the PL259 threaded housing to the chasis ground (batter neg. terminal test point again).

    There IS continuity from the threaded antenna connector on the radio metal box to the chasis ground (neg battery terminal test point again).

    I can't get a good photo of the mount as it is too dark (the flash reflects off the vehicle paint and bounces back).

    At this point, I'm wondering if I'm using the meter wrong. I have it connected between the antenna and the radio as indicated in the accompanying literature. I set it to "FWD" then key the mic on channel 1, while holding the mic keyed, I adjust the knob to the extreme far right of the band where the words "set" appear. While still holding the mic keyed, I flip the meter switch from 'FWD' to 'REF' and read the SWR. I repeat this on channels 19 and 40. It always stays well above 3 as noted in my first post.

    I also mounted the antenna on the top tab of my ARB front bumper (my preferred location as that tab is VERY stout) and I tried a rear hatch location (b/c I have the MK 204 mount just in case I didn't like the MK174 location). I found NO DIFFERENCE in any of the locations. Given this, I'm tempted to just mount it on the ARB as I would like and call it a day. There is definately a good chasis ground at the ARB location despite the powder coat paint, but I guess I'll have near zero ground plane - but maybe it doesn't matter b/c my SWR is so high anyway.

    I have to be up at 5am, so I only have a few more hours to figure this out and pack my stuff into the cruiser. I'm starting to think maybe the meter IS bad :frown:
  6. Miescha

    Miescha

    Messages:
    1,096
    Location:
    St. Louis, MO
    Finally Got It!

    Yep, I'm an idiot :crybaby:

    I decided to follow my usual problem solving theory which states that if whatever I'm attempting to accomplish is not working correctly, I'm probably doing something wrong somewhere.

    I deciding that given a WAY high SWR no matter where I mounted the antenna, I would prefer to have it on the ARB front bumper. I moved it to the PS top-most tab and began checking everything again. This time, I had no chasis ground from the ARB top tab (my new 'mount' point) and therefore no continuity from the radio-end PL259 threaded housing to the tab. This is a definate bummer.

    I had already removed the MK174 mount, but decided to re-check the ground at the hood groove where it was previously mounted. No chasis ground. Big bummer. I then check for chasis ground at the exact OEM bolt I used. No ground. I then checked at the washer of the OEM bolt I was using and got a continuity signal back to the battery neg terminal. Big relief. Still, it seems clear that to get a good ground here I would need to remove some of the paint or run a wire from the MK174 base back to the neg battery terminal.

    Instead, I decided to run a 12 guage wire (I didn't have anything bigger on hand) from the ARB base back to my PS second battery neg terminal (grounded to the PS ground point on the engine). This was tougher than planned b/c the coax that comes with the MK174 kit does not have a seperate ground wire, so I had to ground to the inner 'Firering' ground point without also grounding the bolt or mouting stud. After a ton of continuity testing, I managed to get it.

    So the moment of truth, I wire up the SWR meter and key the mic on channel 1 and get a reading of 1. Yep, SWR was 1 on channel 1. On channel 40 it was up over 2 and after a lot of tuning the Firefly tip, I ended up with 1.8 on channel 1 / 1.5 on channel 19 / 1.8 on channel 40. I figured this was a nice 'dip curve' and decided to call it a night (I still have to pack up my trail gear in the cruiser and hopefully find something to pack for lunch tomorrow).

    I hope I haven't just found a nice way to fool the SWR meter without the associated gains in signal strength, but I did notice a much clearer signal coming in across all the channels.

    Thanks a ton for the advice guys, I hope future readers find this thread and are helped by my follies.
  7. Jerry D.

    Jerry D. SILVER Star

    Messages:
    519
    Location:
    Citrus Springs, Florida
    Glad you got things looking right, now if only you had a field strength meter...

    Jerry D.
  8. Miescha

    Miescha

    Messages:
    1,096
    Location:
    St. Louis, MO
    :doh: It never ends does it?!
  9. Brentbba

    Brentbba Former Golfer SILVER Star

    Messages:
    8,897
    Location:
    The OC, CA
    Thread revival. I think I have a similar situation but I'm not an electronic guru on ohms, resistance, etc. despite having a meter.

    Installing the same radio. Using an existing Diamond K-400 3/8C hatch mount, but have replaced the corroded original coax from the mount with a Firestik K-4A stud mount and have a heavy duty spring on top of that and then a 3 ft tunable tip antenna I used with my old CB.

    I know I've got the transmitter box properly grounded in the engine bay where my old CB was grounded.

    SWR meter is calibrated correctly because when I leave the dummy load antenna on and switch to REF on both channel 1 and 40 the SWR is right at 1. When I put the coax from my antenna mount on the SWR I'm off the charts for the SWR reading on both 1 and 40 with no change at all regardless of how I move the tunable tip. It's got to be the ground at the antenna, right?

    Here are some pics of the mount and where I've got the Cobra box mounted under the center console. I've only got the box on some velcro. It's not screwed into the body of the truck, but shouldn't need to be with the ground to the firewall in the engine bay via the black wire from the box.

    I've noticed on an 'original' pic of a K400 that it's got what appears to be a small ground wire on the outside that feeds into the coax. The coax itself is exactly where the Firestik firering type coax would connect. I've just got the PL259 connectors there. Not sure where I should try to ground this set up.

    Attached Files:

  10. Brentbba

    Brentbba Former Golfer SILVER Star

    Messages:
    8,897
    Location:
    The OC, CA
    Here's a pic of the mount as new. You can see the large ring on the outside of the mount that s/b the ground wire I'd think.

    Attached Files:

  11. george_tlc

    george_tlc SILVER Star

    Messages:
    1,787
    Location:
    Sunnyvale, CA
    First thing to check is you don't have a short on the antenna coax/connector/spring etc.

    I would disconnect the coax connector under the console (from your pics above) and with your meter on ohms measure the resistance from the center pin of the connector (the cable end) to the outside body of the connector. It should essentially read open circuit.

    Then with the coax connector under the console still disconnected. Go to the antenna spring base and measure from the spring to the chassis ground. Should also read open circuit or you have a short from the spring (antenna) to ground/chassis.

    Anyhow, that's something for you to check and verify.

    cheers,
    george.

  12. Brentbba

    Brentbba Former Golfer SILVER Star

    Messages:
    8,897
    Location:
    The OC, CA
    Ok - did all the above and found open circuits. I did retest the 18' coax and it tested fine on outside body connector end to end and on the inside pin end to end.

    I put a ground on the antenna mount to the bolt on the hatch strut and reconnected the coax at the mount. I even ran a piece of wire from the ground point I'm using ont the antenna mount straight to the batter negative ground and tested everything that way as well. The ground point at the hatch strut bold tested exactly the same as the wire run to the battery terminal. With a good ground at the mount I got a good reading at the end of the cable near the radio transmitter. I also regrounded the transmitter straight to the battery negative terminal instead of the top of the firewall just to be sure.

    Everything checks out on the ohm meter that's supposed to right up to the point where I plug in the coax from the antenna to the SWR meter. I still get over 3 on both channels 1 and 40 which makes no sense with a good ground at the antenna. Still at 1 with the dummy load on the SWR instead of the antenna coax. Little 2' cable from the transmitter to the SWR meter checks out ok too.

    I'm at a complete loss here. Everything seems to check out like it should on the coax end to end. I suppose the SWR is shot. It is a VERY OLD Radio Shack Micronta model from my father-in-law that's got to be decades old. Worked fine when I tuned my original CB years ago. Who knows. I'm stumped at this point.
  13. george_tlc

    george_tlc SILVER Star

    Messages:
    1,787
    Location:
    Sunnyvale, CA
    Well, an SWR of 3 is not totally horrific, but an ok starting point.

    Some of the info at this link may help you. Note that the spring base has made your antenna longer, so you may have to trim it a reasonable amount. For grins, have you tried without the spring base to see what SWR you get?

    http://www.rightchannelradios.com/tuning-cb-antenna-adjusting-swr

    cheers,
    george.
  14. Brentbba

    Brentbba Former Golfer SILVER Star

    Messages:
    8,897
    Location:
    The OC, CA
    Well, outside of the way they show calibrating the SWR, I'm doing the testing correctly. I have a dummy load antenna to calibrate the SWR. I calibrate it and remove the dummy load and hook up the antenna coax. For grins and giggles, I'll give their calibration method a try and see what I get.
  15. Brentbba

    Brentbba Former Golfer SILVER Star

    Messages:
    8,897
    Location:
    The OC, CA
    Closure - BAD antenna! The solder joint on the wire that wraps the antenna had completely broken off at the tip. New antenna and I'm tuned in at 1.5 on both channel 1 and channel 40.

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