[Elecraft] KPA1500 PA Current

[Jim Brown]

On 3/16/2019 2:31 PM, Edward R Cole wrote:
> In the same vein:  I recently tried out my new 2m 1500w sspa at 750w 
> in SSB and stations on my net only stated a slight increase in signal 
> 100 miles away vs running 130w.  That should have indicated more than 
> one s-unit stronger (10Log (750/130)=7.6 dB).
>
> Definitely a "knee" in signal strength where change is most 
> significant and where change above is not so much.  HF that should 
> even be more compressed.

What you're calling a "knee" is better described as a combination of 
receiver AGC,  perception of loudness and signal to noise by our 
ear/brain function, and how various signal characteristics combine to 
provide speech intelligibility. A change in OVERALL loudness of 6-10 dB 
is perceived as twice (or half) as loud when the signal is well above 
the noise, and 1 dB is about the smallest change IN OVERALL loudness 
that untrained listeners can perceive.

But when the signal is close to the noise, a few dB change in the signal 
to noise ratio often makes a big difference in speech intelligibility.

And what I learned in my professional life and have been teaching the 
ham community for more than ten years is that speech intelligibility is 
most strongly dependent on components in the 800 Hz to 3 kHz range, with 
higher frequencies making a small additional contribution. Roughly half 
of the ENERGY in speech is below 500 Hz, but this sound makes almost no 
contribution to speech intelligibility. SO -- using TXEQ to remove that 
sound is the equivalent of doubling the effective talk power (3dB)!  
This is why I've always recommended setting TXEQ for max cut in the 
three lowest bands, 6 dB cut in the 4th band (400 Hz), and a small boost 
(3-6 dB) in the top two bands.

Careful use of good speech compression can add another 10dB of talk 
power, so the combination of EQ and compression can improve signal to 
noise by 13 dB, which is equivalent to multiplying transmitter power  by 20!

> Raising antenna ten feet above tree top is worth at least 10-dB in 
> signal improvement at VHF (and way more as freq is increased into 
> UHF+).  I can lower my 2m array to 4-foot AGL by use of a winch. Going 
> from there to about 40-feet (tree top) is worth maybe 5-dB.

Yes, and height above ground can matter a LOT on the HF bands.

http://k9yc.com/AntennaPlanning.pdf

73, Jim K9YC