The short answer is they can. It is only a matter of engineering
time, cost, resulting price, number of customers and competing
projects. In other words, the usual business considerations.
Lets work the idea through for several of the Elecraft RF amplifiers:
The 10-15W K3(s) amp: This amp can have significant IMD at low
voltages as we have discovered with our QRP, all Elecraft, field
day operation. The KX3 seems to do better, so reengineering the
amp may be a better solution. For field day, we try to have
fresh batteries available.
The 100W K3(s) internal amp: This amp also has low voltage IMD
as we found during our 100W California QSO party expeditions.
But, consider the K3(s)'s construction. The front of the radio
is the digital portion, including the DSPs and the front panel
computer. All of this digital noise is isolated from the analog
circuits in the back of the radio. If Elecraft were to include a
boost power supply with the internal amp, that high-current
switcher would be in the analog section, and probably impossible
to quiet. Solution: Get an external boost power supply.
The KXPA100 external amp: This form factor would be an ideal
place to include a boost power supply. The use profile includes
portable battery operation and designing isolation for the power
supply into the package seems straight forward.
The KPA500 external amp: The amp setup procedure sets the
voltage to to 65v to 85v and the specifications call for about
1000 VA of power or about 13A at 75v. That would be nearly 75A
at 13.5 volts assuming 100% efficiency, so it would be a good
idea to put the boost power supply next to the battery and run
75v to the amp. It would make a nice high power mobil rig.
73 Bill AE6JV
In thread "Re: [Elecraft] Chinese ebay amps for KX3", on 2/20/17
at 5:47 AM, [email protected] (Charlie T, K3ICH) wrote:
So now, tell me why a mid-sized radio can't have a built in 12 V to say, 50
V converter to drive some HV FETs for cleaner output specs like the Yuge
radios.
-----------------------------------------------------------------------
Bill Frantz |The nice thing about standards| Periwinkle
(408)356-8506 |is there are so many to choose| 16345
Englewood Ave
www.pwpconsult.com |from. - Andrew Tanenbaum | Los Gatos,
CA 95032
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