I just performed a transmit test on 10M with my radio. CW mode, key
closed, 100 watts into dummy load, PA current 17.38A as indicated on the
radio, PA voltage 13.6 volts as indicated on the radio. After a 2
minute key closed period the PA temp was 56 C and stable. Fans stepped
to max.
Same test on 80M. PA current 18.3A , PA voltage 13.5V and PA settled at
57 C. Fans stepped to max.
Also ran 10M RTTY / AFSK at 100 watts out with a 1 minute transmission
and observed about the same as above.
The 15 second transmit / receive cycle sounds like WSJT-X and FT-8 mode
or MSK-144 mode {not normally used on 10M} Normally I do not run any
analog digital mode at 100 watts due to a bit of compression that
appears to occur in the PA stage. My suggestion, as I do, run 50 to
75 watts with analog data. Likewise with the KPA500, about 300 to 400
watts max for analog data signals.
In working SSB do you get reports of "fuzzy audio" or with PSK-31 get
reports of poor IMD ? If so I would suspect an issue with the KPA3A.
Consult Elecraft Tech Support.
73
Bob, K4TAX
On 12/19/2018 10:34 AM, Robert Harvey wrote:
Hi Bob and Don:
Actually, I am not transmitting data at anywhere near that length of time. I
am talking about a 10-15 second transmission in which I notice this.
Just some observations:
1. There is no cooling fan obstruction and they run normally as far as I've
been able to observe.
2. This is a new problem.
3. The power supply is delivering 14.0 volts under load, with a line drop of
.2 volts on transmit.
4. This occurs into a dummy load, or any one of three matched antennas. Even
bypassing tuners into the DL or antennas shows this same effect.
5. The antenna system SWR is steady, both on the DL and on the antenna's while
this is taking place.
If this is more or less normal behavior on 10M, and not indicative of bandpass
filter failure or imminent failure, I can live with it. I can run the KPA500,
which only requires about 20W input on 10M to get full output, so I am not
concerned about loss of signal all that much.
Thanks and 73!
Harv
K2PI
-----Original Message-----
From: Bob McGraw K4TAX [mailto:[email protected]]
Sent: Wednesday, December 19, 2018 10:43 AM
To: Gadget Lust
Cc: [email protected]
Subject: Re: [Elecraft] k3 High Current Message on 10 meters
Harv:
Per the manual the transmitter is rated at 100% duty cycle for CW and
SSB modes. This is for 10 minutes key down. Then it should be in
standby for 10 minutes. I do agree with Don that RTTY at 100 watts is
likely above the duty cycle rating. As temperature increases so does
current. Which makes for more heat. Most radios and amps are rated
at 50% duty cycle for carrier modes such as RTTY. Most RTTY operations
I've observed do transmit a lot more than receive.
You haven't indicated but is this a new problem or just a problem
observed? Other bands the KPA3A is more efficient and will produce less
heat than on 10M. In fact 6M has restrictions on power level where
power should be reduced to 85 watts or 70 watts depending on segment of
the band.
Fans, ......cooling is the key factor. What temp is the PA running
under these conditions? Has the temperature calibration been done?
Also are the fans ramping up as they should? Is the power supply
delivering 13.8 to 14.8 under load? If it is low the PA will draw more
current to produce 100 watts.
Just a few thoughts.
"Duty Cycle: CW and SSB modes, 100% 10-min. 100 W key-down at 25 C
ambient".
73
Bob, K4TAX
On 12/19/2018 9:07 AM, Gadget Lust wrote:
HI Don:
Understood, but the K3 is rated for full duty cycle on those modes, and this is
a new issue. I can certainly run it way under that and turn on the KPA500, but
still worry something is going south.
73
Harv
K2PI
Sent from Mail for Windows 10
From: Don Wilhelm
Sent: Wednesday, December 19, 2018 10:05 AM
To: Gadget Lust; [email protected]
Subject: Re: [Elecraft] k3 High Current Message on 10 meters
Harv,
I think the key is what you said about "long cycles modes like RTTY".
Things heat up in those instances and the current will increase. The
only 'cure' is to reduce power. I would suggest running RTTY at a power
level of 50% of the CW/SSB rating for the transmitter.
73,
Don W3FPR
On 12/19/2018 9:53 AM, Gadget Lust wrote:
Hi Don:
Actually, my issue is only on 10M. It appears that as I transmit,
current consumption increases, and I get occasional high current
messages. This is more apparent on long duty cycle modes like RTTY,
and at higher power levels (80-100W). If I watch, I can see current
consumption start at 16 amps, and slowly rise to 25-27 amps.
I performed a TX gain Cal successfully, and that made it a bit more
stable (only rising to 20 or 21 amps now), but it still concerns me.
A friend suggested this may be blown coils in the output bandpass
filters. I can wrap new coils if needed, but don’t want to do this if
that’s not the problem.
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