[Elecraft] K3 Two amplifiers 1 key line

[Joe Subich, W4TV]

All the work has already been done by Paul, WD7D.  See "Improved 
Amplifier Interfacing for the Yaesu Mark V FT-1000MP"  QST, 
September 2004, page 51.  The only change necessary to Paul's 
circuit is to add a pair of pull-up resistors ... he even has 
(had?) circuit boards for the project.     

The circuit will switch PTT and Inhibit lines between HF and 
six meter amplifiers based on partial decoding of the Band 
data lines.  

Note: partial decoding will not work if you have any transverters 
on the K3 and are using the band data outputs for switching them. 

73, 

   ... Joe, W4TV 
 




> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Don Wilhelm
> Sent: Thursday, July 03, 2008 5:48 PM
> To: Lee (WW2DX)
> Cc: Elecraft Reflector
> Subject: Re: [Elecraft] K3 Two amplifiers 1 key line
> 
> 
> Lee,
> 
> You should be able to provide control lines for HexFETs or some other 
> kind of switch with just a little bit of logic and the 
> signals from the 
> ACC connector.
> 
> Look at the Band Data outputs - the only time *both* Band3 
> and Band1 are 
> at a high impedance state is on 6 meters.  A NAND gate (with pullup 
> resistors on the inputs) will give you a LOW output on 6 
> meters and HIGH 
> on all other bands - call this 'partial band decode'.
> Now add an inverter to the KEYOUT-LP signal (another pullup 
> resistor is 
> needed at its input) and feed its output to one input each of 2 more 
> NAND gates - the 'partial band decode' NAND gate output feeds the 
> remaining input of one of these NAND gates and that one will 
> have a low 
> output when HF is selected *and* Keyout is active.
> Invert the output of the 'partial band decode' and feed the inverted 
> output to the input of the other NAND gate that you connected the 
> inverted Keyout signal to - that NAND will have a LOW output when 6 
> meters is selected *and* keyout is active.
> I don't know how much voltage and current your amps PTT 
> inputs require, 
> so I leave the final keying of the amps up to you.  A pair of 
> the K2 Amp 
> Keying Circuit on the Elecraft website or one of Tom Hammond's K2 Amp 
> Keying kits can be driven by the circuit I described and be 
> used to key 
> your amplifiers.  A 74AC00 dip and a 74AC04 will do this task 
> with one 
> NAND gate and 4 inverters to spare - it takes longer to describe in 
> words than to draw it.
> 
> To be safe, I would not consider letting the RF path 
> determine which amp 
> transmits - if you ever find the ANT1/ANT2 selection changed (by an 
> inadvertent button tap), you could send RF to the wrong amp.  You may 
> not be able to simply run the KEYOUT to both amplifiers - 
> that will only 
> work if both amplifiers have the same voltage on their PTT IN lines 
> (measure with your DMM with the amplifier on and nothing connected to 
> the PTT IN jack).
> 
> 73,
> Don W3FPR
> 
> Lee (WW2DX) wrote:
> > I have a HF amp on ANT1 and (soon to be) 6M amp on ANT2. ANT2 is
> > dedicated 6M antenna.
> >
> > Has anyone come up with a way to PTT each amp when on 
> desired band? Is
> > it possible to just hook both AMPS to the same PTT key line so both 
> > amps  Key at the same time but the RF path would then take over?
> >
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft    
> 
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com