[Elecraft] Barebone K2 Amplifier?

[Bob Nielsen]

On Dec 7, 2006, at 2:23 PM, Fred (FL) wrote:

> Are there any 50 or 100 watt external amplifiers,
> that a barebone QRP K2 can drive?  Is anyone
> using one, for SSB and CW?
>
> Itch'n to build nother ...........
>

Under the current FCC rules, an external amplifier cannot be driven  
to its rated output win an input of less than 50 watts.  Additionally  
it cannot have more than 15 dB gain.  Under the changes that take  
effect on December 15, the 50 watt restriction is removed, although  
the 15 dB gain limit is retained (don't ask me why).

The KPA-100 isn't subject to the 50 watt rule, because it is designed  
to be integrated with the K2 as a single unit.  It can be operated  
separately (usually á la <http://www.kk7p.com/k2kpa100.html> but this  
is considered a modification by the amateur, which is permitted).

I expect that after the new rule becomes effective, there may be  
other amplifiers on the market suitable for use with a K2 or other  
QRP rigs (some exist now, but their legality is doubtful).  The rules  
prohibit an amp which can easily be modified to transmit between 26  
and 28 MHz, but don't say anything about modification to increase the  
gain, which I think in some cases might be done by removing an  
attenuator).  Since the K2's rated output is 15 W, an amp with 15 dB  
of gain would have an output of 474 watts, so this wouldn't apply in  
the case of 100 watt rig designed to be driven by 3.16 watts or less.

If you want an amp which will operate on 12 and 10 meters, it becomes  
a bit difficult even under the new rules, since high-power filters  
with steep skirts are rather impractical (rejection from 26 to  
28.000,  no loss at 28.001 is physically impossible).  The KPA100  
uses a digital signal from the K2 to know what frequency is being  
amplified, but another amp might require the use of a KIO2 to provide  
similar information (not quite bare bones).

Bob, N7XY