co-phase vs single antenna

[The DB]

co-phased uses a 75 ohm coax, so even if you get a perfect match on the antennas(which you won't) you automatically start out with a 1.5:1 swr

This statement isn't entirely true. When you split a feed line the impedance becomes something other than 50 ohm for both feed lines. The 75 ohm coax cut to a specific length acts as a matching device to match the new lower impedance back up to 50 ohms (or whatever impedance the antenna is meant to run at). I have rarely had to settle for anything worse than an SWR rating of 1.3:1 with cophased antennas, and have on many occasions got 1:1 with no problems.

Even if you only used a length of 75 ohm coax from a radio with a standard 50 ohm output, to an antenna with a 50 ohm input, it is possible to get 1:1 SWR if you use the correct length of coax.

Just because someone uses a 75 ohm coax does not mean your best SWR rating will be 1.5:1.

That being said, should I choose to phase a set of antennas, lets just say imho there are better ways of phasing antennas than the method widely used in the CB world.


The DB

 

[oldslowchevy]

That being said, should I choose to phase a set of antennas, lets just say imho there are better ways of phasing antennas than the method widely used in the CB world.

please explain.

 

[W5LZ]

Figure the resulting impedance of 20 ohms and 75 ohms in series.
That's one phasing line and one antenna. Divide that number by 2 since an identical impedance will presented by the second phasing line and antenna (parallel).
That end impedance is then in series with 50 ohms line to the transmitter.
Depending on the actual input impedance of the two antennas in use, the end SWR will typically average between something like 1.2: and 2:1.
If you go through the same procedure for an input impedance of 35 ohms for the two antennas, then average the SWR results between that first (20 Ohms) and the second (35 ohms) instances, you will find that 1.5:1 is a rough average for the SWR of a dual antenna system.
Don't take my word for it, do the figuring yourself. Then tell me how far off I was. Provide your numbers so we can 'grade' them...
- 'Doc

 

[racetra]

I gotta say, This is a great read. I am about to set my truck up and really want to understant this.........I dont!!! So I asked my Kid......He dont!!:headbang

I'm tryin!!!

On a big Rig, Ya gotta have two weather ya use them both or not. The truck will lean and/or pull to one side if ya dont.....Right OSC....hehehe!!!

 

[roadrage]

I mean what are you hoping to achieve?

Just to see how much difference it really makes. I believe it does make a difference, but not as much as people think. My free set up works way better than I expected it to. It keeps suprising me on how well it works, and it "isn't supposed to." I can park both my trucks side by side (have done) and I only had 1 S unit difference between my co-phase set up with a 29 Cobra, and my Galaxy 95t2 on a Wilson 1000 on the roof. I radio checked from both trucks to my wife. Now that Galaxy has a 32W carrier and swings over 100W. The Cobra is 4W and probably swings 14W. By doing the math of db gain (2X power = 3 db gain, 6 db gain = 1 S unit), my Galaxy should have gained 2 S units, not just 1. And that would be using the same Wilson 1K for both radios. But I only gained 1 S unit with each radio in its respective location. Now, if an HP radio with a single antenna that is also 14" longer than the co-phased antennas, and the single is mounted on the roof; can only gain 1 S unit on transmit over a Cobra 29, than it can't be all that negative having the two antennas. Maybe those old Archer antennas are just really good to start with?

The receive is better on the co-phase set up. But both my Grant and Cobra were pulling in stations good enough to understand what they were saying. I turned to the other truck and the Galaxy's meter was barely moving, and I couldn't understand what they were saying. I am guessing that the receive is probably better on the Cobra and Grant than the export. That makes it an apples to oranges comparison being that it is two different radios. The co-phase antennas still seem to be receiving quite well either way.

The testing (when I can actually get 5 seconds to do it) will all be at the same time. I will record TX and RX, then swap coax and go single and retest. I will use my compass to orient truck 1 to 0 deg facing truck 2. I will set a decernabe stone on the ground at the center point of truck 1. I will repeat the test with truck 1 at 90 deg, and then 270 deg. At each orientation, truck 1 will be parked precisely centered over the stone marker. I can gauge the directionality of the single vs. dual. I will perform each of these steps at 3 different distances starting at 2 miles and up to 6 miles. My son, in truck 2, will remain stationary in the driveway for the duration. He will record my TX for each of my locations, truck positions, and antenna set ups. I will record his TX on my end with each position and set up. I will use my topographical map to give set distances "as the crow flies" and also try to use similar elevation for each of my test spots for truck 1. It will be as close to a controlled experiment as I am capable of.

 

[binrat]

R.R.
Sounds like you are having fun with it and learning that sometimes in theory is not the same as real world. Every installation on a vehicle is unique and slightly different.

 

[roadrage]

I don't know if I should say that I'm lucky that my boss didn't have any work for me today, but it gave my son and I a chance to give this a whirl. And yes, we had a lot of fun doing it. I have to say that for this particular install, I was suprised at my results.

 

[roadrage]

The tale of the tape:



The constant: My wife's Honda Civic Hybred parked in the driveway of our house. Installed is a Galaxy 929 with a 36" K30 mag mount antenna, mounted center roof. My son operating the radio.



The variable: 1996 Ford F150 positioned at 1 mile, 2 mile, and 3 mile. Installed is a 29 Cobra WX ST NW with twin Archer 4' flexible fiberglass whips, mounted behind cab on bedrails, and raised so 3/4 of whips are above the cab. Each position tested with truck oriented 0 deg (front end facing home), 90 deg, and then 270 deg. With each orientation a radio check given and received both with dual antennas and then with single antenna. An X was placed on the ground to mark center of the truck so each orientation of the truck was centered to the same position as to avoid any terrain feature or man made objects from interfering.





Tools: SWR meter, RG59 75 ohm co-phase coax, RG58 50 ohm coax, Garmin GPS Map 60CSX, pen, and paper.

 

[roadrage]

The results

Radios set on ch 20
TX indicated by S meter in the car recorded by my son
RX indicated by S meter in the truck recorded by me

Truck at position 1: 1.07 mi

-Co-phased SWR 1.1: 1
0 deg : TX +20 / RX 9
90 deg : TX +20 / RX 9
270 deg : TX +18 / RX 8

-Single antenna SWR 1.1: 1
0 deg : TX +20 / RX 8
90 deg : TX +20 / RX 8
270 deg : TX +18 / RX 9


Position 2: 2.01 mi

-Co-phased
0 deg : TX +15 / RX 9
90 deg : TX +10 / RX 9
270 deg : TX +15 / RX 9
-Single antenna
0 deg : TX +13 / RX 8
90 deg : TX +10 / RX 7
270 deg : TX +13 / RX 9


Position 3: 3.22 mi

-Co-phased
0 deg : TX 9 / RX 5
90 deg : TX 7 / RX 5
270 deg : TX 8 / RX 5

-Single antenna
0 deg : TX 7 / RX 6
90 deg : TX 4 / RX 4
270 deg : TX 8 / RX 6



The final result is:

RX tests in favor of Co-phase - 4
RX tests in favor of single ant - 3
RX tests of equal signal - 1

RX is in slight favor of Co-phase in the "win/loss" category. Though the biggest difference between single and dual was in favor of dual with a reading of 2 S units higher than the single.

*side note* is that the co-phased system, in all orientations of the truck yielded equal RX signal except at position 1 oriented 270 deg. This showed me the co-phased antennas had very good balance in directionality for incoming signal. The single antenna, in contrast, showed up to 2 S units difference at location 2, depending which way the truck was orientated. It was common for 1 S unit difference in RX between each orientations at every location.

TX tests in favor of co-phased - 4
TX tests in favor of single ant - 0
TX tests of equal signal - 5

TX Was constantly stronger on the co-phased set vs the single. It as still a little directional, but it was slightly less directional on TX than the single antenna.

*side note overall* I originally was going to use the driver's side antenna when performing the single antenna tests, but the SWR on that antenna was 2:1 on ch 20. I hooked up the passenger side and it was 1.1:1 so I used that one. My meter showed an SWR of 1.1:1 for the co-phased set up, but the DS antenna may be limiting the performance when used as a pair. If it was better tuned, the co-phased set up may have performed even better than it already did.

That is my test results, without bias or favor. It just is what it is.
In the given location of installation for these antenna(s). Co-phasing doesn't limit the performance on this set up, but in fact is less directional, and has stronger TX than single. If I get time to perform another test someday. I'll be using the same antennas as a co-phase vs. one of them relocated to the center of the roof. I think the results may go the other way on that one.

 

[The DB]

I'm curious about two pretty important yet unmentioned details. One, which antenna did you use for the single the left or the right? Also when your saying you turned 90 and 270 degrees are those to the left or right?


The DB

 

[roadrage]

Its right at the end under the side note. It was the passenger side antenna. The orientation of the truck was the front of the truck facing the car. It was oriented by a back azmuth with a compass and GPS reading. Then the truck was turned 90 degrees right so that the left side of the truck was facing the car, while keeping the center of the truck over the X drawn on the ground. Then the truck was then turned to 270 degrees so that the right side of the truck was facing the car, again keeping the center point of the truck over the X drawn on the ground. SWR on the used channel was 1.1 on the single antenna and 1.1 on the co-phased set up.

Here is an example of orientation at each distance and with each antenna set up.

 

[The DB]

I'm glad you ran some tests yourself, however...

Two to three s-units difference? I think there was (is) something up with the s-meters in question. I don't doubt that you got those results, however, I don't know that I would trust them at all.

To make 1 s-unit difference it takes 4 times, 2 s-units takes 16 times, and 3 s-units takes 64 times the effective power difference.

I have seen no believable data anywhere ever that would lead me to believe for a moment that adding a second antenna would have anywhere near this much of a gain, especially means that you were pointing the antennas exactally opposite of the direction you should have had any gain at all.

I'm also concerned with the lack of consistency of your results at different distances apart. For example, at your 270 degrees, you moved further away and the received s-units are higher then when they were closer.

Also, while I am not specifically sure with the radios in question offhand, when most radios get to 9 s-units the scales tend to lump bunches of s-units together, and as such tends to get much less accurate, not that most of them even resemble being accurate to begin with.

I though I mentioned about s meters early on in this thread, however when I went to look for it I now cannot find it. I would never take anything a s-meter shows as written in stone. In most radios they are wildly inaccurate, in some cases even after being aligned. Also for testing purposes such as this one they tend to require to much power difference to show any appreciable results.

I have noticed in your pictures the way the antennas are mounted are likely not the best for a single antenna which is also much more dependent on counterpoise than the cophased antennas working together. Mounting on posts such as those you used will definitely have an effect. That being said, That doesn't explain two much less three s-units of difference.

If you were anywhere near me I would offer to try and duplicate these tests, and based on my experiences I also doubt that they would repeat themselves.

I applaud your efforts and am glad you took the time to run your experiment, but it simply doesn't match with what I have seen on countless occasions myself.


The DB

 

[High Voltage Mobile NJ]

offended brother. The bible tells you not to take offence <gotproof>

I have plenty of Hill Billy (and they are proud of it too) friends, even they agree co phasing on a passenger vehicle is just for looks. If it floats your boat then do it.

Don't take my opinion to heart brother, I mean I use baling wire for antennas, now that is hill billy

As for have I tested the difference, I really don't have to, the antennas are too close, it's simple math...

co-phased uses a 75 ohm coax, so even if you get a perfect match on the antennas(which you won't) you automatically start out with a 1.5:1 swr

that being said I have read many true reports, and I HAVE tried it myself, in my case the signal with 2 antennas co phased was lower on output by almost 1 full s unit according to 3 different local stations and 2 DX stations, but this was a long while back

I mean what are you hoping to achieve?

HELLO EARTH HAVE WE MET ??? YOU DO NOT HAVE TO USE 75 OHM COAX FOR STARTERS MUDDUCK OK . LOL NOW SIT YOUR BEANNY LITTLE EYE BRAIN DOWN AND LEARN SOME KNOWLEDGE . I HAVE SET UP AT LEAST 10 SUBUBANS UP , SOME WITH A BOUNCE BACK SYSTEM , AND THE REST OF THEM WITH DUAL HOTTS . AND I HAVE ACHIEVED MORE GAIN THAN YOU STATE UP IN HERE . I HAVE DOWN AS CLOSE AS 5 FOOT SPACINGS WITH DUAL HOTTS ALSO. I USED 2 PIECES OF 8 FEET HALF INCH HARDLINE.
I WAS 90 DEGREES OUT OF PHASE GAVE ME THE BEST TUNE FOR MAX BROADBAND . PERFORMANCE WAS AMAZING AND VERY IMPRESSIVE. AND IT IS THE BEST WAY TO TALK SKIP AND HOLD LONGER CONDITIONS . THAT PHASE WILL GET YA ALL THE TIME . :bdh:

 

[The DB]

HELLO EARTH HAVE WE MET ??? YOU DO NOT HAVE TO USE 75 OHM COAX FOR STARTERS MUDDUCK OK . LOL NOW SIT YOUR BEANNY LITTLE EYE BRAIN DOWN AND LEARN SOME KNOWLEDGE .

Already starting with the attacks I see, you don't wait around do ya...

I HAVE SET UP AT LEAST 10 SUBUBANS UP , SOME WITH A BOUNCE BACK SYSTEM , AND THE REST OF THEM WITH DUAL HOTTS . AND I HAVE ACHIEVED MORE GAIN THAN YOU STATE UP IN HERE .

As you should have, but then you are comparing apples and oranges... So how would you compare your yagi beam setup with your enfire beam setup?

I HAVE DOWN AS CLOSE AS 5 FOOT SPACINGS WITH DUAL HOTTS ALSO. I USED 2 PIECES OF 8 FEET HALF INCH HARDLINE.
I WAS 90 DEGREES OUT OF PHASE GAVE ME THE BEST TUNE FOR MAX BROADBAND .

So it was tuned to be more broadbanded? Why not simply tune for best gain? Antennas used for this type of setup will be plenty broadbanded as it is...

PERFORMANCE WAS AMAZING AND VERY IMPRESSIVE. AND IT IS THE BEST WAY TO TALK SKIP AND HOLD LONGER CONDITIONS . THAT PHASE WILL GET YA ALL THE TIME . :bdh:

I'm glad you are happy with it.


The DB

 

[roadrage]

I'm glad you ran some tests yourself, however...

Two to three s-units difference? I think there was (is) something up with the s-meters in question. I don't doubt that you got those results, however, I don't know that I would trust them at all.

To make 1 s-unit difference it takes 4 times, 2 s-units takes 16 times, and 3 s-units takes 64 times the effective power difference.

I have seen no believable data anywhere ever that would lead me to believe for a moment that adding a second antenna would have anywhere near this much of a gain, especially means that you were pointing the antennas exactally opposite of the direction you should have had any gain at all.

I'm also concerned with the lack of consistency of your results at different distances apart. For example, at your 270 degrees, you moved further away and the received s-units are higher then when they were closer.


Also, while I am not specifically sure with the radios in question offhand, when most radios get to 9 s-units the scales tend to lump bunches of s-units together, and as such tends to get much less accurate, not that most of them even resemble being accurate to begin with.

I though I mentioned about s meters early on in this thread, however when I went to look for it I now cannot find it. I would never take anything a s-meter shows as written in stone. In most radios they are wildly inaccurate, in some cases even after being aligned. Also for testing purposes such as this one they tend to require to much power difference to show any appreciable results.

I have noticed in your pictures the way the antennas are mounted are likely not the best for a single antenna which is also much more dependent on counterpoise than the cophased antennas working together. Mounting on posts such as those you used will definitely have an effect. That being said, That doesn't explain two much less three s-units of difference.

If you were anywhere near me I would offer to try and duplicate these tests, and based on my experiences I also doubt that they would repeat themselves.

I applaud your efforts and am glad you took the time to run your experiment, but it simply doesn't match with what I have seen on countless occasions myself.


The DB

The greater distance showing higher reading on the receiving radio's S meter could have been as simple as the location being higher elevation, high concentration of salt in the ground, whatever. I don't know why some of the readings were the way they were. They just were. And the truck wasn't closer or farther at any of the given locations. I marked the ground with an X under the center of the truck. Each time I oriented the truck, I centered the truck over the X as to keep the same exact distance. And I never said that behind the cab is the best location for a single antenna. But the roof isn't always an option. If I had an antenna on the roof of that truck, it'd last about 10 minutes on the trail to my fishing hole. If you saw the dents on my roof, you'd understand. I did put dual antennas on my truck because they were free, and I didn't want my system to be directional. It was fun doing my testing. I know there are holes and variables. I'd have to test 100 locations to really have conclusive data. The one thing I do know, is the two antennas transmit better than the one. Firestiks, or Wilsons, or Everhardts may have different results all together. But my truck with my make and model antennas, mounted in their respected locations work better co-phased than not. And I don't think that it has more antenna gain, per say, but less loss.


Being that my current radio is out of commision in the Chevy, it frees up the Wilson 1K. I want to retest the Ford with the co-phase set up VS a Wilson 1K mounted center roof. I expect different results from that test, but we'll see.