[Antennas] What is Max Power

[George, W5YR]

Oooopppps!

Jim, the voltage and current in the unmatched line go up as the square root
of the SWR. So a 2:1 SWR will increase peak voltage and current by a factor
of 1.414.

I think you fat-fingered the attenuation at 0.3 db/100 ft at 2400 MHz!  
<:}

The loss is nearly 10 db/100 ft at 1000 MHz and is going up
logarithmically. The only cables shown in the Antenna Book that are 0.3
db/100 ft are RG-58 and 59 at 1 MHz.

I didn't check your figures for the power rating for a matched line, but
they look about right. Note that the source impedance - whatever it might
be and God only knows - doesn't really enter into any of this. The only
parameters that matter are cable Zo and load impedance , hence SWR.

73/72/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437


Jim Reid wrote:
> 
> > How do you determine the maximum power a coax cable
> > can handle?   For example RG-214 has a dielectric breakdown
> > voltage of 2500 volts what kind of power can it handle?
> 
> The voltage on the line will increase dramatically as the
> VSWR increases;  thus the power handling decreases
> as  vswr goes higher.  If the load,  source,  and cable
> are all 50 ohm,  the answer is 6.6 kW,  with about
> 0.3 dB attenuation in a 100 foot run at 2.4 GHz.
> 
> See this site for answers:
> 
> http://www.timesmicrowave.com/cgi-bin/calculate
> 
> Select the cable type, input a frequency and run length.
> 
> However,  as the vswr goes up,  the voltage peaks also
> rise,  and power handling drops quickly.  At amateur
> power levels,  you should have no problems; unless
> you are to have very poor Z matches,  hi.
> 
> 73,  Jim  KH7M
>