[Elecraft] Max power for JT9 with K3S 100?

Sun Apr 5 09:31:32 EDT 2020

A weak signal mode does not imply a low power mode. 

Bob, K4TAX

Sent from my iPhone

> On Apr 4, 2020, at 11:15 PM, brianchapnick <brianchapnick at rogers.com> wrote:
> 
> 
> This discussion fascinates me only in that I wonder why you are using so much power for weak signal modes? 5 or 10 watts should be plenty even with a compromised antenna and poor band conditions......or am I missing somthing.
> 
> Brian VE3GMZ 
> 
> 
> 
> 
> 
> Sent from my Samsung Galaxy smartphone.
> 
> 
> -------- Original message --------
> From: Bob McGraw K4TAX <rmcgraw at blomand.net>
> Date: 2020-04-04 8:19 p.m. (GMT-05:00)
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] Max power for JT9 with K3S 100?
> 
> Frank et al;
> 
> 
> Just quoted what is in the K3S manual.   No interpretation provided.   I 
> agree that 100 watts key down is a lot for a SSB amplifier running in CW 
> mode.   To me that says 100 watts for 10 minutes and then RX for 10 
> minutes.   Otherwise equal TX and RX times.   Who does that?
> 
> And if one is running "100 watts" then running CW or SSB for 10 minutes 
> might be the limit.  Just speculation.   On AM I might talk for 10 
> minutes but that is at 25% rated power output for carrier, yet it is 100 
> watts PEP.   The 60 C is MY guideline. The KPA3A will shut down about 85 
> C or so.
> 
> On 6M I run my KPA500 at about 300 to 400 watts.  The K3S is running 
> about 25 to 30 watts on 6M.   At this point I'm watching the KPA500 
> temperature.
> 
> There is NO DX worth blowing a PA either in the K3S or the KPA500.    
> But I know guys that will blow things up, pushing things to the max and 
> beyond  trying to work that DX station.  I say bah humbug to that!
> 
> I just pay attention to the PA temp, specially when running digital 
> modes. Likewise for the KPA500.
> 
> 73
> 
> Bob, K4TAX
> 
> 
> On 4/4/2020 3:41 PM, Frank O'Donnell wrote:
> > Thanks for the replies.
> >
> > I've enabled the PA temp display (currently showing 22C right after 
> > power-up but before transmitting), and will keep an eye on that.
> >
> > Bob, I noticed that line in the K3S manual about the CW/SSB duty 
> > cycle. Does "100% - 10 min, 100 W key-down" mean that if you key down 
> > without stop in CW mode it can go 10 minutes at 100 watts? That seems 
> > like an awful lot.
> >
> > Where do the recommended TPO's for 6 meters, the 50% value for JT9, 
> > and the 60C guideline for the PA temp come from?
> >
> > Thanks again,
> >
> > Frank K6FOD
> >
> >
> > On 4/4/20 6:22 AM, John Simmons wrote:
> >> Fred Cady's book:
> >>
> >> "There are four fans speeds that turn on at different temperatures."
> >> "If the temperature reaches 84 degrees C the KPA3 will be bypassed 
> >> until the temperature falls to stop any damage as a last-ditch backup 
> >> measure to protect your expensive power transistors from the excess 
> >> heat."
> >>
> >> -de John NI0K
> >>
> >>
> >> Bob McGraw K4TAX wrote on 4/3/2020 6:39 PM:
> >>> Frank:
> >>>
> >>> The duty cycle for the transmitter, as stated in the manual, is;  CW 
> >>> and SSB modes, 100% - 10 min, 100 W key-down at 25C ambient.   Do 
> >>> note that 6M has reduce power values of 85 watts {51 -52 MHz} or 70 
> >>> watts {52 - 54 MHz}
> >>>
> >>> The duty cycle for JT-9, 1 minute transmit, 1 minute receive would 
> >>> be 50%.   I frequently run 100 watts on WSJT-X FT-8 with no issues.  
> >>> Just pay attention to PA temperature.  It should be 60 C or less.   
> >>> Also this is with FANS in the automatic mode.
> >>>
> >>> 73
> >>>
> >>> Bob, K4TAX
> >>>
> >>>
> >>> On 4/3/2020 4:18 PM, Frank O'Donnell wrote:
> >>>> I've been using JT9 mode on 630m this winter with my K3S outputting 
> >>>> to an external class D amp.
> >>>>
> >>>> Now I'm interested in trying some JT9 QSOs with some people 
> >>>> currently operating on 160m. For me this would mean outputting 
> >>>> directly from the K3S (with internal tuner) to the antenna.
> >>>>
> >>>> Given the 1-minute cycle time for JT9, are there recommendations 
> >>>> (official from Elecraft, or otherwise) on maximum power to use in a 
> >>>> situation like this? And/or, is the answer dependent on the SWR I 
> >>>> can achieve with the antenna?
> >>>>
> >>>> Thanks and 73,
> >>>>
> >>>> Frank K6FOD
> >
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