From: [email protected] [mailto:[email protected]] On Behalf Of Nik VK4PLN
Sent: Sunday, March 18, 2018 6:06 PM
To: [email protected]
Subject: Re: [BITX20] RD16HHF1 power curve flattening...some

?

THanks Glen.

I am making progress, got it working on 80,40,20, but still feedback on 15m, and 10m.
I put 220pf across all 7 emitor resistors. tried with and without, definitly a flatter output with. no effect on the feebback issue.
Changed back to the BN42-202, but a 2:4 ratio winding giving 1:4 transformation. Runs cool at 20+w with 330pf Mica cap. 1K feedback reistor.

80M - 22W
40M - 20W
20m - 18W

I did remove the SSM2167 Mic preamp and the feedback went away, but the mic output was very low... I then put in a MAX9814 mic chip/board via a BS170(same as the TX-POP setup) connected to the T/R line, To mute MIC on RX(DRAIN to GND on mic board..). Worked sortof. Got rid of the feed back, but when exiting TX I got a LOUD pop which causes the uC to reset?!?! so i removed the charge capacitor between GATE and SOURCE, Now the BS170 Switched off straight away, BUT the feedback is back ON TX.

I am thinking that the feedback is being caused by some sort of frequency interaction with the mic preamps and their power supply. Might be related to the TX-POP BS170 that is in the Audio path too...

Basically, the RD16 mods work. BUT when I intorduce any mods to the Mic amp side I start getting feedback. Adjusting RV1 reduced the feedback relative to power. SO I dont thiink I am overdriving the PA. I did try all number of combos of FB resistors and output transformer CAPS, and none made any difference in the feedback issue.
Also of not, is that if i Key CW, not feedback happens. I get full power, 22,20,18,16,14W... So if I can get the FB issue sorted Ill just stick to 20M and below on SSB and use the CW on the upper bands..

So Im thinking of using some inductors(filtering) in series with 5V to the Mic mute, as well as on the D7 pin thats triggering the BS170...

Any other suggestions?

73 Nick.