First, I must say that setting up a base radio (11 meter)
and accompanying antenna is a new hobby for me. I'm a complete newbie.
When I first started working on my 11M CB base station, I knew I had to
figure out a way to get an antenna up without breaking any of my
neighborhood rules. I live in a subdivision governed by a Homeowners
Association, so we have certain rules that prevent homeowners from
erecting/mounting antennas on their houses. An 18ft Solarcon A99 was out
of the question. After doing some research, I learned that a dipole
antenna mounted in my attic might do the trick. About this same time, I
came across John's article on Hamuniverse.com describing a dipole antenna
he made using mobile fiberglass type CB antennas. Making a dipole antenna
from off-the-shelf items that could easily be purchased from the local
truck-stop (Travel America) and hardware store (Lowes) sounded great to
me. Plus, with it mounted in my attic, it would be the perfect "stealth"
antenna to keep the homeowners assocation happy. Could it work for 11M CB?
I didn't know. Afterall, his article was on a "HAM RADIO" website. After
reading John's article, I had some questions so I emailed Don,
N4UJW at Hamuniverse.com. Don responded to me promptly and put me in
touch with John directly. John was glad to answer any questions I
had.
Before we get into
the actual antenna assembly, let's look at a few pictures illustrating my
installation. The antenna is in my attic, and my 11 meter CB base radio is
in my kitchen. To connect the two, I purchased 100ft of "Davis RF 9914F
Bury-Flex 50 ohm Heavy Duty Coax". I found it on eBay for about $90 (US
Funds). It's GREAT stuff!
Picture showing which attic in the house I mounted
the antenna. The back of the house faces South. As you can see, there are
lots of other houses around.
Antenna Mounted Vertically In Attic
Antenna Mounted Vertically In
Attic
I fished the
coax to the basement through a cold air return duct (not within
code, I know) with the help of a friend. I took this picture when
the house was being built because I thought it would come in handy
someday for projects like this. That was a good decision.
Ran the coax across the basement ceiling, and up into
the kitchen. I like that brush wall-plate.
The coax terminates at my
Uniden Washington base station. Nice
radio.
Antenna Tuning - High SWR
After getting everything installed, I realized the antenna
was giving me high SWR readings. The SWR was in the high 2's on Channel 01
and 20, and 3+ on Channel 40. It was time to start tuning the antenna. In
my case, the SWR on channel 40 was greater than on channel 1, so the
antenna was considered "LONG" and a reduction of conductor length is what
was needed to correct it. There's a tiny wire that wraps around the
Firestik® fiberglass antenna forming a coil and goes all the way up to the
tip. You can actually see it through the plastic sleeve of the antenna
when looking at it closely. This wire is what needed to be shortened, not
the fiberglass itself. Here's a link to FireStik's website with
information about tuning an antenna: http://www.firestik.com/Tech_Docs/Setting_SWR.htm
Basically, you unwrap the coil and then snip (NOTE: The following was done to both the top and bottom antennas).
The first time I was a bit nervous, so I unwrapped and snipped off only
two coils of wire. This didn't change the SWR much. The next time I
unwrapped/snipped off 4 coils. I saw a change in the SWR and it was
getting closer to where it needed to be, but it was still not good enough.
The next time I snipped off 5 coils (I probably shouldn't have gotten this
bold, but it ended up ok). After removing 11 coils of antenna wire so far,
here were my SWR readings:
It's not too bad, but I wanted to snip some more. I decided
to be SUPER conservative though. I didn't want to cut too much wire and
then end up back in the 3's for my SWR because of a "SHORT" antenna. I
made two more snips. The 1st snip I took off about 1/4 of a coil of wire.
I saw a small change in the SWR reading. With the 2nd snip I took off
another 1/4 of a coil of wire. My final SWR ended up being:
I'm happy with those readings. During the tuning process,
you may have noticed that channel 01 got down to a 1:1 SWR. On my last
snip, it creeped back up to 1.05:1. I figured it was time to stop tuning,
especially since the other two channels were both within spec now. It's
nice to know that this antenna was very tunable and a tuner is not
required to use it. I think the hardest part of this project was tuning
the antenna without a helper. It took some extra time to climb into the
attic, snip some of the antenna, climb out of the attic, check SWR
reading, climb back into the attic... I probably did that 5-6 times. I
think my patience paid off though.
Long Distance Exchange (DX) And Local Talk
Results
I'm in Ann Arbor, MI, USA.
Over the last couple of days, I've heard 11 meter DX from Illinois, the
Carolinas, Georgia, Texas, New York, New Jersey, Minnesota, Michigan,
Ontario Canada, Ohio, Tennessee, Alabama, West Virginia, and Florida.
Unbelievable to me, and very exciting! All from a home grown antenna built
from mobile antennas and mounted inside my attic. How cool is that? When
the DX isn't active, I'm able to talk locally up to 3-4
miles.
Here is a video below showing some of the DX I've
heard:
Antenna Assembly
The antenna assembly was really straight forward. The
only difference between my assembly and John's (KL7JR) were the holes I
drilled for the antenna mounts. The antenna mounts I purchased must have
been a little larger than what John used because there wasn't enough space
for them to mount properly in the existing holes after bending the
Strong-Tie "T". If you choose to use the existing 3/8" holes then you'll
need to drill them out since they aren't quite large enough for the lip of
the plastic spacer to fit properly. They need to be bored out to a 1/2"
diameter. Lets get started...
Parts List:
QTY
ITEM
1
Simpson Strong-Tie "T" (Part #: 66T) - Purchased At
Lowes
Plug To Lug Connection - Stud Mount (Diesel Part#:
360-53401)
1
Plug To Plug Connection (Diesel Part#: 360-53402 or
360-53403)
Hints - If you get the "T" from Lowes website, search
for Simpson 66t. The last 2 items on the list can be found at many CB
shops, truck stops, or antenna accessory
suppliers.
Step 1: Mark the locations for the new antenna
mount holes, and the lines where you'll bend the Strong-Tie "T". See
the image for measurement locations. The
measurements in the photo above are: 1. 1/2 inch from
edge to center point between 2 small existing holes on each side of
the "T". This is where you will mark and use a center punch to drill
the hole for the antenna mount in the next part of the project. See
picture below.
2. 1 5/16 inches to bend point on T from each
side.
Step 2: Before drilling the antenna mount holes,
take a center punch and punch a mark in the Strong-Tie "T" at the
hole locations. This gives the drill bit something to bite into when
starting the hole.
Step 3: Drill the holes where the antenna mounts
will attach to the Strong-Tie "T". Make sure you use a 1/2" drill
bit.
Step 4: You'll probably end up with some sharp
metal burs after drilling your antenna mount holes. Just take a
metal file and file them
down.
Step 5: This is what your Strong-Tie "T" will look
like once you're done drilling the holes. Lookin' good! Next you'll
be making the appropriate
bends.
Step 6: Mount your Strong-Tie "T" in your vise so
the top edge of the vise lines up with one of the lines you drew in
Step 1. Once you're confident you have it locked tight in the vise,
and square, then take your hammer (I used a 3-4lb hand sledge) and
start hammering the bend into place. I started gently hammering near
the black line to get it started. You may want to use your free hand
to pull the top in the direction you're hammering too. Once you get
it started you'll be able to hit it a bit harder. Note: John (KL7JR) says. "If you don't
have a vise, you can use the rear bumper on your truck and a hammer
to shape the Strong-Tie "T" like I
did." Hi-Hi
Step 7: Keep hammering until you have a 90°
bend.
Step 8: Flip the Strong-Tie "T" around and line up
the other line just like you did in Step 6. Hammer
away!
Step 9: Keep hammering until you have a 90°
bend.
Step 10: The completed Strong-Tie "T" antenna
bracket. Lookin' good!
Step 11: Mount the antenna stud mount (Diesel
Part#: 360-53401) to the lower portion of the bracket. The mount may
come with two plastic insulator/spacers. You'll want to use only one
of the plastic spacers (or none). Some part of this stud mount
*must* come in contact with the metal Strong-Tie "T" bracket. This
antenna will be the "cold" antenna (see Step 12 for an
explanation).
Step 12: Mount the "plug to plug" antenna mount
(Diesel Part#: 360-53402 or 360-53403) to the top part of the
bracket. It's important that this mount be attached to the top
antenna in a vertical dipole scenario. You'll want your coax to
attach to the top antenna. It's also very important that the plastic
insulator/spacer goes between the bracket and the actual mount that
the antenna will thread into. This will isolate the antenna from the
bracket. John (KL7JR) said, "One of the antennas on the dipole (hot)
is isolated from the mount and the other is not (cold). They are
paired up with your center conductor on the coax (hot) and with the
shield (ground-cold). For horizontal polarization, either antenna
can be hot but for vertical polarization you want the top
hot."
Step 13: Mount the PL-259 L-Connector to the "plug
to plug" antenna mount (Step 12). That's it for the bracket. You'll
now need to find a place to mount it (if you haven't already) and
connect your mobile antennas. Hopefully you'll have a helper when
dialing in your SWR.
Editors
note: "Although this could be taken as a CB radio
related article which normally do not appear on Hamuniverse.com,
Scott did such a fantastic job in showing us how to use the "T"
mount taken from the article by KL7JR, that we wanted to share
it will ALL radio buffs....thanks Scott for a really nice
job with the article, photos, and helping us get this project on
Hamuniverse.com.....73 Don, N4UJW"
