Help with swr readings.

#409455

I’m currently running a cobra 25ltd with a peak and tune coupled with a hustler IC100SW antenna going into an astatic swr meter and an astatic mic. I’ve been having nothing but issues getting the radio to work right, every time I’ve taken it to a shop they can find nothing wrong with it. I had it to a shop in Fort Worth Texas where the guy told me it was one of the best running 25s he had seen. I had tuned my antenna and my swr was right at 1. Checked last night and they were over 3. Took almost an inch off the antenna and it’s right around 1.5 on 19, 2.7 on 40, and the meter won’t read low enough at 1. I don’t know if it’s a radio, antenna, mic, or meter issue at this point. Any help would be awesome as I don’t have a cb shop close

#409457

If I’m reading your post correctly, the antenna is to short since the SWR is increasing as the channels go higher. A couple things you have to watch out for on magnet mount antennas, one is the coax where it enters the vehicle, check it for being mashed, it is probably starting to short or because it is mashed the center conductor is not uniform with the insulation surrounding it. Two is the antenna needs to go back at the same spot it was tuned at or everything changes, but being a mag mount you can move it around the roof to find where it’s sweet spot is. Last thing is jumpers, they could go bad, need to check them too.

3’s

Greg

#409459

...what MD said...move antenna around till you find the sweet-spot where it tunes the best, and leave it there!....moving it to a different location, even if it's just inches away, will cause it to lose it's tune because of the ground plane changing from where it was originally tuned...

Best to have done this BEFORE you started trimming the stinger...could be now you have trimmed too much off the stinger and it will never tune right...get a new stinger and start over...

#409460

jessejamesdallas wrote: ↑October 9th, 2022, 9:04 am ...what MD said...move antenna around till you find the sweet-spot where it tunes the best, and leave it there!....moving it to a different location, even if it's just inches away, will cause it to lose it's tune because of the ground plane changing from where it was originally tuned...

Best to have done this BEFORE you started trimming the stinger...could be now you have trimmed too much off the stinger and it will never tune right...get a new stinger and start over...

You can get a new stinger off Amazon, they will be longer then needed, check the diameter before ordering. When you start trimming it, go in 1/4” steps so you don’t remove too much.

3’s

Greg

#409461

So, I have not moved the antenna location from where I tuned it. I do have a rack on the top of my vehicle but it was there when I originally tuned. I did try making it longer last night and the swr read higher across all channels. I did have a bad alternator that was interfering with the reception, replaced it and immediately had the replacement go out. Would there be any connection with that that could have affected anything in the radio? I’m close to totally getting rid of that radio altogether with all the problems it’s giving me

#409464

I am going to say the alternator unless it spiked wouldn’t affect the SWR, you said the radio is fine. The problem is the antenna which now a days they costs as much as your cobra radio. I would set the SWR to its lowest on channel 19 or 20, (middle of the band), then move it around to find the best spot. Get it there then adjust the stinger for the best SWR on 1 and 40, it probably won’t be a 1:1 match but anything under 1.5:1 is fine.

3’s

Greg

#409466

Would it be stupid to put more money into the setup and change my antenna setup completely? It is on the roof of a 98 blazer. I have a roof rack for my spare tire I could mount a Wilson 305-700 mount to and put a hustler hq27 55 inch center load antenna onto. I’m a little worried about getting to much height with going through drive throughs and stuff like that and with needing to put it so close to the tire that way. I’m bidding on a teaberry titan t on eBay which if it works would probably become my main radio over the cobra so I was thinking of redoing the antenna setup anyway

#409467

I ran one of them on the roof of my van mounted to a homemade puck mount, great SWR, took a beating from low tree limbs, it went with the van when I sold it. That Teaberry was a nice radio in its day but I believe your Cobra is a tad better. I would use that money toward reducing the noise problems.
FYI, on Father’s Day every year there is a hamfest just south of you below Hampstead, MD, at the fairgrounds in Arcadia, good place to look for deals on CBs and antenna, you’ll probably find me there.

3’s

Greg

#409469

I have a roof rack for my spare tire I could mount a Wilson 305-700 mount to and put a hustler hq27 55 inch center load antenna onto

Don't do it!..........It's almost impossible to get a decent ground off a rack...best-bet is to stay with the magnet mount, or do a permanent mount where you drill a hole in the roof and install either a hockey-puck type mount or ball mount...but don't waist your time or money on the roof rack....been there done that...never worked!

Now they do make "quick-releases" for antennas so you can easily remove the antenna before driving under something low...

Google "Breedlove antenna mounts"...he has by far the best antenna mounts available for just about any situation...you won't find them in stores, he only sells threw his web page...they are expencive, but they will outlast whatever you mount one to.

#409470

JJD is right, installing an antenna on a mount to a rack creates capacitance problems, a puck or ball would be the better mount. Permanent mounts are the only way to go to achieve the best SWR reading. Magnet mounts rely on capacitance and the coax for their counterpoise, when using a mag mount the radio should be grounded to the vehicle and don’t rely on the negative lead to ground it.
I did say I made my puck mount on the van roof.

3’s

Greg

#409471

That was one of my other questions, I’m powering the cobra with a cigarette lighter adapter and when I was running the Johnson messenger ( which I really like but need to figure out a good way to clean mic contacts) I had it hardwired in pulling power from my flood lights. The hardwired Johnson seemed to perform better stock than this cobra with a peak and tune.

#409472

In reply to JJD, I’m just curious if I grounded the chassis of the radio to my vehicle, would that then allow me to run the mount off the roof rack? I’m thinking that would be the same as a magnet mount but maybe there is something I’m missing there

#409473

Roof racks...tire racks...never work...

Jeep guys are bad about wanting to mount antennas to tire racks on back of their Jeeps...then they all pop up on the forums and fb with posts of high swr... fortunately they make brackets that bolt on where the tire racks are bolted that let you mount the antenna that way...never seen any kind of bracket made for roof racks, probably because you would need to remove a bolt that holds the rack to the roof, then insert the mounting bracket and put the bolt back in place...that would end up causing the roof to leak if you didn't get a decent seal

But hay...never hurts to try it...maybe you'll get lucky and be able to come back here with some pictures of how you made a roof rack mount work!

#409476

RenegadeBird01 wrote: ↑October 9th, 2022, 6:49 pm That was one of my other questions, I’m powering the cobra with a cigarette lighter adapter and when I was running the Johnson messenger ( which I really like but need to figure out a good way to clean mic contacts) I had it hardwired in pulling power from my flood lights. The hardwired Johnson seemed to perform better stock than this cobra with a peak and tune.

There is the main problem with your radio and noise, cigarette lighter sockets are terrible. Best is to wire the positive lead straight to the battery and the negative to a good ground screw under the dash, on your vehicle I think it has a bolt on the steering column bracket. Dimming lights are mainly a too small alternator, your vehicle probably has at most a 90A alternator, add a couple items like lights stereo amplifier, etc. it takes a lot away from the amperage needed. On my Dodge Ram, it has a 250A aftermarket alternator.

3’s

Greg

#409478

100 amp heavy duty, haven’t really had issues with power other than just buying reman junk. As of now my swr magically got better last night. Sitting right at 1 on channel 1 and 2 on 40. About 1.3 on 19

#409480

RenegadeBird01 wrote: ↑October 10th, 2022, 12:04 pm 100 amp heavy duty, haven’t really had issues with power other than just buying reman junk. As of now my swr magically got better last night. Sitting right at 1 on channel 1 and 2 on 40. About 1.3 on 19

Cool, adjust the sting in a 1/4 inch, looks like it is still a tad long, that should bring up the SWR on 1, lower it on 40, and do check your coax for kinks, could be the problem.

Make another post here to get your “post count” going, viewtopic.php?t=54422

3’s

Greg

#409481

so how do you have the coax routed? if your slamming a door on it,

its going to fail.

if you stick with CB, you will learn more than you think.

#409482

It’s routed over the roof in through the top of my back hatch. Rarely gets opened, I did check it for pinching and couldn’t find anything. I’m chalking it up to a swr meter that may not be completely on at this point. I’ve been able to check it a few times without changing anything and have different results each time. For now it’s where I’m not worried about burning the radio up

#409483

Thanks for all the info, once I get my current vehicle issue worked out that I didn’t have time or money to work on I’ll probably build some kind of adapter for the hardwiring I installed for the messenger 123 so I can swap the radios easily if I feel like it. Hopefully I didn’t make the stinger short to where I can’t move it up if they change when I do that as I did end up snipping a good bit off to get my swr to where they are now. Wish me luck on getting the blazer running again I’ll need it

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