That whole coax length thing...

[bob85]

phase or line length makes or breaks an array when feeding two or more verticals,
antenna impedance terminating the two lines is also important, when its not what its supposed to be lets say its 35ohm not 50ohm then phase shift for a given line length won't be what you expect either,

getting the shift you want by using the published VF of your coax only works when the coax is terminated with its own characteristic impedance & no reactance.

 

[trees]

Yes length is a factor then but ONLY in regards to phasing or in some cases impedance transformation.



Yes it does. It becomes 25 ohms. This is the reason that you either use stubs to transform each element impedance to 100 ohms or you use a proper RF power splitter which is actually a tuned piece of feedline that transforms the 50 ohms to 25 ohms. This is called a conjugate match. My pair of 50 ohm 13B2 yagis for 2m will be combined/split thru a home made power splitter/combiner that has a characteristic impedance of about 35 ohms. When placed in at the junction of the two yagis it presents an impedance of 50 ohms to the main feedline. The result is that each antenna is tuned perfectly to 50 ohms on it`s own and the combination still presents a perfect 50 ohm match to the main feedline.

You are starting to confuse me. The questions you ask would lead me to believe that you in fact know more than you are letting on. Talking about making Q-sections and phasing lines etc yet you don`t know about common mode currents? Hmmmmmm.............


Hopefully I don't have to use this

Lol.....

I have been out of the radio thing for a looooong time.

I never understood cmc back then, although I probably should have....

Anyway..

I've been doing some reading. I'm interested in driven verticals and getting some gain from the array.

I've been learning that correct phasing is tricky, and that mutual coupling will cause the feed point impedance to shift.

Stuff like that.

 

[trees]

phase or line length makes or breaks an array when feeding two or more verticals,
antenna impedance terminating the two lines is also important, when its not what its supposed to be lets say its 35ohm not 50ohm then phase shift for a given line length won't be what you expect either,

getting the shift you want by using the published VF of your coax only works when the coax is terminated with its own characteristic impedance & no reactance.

So, both verticals will need to be transformed to 100 ohms each, at the feed point. That makes them 50 when driven in parallel? What about coax, both legs 100 ohm also?

 

[bob85]

Have a look at the old arrl antenna books for info on using odd multiple 1/4wave 70-75ohm transformers.

 

[StrangeBrew]

....

CBers, especially truckers, have been advised to use 18' for this very reason.... And not to coil, or "choke off the coax", because the the coax is acting as the opposite half of the antenna.

....

Installations for truckers are a bit of an issue because you usually don't own the truck, as such you usually want to limit the time/effort invested in the installation because you may be in a different truck next week. For this reason a lot of half-assed solutions have been developed in order to make a system work good enough for highway coms and the ones doing it back then usually knew that what they were doing was not the best way, the problem is that over time these tricks have been repeated and people forgot that they were originally nothing more than band-aids meant to work around a problem rather than fix it.

You have to be able to separate the wheat from the chaff when talking to truckers about CB stuff, if you figure out how to do that please let me know.

 

[trees]

Installations for truckers are a bit of an issue because you usually don't own the truck, as such you usually want to limit the time/effort invested in the installation because you may be in a different truck next week. For this reason a lot of half-assed solutions have been developed in order to make a system work good enough for highway coms and the ones doing it back then usually knew that what they were doing was not the best way, the problem is that over time these tricks have been repeated and people forgot that they were originally nothing more than band-aids meant to work around a problem rather than fix it.

You have to be able to separate the wheat from the chaff when talking to truckers about CB stuff, if you figure out how to do that please let me know.

Copy that. I'm lucky enough to own my truck..lol... I'm running Wilson's with lmr 240 75, cut to 1/2 waves, which I believe is 0° phase. I'm pretty sure there is cmc present, as I haven't choked the line at the feed point. Just ordered some ferrite snap beads from Palomar today, the big 1" diameter type 31, I think. Plan on coiling the coax at the feed point and clamping the ferrite on, hoping to get 4 turns.

Anyway..

Using the 0° angle because both feed points are supposed to stay the same at that angle...but not much gain. Would like to phase them at 135°, but have to figure all that out...still reading about mutual coupling and feed point impedance shift... If I could get 4-5 db gain I'd be really happy..I might try adding another half wave line to one side, 180°...

 

[StrangeBrew]

Keep in mind that antenna gain is directional, in order to get a stronger signal in one direction you'll lose it in another. Make sure you know where you're going to gain/lose this signal in relation to your truck. There's others on here that understand this much better than me so I won't go to far into that subject but antenna gain can be a double edged sword.

 

[mechanic]

Any change in conditions will modify the forward (blue) and reflected (red) voltages and in turn change the SWR (black line). These can be applied power, coax impedance, resistive points as in poor connections or loose ones. Since coax is unbalanced the run of it may affect the 'flow' of power.

mechanic

 

[arcone]

Most of you people are stupid. The only reason why I would run a certain length of coax is to take it out of the equation. Reasons I am not bothered to discuss. And by the way, don’t forget the velocity factor... this 18ft garbage and the patch lead thing.
Let’s face it, you’ve been fed garbage all your life, and you’re some of the biggest consumers on earth. Have a think about it. I’m sick of listening to the ‘bs’ as you.
Jeremy.

 

[arcone]

Most of you people are stupid. The only reason why I would run a certain length of coax is to take it out of the equation. Reasons I am not bothered to discuss. And by the way, don’t forget the velocity factor... this 18ft garbage and the patch lead thing.
Let’s face it, you’ve been fed garbage all your life, and you’re some of the biggest consumers on earth. Have a think about it. I’m sick of listening to the ‘bs’ as you.
Jeremy.

Sorry you say.

 

[Captain Kilowatt]

Most of you people are stupid. The only reason why I would run a certain length of coax is to take it out of the equation. Reasons I am not bothered to discuss. And by the way, don’t forget the velocity factor... this 18ft garbage and the patch lead thing.
Let’s face it, you’ve been fed garbage all your life, and you’re some of the biggest consumers on earth. Have a think about it. I’m sick of listening to the ‘bs’ as you.
Jeremy.

You might be used to brash trash talking Down Under but may I suggest you tone it down a bit here? No need of calling everyone here stupid. I am sure there are things you do not know that others do.

 

[Road Squawker]

Any change in conditions will ... change the SWR (black line). These can be applied power,...

Gee, "forward" and "reflected" voltages?????

The only thing that sine wave tells me is the phase relationship
between voltage and current.

 

[Tallman]

You are starting to confuse me. The questions you ask would lead me to believe that you in fact know more than you are letting on. Talking about making Q-sections and phasing lines etc yet you don`t know about common mode currents? Hmmmmmm.............

 

[arcone]

We don’t talk trash, we just tell it straight.

You might be used to brash trash talking Down Under but may I suggest you tone it down a bit here? No need of calling everyone here stupid. I am sure there are things you do not know that others do.

 

[bob85]

You added nothing useful to the topic of coax length, you cut lengths to take them out of the equation but don't care to discuss when that is or why,

if the only time you cut coax to a specific electrical length is to take it out of the equation you don't understand feedlines as well as you think you do.