6 Band "CB Special"
Multiband Vertical Ground Plane
collecting the "gold:
A couple of years ago, my XYL heard of a person that had
some "antenna stuff" to give away so she was very reluctant to tell me
knowing that I was usually not one to turn down a "good deal" when I saw
it, but, long story short, she let the cat out of the bag. I drove about 5
miles or so and there it was, a "gold mine" of aluminum tubing just laying
there to be panned.
How I did it:
Well, longer story shorter, here is how I converted that old CB relic into at least a 5 bander vertical ground plane for use on the hf ham bands. Yes I know, I said 6 bands earlier, this may depend on your setup and tuner. No, you can't get something for nothing. A decent tuner will be required for this project.
(I used the MFJ 901B).
Now really getting started with the help of "Murphy's Law":
The first thing I had to do since it had been laying out behind my house for a couple of years, was to get it apart and do some cleaning of all of the tubing where the sections went together. The screws were extremely rusted and they were a bit difficult to get out of the tubing sections. Then as Murphy's law would have it, the tubing sections were stuck together; so with the aid of a pair of good Channel Lock type pliers, apart they came except for the bottom section that went inside the loading coil?/matching portion of the base.
With much effort, I was able to get the outer case "protecting" the coils inside, pushed up toward the mounting bracket just enough to see the coils.
Murphy stepped in...the coil cover had not done it's job!
The coils were in very bad shape having been subjected
to years of rain, dirt, corrosion, etc....so I just took them out of the
circuit by clipping a couple of the wires. At the very bottom of the base
of the coil cover, there was an SO-239 connector with a nut attached for
connecting the coax feedline. The nut would not budge much
(rust) and the threads were striped in the process of my trying to
loosen it....junk. I did not use this connector due to it's
About the length of the vertical and the radials:
From ideas on other projects like those of KL7JR and others on this site and on the web, I had learned that to make this antenna work well on many HF bands...the radiating portion of the antenna was to be of a non-resonant length on any ham band.
I did some more research on the web and determined that the length of 15 feet for the vertical radiator should work well when the radiator was fed against a few radials of the same or longer length and with a tuner. I used 3 radials of equal length of about 15 feet of #14 insulated wire.
So the next step was to put the telescoping sections back
together, adjust the length to about 15 feet from the now non-existing feed point near the top of the mounting
bracket and secure everything with screws. I had sort
of reversed the procedure by not having a feed point ready, and
this is when I saw Murphy looking over my shoulder again! He laughed and
Now I had to come up with a feed point on the bottom section of the tubing near the base so I could get the radiator length right....get away Murphy!
I wanted to feed the antenna with coax so now I had to come up with a way to connect the PL-259 from the end of the feed line to a non-existing SO-239 that I wanted to use!
As luck would have it, there hidden within the pile of "gold" aluminum tubing, was an old bracket from another "junker" antenna that contained not one, but two SO-239's! Murphy must have taken a nap!
I cleaned the old bracket containing the SO-239 with fine grade sandpaper and also gave the SO-239 a good cleaning inside and out with an assortment of small steel wire brushes, and then it was a simple matter of just drilling a small hole or two for a couple of small bolts to mount the connector bracket to the original mount near the future feed point on the vertical portion of the radiator. I won't mention here that Murphy came back from his nap and proceeded to scatter nuts and bolts everywhere!
The hookup to the
The "tip" end of the connector was facing up toward the top of the radiator just like I wanted it so it was a simple matter of eyeballing the length of wire needed to connect the center pin tip to the vertical section only a couple of inches away. Oooops...now I have to drill another hole for the wire to wrap around a screw on the radiator.
When I was finished drilling and adding the screw, connecting the wire from the connector to the radiator was a simple process that Murphy did not interrupt.
Now I was finished......but that darned Murphy was still
around laughing at me!
Yep, sure enough.....I had forgotten tomechanically secure the sections together with screws! Upon lining up all of the holes in the several sections of tubing, I realized that all would not match up......DARN! I looked over my shoulder.....you know who.... was right behind me....DRATS! Out came the drill again....I finally found some screws that should be OK to use and the correct size drill bit, so I drilled the holes in each section for them, then added the screws and tightened them......
I must be finished now! You guessed it.....the radials were missing and Murphy was holding the wire cutters and the tape measure.
Finally after measuring out 3 equal length radials of about
15 feet each using #14 size wire and getting them cut without
"incident", I mounted them in three fairly equal distance locations around
the mounting bracket just below the feed point! The angle of the radials
was just random, no specific angle, maybe about 20 to 30 degrees as a
Swr and resonance testing without Murphy:
Using an MFJ 259B these are the results at the end of the feed line below.
7.200mhz 15:1 swr
10.100mhz 7.3:1 swr
14.275mhz 2.3:1 swr
16.216mhz 1:1 swr (R=55, X = 0)
18.281mhz 1.2:1 swr (R=49. X = 10
21.350mhz 3.7:1 swr
24.960mhz 5.2:1 swr
28.400mhz 4.4:1 swr
(Notice the resonant point at 16Mhz...for some strange reason about 2 weeks later, this frequency changed to the bottom end of the 20 meter band around 14.00Mhz!
I have not had the time to figure out why, but the antenna still works great with the tuner).
ON THE AIR PERFORMANCE. The proof is in the pudding!
Over a few days of on the air testing in the low part of the solar cycle in 2008,
I have managed to make really good contacts every time I operated with at least 5 8 reports, with most of them being 5 9 or better on 40, 20, and 10 meters using 100 watts and the tuner.
The 40 meter contacts were late in the day.
The 20 meter contacts were late afternoon. All contacts above were stateside.
17 meter band- Received many reports of S9 plus...some even S9 plus 20db over!
15 meters has been dead here for some time but I managed to make a schedule with a local ham some distance away, who gave me a good report on a test transmission.
10 was "dead" at the time of testing but I received a nice report from the same local station several miles away that usually only could read me about S5 or S 6 on a multiband doublet, but received me much stronger on the vertical. I could hear him also much better when compared to my Hustler 4BTV or multiband doublet. He was using an Inverted V if memory serves. I did not check 12 meters on the air as I recall but I am sure it will "work" there also.
6 Meters...a plus discovered later....low swr (R and X) but used a tuner with it....band dead. More testing to follow.
DX results.....TA3D !!!!!!
The antenna and the YAESU FT-107 running 100 watts really shined on 20 meters during this contact. I managed to break a HUGE pile up with him and received the usual 5 9 report in TURKEY!
More DX Results (Updated 01-24-09)
While tuning around 40 meters about 5 PM CST in January, 2009, I heard a giant pileup on 7.194Mhz.
I broke the pileup with one call using my trusty Yaesu FT-107 and received a nice 5 7 report from I2VRN in Italy. He was 5 9 plus about 5db running a 4 element yagi and about 500 watts. I was running this antenna described in this article and 100 watts!
Then the next day January 25, 2009 on 10 meters,
received a nice 5 9 contact from a Florida station. I stoped there for a
while with on the air
More on the air testing coming as time permits.
Final comments and suggestions:
My overall impression of the base station CB antenna converted to use on many hf bands using a tuner has been a pleasant and rewarding project for me and the good thing about it was the fact that I only had TIME invested in it and a few inches of wire, a few screws plus dealing with Murphy while I used other peoples "junk" to make a multiband hf vertical antenna that has worked around the globe, coast to coast and locally!!
When using the MFJ 901B tuner, the "6 Band" CB to 10 meters Multiband Vertical Ground Plane tunes up nicely on ALL ham bands from 40 thru 10 meters giving a great match near or at 1:1 swr on all the hf bands from 40 thru 10 meters. I found that 6 meters may be useable also.
It also allows me to "hear" 80 meters as if I had an 80 meter dipole up. Also to my surprise, it does not seem to be as noise prone as most verticals I have tried or maybe my noise level has just been low lately.
I look forward to more on the air testing as time progresses.
So to repeat my self, I guess it "works"!
Below is a drawing with lengths that I used and the location of the connector bracket:
This from Bob, KF7DRC (05-
Using the idea from the project above, I decided to just go
ahead and put it up at an experimental configuration using an Antenna
Specialists 5/8 wave 11 meter (CB) all aluminum
I removed the gamma from the original CB antenna and went
direct to the so239 for the vertical element, not much change from the
original 11m setup except for removing the gamma match and raising the
mast height another 10 feet approx. I am amazed it is working this
KF7DRC, Bob cherokee376 > hotmail.com (remove the > and add the @ symbol and close the spaces afterwards.)
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