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[AMPS] Benefit

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Subject: [AMPS] Benefit
From: (Jon Ogden)
Date: Fri, 13 Mar 98 23:14:47 -0600
>As any serious DXer will tell you, that extra 500 watts is sometimes
>the difference between QSO and no QSO.  If you're not serious about
>DXing then right, you don't need it.  Your call.

Think noise floor...What is the noise floor at the station to which you 
are transmitting?  With a big pileup, it might be a S9 +10 dB noise 
floor.  Then yes, the extra 500 watts would help.  Yes, it can DEFINITELY 
make the difference between QSO and no QSO.  I agree.

However, I disagree that you can't be serious about DX without it.  I 
have worked stations on 100 watts and a vertical antenna faster than some 
people running beams and kilowatts.  I have also spent 2 hours trying to 
get one station (S92SS) with the same setup.  So while power helps, it 
doesn't always.  I've worked lots of DX running barefoot.  And sometimes 
it's more fun that way.  To know you got the rare guy and all of the big 
guns are still fighting for him!

Also, we need to think about total system performance as well.  But I 
repeat myself:  1000 watts with a 9 dB gain Yagi will do much better than 
1500 watts into a 6 dB gain yagi.  Also, keep your coax runs as short as 
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 additional 
loss.  An SWR of just 1.5:1 can reduce your power by as much as 4% (4% of 
power is reflected back from antenna).  At 1500 watts that is 60 watts 
(some of that 60 watts does get eventually radiated after it is reflected 
back from the source, travels back downt the transmission line and out to 
the antenna, but there are losses with each trip through the coax).  An 
SWR of 1.8:1 can result in an 8.2% reflection.  As well the high voltage 
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 the 
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 other 
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 antenna, 
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 an 
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 if 
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 poster 
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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