Re: RD16HHF1 power curve flattening...some

Henning Weddig

even with the mods. the TX string shows a 3 dB drop in output power...

Please exchange the two single chokes L8 / L9 with a bifilar wound coil on a e.g. FT43-50 core, see the reasons for that mod in the description already cited in this forum  "".

BTW: how was the output power determined?

How does the power curve PIn - POut look like,

Is the output power measured at the 1 dB compresion point?

Tests on my tries to build a PA with the RD16HFF1´s using different output transformer configurations (even with a 1:4 guanella transformer with 25 ohm coaxial cable on two BN43-202 cores + Balun with 50 ohm coaxial cable on a FT43-80 torroid core + bifilar choke (FT43-50 torroid) + extra choke on the center tap  with a R-C combinaiton to terminate even harmonics) I was not able to get more than 10 W output power at P1dB.  Therefore I am really sceptical about the high power results of > 16 W.

The "hot" cores show that something must be wrong!

Did You measure the suppression of the even harmonics which should be well suppressed  (at least 40 dB) ? How good are the odd harmoncis suppressed?  If the third harmonic is only 10 dB down (1/3 of the amplitude of the fundamental wave) the PA produces square waves, which is not a performance of a linear amp.

IM performance??

Henning Weddig

Am 21.03.2018 um 12:41 schrieb John:

Hello Nik,

How did you go with the feedback issue?

My power amp mods in summary:  finals as RD16HHF1s, feedback resistors R261/R262 as 820 Ohms, Transformer 2T primary / 3T secondary on BN43-202, 180pF across the output transformer primary and 330pf across R87/R88. That's a way.

Heavily inspired by Erhard's (DF3FY) information as displayed on

Results per band at 14V supply, RV1 at %60, RD16's biased at 250mA each:
Band      output power   Total current
80M        22W                         2.9A
40M        20W                         3.2A
30M        16W                         2.3A
20M         16W                        2.7A
17M         15W                        2.4A
15M         12W                        1.6A
12M         12W                    not measured
10M         12W                        1.7A

At 22W the output transformer does get warm but not the LPFs.

Wound back RV1 to get 9-10W on the high frequency bands and 16-18W on the lower ones.

All the best,

73, John (VK2ETA)

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