Questions about choosing a directional CB base station antenna

Thread Starter

Lectraplayer

Joined Jan 2, 2015
99
I've decided to start dabbling in the two way radio scene, and while a simple CB radio for my vehicle is adequate for now, I'm wanting to set up a base station at home. Problem is, where I live, there is absolutely nobody around close enough for a standard vehicular omni, so I'll need something with good directional characteristics to reach far. I'm wanting to stay with my standard 5 watt output so I can hear them and not just them hear me. Given that, what's a good antenna to look for? I'm not quite sure what to look for and where, or what to expect.
 

Papabravo

Joined Feb 24, 2006
12,389
A multi-element yagi with a rotor is directional and horizontally polarized. It won't do you a lot of good if everybody else is using a vertically polarized omni. This is for LOS communication with a radius of 50 miles or so. The 11 meter CB band will propagate over the horizon when propagation conditions are right and then polarization doesn't matter. I think you are stuck.
 

bertus

Joined Apr 5, 2008
20,048
Hello,

You could look for something like this:


Bertus
 

MrAl

Joined Jun 17, 2014
6,469
Hi,

One of the key points is altitude. You want to get it as high up as you can.

Long time ago when CB was super popular, i used a magnetic base car antenna for a while and got people all around town i'd say within a 2 mile radius.
Then i built a custom 1/2 wave vertical dipole and put it on top of the house which was about 20 feet up. I got out over two or three towns. The antenna was simple to build. Just two lengths of 1/2 inch copper tubing with a diamond shaped insulator to hold the two halves ends close to each other and of course lined up straight. The cable came out at a right angle to both tubes. The matching didnt look too bad so i used it like that.
It made a huge difference in the reception and transmission distance.

Some people claimed that stuffing the tubes with carbon would help increase the transmission power but i rejected that on the basis of knowing about skin effect and also didnt feel like going through that anyway and was getting good distance as well without it.

You could also get a book on building your own antenna. There are lots of designs you could experiment with. You could also have two antennae one for directional and one for omni. Switch between the two when you feel the need.
There are also the dual antenna systems which are supposed to be the best and most directional but i've never tried that design.
 

Thread Starter

Lectraplayer

Joined Jan 2, 2015
99
I have been thinking quite a bit about the yagi off and on, though I believe it would be just as easy to allign it vertically as it would horizontally. The 50 mile range would easily reach some of the places where I'm trying to get to as well. Main thing I'm contemplating right now is what to build it out of that will last given my current (lack of) building skills overall. ...though some new things I found makes me wonder how far a good omni with a ground plane kit would reach if put 20 to 30 feet up. I plan to have both at the moment. I'm assuming, though, that I'll have to put them one atop the other for them to work right.
 

SamR

Joined Mar 19, 2019
1,138
Antennas are the most effective part of a radio installation. First is impedance match tuning an antenna to obtain minimal SWR (standing wave ratio) to ensure maximum signal propagation. Whether vertical or horizontal depends on what you are trying to accomplish communication-wise. Almost all CB antennas whether mobile or base for CB are vertical. A horizontal antenna will attenuate signals verically aligned and improve signals horizontally aligned. That is useful for communicating with other horizontally aligned stations. Then there are some directional beam CB antennas that combine both vertical and horizontal propagation. Antenna Elevation is also important. The CB wavelength is 11 meters and a vertical antenna improves when its base is above 1/2 wavelength and also with an additional ground plane on its base. At 4-5 watt during daytime operation, your communications are limited to ~5 miles at best and very noisy. Nighttime operation maybe ~30 miles on a clear cold night. And depending on Solar Cycles and Sun Spots, once in a Blue Moon you might get lucky with ionospheric reflection and communicate with someone a few states away as if they were next door. A beam antenna will give you a couple of dB signal gain in the direction it is pointed and attenuate the "noise" from elsewhere. Also important is good quality coax and connectors. You are terribly limited watt-wise with CB so you have to squeeze what you have for every small gain (true for all radios actually). With a Ham License and a repurposed CB 11 meter horizontal 3 element yagi retuned to 10 meters, I have communicated on the 10 meter band with Australia from Coastal Georgia with a 100W old HW-101 tube type transceiver.
 

MrAl

Joined Jun 17, 2014
6,469
I have been thinking quite a bit about the yagi off and on, though I believe it would be just as easy to allign it vertically as it would horizontally. The 50 mile range would easily reach some of the places where I'm trying to get to as well. Main thing I'm contemplating right now is what to build it out of that will last given my current (lack of) building skills overall. ...though some new things I found makes me wonder how far a good omni with a ground plane kit would reach if put 20 to 30 feet up. I plan to have both at the moment. I'm assuming, though, that I'll have to put them one atop the other for them to work right.
Hi,

Get a book or search online so you can see the gain factors of each type and go from there.
Sounds like you are going for optimum gain which i think means narrowest directionality.
 

nsaspook

Joined Aug 27, 2009
6,270
I have been thinking quite a bit about the yagi off and on, though I believe it would be just as easy to allign it vertically as it would horizontally. The 50 mile range would easily reach some of the places where I'm trying to get to as well. Main thing I'm contemplating right now is what to build it out of that will last given my current (lack of) building skills overall. ...though some new things I found makes me wonder how far a good omni with a ground plane kit would reach if put 20 to 30 feet up. I plan to have both at the moment. I'm assuming, though, that I'll have to put them one atop the other for them to work right.
Good plan as you will need a omni with a highly directional antenna. I left my old RadioShack SSB CB station to my brother in the 70's. (traded it for something better ships) I set him up with a two element V-quad on a rotor overlooking most of Dallas from the hill his house was on. He could easily talk to people in Oklahoma on side-band when conditions were good and noise was low.

http://www.macoantennas.net/Gallery.html
 
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Thread Starter

Lectraplayer

Joined Jan 2, 2015
99
Quick question. I have some ideas for my build now... I may start with a center fed dipole made of 1/2 inch copper supported by PVC, and am trying to figure out how to estimate the impedence once I have it tuned given my materials and setup vs electrically.
 

SamR

Joined Mar 19, 2019
1,138
Look into antenna tuners and baluns. I have made several dipoles, trapped dipoles, and off-center dipoles over the years with both copper coated steel wire and plain old #12 THHN insulated stranded copper wire, but making a beam is not an easy task. Several other purely receiving antennas such as long wires and slopers. Also look at dip-meters, SWR meters, and antenna analyzers that are used as tuning aids.
 

Thread Starter

Lectraplayer

Joined Jan 2, 2015
99
Believe it or not, your response is part of something that will come later in the process and such is being treated as a seperate discussion. I know I will need a balun to convert from unbalanced coax to the balanced dipole, and the dipole is to be my omni (and probably the basis of my directional yagi). I'm guessing based on research so far that the dipole runs at 73 ohms and a 1:1 balun gets me to a SWR of about 1.5 on a 50 ohm feed. My question though is how to be sure my research is accurate and what my impedance at tuned frequency will be given my choice of materials and configuration for the dipole.
 

SamR

Joined Mar 19, 2019
1,138
One possible online resource would be old ARRL Handbooks that have been converted to PDFs online. They always had some homebrew antennas in each edition that should give you some insight. Google arrl handbook pdf download
 

MrAl

Joined Jun 17, 2014
6,469
One of the other points is to use the right coax cable.
CB outputs are 50 Ohms yet the 1/2 wave dipole impedance is around 75 Ohms.
1/4 wave dipole is lower so maybe something between 1/2 wave and 1/4 wave would match better then you can use 50 Ohm cable.

When i was experimenting with near the 100Mhz band long time ago the way i measured performance was to actually drive out away from the house and check for reception. If i got good reception out at 1 mile and then made an adjustment and got out 1.5 miles i would consider that adjustment to have helped.
When i was experimenting with near the 27MHz band i used the meter on the CB radio to judge if i got a decent match. I dont remember what it was measuring though that was so many years ago. But i did get a bit lucky too and i think the antenna might have been closer to 1/4 wave than 1/2 wave but cant remember exactly going back that many years (probably 50 years now wow). I do remember using really heavy duty fishing line for the guy wires as that offered strength plus electrical insulation from the antenna metal.
 
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SamR

Joined Mar 19, 2019
1,138
Monofilament is pretty good (most is not UV resistant though) but down here the marine hardware stores have "tarred" net twine used to patch shrimp trawl nets. It is 3 part nylon twine impregnated with green wear resistant water repellant and blends well into the trees. My ~30' tall 10-meter band white fiberglass vertical on top of 30' of 1-1/2" galvanized pipe is pretty noticeable, but my 140' off-center fed dipole is virtually invisible. Even I, who know it's there, have to look hard to find it. A lot of the newer radios have a meter switch to go from Watts to SWR.
 
You can use an SWR meterand a variable frequency source to adjust the antenna to resonance and then adjust the matching network to give you a good SWR. There are a lot of antenna analyzers available that will allow you to first tune to resonance by adjusting the dipole length, and then adjust the match to the desired impedance. And for a center fed dipole you will need some sort of balun arrangement, but that may be able to be part of the matching system, which could be a coil of several turns connected between the two dipole halves. At that point you will need to study a book on antenna matching. There are hundreds of published yagi antenna designs, and copper pipe is the most efficient material. but it does cost more than aluminum. But if you solder all of the connections once it is tuned it will last a very long time.
 

Janis59

Joined Aug 21, 2017
767
However I see no any joy in the voice telling the need for directional and condemning an omni. Did You ever tried about J-pole? It is still omni, but have a narrow diagram in the vertical plane, thus it not illuminates the Kosmos and the sand as well. All that energy goes at narrow angle parallel to the ground, therefore probably it may be enough for Your application?
 

Janis59

Joined Aug 21, 2017
767
MrBill2 - Note that impedance of Yagi is dependant too (and adjustable) by changing the distance between elements, and as the last method, by inclining the director in small angle (maybe 5...20 deg) ends toward mirror. Such manner is not difficult to get 50 Ohm out of typical 73 Ohm construction as I described here time ago this summer.
 
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