Change Antenna and High SWR- Help

[mcculley4]

A few weeks ago I installed a CB in my new 2016 Colorado Diesel. Offset Stake Pocket mount from Firestik with a fire ring coax. I intially installed a FL-4 4 foot Firestik and then realized it was the lightweight version 100 watt antenna and so I ordered and switched out the antenna with a FS-4 4 foot Firestik 900 wayy antenna.

With the original antenna I got SWRs of 1.9 at 1 and 40 and 1.2 on 19 after tuning.

With the new antenna and no other changes, the best I can do is 2.9 on 1 and 40 and 1.8 on 19.

No other changes except unscrewing one antenna and screwing in another. Does anyone know if there are characteristics of this antenna that would cause this or require some additional measures to lower SWR? Not an expert but not my first install. I e-mailed Firestik several days ago but no response and was hoping someone here could help out.

Thanks in advance!

[231]

A few weeks ago I installed a CB in my new 2016 Colorado Diesel. Offset Stake Pocket mount from Firestik with a fire ring coax. I intially installed a FL-4 4 foot Firestik and then realized it was the lightweight version 100 watt antenna and so I ordered and switched out the antenna with a FS-4 4 foot Firestik 900 wayy antenna.

With the original antenna I got SWRs of 1.9 at 1 and 40 and 1.2 on 19 after tuning.

With the new antenna and no other changes, the best I can do is 2.9 on 1 and 40 and 1.8 on 19.

No other changes except unscrewing one antenna and screwing in another. Does anyone know if there are characteristics of this antenna that would cause this or require some additional measures to lower SWR? Not an expert but not my first install. I e-mailed Firestik several days ago but no response and was hoping someone here could help out.

Thanks in advance!

First of all welcome to the forum. When you get a chance do an intro' in the New Member Intro section and tell us a little about your equipment.

I would not look forward to a response from Firestik...frankly I am not a fan of that antenna, although back in the day they were a terrific performer. That being said, I have several questions...it sounds like not only is your counterpoise (aka 'antenna ground') a problem, but I can almost guarantee that 'Firewire' connection you are using will be problematic. I cannot tell you how many I've seen fail in short order. If you looked at the solder connection they do it's pretty cheesy.

Q1: How close to the cab is it (in inches or cm's)?
Q2: Exactly what are you using for an SWR meter & what brand/model? (i.e. internal radio meter, external Bird, etc.)
Q3: What procedure are you doing for calibrating your SWR meter?
Q4: Where are you parking when you are testing and is there anything close by like a building or big truck? (i.e. inside garage, etc.)

That's for starters. I'm sure I'll have more later...but almost always the problems you are experiencing are related to the counterpoise (aka 'ground') connection(s). The antenna is sort of showing it's a little too short (judging by the standing wave you've posted)...throwing a spring under might help make it a little longer, but if it's up against the cab (or super close) you'll likely need more than that. It's seeing reflection off the cab which often requires relocating the antenna. To me a 1.5:1 or lower standing wave (SWR) is acceptable...anything higher not. Although most say today's radio's can handle a 2:1 standing wave, that's not necessarily true nor does it help with performance. If in fact there is a problem the radio will sometimes cut back power to protect the final transistor in it. The antenna is literally 90% of the performance.

If you are using this in an offroad type deal, there are other antennas to choose from too...they don't cost as much as Firestik and will handle 1kw all day long. An example would be the Everhardt TSM-4' Superflex. I've yet to break one offroading.

Best of luck and let us know how it goes.

231

[mcculley4]

Thanks for the quick response. I have done a ton of research and this is not my first install. The thing that puzzles me is the SWR differences between the antennas with all else being equal.

Q1: How close to the cab is it (in inches or cm's)?

Will need to go measure, but it is offset (because of tonnaeu cover) in stake hole pocket closest to cab, so my guess would be about 2'. Same location for both antennas since I only unscrewed the one and screwed in the other.

Q2: Exactly what are you using for an SWR meter & what brand/model? (i.e. internal radio meter, external Bird, etc.)

ASTATIC PDC1 100 Watt SWR/RF TEST METER W/ Workman 3 foot jumper CX-3-PL-PL for both antennas

Q3: What procedure are you doing for calibrating your SWR meter?

The procedure stated in the instructions for both antennas.

Q4: Where are you parking when you are testing and is there anything close by like a building or big truck? (i.e. inside garage, etc.)

Big open field with nothing nearby for thousands of feet for both antennas.


I have a heavy duty spring under the antenna and it has not moved during the process so it was there for both antennas.

I do work off road sometimes and so I need a somewhat flexible antenna.

I guess I am wondering if anyone knows something that would create the difference in SWR just by switching the antenna. Does this antenna need a bigger ground plane for example than the other.

I get full continuity between the mount and various grounding points on the body (door jam screws, frame, etc.) I could run a short ground wire from the mount to a ground in the bed about 6 inches away but not sure if that will help.

Everything else is the same (coax, mount, spring, etc.) just changed antenna and got the elevated readings.

I guess I could go back to the lighter antenna but I am thinking performance will suffer.

For what it is worth, I have been clearly transmitting and receiving over 8-12 miles with the current antenna and high SWR readings but have kept transmissions to a minimum until I can sort out the problem

Thanks again for the quick response and help! I appreciate it!

[sonoma]

from what you are showing for swr makes me think the last antenna is not broad banded enough for your application. the swr gets higher on each end of the bands. I am not a big fan of the firestick antennas . ever one I ever used were like what you are getting. K40 makes 2 4 foot antennas and one is stiff and it has a higher swr when used behind the cab. they have a flex whip as they call it with a tunable tip that is a good antenna and the swr is lower than the heavier one they make. these are both a fiberglass antenna. the flex whip is good to about 700 watts if memory serves me right. the way the copper wire is wound around the fiberglass makes a difference in how the antenna performs. I have my antenna about 1 foot behind the cab of the pickup and like I said the flex whip has a lower swr. the fire stick antennas just do not seem to be as broad banded as the K40 for my application. the K40 flex whip usually cost about 20.00 to 25.00 verses just over 12.00 for the firestick. you will find that different brands will work different in each application. so it will be a trial and error to find the right antenna for your application. to me the K40 works best for me that is the flex whip.

[d-minus]

well i will tell you what i done to my pickup. I had the same problem with antenna mount screwed directly to bed of truck in the middle behind back glass. I knew i needed a good ground so i crawled under truck drilled a hole in bottom of bed lip sanded down to bare metal put screw and nut in with 12gauge wire run to hole in frame did same thing there. I used a firestik roadpal instead of there regular size 3/8 stick ?. swr was 1.2 on ch 19 and 1.4 on the others. Hope i helped. Please ask any more questions if you need to. Daniel. P.S. welcome to the forum. I run a cobra 29ltd with a ad-203 mounted in radio. Every one says it is clear. I get out about 6-7 miles here in the mountains.

[MDYoungblood]

It sounds to me that the antenna is still a bit too long judging by the SWR curve. I'm guessing the tuning tip is screwed all the way in. Are you using a spring on the mount, if so remove the spring and check the SWR.

3's

Greg

[231]

I guess I am wondering if anyone knows something that would create the difference in SWR just by switching the antenna. Does this antenna need a bigger ground plane for example than the other.

I get full continuity between the mount and various grounding points on the body (door jam screws, frame, etc.) I could run a short ground wire from the mount to a ground in the bed about 6 inches away but not sure if that will help.

First off, the single most important thing is the counterpoise connection. This is the place most ignored for the reason you said...the ohm/volt meter shows continuity. Hate to tell ya', but you are dealing with an added component with radio, it's call RF which our volt/ohm meter won't show. As such, an RF ground MUST be present. Shiney metal is your friend on this connection. I hate those Firewire connections because they are very light duty. That is likely to be a failure point if you ask me (if not now certainly down the road)...along with your counterpoise connection. I personally don't see a good SWR even with your previous antenna. Acceptable to you perhaps, but certainly not for any CB amplifier I know of. They will want less than a 1.5:1 standing wave in order not to fry the finals.

That being said a simple self tapping screw into the metal bed will be enough...assuming it's metal. Not all are metal these days, but from there you ground the bed to the truck. Even though it probably already is, it's only an electrical ground, not an RF ground. Things like paint, under corrosion material, etc. will significantly reduce it's ability to act as an RF ground. So, another couple of good self tappers to the 'shiney metal' is usually enough with a couple of good stainless washers. It doesn't have a be huge wire but most of us running amplifiers prefer a good braided ground strap.

Range is subjective...not always a good indication of performance because it can be misleading...especially talking to base stations their set up significantly changes things. I used to talk daily to a station 60 air miles away out of my mobile...but he was on a 1000' hill running an Astro-beam, and I was on a 300' hill parked in the same spot daily. See what I mean?

If you plan on running an amplifier you will absolutely need to bring that standing wave down...the first place to start is dumping that Firewire (it's not heavy duty enough in the first place) and improve your counterpoise connection. 'Ground plane' is again subjective because it just doesn't take as much as people think. A few ground plane radials is all that's needed...provided the counterpoise connection is sufficient.

Hope that helps.

231

[The DB]

The antenna is sort of showing it's a little too short (judging by the standing wave you've posted)...

It sounds to me that the antenna is still a bit too long judging by the SWR curve.

I'm confused... With the new antenna he said...

With the new antenna and no other changes, the best I can do is 2.9 on 1 and 40 and 1.8 on 19.

2.9 on channel 1, 1.8 on channel 19, then 2.9 again on channel 40. How is that to long or to short when referring to the new antenna?

This is, at least in part, a ground plane issue, and the cab of the truck being so close is not helping either. At this location on pickups it really can be hit or miss when it comes to mounting/tuning antennas, I've seen one work, then another not work at this location multiple times in the past. The fact that instead of a ground plane you essentially have a ground "line" isn't helping matters much either, this affects the antenna's impedance, in a mobile environment making it higher than it normally would be, causing SWR to go up. Mobile antennas really do like a nearly flat piece of metal (ground plane) immediately under them, which you don't have.

While antennas like metal underneath them, they really don't like metal to be next to them, like your cab, as that affects another part of the antenna, adding "reactance", which is another component that makes up SWR. This affects the antenna by raising the impedance mentioned above even more, further pushing it away from the desired low SWR.

The fact that you don't have anything that resembles a good ground plane also means that you might well have something called common mode currents flowing on your coax, and these can also have an effect on the antenna's SWR, and can affect it in any number of ways. There are people that will tell you that you don't have to worry about these in a mobile environment, however, when I check for them while tuning mobile antennas, I see this type of problem fairly often. If you have a coupler and a near three foot coax jumper, hook it up, if SWR changes noticeably then you have a problem.

Have you tried any other locations? That would be the first thing I recommend trying in your case if possible, try the next stake hoke back if you have the coax to get to it and see if it helps.

I don't think anyone mentioned it here yet, but the ideal place to mount an antenna is the middle of the roof. I'm guessing that it is not an option for you, but everything other than that is a compromise for the antenna, both when it comes to performance, and the likely hood of having tuning issues.


The DB

[mcculley4]

WOW Lots of good information. Thank you everyone. I think I will try a different antenna and some ground straps between the bed and frame and cab and frame (as soon as it warms up a little).

[mcculley4]

I ordered the KW Antenna and 4 copper ground straps and a new Coax connector and Coax. Thanks!

If someone could give me detailed instructions on the ground straps I would appreciates it. So I sanded the underside of the stake hole before mounting to bare metal, should I still run a short 10 gauge wire from the mount to bare metal on bed?

I am thinking I will grind some small areas on the frame and bed and cab and connect the copper ground straps with self tappers and stainless steel washers. Is it that simple?

[MDYoungblood]

You really don't need to run a ground (bond) from the antenna mount to the frame if the mount is secured to clean metal in the stake pocket. I would check to see if the bed itself has a ground (bond) to the frame, most are just a spring scratch hook and eventually comes off after a few years, if you don't see any or just add a couple anyway, I'd do the cab too, never hurts. Bonding has been discussed quite a few times on the forum, best search it. I hope the FireStik KW antenna works for you, I've had a couple and didn't care for them, a better choice would have been a Everhardt SOTT in my opinion.

3's

Greg

[231]

The antenna is sort of showing it's a little too short (judging by the standing wave you've posted)...

It sounds to me that the antenna is still a bit too long judging by the SWR curve.

I'm confused... With the new antenna he said...

With the new antenna and no other changes, the best I can do is 2.9 on 1 and 40 and 1.8 on 19.

2.9 on channel 1, 1.8 on channel 19, then 2.9 again on channel 40. How is that to long or to short when referring to the new antenna?

I miss read the last 2 words "...on 19."

This is, at least in part, a ground plane issue, and the cab of the truck being so close is not helping either. At this location on pickups it really can be hit or miss when it comes to mounting/tuning antennas, I've seen one work, then another not work at this location multiple times in the past. The fact that instead of a ground plane you essentially have a ground "line" isn't helping matters much either, this affects the antenna's impedance, in a mobile environment making it higher than it normally would be, causing SWR to go up. Mobile antennas really do like a nearly flat piece of metal (ground plane) immediately under them, which you don't have.

While antennas like metal underneath them, they really don't like metal to be next to them, like your cab, as that affects another part of the antenna, adding "reactance", which is another component that makes up SWR. This affects the antenna by raising the impedance mentioned above even more, further pushing it away from the desired low SWR.

The fact that you don't have anything that resembles a good ground plane also means that you might well have something called common mode currents flowing on your coax, and these can also have an effect on the antenna's SWR, and can affect it in any number of ways. There are people that will tell you that you don't have to worry about these in a mobile environment, however, when I check for them while tuning mobile antennas, I see this type of problem fairly often. If you have a coupler and a near three foot coax jumper, hook it up, if SWR changes noticeably then you have a problem.

Have you tried any other locations? That would be the first thing I recommend trying in your case if possible, try the next stake hoke back if you have the coax to get to it and see if it helps.

I don't think anyone mentioned it here yet, but the ideal place to mount an antenna is the middle of the roof. I'm guessing that it is not an option for you, but everything other than that is a compromise for the antenna, both when it comes to performance, and the likely hood of having tuning issues.


The DB

I'd agree with most of this, but I'd beg to differ the ground plane component...I've not seen him post whether his bed is metal or not and if not absolutely it will affect performance. But nothing some lengths of wire won't help out usually. The counterpoise connection is almost always the culprit. I've run top loaded & whip antennas where he's got his mounted without any problem whatsoever, but a foot or two back like he says his is should be okay provided the top loading coil is above the roof line. Most 4' should be okay there. Unfortunately people are stuck with the Firestik adjustment nut on top which requires the cap be on it. I'm just not a fan of them since the 80's when they changed things. I'll take the old TSM any day that's a tad more broad banded. Personally I think it's possible he's got more going on here than he thinks which you touched on.

CMC is indeed a problem that happens often...but almost always the counterpoise connection is to blame IMHO. I've run into it allot with other people's systems but mostly because people don't understand how critical the counterpoise connection is. No such thing as too much grounding and having a couple of torroids around is helpful too. I had that problem (slightly) on my Hi-Q screwdriver when I was first setting it up (switching from the Don Johnson DK3)...and using the radio's separation kit didn't help any because I was using a BetterRF motor controller. Once I added a couple of torroids though life was good and she tuned right up...until the motor fried 9 months later anyway. My Scorpion screwdriver notta' a problem 1. Hardest thing on that one was accommodating for the 17 lb weight of the antenna. 10/11 (and above) meter antennas are cake...but still held to the same need for a better than average counterpoise connection. Especially if one plans on running an amplifier.

Just my input.

231

[231]

I ordered the KW Antenna and 4 copper ground straps and a new Coax connector and Coax. Thanks!

If someone could give me detailed instructions on the ground straps I would appreciates it. So I sanded the underside of the stake hole before mounting to bare metal, should I still run a short 10 gauge wire from the mount to bare metal on bed?

I am thinking I will grind some small areas on the frame and bed and cab and connect the copper ground straps with self tappers and stainless steel washers. Is it that simple?

I'm not familiar with the KW antenna, sorry. HERE is the Everhardt TSM Superflex I was mentioning though...not many left as Everhardt closed their doors a few years back. I bought a bunch of them because I knew my offroading buddies would need them eventually. They don't have the twist adjustment for tuning but very easy to tune and flexible. Most are out of the package at 26.700 MHz or so...way long, but easy to trim up and dial in. A good antenna doesn't have to cost allot...and I've been using these on my Jeep wheeling in some heavy foliage since '03. What some do (me included) is use quick disconnects and switch to whatever antenna I want from there. I have about 30 antennas or so to pick from (collection over the years)...some on my Jeep, some on my pick up, and soon to be on my motorcycle. LOL

As far as the detailed drawing goes, if your counterpoise connection at the mount is sufficient and the bed of the truck is metal then all you have to do is run ground strap(s) from the bed to the frame (usually someplace under the truck that is convenient). Every standard metal truck bed already has this from the factory, but it's only an electrical ground and often not in good shape or painted, etc. This grounding is called 'Bonding' the vehicle. You don't need a detailed diagram for this...we basically go around to each component (doors, hood, bed, cab, motor, etc.) and bond all of them together so it's one big bonded ground. The vehicle is usually this way from the factory but for us who play radio not nearly enough.

However, if your bed is fiberglass (which like I said allot of the newer models are nowadays like Toyota) then you'll certainly need more than bonding which is a little more difficult (but not impossible). What I've seen guys do successfully is run wire (#18-#14 is perfectly fine...doesn't have to be heavy gauge) around the bed to act as radials. A few more in the bottom of the bed for the same...they don't even need to be resonate lengths but start them at a common point somewhere (even the mount would be okay) and then run a ground strap from there to the frame. Or, some will mount strips of aluminum or other metal they happen to have around to pretty it up some. Bond them together and run a strap from there. I like using self tapping screws (drill a pilot hole first) in the frame and/or counterpoise connections. Once all tuned up and working well throw some silicone over the connections to help keep corrosion out.

Now as far as that firewire coax connection I've posted an image below of a mount set up and what should happen. If you are planning on running an amplifier just get decent RG-8x (aka mini-8 ) coax instead of the RG-58U which is what the Firewire is. RG-58U will handle a few hundred watts okay but the RG-8x will do better (up to 1kw+ if memory serves).

Here is a drawing of what should happen. You can take your shield connection directly to your mount or even truck bed (if metal) if you want...just like I did on my Jeep (the shield is the counterpoise). It doesn't have to be complicated but what you see below is all that needs to happen. The antenna is only half of the antenna...your vehicle is the other half. The antenna is isolated from ground (counterpoise).



My Jeep connections using a ball mount:




Jeep with TSM-4



Hopefully this will help simplify things a little for you.
Best of luck.
231

[nk14zp]

Just a comment on bonding. You can never have to much of it. Bond the bed in at least two spots. **Censored** has video where he bonds the truck every foot down each frame rail off set 6in from each side. Remember a dc ground is not a rf ground.

[mcculley4]

Thanks again everyone. I am on my way to Florida in a few minutes but when I get back I will switch out the antenna, coax and start bonding. My bed is metal so that is a good thing.

Can't believe how helpful everyone has been.

Thanks!

-- Monday, 16 January 2017, 10:02 AM --

Back from Florida and so far all I have had time to do is screw in the new KW Superflex 1700 watt antenna and the SWR is even worse. 3.2 on 1 and 40 and 2.8 on 19 was the best I could do. Screwed the 100 watt Firestik back in and SWR is decent but not great 2.5, 2.5 and 1.2.

This week I will try to move the mount to the rear stake-hole, is it will work (this is elongated to provide a handle for the bed step). Add all of my bonding and new cabling and antenna stud. Then I will test all 3 antennas again and see what I have. I now have 100 watt firestik, 700 watt firestik and 1700 watt KW Superflex.

-- Saturday, 21 January 2017, 14:21 PM --

Moved the antenna mount to the rear stake hole. Really sanded the paint off for a good connection. Used a new K4A stud mount and a brand new coax cable (not fire ring) heavier duty than previous. No cab blocking transmission now. Have not added any copper strapping yet but was able to tune the KW 40 Superflex 1700 Watt antenna to 1.9, 1.9 and 1.2 on 1, 40 and 19. This is much better than the previous setup where it was over 3 on all channels.

Going to get my buddy to weld the copper straps sometime soon but pretty happy with the numbers so far.

Just talked to one person after tuning about 5 miles away and was crystal clear on both ends.

Thank you for all of the help everyone. Will report back after putting copper straps on.

I did get the Everhardt 4' antenna too but don't want to tune it until I have strapping in place since there is no going back. But the untuned numbers were similar to the K40 but it was reporting too long. Just don't want to cut the wires yet.