[Elecraft] KPA-200

[David Gilbert]

I think it all depends upon how you operate. 

About two years ago I put together some audio files to determine how 
much difference a couple of db would make for readability, as at the 
time I was trying to decide between a couple of different antenna 
options.  I generated some CW using CW Player, a free text-to-audio 
application, and then I mixed that with some 80m background noise I had 
recorded.  I varied the relative signal-to-noise level in one db 
increments relative to to the noise until I got below the noise level.

At the noise level, I had to work pretty hard to convince myself that I 
could hear the difference that one db would make.  Two db was 
noticeable, but just barely.  Three db was definitely noticeable and in 
my opinion could easily make the difference between making a weak signal 
DX contact or not.  I think I still have the audio files around 
somewhere if anyone wants a copy.

However, do I think it makes sense to jam a 200 watt amp into the K3?  
Nope.  First off, I doubt it makes sense to double the heat dissipation 
inside such a small rig.  Secondly, 3 db more power out doesn't have the 
same utility as three db from the antenna, where it also benefits 
reception (I did buy the more expensive antenna, by the way).  Thirdly, 
my testing indicated that even at signals as low as only 10 db above the 
noise level, a 3 db difference was barely noticeable.  If you feel the 
need to be heard, buy a real amp and give yourself a couple of S-units 
instead of a couple of db.

73,
Dave   AB7E




Ron D'Eau Claire wrote:
> IMX, it would be an undetectable change in signal strength under almost any
> conditions. 
>
> Over the years most engineers working in HF radio systems have found that
> the minimum discernable change in a signal is about 3 dB (2:1 change in
> power) under "ideal" conditions. That's 3 times greater than the 'standard'
> for audio lab work, but what is found in practice given typical background
> noise, minimal QSB, etc. on an HF signal.
>
> You can test this "on the air" very easily. Just hook up with someone in a
> normal QSO and then cut your power in half and see if they notice any
> difference. Don't tell them what you're testing, just that you are making a
> change, and see if anyone can tell you what you changed. 
>
> If they're looking at the S-meter on one of those absurd rigs that jumps 1
> or 2 S-units for every 2 dB or so of signal change, they'll see something if
> you're close enough for a rock-solid signal, but they're not likely to hear
> it. 
>
> I don't normally get excited about any major change that doesn't give me a
> 10:1 (10 dB) improvement in power. 
>
> Now, let's not confuse that with having an efficient station. As any QRP
> enthusiast (or smart Ham at any power) will tell you, a dB here and a dB
> there eventually adds to a significant change in signal strength. But the
> cost/benefits ratio of doubling the power compared to the same ratio going
> to the "legal limit" usually makes such a small change a bad investment. 
>
> Ron AC7AC
>
>
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