[Elecraft] K3/K3S 10W models with KXPA100

[Vic Rosenthal]

I don't like circuits like this because they guarantee hot-switching of the amplifier. Unless you have a time-reversal device, the amp won't switch until RF is already flowing. Maybe it wouldn't damage the amplifier in this case, but it would certainly mess up the shaping of CW elements.

Much better to add an amp key circuit to the transceiver if it doesn't have one. If done correctly (like the N0SS circuit for the K2 that was mentioned), the amp key line is activated a few ms before RF is produced. 

Vic 4X6GP

> On 21 Feb 2016, at 11:01 AM, Edward R Cole <kl7uw at acsalaska.net> wrote:
> 
> Brendon,
> 
> Yes, though you would need to construct it.
> 
> A simple RF sense ckt would be 1pF coupling cap from the coax line (maybe use a coax tee and connect the RF sense box to the tee).  At HF the tee will not show significant impedance bump.
> 
> The cap feeds a diode like the BAS-16 followed by bypass caps to ground (0.01uF and 10uF ought to suffice).  This feeds thru a 1K resistor to control a NPN transistor that will key the amplifier to ground.  You might add a 1uH choke in line before the resistor if concerned that the RF is not completely smoothed to dc.  The circuit I described is used in the W6PQL 2m 80w amplifier for RF sensed PTT (except different values for bypassing 2m).
> http://www.w6pql.com/2_meter_80w_all_mode_amplifier.htm
> 
> Another way is to buy a kit.  W6PQL sells an ALC detector board which passes RF thru and detects RF providing a negative voltage.  The kit includes 750-ohm resistor which is good for 1-2w.  Probably better to use a 2K resistor for 10w.  I am using this board kit with 10K resistor to sample 2m 80w RF for a RF output meter.
> http://www.w6pql.com/Sampling_RF_Power.htm#alc
> 
> Let me also comment about using the KXPA-100 with either K3/10 or KX3.  I recently bought a KXPA-100 for just those two radios and its a perfect companion.  One plus is heat is kept out of either radio which reduces frequency drift when running digital modes.  Of course digital modes don't need 100w but you can reduce drive to 20w with either radio driving the KXPA-100.  I don't plan to use my K3 outside the shack but the KX3 may go mobile with the KXPA-100.  I incorporated a PTT switch in my new station control panel to select either K3 or KX3 PTT which is provided to several accessories including the KXPA-100.
> 
> 73, Ed - KL7UW
> 
> From: Brendon Whateley <brendon at whateley.com>
> Cc: Elecraft Reflector Reflector <elecraft at mailman.qth.net>
> Subject: Re: [Elecraft] K3/K3S 10W models with KXPA100
> Message-ID:
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> 
> Ron,
> 
> Would it be possible to put some sort of RF detector between the rig and
> the amp to trigger the KEY line? That would seem to be a relatively simple
> DIY project if need be.
> 
> - Brendon
> KK6AYI
> 
> 
> 
> 73, Ed - KL7UW
> http://www.kl7uw.com
>    "Kits made by KL7UW"
> Dubus Mag business:
>    dubususa at gmail.com
> 
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