Sorry if this is argumentative, but your post seems to be in conflict
with Wayne's post earlier today.
Wayne: "...heat sinking that is entirely adequate in all modes at full
power, even from a 14 volt external supply."
The manual also says "all modes" which I don't see why that would
exclude JT65. JT65 is *not* 100% duty cycle. It transmits about 50
seconds out of the 1 minute interval, then receives for 1 minute. Sounds
to me like slightly less than 50%.
Wayne's results were 7 mins key down until reduced power at 25c ambient.
Running JT conditions of 1 min xmit and 1 min receive, how long does it
take to reduce power, if ever? How much is this performance reduced at
30 or 35c? Without this data I don't see how we evaluate whether an
additional heat sink is required.
Thanks & 73,
Josh W6XU
On 5/14/2017 2:18 PM, Howard Hoyt wrote:
Hi Kev,
The issue is related to the fact that Elecraft, as do virtually all
amateur radio manufacturers rate power output with 50% duty cycle
SSB/CW modes only. As is stated in the KX3 specifications and here
copied from the KX2 manual:
/"80-17 meters, 10 W PEP max (+/- 1 dB); 12 and 10 meters, 8 W PEP max
(+/- 1 dB).//
//Recommended transmit duty cycle: 50%, all modes. (If power amplifier
temperature or//
//current drain is too high, power will automatically be reduced.)//
//NOTE: When using over 5 W in SSB, DATA-A and AFSK-A modes, the//
//recommended supply voltage is 12 V or higher to minimize transmit
intermodulation//
//products. Higher power with lower voltages should be used only when
necessary."/
I believe many or most of the requests we have had to make an
aftermarket heatsink have come from hams using these rigs in digital
modes such as JT and desire full-power operation, which Elecraft does
not explicitly endorse, but which is possible with additional
cooling. Elecraft designs and specifies operation of their rigs very
conservatively compared to many other manufacturers, and the KX2 and
KX3 specifications are spot on.
Also as is stated in the specification, the KX2 internal battery, at
10-11V depending on state of charge is considered adequate for 5W or
less, and we have supplied many Kx33 14V supplies to KX2 owners who
want to use the rig at 10W power when AC power is available.
I conclude many of these KX2 rigs are being used in digital modes from
fixed location AC power, not from batteries. I can't blame the hams
who do this, the KX2 is a fantastically full-featured rig for fixed
operation, I have used it at home to check into local 10M SSB nets
driving a KPA500 and no one was the wiser compared to my K3.
Cheers,
Howie - WA4PSC
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