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[AMPS] Benefit

To: <>
Subject: [AMPS] Benefit
From: (km1h @
Date: Sat, 14 Mar 1998 11:54:57 EST
On Fri, 13 Mar 98 23:14:47 -0600 Jon Ogden <> 


> Also, keep your coax runs as short 
>possible and use good quality coax and connectors.  Minimize losses as 
>much as possible.  This includes making sure you have a well tuned 
>antenna.  Bad SWR basically causes losses as every time your RF is 
>reflected back and forth through the coax, there is a little 
>loss.  An SWR of just 1.5:1 can reduce your power by as much as 4% (4% 
>power is reflected back from antenna).

I believe that is erroneous Jon, but I am not sure what you are saying please bear with me.

Here are the published flat and additional VSWR losses for RG-213 per

Freq    Flat Loss    Add loss  2:1 VSWR     Add for 4:1 VSWR
4 Mhz   0.32dB    <0.1dB                      0.3dB     
15      0.8                 0.18                      0.7
30      1.2         0.22                      0.9       

It would then appear that even a 4:1 VSWR at 20M is of no real
consequence for many styles of operating. On 80M I really could care less
about  the.3dB when I go from CW to SSB. 

Losses are much less with CATV hardline and .5 or .875" Heliax. For
instance .75" CATV has a flat loss of 0.25dB at 30MHz;  a 2:1 VSWR would
add < 0.1dB and a 4:1 VSWR would add 0.25dB.
I use all CATV and Heliax line here.

The only feedline I have ever punctured was RG-6  CATV drop cable when
trying to make a LP array work on 75M
RG-213 is rated at 5KV continuous. The amp load capacitor is more apt to
arc first. 
I know of many hams that have accidentally operated into the wrong
antenna, they have blown loading coils and traps but never RG-213. 

73   Carl   KM1H

  At 1500 watts that is 60 watts 
>(some of that 60 watts does get eventually radiated after it is 
>back from the source, travels back downt the transmission line and out 
>the antenna, but there are losses with each trip through the coax).  
>SWR of 1.8:1 can result in an 8.2% reflection.  As well the high 
>peaks in a condition of high SWR along the coax can cause problems if 
>your coax isn't high enough quality (dielectric can literally break 
>down).  Remember that if you have 1.5 dB of total loss in all of your 
>feedline, connectors, etc. you can make your 1500 watts into 1000 at 
>antenna!  You've also done a lot to heat up the coax!
>To anyone buying an amplifier, I would urge them to think in terms 
>than just transmitted power.  It's best to think in terms of ERP 
>(Effective Radiated Power).  Again, what can you do to improve your 
>station over just adding more power.  What can you do with the 
>the feedline, etc.  It all matters quite a bit.  It's an entire system 
>working together and it is only as good as the weakest link.
>In the final analysis however, after all is said and done, I would buy 
>amp that is rated continous duty at 1500 watts.  If you are going to 
>spend the money you might as well do it right.  That way you know that 
>you run 1200 or 1300 watts that your amp is well within its limits.  
>However as another person put it, the 1000 watt amp the original 
>asked about may not even cut it at 1000 watts but more like 700 watts. 
>>From 700 to 1500 is a BIG difference.
>I apologize for the length of this and if any was too technical for 
>anyone out there.  I just got on a roll!  :-)
>Cheers to all,
>Jon Ogden
>"A life lived in fear is a life half lived."
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