7000DLE MkII PA temp overcompensation?

N7CXI
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Joined: Sun Apr 09, 2017 5:20 pm
Location: Spokane Valley, WA

7000DLE MkII PA temp overcompensation?

Postby N7CXI » Mon Jan 17, 2022 4:24 pm

My 7000DLE MkII (big silver box version with no PC) has an interesting, if minor issue and I'm curious if anyone else has seen it.
The PA bias compensation appears to be over-compensated:

(1) Boot the rig from ambient (cold)
(2) Quickly set the PA calibration [for some band] so that the output power is 100W when the drive slider is at 100%
(3) Key the rig for 30 seconds in TUNE mode, unkey for 30 seconds
(4) Repeat (3) above 10 times
(5) Measure the TX power output, still with the drive slider at 100%

In my case at least, the rig will show something in the range of 88-90W. Let it cool for an hour or two and re-check the TX output power, and the "cold" calibration will be back at 100W.

You might ask "who cares", and you'd be right to do so. For most people in most "real" situations it really doesn't matter.
The exception, of course is that I would like to use the rig for characterizing/testing HF power amps - something I do a lot of.
I have other rigs I can use, but it since the 7000DLE MkII has that nifty RX2, I can monitor the amp output with a sampler and immediately "see" when something isn't right, or what I would expect. It would be very handy to be able to use it.

Has anyone normalized the PA output on their radio?

Thanks!
Jim N7CXI
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w-u-2-o
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Joined: Fri Mar 10, 2017 1:47 pm

Re: 7000DLE MkII PA temp overcompensation?

Postby w-u-2-o » Mon Jan 17, 2022 5:22 pm

Perhaps your title should read "undercompensation"?

Funny, two separate questions about the same thing at the same time (this one and one about the 8000).

See this topic from back in 2017: viewtopic.php?f=17&t=2652&p=4413

Note that the power difference you are seeing is less than 1dB variation, which is a very small amount.

That's actually pretty good since the gain flatness of the Apache designs is not great over both temperature and frequency. But it's not test equipment, after all, just a ham radio. If you want to use it as test equipment it would be best to monitor the input power to the amp as well as the output power.
N7CXI
Posts: 83
Joined: Sun Apr 09, 2017 5:20 pm
Location: Spokane Valley, WA

Re: 7000DLE MkII PA temp overcompensation?

Postby N7CXI » Mon Jan 17, 2022 6:14 pm

Perhaps your title should read "undercompensation"?


Maybe? Since the PA gain will normally increase with temperature, overshooting the stabilization isn't "over" compensation? I'll ponder that when I'm more awake.

And you're correct about it being less than 1dB. Characterizing the bias stabilization of a power amp requires a driver with stable bias stabilization, but I'll concede that my expectation might not be reasonable. ;-) It just irks me that my IC-7300 is far more stable.

73,
Jim N7CXI

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