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Co-Phase

C

Coax Kid

Member
May 5, 2006
21
0
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Hi Guys
I bought some coax it's co-phase and I will be putting in my work truck( KW ). I cut the ends off to get it thru the dash and doors, Does it need to be 18', cuz I put a tape on it before I cut and the coax is 18'3.5". Also the coax has no label makes on it. Would this be a cheap coax, what ga. should the center be? Thanks Coax kid
 

Coax Kid,
First, let me say that I'm not a 'fan' of 'co-phasing' antennas. I've found that they seldom perform as expected/desired, and most 'co-phased' harnesses are not close to being what they should be.
To answer your question, it probably won't make any practical difference if you just put new connectors on the coax. If the resulting SWR is close to 1.5:1, it's really about as good as it'll get without a lot of work.
A 'phasing-line' has to be a particular length because it manipulates the signal so that it gets to the two antennas at the same time, or in the correct electrical 'phase'. There are formulas that can be used to get you very close to that correct phasing. The problem is that all coax isn't of the same impedance, and have the same 'delay' as advertised. That's because of variations in how the stuff is manufactured, the next 50 feet may not be exactly the same as the last 50 feet of cable. which a normal thing when making ~any~ cable. That means that to really get close, it has to be measured electrically in each instance. The equipment to do that with would probably cost more than your whole radio system, and while certainly nice to have, just isn't very practical for everyone. The best you can expect is something about 10% plus or minus what you expect, sort of.
So, the 'quick-n-dirty' way to do it is to just add the connectors and see what you end up with. If it's acceptable, but not great, you have two choices. Take what you got, or throw more money at it. (Hope you have lots of 'ammunition' for that 'throwing' part.)
Sort of like trying to get rid of a particularly irritating 'squeak' noise. You might, after a lot of work, but you'll get it back shortly, you know?
Hope it works for you!
- 'Doc
 
Coax Kid said:
Hi Guys
I bought some coax it's co-phase and I will be putting in my work truck( KW ). I cut the ends off to get it thru the dash and doors, Does it need to be 18', cuz I put a tape on it before I cut and the coax is 18'3.5". Also the coax has no label makes on it. Would this be a cheap coax, what ga. should the center be? Thanks Coax kid
Click to expand...

Make sure its 18' and when using the antennas(are they adjustable whips?) you need to hook up one with a dummy load on the other end and adjust the SWR do the same with the other end :)
Doing that should get you in the ballpark of 1.5 or lower
good luck ...and keep in touch..and please don\t get them radio shack crimp on ENDS...lol


oh and where did you get the coax at? most coax even the cheap stuff is rated for 300 watts :)
 
Co- Phase

Thanks for writing back, Ok Do you feel than a single ant. would do as well as the co-phase? I'm in a KW conv. and I pull 48' dry vans. It seems that I had a problem before with a dif. conv. and I used a single ant. It would talk fine toward the right forward corner, but it was poor towards to left side/rear, I know it had to do with the gound plane, so that is why I'm thinking of the co-phase. The coax I bought was from a truck stop and no writing on it at all.
Thanks
coax kid
 
unless the cable is positively identified as either RG-59U/AU or RG-6 you're wasting your time.

@ 27.185 Mhz. for .66VF (polye) the length is 17.91' or .796" per degree of phasing (RG-59)
@ 27.185 Mhz. for .78VF (foam) the length is 21.17' or .940" per degree of phasing (RG-59)
@ 27.185 Mhz. for .82VF (foam) the length is 22.26' or .989" per degree of phasing (RG-6)

discrepancies of less than 3/4" to almost 1" depending on the RG type will not produce significant phasing error.
 
Yep, people have been running those things for 30 years. Which doesn't really mean much, other than that it will work. Doesn't say how well it would work in relation to another type antenna.
Any antenna on a semi truck is working under a bigger disadvantage than on smaller vehicles. That's because there's a lot more metal usually too close to the antenna than it should be, and in worse 'spots'.
Dual antennas do not make the radiation symmetrical necessarily (same on both 'sides' of the truck). Just depends on their environment, just like all other antennas. 'Where' the signal goes, the antenna's radiation pattern, makes all the difference. A lot of metal one side or the other doesn't mean that there's nothing going in the direction of the metal. Just that it's probably less than what's going in other directions, but not ~that~ much less.
If you knew exactly where the 'other' party is in relation to you, you might be able to direct more signal to/from that direction. That's certainly not as easy as it may sound, and would cost a fortune to say the least. So what you have to accept is that sometimes it just ain't gonna work. There's no such thing as a 'sure thing' in every circumstance. You go ahead and spend a gob of money on whatever antenna you want. I'll still be able to do almost the exact same on my old 'Rat Shack' magmount, at a tenth the cost... if I can remember what i did with it.
- 'Doc
 
If I'm wrong "all well". I believe that dual antennas(co-phased) are in phase with each other-that they act 1/2 wave not needing a ground.That is why they work good on 18 wheelers(bad grounding),But also they need at least 1/4 wave spacing between them(don't work as well on cars).
 
Fuzzybr,
It sounds like it ought'a be that way, but it isn't, oh well. It -is- possible to use two 1/4 wave antennas and make a 1/2 wave antenna, but it depends on several things, like their positions relative to each other, which will determine the input impedance and the phasing/timing of when the transmitted signal reaches each antenna. The impedance thingy can be dealt with without a huge hassle, but the 'timing' of when the signal reaches each antenna changes the resulting radiated signal pattern like you wouldn't believe. Sort of like two magnets. If the separation distance is 'right', the magnetic fields 'compliment' each other. If the distance isn't 'right', the two magnets either act as one magnet (don't get your finger caught between them) or you loose one when it skitters off the table. Terrible analogy, still waiting for the coffee to be made. That 'magnetic' attraction/repulsion thingy can also be a way of thinking about shaping the direction of the radiation pattern, broadside or end-fire, or something in between the two, called 'steering'. Come to think about it, that's sort of how electric motors work. If you should see a car spinning like a top, that's what happened, wrong phasing between dual antennas. Think I'll go to 'Starbuck's and get coffee...
- 'Doc
 
Coax Kid,
Alot of people will give you their ideas on how thing work,me included. The best advice that I can give you is to do a search on the internet on "mobile co-phased antennas",read over the results and decide for yourself if it is something you want to do.
Good luck on your antennas.
Fuzzybr
 
I was driving back from the daughter's last Saturday afternoon when a flatbed semi passed me and I had to laugh out loud. He had two of those center-loaded antennas that look like an upside down teardrop mounted on top of the truck------about
4 feet apart! :p If he'd known how hard I was laughing at him.......................... Sad thing is, the antenna(s) had a clear view from on top, nothing in the way, and this dude thinks
he's "co-phased". :p :D


CWM
 
What antennas are you using?

these would work but shorter shaft.

DSC02041-2.jpg


rated @ 1000 watts...

http://www.hyelectronics.com/prodinfo.asp?number=B-500M
 
On this particular vehicle(freightliner day cab FLD) I had drastic improvement running 2 antennnas over 1 on either side. mirror mounted... I didn't try a single antenna mounted on the back of the cab in the center but I am going to.. I just don't like all that excess coax--36 feet in a daycab :oops: but it works well...

Could I cut the coax to say 9 feet per side? I am using Belden 9959(?) Rg 59
 

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