[Amps] High SWR

[Roger]

James R Carr wrote:
> One could use ladder line. It's relatively lossless and can handle gobs of 
> hi voltage.
> Jim
> N7FCF
> ----- Original Message ----- 
> From: "Bill, W6WRT" <dezrat1242 at yahoo.com>
> To: <amps at contesting.com>
> Sent: Wednesday, April 22, 2009 4:53 PM
> Subject: Re: [Amps] High SWR
>
>
>   
>> ORIGINAL MESSAGE:
>>
>> On Wed, 22 Apr 2009 17:39:22 -0400, Pete Smith <n4zr at contesting.com>
>> wrote:
>>
>>     
>>> , but SWR, per se, is not
>>> something to worry yourself about, so long as the amplifier can match the 
>>> load.
>>>       
>> REPLY:
>>
>> I agree up to a point. The main villain with SWR, IMO, isn't loss, it
>> is the excess voltage present on the line. Most coax, even the RG-213
>> size, is rated for only 600 volts. If you have a 2:1 SWR at 1500 watts
>> you are living on the edge already. Go to 3:1 and you have crossed the
>> line.
>>     
>> I won't say it can't be done, but a wise op won't.
>>
>>     
Why not.  I typically have been using LMR-400 on center fed dipoles for 
75 and a half sloper on 160 across the entire bands with the aid of a 
tuner at the rig end of the coax and using an Alpha to pump about 1500 
PEP in.  SWR runs on the order of 3:1 or a bit higher on 75 at the band 
edges and considerably higher than that on 160.  I've never had a 
problem and those voltages are considerably higher than 600.  Actually I 
run a KW into LMR-240 on 40 meters, across the entire band.  I've also 
tried it on 75 with both LMR-240 and RG8X with the dual shield.  I've 
found I'm much more likely to lose an N-connector than the cable.

Admittedly there is a big difference between DC voltages and RF, but we 
really need to specify the frequency being used as any specific coax can 
handle much more RF voltage at 160 than at 30 or 50 MHz.  I use RG8 
style coax to handle as high as 4KV DC, but that'd be more than pushing 
my luck at 50 MHz. I think I'd also be more than pushing the legal limits.


73

Roger (K8RI)
>> 73, Bill W6WRT
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