Amp coax jumper length

[fireman32_14]

Does the jumper length affect the performance of the radio any on tx/rx.. I'm going to be using a fatboy 450- 2x2879 with my general lee and Wilson 1000 and need to use a 6 foot jumper between the amp and radio

 

[Mudfoot]

Go ahead and place a good quality jumper.

Sent from my DROID X2 using Tapatalk

 

[ROC1]

Does the jumper length affect the performance of the radio any on tx/rx.. I'm going to be using a fatboy 450- 2x2879 with my general lee and Wilson 1000 and need to use a 6 foot jumper between the amp and radio

If the amp is presenting a 50 ohm load at the input you can run any length of coax and it will present 50 ohms to the radio. If it's not you're better off cutting the coax at 1/2 wave-length. Or, if it's not and you have the means to model the transmission line you can cut it specifically to present a 50 ohm load to the radio - assuming the load at the input isn't waaaay out there, which it shouldn't be.

Regardless you won't see much difference between between a six foot jumper and a 12 foot jumper. Line losses don't really impact unless the line is really long or you're running gobs of power.

 

[BOOTY MONSTER]

using a certain length of coax does not compensate for a amp that does not have a 50 ohm input/output . it also does not change the vswr . using a electrical half wavelength of coax can help meters read vswr more accurately .... but it doesn't change the actual vswr of the antenna ....... or the input tuning of a amp . if your anp has crappy input/output tuning getting the amp fixed is the only way to truly fix the problem .

your six ft jumper should be fine if its in good condition . tune the antenna without the amp inline , then add the amp . when setting or checking vswr always do it with nothing between the antenna and meter except for coax , and ill suggest always using a external meter for vswr tuning and checking .

 

[Robb]

Wouldn't using a better grade of coax have better RF shielding and keep any RF feedback looping to a minimum?

Wouldn't a 1/4 wavelength of jumper act as a transformer/impedance matcher between the amp and radio?

 

[BOOTY MONSTER]

what is "RF feedback looping" ?
how would the small %5 difference between typical vs. %100 foil shielding fix "RF feedback looping" ?

wouldn't be better get a properly built amp ?

 

[ROC1]

... never mind. not gonna argue with booty over this. I've watched him for years parrot what somebody else told him. this one is probably better left alone.

 

[BOOTY MONSTER]

im not arguing . and if i'm wrong it shouldn't be difficult to explain why ......
of course , if you dont have a leg to stand on and are parroting CB BS yourself any excuse to not put forth your evidence will do to try to keep from embarrassing yourself . i'm not afraid to be wrong and i dont mind being shown why im wrong when i am , it gives me a chance to learn ... and i certianly dont know it all .

common good buddy , don't be afraid

 

[W5LZ]

It's pretty simple. If the source, the transmitter has a 50 ohm output impedance, and if the load, the amplifier, has a 50 ohm input impedance, then connecting the two with 50 ohm impedance feed line should result in a very low SWR. If that SWR isn't very low, then correct the problem where the problem exists, not where is doesn't. Typically, the problem is with the input impedance of the amplifier. That's because of that 'no-tune' input circuit most all of them use is miss-adjusted to start with. Why try to make the jumper/feed line do something it was never designed to do instead of correctly adjusting that amplifier's input circuit. Sure, it's a quick-n-dirty way of ~seeming~ to correct things. But nothing has been corrected at all, it's just hidden because an SWR meter can't tell the difference between reactance and a strawberry malt.
- 'Doc

(Reactance and resistance is what impedance consists of.)

 

[WR0220]

^^^ What Doc said ^^^

 

[JustinDePolis]

But strawberry malts are good...

 

[ROC1]

im not arguing . and if i'm wrong it shouldn't be difficult to explain why ......
of course , if you dont have a leg to stand on and are parroting CB BS yourself any excuse to not put forth your evidence will do to try to keep from embarrassing yourself . i'm not afraid to be wrong and i dont mind being shown why im wrong when i am , it gives me a chance to learn ... and i certianly dont know it all .

common good buddy , don't be afraid

LOL. You never cease to dissapoint me. Polly wanna cracker?

 

[ROC1]

ARRL Guide to Antenna Tuners.
Chapter 7 Transmission Lines
Page 7-4

"There are some interesting special cases with a mismatched line. The load impedance, resistive and complex, repeats evey "half-wave", for example. The impedance goes to the opposite extreme in odd multiples of "quarter-wave". For example our 25 ohm load would get TRANSFORMED to 100 ohms in a quarter-wave or 3/4 wave tranmission line sections and vice versa. This effect can be used to our advantage if we wish to TRANSFORM impedances at a specific frequences."

Booty-Kisser - instead of parroting shit you hear all the time why don't you stick your nose in a book once in a while and then actually go do some real world testing.

 

[Se7en]

It's pretty simple. strawberry malt.
- 'Doc

(strawberry's and ice cream is what malts consists of.)

yum, get in my belly

 

[BOOTY MONSTER]

ARRL Guide to Antenna Tuners.
Chapter 7 Transmission Lines
Page 7-4

"There are some interesting special cases with a mismatched line. The load impedance, resistive and complex, repeats evey "half-wave", for example. The impedance goes to the opposite extreme in odd multiples of "quarter-wave". For example our 25 ohm load would get TRANSFORMED to 100 ohms in a quarter-wave or 3/4 wave tranmission line sections and vice versa. This effect can be used to our advantage if we wish to TRANSFORM impedances at a specific frequences."

Booty-Kisser - instead of parroting shit you hear all the time why don't you stick your nose in a book once in a while and then actually go do some real world testing.

thats a "interesting special case" example using a antenna tuner to tune a antenna to a non-resonate band , and using miss-matched coax . its also tuning a antenna ..... not attempting to compensate for a poorly designed amp input impedance .

like doc said ...
"If the source, the transmitter has a 50 ohm output impedance, and if the load, the amplifier, has a 50 ohm input impedance, then connecting the two with 50 ohm impedance feed line should result in a very low SWR. If that SWR isn't very low, then correct the problem where the problem exists, not where is doesn't."

rather than wasting your time flaming and calling names ...... how about learning to comprehend what your reading .... in the context that its written in .