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[AMPS] Benefit

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Subject: [AMPS] Benefit
From: (Jon Ogden)
Date: Sat, 14 Mar 98 11:54:22 -0600
>> 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.

No, it is not erroneous.  This is from an engineering handbook.  A 1.5:1 
VSWR will reflect 4% of your power.  You can calculate that.  That 4% of 
power goes back down your coax where it weakens do to coax losses.  It 
then sees a mis-match of some sort when it arrives back at your antenna 
tuner/pa.  Some of that power is sent back into the antenna tuner/pa and 
some is reflected again to go back up the antenna.  So whatever power is 
no reflected back to the antenna is reduced by the loss in the coax and 
then when it gets to the antenna, 96% of it is sent out and 4% is 
relected back to do the same thing.  Reflections basically go back and 
forth continually ad infinitum.  This is why it is called a Standing Wave.

Is your total power loss 4%?  No, I never did say that.  But SWR does add 
to the loss in your system.

I am willing to go round and round on this one.  I am an RF engineer both 
by degree and trade.  So I feel that my knowledge is sufficient.

Fortunately on HF, coaxial line loss is not a huge problem unless you 
have a monster length feed line.  On VHF and UHF however, losses can be 

>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. 

I don't fully understand this chart.  But the columns aren't aligned 
properly so I can't read it either.

Many people are misinterpreting my comments about antennas vs. PAs.  I am 
not a psycho contestor or DXer, but I do do both of them.  I'd rather do 
this than ragchew.  I DO want as much power as possible.

However, if a guy is interested in say 20 meter DX and has a 3-element 
beam and can buy a 1000 Watt amp for $1000 or a 1500 watt amp for 2000, I 
would say buy the 1000 watt amp.  Put the other 1000 into either a larger 
beam (7 element) or get a higher tower.  Adding on a couple of sections 
of Rohn 45 to take you to 60 feet from 40 feet will make a huge 
difference.  Much more difference, IMHO than another 1.5 dB of Pout.

You guys are missing the point totally about what I said on taking things 
as a whole SYSTEM.  If you can't get any more gain out of your antenna, 
then fine, get the bigger PA.  All else being equal and if you have the 
money to spend, then get the bigger PA.

The level of Power out is a very emotional argument.  People generally 
want to run the legal limit (or more!).  However, 1000 watts into a 7 
element beam at 60 feet is far more effective than 1500 watts into a 
dipole at 30.  That is my point.  Power out is not everything.



Jon Ogden

"A life lived in fear is a life half lived."

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