Re: #ubitx Power output on 40 / 80 m with high current levels #ubitx

Alex - PA1FOX

Hi Nigel,

Great to hear from you :)


I think I have made a big mistake, or actually two:

The first is that I thought I was using T37-10 for the output transformer but in fact it was an FT37-43. As both are black and equal in size it took some time to find out (only that I had not used any of the newly bought T37-10's since they were all still present in the purchase package.) I did try the T37-10 but it gave no improvement.

The second is that I had not found the correct winding details for the transformer. I was using the trifilair setup which is used all over the rig and what would be indicated by the way the inductors in the schematic are drawn. It was later that I found a message on this board from Ashhar stating the transformer should be 8 windings input and 10 windings output.

I changed this and a whole new situation occurred. After all it is all about impedance matching.
At 80m I now get a whopping 18 watts at 3,75A overall rig current which is still too high for battery powered. At 17m it reduces to 3 watts. On all bands I have a reasonably good efficiency now so I am making progress and getting closer. I need to work out the loss of 8 dB's in gain of the overall TX chain when going from 3.5MHz to 18 MHz. ( 3 versus 18 watts) Thanks to the WA2EBY article I have some ideas. 

Incidentally, it would be nice to see exactly how your particular layout
differs from that of hfsigs. Can you upload a picture or two?
And I presume it is more through-the-hole and not smd parts. No?
It may be that the choice of parts is more critical than first believed.

Well John, I will do so after I get some things sorted out. It's always a problem when you start with a nice idea and layout and after spending hours and hours of testing the end result looks less nice than it was when you started. It is mainly built in SMD style, using a mill to create the PCB lines. This is ideal for experimentation. I think my PCB size is about the same as the commercially sold one, but I use both sides of the PCB:

One side: Mic audio and speaker audio, modulator, crystal filter (with room for extra narrow crystal filter for CW) bitx blocks and all frequency converters, TX chain, LPF's and relays.

Other side: mic preamp, 3 holders for batteries, 4xAAA, 4xAAA, 2xAAA. (total of 10 penlights AAA makes 12 volts). charging circuit for these batteries to charge them from an external 12 volt power supply. (by splitting the battery pack into two parts and charge both parts seperately. I stole the idea from an ICOM CM7 battery pack) Also the speaker is included as well as connections to the arduino and SI5351 Adafruit board. I don't use the Raduino.

All is built in a single Teletron T813 housing. If all is well I will have a self powered uBitx with about the size of the housing of Ashhar's in his first uBitx video but about half the height. Google for the T813 or look here for an idea.
I'll make some photos soon.

Thanks for sharing ideas and experiences, it all helps.

73, Alex

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