[Elecraft] FW: Testing IMD3 (dB) K3S (#10490)

[K9MA]

On 2/8/2020 21:45, Joe Subich, W4TV wrote:
> Note: this is into a *non reactive* 50 Ohm load.  If the load
> differs from 50 ± j0 Ohms, IMD is likely to be worse due to
> the mismatched load. 

Joe makes a very good point. Even with 14.5 V and a perfect 50 Ohm load, 
12 V PA's have marginal IMD at 100 W. If there is a moderate mismatch, 
like 1.2:1, it can be much worse. Given that  ATU's don't consistently 
get the SWR below that, IMD is often likely to be pretty bad. (It would 
be very interesting to see some test results with 1.2:1 at various phase 
angles.)

Fortunately, a lot of amplifiers, including all the solid state ones, 
require much less drive power. Unfortunately, some of the solid state 
amplifiers are also likely to generate more IMD if they aren't perfectly 
matched. (And they're not that great when they are matched.) Reducing 
power a bit should help. Running an amplifier capable of 2.5 kW at 1.5 
kW would probably keep the IMD pretty low, even with a moderate 
mismatch. It would also be very expensive.

73,

Scott K9MA


-- 
Scott  K9MA

k9ma at sdellington.us