I never said anyone proposed it. But I am now saying it has come up several times. After the earliest conversations of operating CW, on this BITX someone had looked it up and provided greater detail on it. And now we know we can't, and why we can't.

Now for a serious request of you Jerry. Between several to many times you have offered your opinion of running the VFO at 19Mhz instead of 5Mhz. But I don't recall you ever detailing how to do it. You know I can follow along and change the code. But what else is involved. Any other specific changes? As much as you seem to think it would solve a lot of problems and make some hacking easier. I would have expected you to have written a paper, or constantly instruct people how to do it, or upload a sketch with it all done for us by now.?

Is this where the VFO get's set at 19Mhz? This is just a cut and paste.

#define INIT_BFO_FREQ (1199800L)

unsigned long baseTune = ?7100000L;

unsigned long bfo_freq = 11998000L;

Finally, I think your ragging on me for being wrong now is because I said the toroid band pass filter put's it on LSB. But it's the crystal filter that does that. Right? I would rather be corrected and learn, than get a blow up about it later. Or continue the same debate without ever making progress. We are licenced communicators. We can do better.

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So the high value resistor will get swamped by that low impedance node when you power up the microphone amp. ?I think.

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When the microphone amp drives the modulator, it sees the two diodes plus R37,R38,R39. ?A very low impedance load.

The transformers are to transform the 50 ohm bidi gain blocks of the uBitx to the 200 ohm impedance of the crystal filter. ?The 2-to-1 winding ratio gives 4-to1 impedance ratio. ?The spare winding is just that, as on the Bitx40 they wind all those transformers trifilar but not all of them make use of the third winding.

Slipping in the uBitx filter might not be trivial. Google "Dishal Crystal Ladder Filters" and read up. ?The Bitx40 does not have 50 ohm bidi gain blocks. ?Likely on the order of 200 ohms around the filter, but note that the Bitx40 gain block's input port impedance depends on output port impedance and vice-versa. ?They are what they are, and it is not obvious exactly what that is. ?

Jerry

I cranked up the Raduino drive level when selecting USB, and that helped. I think I'll pull the un-needed caps, also. The final thing is to tweak the firmware so that the "center" frequency is the same for USB/LSB.

Finally - I have seen some of the ubitx schematics - is there any reason I couldn't build an equivalent filter & drop that into the bitx40? I see that the filter schematic shows transformers on the input/output, with one winding connected to, what? Nothing? Could you just use a 1:4 balun for this application?

Switching between LSB and USB by moving the VFO from 5mhz to 19mhz works, and is the way that Farhan wrote the sketch. ? ?Disadvantages are: ?More trouble with harmonics and mixer products when at 5mhz, such as those SW Broadcaster images and the 7.2mhz birdie. ?Also, drive level out to the final changes some between 5mhz and 19mhz, could be due to how the diode ring and transformer respond, in addition to ?C91,C92.

The other method is to move the BFO by a few khz using the Si5351's CLK0. ? ?Leave the VFO at either 5mhz or 19mhz, your choice. ?(19mhz is preferred to reduce images.) ? ?Disadvantage is that the crystal filter skirt is not as steep on one side as the other, so LSB with a 19mhz VFO and USB with a 5mhz VFO will have less rejection of the residual carrier and opposite sideband. ?A better crystal filter such as on the uBitx would help here. ?

Marc,

If you want to stick with Raduino as a VFO remove C91 and C92. They are not required.

Now for any frequency below 10MHz you should use LSB and your VFO shall generate 2MHz to 8.6 MHz for a coverage between 10MHz to 3.4MHz

At frequencies above 10 MHz you switch to USB by moving the VFO frequency above input frequency,?

That will translate in VFO generating 22MHz to 26.5MHz for input frequencies between 10MHz and 14,5MHz.

BTW if you can cover 160 m band that means your VFO runs at (12MHz - 1.8MHz) = ?10.2MHz, so it goes higher.

For a displayed frequency of 8.5MHz your VFO actually generates 3.5MHz.
--
Ion

VA3NOI

@Tim

You don't need C91 and C92 if you use the Raduino. They are a part of the analog VFO originally designed. As long as you use Raduino you can take them out for good.

The change from USB to LSB can be done by changing the VFO (Raduino) frequency range from (19MHz - 19.3MHz) to (4.7MHz - 5MHz)
--
Ion

VA3NOI

First off, I like that you have a sense of humor. ?I was going to say "Bull ?;-)", but replaced it with "No" at the last minute. ?Figured you'd take it the right way, but that was a bit coarse for the refined tastes prevalent in this forum.

But you are wrong at least as often as you are right, and somebody has to throw something back at you before the entire discussion runs off the rails.

You did say: ?"CW on sideband might be legal somewhere, not in U.S". ?Nothing illegal in the US has been proposed, assuming it was done correctly. ?An audio tone into the microphone input can create legal A1A transmissions, but is difficult to do correctly as Collins Radio found out 60 years ago: ?/g/BITX20/message/22372. ? (The crystal filter must also be perfect, by the way.) ?I much prefer something like what Farhan is doing on the uBitx. ?

> Ruff.?

A bit off topic, but these were our birds: ?? ?And we now have yaks about to calve. ?And I'm several months behind on an engineering project. ?So unfortunately, I haven't gotten back to tinkering with my Bitx40 for over a month now.

Jerry, KE7ER

I only mentioned CW because it is considered a digital mode. And digital was the context.

I wasn't condemning anyone for it. You seem a little barky in the morning Jerry. Ruff.?