Re: uBitx V3 low power continues

MVS Sarma

as and when time permits  take a photo of the Post PA  LPF sections. you would locate the LPF covering 40m band.
 check the turns of coils L17, L18 and l19.
Cross check with ft37-43 core on site calculator   at kits and parts. you will find that it  might be having additional turns.
   we can remove coils from top itself   no need to pull board out. try to tweak the coils by reducing and measuring, if possible.
 The power on 40m would come up.
 perhaps one could try increasing the  local VFO , intermediate and BFO osc levels. by manipulating the code in si5351 firmware.
 they are set at 2mA by defining 1, 1, 1  for clocks 0, 1 and 2
we can perhaps try with 2, 2, 2 instead.

 notice that on v5 the designer had made it 3, 3, 3

 we can always restore them to old levels by a click of button on arduino ide.

all the best for a speedy recovery from spinal issues.

 sarma vu3zmv

On Thu, Oct 31, 2019 at 12:13 AM Ted via Groups.Io <> wrote:
This is a follow-up to another thread that is months old. I'm now recovering from cervical spine surgery & attendant complications of infection, so I've had time to repeat tests though not necessarily any clearer mind. Having only 15-20 degrees of rotation of my neck isn't helping, either, with bench work.

To review: a perfectly-functioning radio with typical RF out levels (12w out in 80, 10w in 40, 8w on 20, etc) has devolved to less than a watt on CW on all bands and even less on SSB. The exception is 20 meters, where a couple of watts in CW show up.

Let us assume the finals are fine and that all drivers and pre-drivers are OK. They all get warm, in fact. Suggestions were made to trace the RF thru the LPF array to ensure power wasn't being eaten by a stuck relay or bad filter. I think that this possibility has been eliminated, though I can't explain why the finals get warm and yet the output generally stinks AND worse on one mode than on another.

Again, the SSB signal is far below the CW/dead carrier level, perhaps it is 25-30% of carrier level (according to my oscillscope).  Output at the antenna connection shows approximately the same level as measured at the final transistors.

What dies, prior to Q90, that kills SSB and CW as described?   My sledge hammer works just fine and requires little skill to operate - and at this point makes a better communication tool than my uBitx. I'm not allowed to pick up 15 lbs, though, so that option is on standby. I just don't get it. 


Ted   K3RTA

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