SWR Meter

Discussion in 'General Electronics Chat' started by DC_Kid, Jun 18, 2008.

  1. DC_Kid

    Thread Starter AAC Fanatic!

    Feb 25, 2008
    just wondering if anyone has any suggestions for SWR meter for CB radio. i'm looking for a inexpensive SWR meter but it needs to be somewhat reliable, etc. radioshack has one for $50, but i'm not sure if $50 is worth it.
  2. roddefig

    Active Member

    Apr 29, 2008
    If you don't get any helpful replies here I'd suggest asking on an amateur radio forum or newsgroup. They would know about this kind of thing.
  3. beenthere

    Retired Moderator

    Apr 20, 2004
  4. SgtWookie


    Jul 17, 2007
  5. theamber

    AAC Fanatic!

    Jun 13, 2008
    I think the price is ok if you order a cheaper one from the NET you still have to pay shipping. If you build one the parts, work, time + shipping or gas expense amount to more. I do have the radio shack one since 1993 and is good.
  6. SgtWookie


    Jul 17, 2007
    I bought a Radio Shack VSWR meter 30 years ago. It seemed to work just fine, for as long as I had it. I didn't pay anywhere close to $50 for it, but everything was less expensive back then.

    You could build one yourself, but you would be better off buying a kit to build one. Getting the PCB right might be somewhat of a chore; if you don't get the layout right you could make the VSWR considerably worse than it was before you started. The meter alone would likely set you back $10 or more - and then you have the connectors, the enclosure, making the PCB - whoops, we're already over budget and we don't have the rest of the parts yet.
  7. DC_Kid

    Thread Starter AAC Fanatic!

    Feb 25, 2008
    my moddo is not to build unless i cant find it on the shelf, etc.

    i'm just questioning these cheapo swr meters like the Para Dynamics units. do i get accurate/reliable readings for just $20?
  8. SgtWookie


    Jul 17, 2007
    They'll be accurate/reliable enough to use with a CB.

    They won't be laboratory quality, of course. If you want real accuracy, you can waltz down to your local Agilent (formerly Hewlett-Packard) store and plunk down $8,000 for an entry-level network analyzer. If you get the TDR/FDR option, you can tell precisely where that kink in your coax is - but that's an extra-cost option.

    All you really need the VSWR meter for is to set up a good antenna for a nice low VSWR on the channels you're using most often. If they're far apart, then start off taking VSWR measurements at channels 1, 20, and 40. Ideally, you should have 1:1 at 20, and both ends should be below 1.3. It is not hard to accomplish this with a decent antenna and a coax in good condition.

    Many antennas are a good bit too long when you buy them. I bought a decent bottom-loaded magnetic mount CB antenna for trips; I wound up having to grind nearly 3/4" off the bottom of the whip before it would insert into the load far enough.

    When I started, my VSWR was around 2.5:1 at channel 40, 1.4:1 at channel 20, and 1:1 at channel 1. This told me the antenna was too long; it was resonant at too low of a frequency, but not WAY too low. By the time I got done cautiously trimming and tweaking, I was reading 1.1:1 at the center, and around 1.22:1 on each end. I used Loctite on the Allen setscrew to keep it from loosening up. It hasn't changed a bit in the last 10 years.

    If you kink the coax, your VSWR will promptly skyrocket. The only real fix is to replace the coax.

    I just have two CB radios; pictures of those models (while the same, not mine) are attached.
    The TRC-449 is my 40-ch SSB portable rig for the road.
    The TRC-457 is my 40-ch SSB base station.
    Basically, they're very similar, except the TRC-457 has a built-in VSWR meter, a clock, and a CH-9 button. They were the best that Radio Shack had to offer at the time, and they are still doggone good radios.
    They're 30+ years old, and they still work just fine.
  9. DC_Kid

    Thread Starter AAC Fanatic!

    Feb 25, 2008
    i have a handheld Midland CB. it comes with a car adapter that allows for 12v from car and external antenna hookup. using the bnc rubber antenna i didnt get much reception. i then bought a inexpensive base loaded magnet mount antenna, its approx 36" long, i now pick up CB transmissions about 250 miles away! the only issue now is i cant seem to get anyone to hear me (not the folks 250mi away, just anyone local, etc). hence i would like to measure vswr and tune the antenna if need be.

    i bought a Para Dynamics 100w unit from http://www.rightchannelradios.com

    i'm guessing its a cheapo from china but should do the job for my current and future CB radios.
  10. SgtWookie


    Jul 17, 2007
    Midland used to make decent radios. I haven't looked at their offerings in quite awhile though. Which model number do you have?

    Cheap antennas are likely to cost you more than you paid for them in repairs to your CB's transmitter section when they go bad.

    Wilson or K40 antennas are a good choice. That site you referenced seems to have good prices on them.

    I neglected to mention that when you're performing the initial VSWR tuning/adjustment on your unit, that the antenna should already either be installed (if permanent) or stuck on the vehicle (if magnetic mount).

    If the antenna is mounted in the center of the roof, your reception and transmission patterns will be nearly omnidirectional, with slight emphasis towards the front and rear of the vehicle. With a trunk lid mount, your transmission/reception lobes will be mainly in the direction of the center mass of the vehicle; in this case towards the front. I generally plunk my antenna dead center of the roof; it makes for a reasonably decent ground plane.

    If you REALLY want to emphasize lobes to the front and rear, you could use dual Firestiks, one on each side of the vehicle. You'll have to tune VSWR on each antenna, of course.
  11. DC_Kid

    Thread Starter AAC Fanatic!

    Feb 25, 2008
    i have the Midland 75-822 handheld. its only a 4watt radio but it serves me well since i can take it on trails when hiking or use it in my truck while on the road, etc. it also has a 10ch NOAA receiver.

    the antenna i got is just like the ones at Radioshack, so i think it should be ok. the whip is 1/8" stainless held in by a set screw. i'm hoping if i need to tune i will need to trim this whip otherwise i have to go find a longer whip.

    since the radio is only 4watt i wanted to be sure the vswr was good otherwise my transmission could be like .1 watt, etc.
  12. DC_Kid

    Thread Starter AAC Fanatic!

    Feb 25, 2008
    just a update.

    i got my cheapo swr/pwr meter and it was showing bad #'s. around 3 on ch1 and about 3.5-4 on ch40. so it meant electrically long antenna. i went to ch 20 and trimmed 1/4" off, swr went down some, then i went to 1/8" increments until i got swr just below 2. however, tuning here seemed to have thrown off ch1 since ch1 was now above 2.

    ok, i thought cheapo antenna (thin ss whip, about 1/16" dia.) is giving me some cheapo results. so i swapped out the whip with a longer piece of 1/8" brass (about 36") and had to trim some off to bring down swr. i also stripped back some insulation on coax close to the antenna but still inside the back window. i then wrapped some wire (stripped) around the coax ground sheath and then soldered it. simply draping this 22ga wire (approx 5ft worth) on the floor of my truck back-to-front helped 1000x. ch1 swr was at 1 on the meter, and ch40 was under 2.

    it is also apparent that the setup is better because the Midland power meter when in TX pegs out at 4w from ch1 to about ch35, ch36-40 the Midland power meter flickers between 3.5-4w.

    i suspect (just as many others do) the ground plane is utmost important. i guess the bad thing now is that i have a brass whip, but i can eventually get a piece of 1/8" stainless to match length, etc.

    note: the ground tangs on the cb 12v cigarette lighter plug is also grounded to the ground sheath of the coax, but this apparently does not work very well.
    Last edited: Jun 24, 2008
  13. SgtWookie


    Jul 17, 2007
    OK, sounds like you figured out most of the immediate problems. Sounds like you need to trim a bit more off the antenna to get the high end dialed in better, along with the all-important Channel 19.

    If you find yourself on a particular channel most of the time, tune for that channel by selecting frequencies of equal displacement on either side of it that are as far away as possible.

    For example, if you're on 19 most of the time (like I am with my "road warrior" rig), then try to make your VSWR equal on channels 1 and 40, because 19 is exactly halfway between those two channels frequency-wise.

    If you are on channel 26 most of the time, make your VSWR equal on channels 14 and 40.

    For antenna tuning purposes, here is a chart of the CB frequencies in MHz, sorted by frequency, with the "gaps" filled in with "--" for channel numbers. If you find that the channel you're tuning for has a high or low "bracket" channel that is a "gap" channel, then move both ends in one step.
    Code ( (Unknown Language)):
    2. Ch, Freq (MHz)
    3.  1, 26.965
    4.  2, 26.975
    5.  3, 26.985
    6. --, 26,995 [I](Not legal for CB)[/I]
    7.  4, 27.005
    8.  5, 27.015
    9.  6, 27.025
    10.  7, 27.035
    11. --, 27.045 [I](Not legal for CB)[/I]
    12.  8, 27.055
    13.  9, 27.065
    14. 10, 27.075
    15. 11, 27.085
    16. --, 27.095 [I](Not legal for CB)[/I]
    17. 12, 27.105
    18. 13, 27.115
    19. 14, 27.125
    20. 15, 27.135
    21. --, 27.145 [I](Not legal for CB)[/I]
    22. 16, 27.155
    23. 17, 27.165
    24. 18, 27.175
    25. 19, 27.185
    26. --, 27.195 [I](Not legal for CB)[/I]
    27. 20, 27.205
    28. 21, 27.215
    29. 22, 27.225
    30. 24, 27.235
    31. 25, 27.245
    32. 23, 27.255 [I](Note:out of sequence; from early CB allocation)[/I]
    33. 26, 27.265
    34. 27, 27.275
    35. 28, 27.285
    36. 29, 27.295
    37. 30, 27.305
    38. 31, 27.315
    39. 32, 27.325
    40. 33, 27.335
    41. 34, 27.345
    42. 35, 27.355
    43. 36, 27.365
    44. 37, 27.375
    45. 38, 27.385
    46. 39, 27.395
    47. 40, 27.405
    If you get yourself a Wilson or K40 antenna and tune it properly, you will not have the kinds of problems that you have been experiencing - unless you manage to kink/pinch/crush/damage your coaxial cable in any way.

    It is certainly possible to effect repairs on coaxial cables. It is a meticulous and painstaking process to perform a truly serviceable and reliable repair that few could learn in a day. For this application it would be best to replace the entire coaxial cable if the original becomes damaged.
  14. TanTJ


    Mar 6, 2008
    If you are planning on using a ground plane I would highly suggest going to Radioshack and picking up a 102" Stainless steel whip antenna. If you run that and still have high SWR's you can be rest assured it's not the antenna as I have gotten a max SWR of 1.1:1 across all channels with this antenna on my Jeep. The only variable to deal with after that is the coax and ground.
  15. DC_Kid

    Thread Starter AAC Fanatic!

    Feb 25, 2008
    the 102" 1/4 wave ss whip needs a hefty base mount, which i dont have. for my needs (a whimpy 4w max handheld cb) my vswr ranges from 1:1 to 2:1 and the cb radio power meter peaks out on the 4w line across all channels. for now this is acceptable. when/if i go to a better radio cb i might think about doing a better antenna setup....
  16. SgtWookie


    Jul 17, 2007
    102" whips work great if you have a sturdy bumper. I had one on my '74 Olds back in the 70's. I liked having a fiberglass whip better than the stainless for as long as it lasted; the fiberglass whip was more rigid, so remained more vertical when driving down the highway.

    I had to exchange it for a stainless whip when I was working in California; parking ramps + 9' whips = bad combination. It got to be too much of a hassle having to clip the antenna to the gutter, so I eventually went to a magnetic mount. Not nearly as good, but infinitely more convienient.