7000DLE Variable Output Power

spinomaly
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Joined: Fri Oct 20, 2017 5:44 pm

7000DLE Variable Output Power

Postby spinomaly » Sat Dec 09, 2017 4:52 pm

Has anyone noticed that the output power (read in PowerSDR) seems to change as a function of temperature? I power calibrated after a warm-up period and have been noticing that the output power is up 5-7 Watts until the unit reaches a stable temperature point which could take 5-10 minutes of transmitting.
Dr. Loren Betts
W6VH
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w-u-2-o
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Re: 7000DLE Variable Output Power

Postby w-u-2-o » Sat Dec 09, 2017 5:38 pm

Loren,

A lot of things change with temperature in the openHPSDR and Apache Labs hardware designs. This is true of all of the various radio models, from the 10 to the 7000 and 8000, although it is more apparent in the 100W+ radios because, obviously, thermal states change much more significantly during transmissions in those radios.

While receiver gain and linearity is generally outstanding, many RF characteristics associated with transmit do not demonstrate terribly good gain flatness and gain linearity over both frequency and temperature. This includes the measurement of forward and reverse power on transmit. In particular, the linearity of the RF drive control is pretty poor, something easily observed. Some people calibrate for maximum power at 100W, others such as myself calibrate for maximum accuracy around the nominal drive power levels we use with our external amplifiers. None of the radios, with the exception of the 7000, have temperature compensated amplifier bias supplies. Adjusting bias on those radios is like chasing your tail, you can watch the drive currents vary by quite a bit during test transmissions as the parts warm up. This makes choosing a bias setting an exercise in guesswork to a certain extent. BTW, it would be interesting to know how much better this is on the 7000 given the bias compensation mentioned in the spec. sheet.

On my 100D I added an external fan to maintain maximum thermal stability (and it will overheat on long-winded AM sessions even at only 40W without it, too). While the cooling in the 7000 is supposed to be better (I have yet to see any public internal photos of it), Apache did provision an external fan connector and I applaud them for doing so. The case still remains the heatsink for the amp FETs and essentially relies only on free convection. Adding just a tiny bit of forced convection to the proper spot above the FETs make a HUGE difference in thermal stability. My suggestion is to grab yourself a quiet 120mm or 140mm PC case fan and put it on top of the case over the FETs, blowing downwards, with a small, 0.5" stand-off.

73,

Scott

P.S. I moved this topic since it was not related to 7000 firmware and it is not an issue only for 7000's, either.
dl4zbg
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Re: 7000DLE Variable Output Power

Postby dl4zbg » Sun Dec 10, 2017 11:14 am

Yes Loren,

the impact of the case temperature is noticeable, (almost) regardless of the power level. When you key down the transmitter, the output level rises slightly (abt 0,5 watts at 100W) and then slowly starts to decrease. Same at moderate levels (30 Watts) in almost the same percentage.
No problem for me.

To be honest, I never made this test with my ANAN 100, but I remember there was almost no degradation with my QRP ANAN-10 at 10 Watts.

my ANAN-7000DLE first impressions:
+: The internal wattmeter is very good
+: chassis stays much cooler than my 100

-: rattling fan, this does NOT change with higher speed (maybe I just try a different one or I'll get rid of the rig)
-: noticeable LPF roll-off at 10m (Power decreases from 100 watts at 28,0 MHz down to 93 watts at 28,5 MHz and 90 watts at 29 MHz
-: TX IMD on 10m and 17m only -20dBc at 100 watts and higher products don't fall at all, -30dBc at 70 watts and higher products fall (filter saturation?), fairly good at all other band including 6m!

73

Volker

DL4ZBG

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