Coax length question !

[terryj]

Your power loss @ 2db for 200 feet of RG-213 will be about 1.75 watts, the gain of your antenna should make up for this loss.

 

[GnG8d]

Your power loss @ 2db for 200 feet of RG-213 will be about 1.75 watts, the gain of your antenna should make up for this loss.

:blink:

At 27.2 mHz and a perfect 1.0:1 match, 100w out @ a 2db loss is 38.3 watts lost, or 61.7 watts at the antenna.

At a 4 watt legal CB carrier, the loss is 1.5 watts, or 2.5 watts at the antenna. Fully modulated to 20 watts, the loss is 7.7 watts.

 

[Kamikaze]

Your SWR will get better with longer cable because the loss effects reflected power too!

 

[GnG8d]

I'm not even going to touch that, lol

 

[BOOTY MONSTER]

Your SWR will get better with longer cable because the loss effects reflected power too!

how does the distance of the run change the voltage standing wave ratio ?

 

[bob85]

reflections from the mismatched load are attenuated on the return trip by loss in the feedline booty,
longer runs of coax make your vswr seem lower and your vswr bandwidth wider if the meter is at the transmitter end,
the divine wind has spoken

 

[BOOTY MONSTER]

the divine wind has spoken

thank you divine wind

 

[GnG8d]

longer runs of coax make your vswr seem lower

key word

 

[Kamikaze]

Nope. It will actually BE lower at the generator end.

key word

 

[GnG8d]

But your measuring unattenuated forward power against attenuated reflected power.

EDIT_____
Nevermind, your always measuring unattenuated forward power against attenuated reflected power.

But anyway, longer feedline looks better on the meter, but does nothing for your antenna.

 

[hookedon6]

Nope. It will actually BE lower at the generator end.

not if it is loaded into a 50 Ohm load

 

[Marconi]

not if it is loaded into a 50 Ohm load

We're just lucky we don't have to operate into a perfect load in order to work our radios.

 

[Captain Kilowatt]

Nope. It will actually BE lower at the generator end.

Nope, for all practical usesthe system SWR will just APPEAR to be better due to attenuation of the reflected power. That's a moot point anyway as we all know that it's what the SWR is at the feedpoint that determines the efficiency of power transfer to the antenna anyway which is what really counts.

On second thought, maybe we don't all know that.

Try loading a 20 watt transmitter on 440 MHz into a long roll of RG-58 coax with the far end unterminated. You will see a good SWR at the generator end yet there is no antenna or load of any kind at the far end. Yep, that low SWR really means something in that case.

 

[W5LZ]

 

[bob85]

its the transmitters ability to deliver power into the load it sees at the input end of the feedline that has by far the most effect on efficiency,

whatever the transmitter can deliver into the input end of the feedline will reach the antenna, some will be radiated and some reflected,
the reflected wave suffers loss on the return trip to the transmitter, its then rereflected from the transmitter tank circuit adding to the incident wave and eventually will be radiated by the antenna,

thats if i understand walt maxwell and he is correct, the conjugate match is still hotly debated and im not einstein.