Congratulations to you and your daughter getting your tickets. I wish her luck on the general class exam. I would build the bitx stock and run it for a few weeks, then upgrade to one of Allard's sketches and do the hardware mods. I am using my bitx for the same purpose as you, ft8 and phone. I find the dual VFO option very useful to switch between these modes. The modifications associated with Allard's sketches are not hard to do. I think I am at 1.21. It is a fine ft8 radio. I have it tuned for lower output, with no additional heat sink, and drive a small amplifier. I have made contacts with a couple watts. At the present, I have worked all 50 states digital and would guess 30+ countries mostly Europe and the South Pacific due to the antenna favoring those directions.?

Here is a link to my build. I have included the duinovox for ft8 as part of the build.??/g/BITX20/topic/new_bitx40_build/5769825?p=Created,,,20,1,0,0&jump=1

If you facebook, the group "QRP Bitx40v3? 40 m radio kit" by Ryan W7RLF is a good one to join.

Good Luck, and have fun with new radio build.?

Somebody already has. Michael (WA6ISP) did it, I think. There's another one out there somewhere too. I'm sure Michael will chime in shortly.

Vince.

--
Michigan VHF Corp.

HI Allard and all on the group

I do not know about aruino programming,
my query is simple, maybe the answer is difficult.
It is possible to modify the raduino sketch, to use a
rotary encoder instead of the potentiometer?

Thanks in advance.

Carlos
CX8ABF.



-----Mensaje original-----
From: Allard PE1NWL


73 Allard PE1NWL

There is an excellent posting by Jerry Gaffke, KE7ER, that explains it all:

/g/BITX20/message/24724

73 Allard PE1NWL

Apologies...
I oversimplified and therefore stated wrong.


I should have written...?

''That we can pass the carrier and a small portion of each sideband by changing the frequency of the signal that we feed into the filter.''

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The crystal filter is just a gateway it doesn't carevwhat type of rf gets through...? We're simply choosing which half of an am signal to pass...? By moving the signal up or down the spectrum by changing the signal frequency. We can theoretically pass the carrier and a small portion of both sidebands by selecting the proper frequency on the dial

Yeah you could try an external pull up resistor of 10-47K.
Perhaps the internal pull up resistor is faulty.

73 Allard PE1NWL

Gordon, thanks for that explanation. Although I understand sidebands in general, I now better understand how the crystal filter works! 73!

--
Ryan Flowers - W7RLF

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Hmmm....? some confusion here.? ?

If double sideband looks like

..;;\\? //;;..

then upper sideband looks like

//;;..? no matter whetehr it is made by a bitx, an iCOM or a Heahtkit......

In all cases, the lowest audio frequencies go with the lowest RF freequencies for Upper side band

In the bitx the BFO is above the crystal filter in frequency, so the filter passes the lower sideband;? ?subtracting it from a 19 MHz VFO inverts the spectrum and converts it back to upper sideband.? ?Two subtractions make an addition, so to speak.? ?

I had to walk through it with a couple of audio frequencies to convince myself.

And....from practical experiments, upper sideband coming out of my bitx is perfectly decoded by a 45 year old heathkit (in USB mode); and?

lower sideband coming out of my bitx is also perfectly decoded by my 45 year old heathkit (in LSB mode)?

Perhaps, I'll have to check that.

However, both my test sketch and the B40 sketch are using the same hardware and setting or attempting to set the same 5Mhz frequency on the AD9850.?

With that set of data and circumstances, it would seem to point to something in the B40 sketch that is overwriting or somehow messing with the output frequency on the AD9850. I'm unfamiliar with the AD9850 and the?AD9850SPI library. I'll have to do some deeper investigation.

Thanks,
-Rob (N4MN)??

Richie, ok so I guess the passband crystal filter is symmetric in which case it doesn't care.

Gordon, so if the receiver is decoding in USB and receives a USB signal like "..::?" (as would come from the bitx) where the lower frequency audio in the vocal range ends up on the higher end of the signal, wouldn't this lead to some strange sounding audio?

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?typo:? meanto to say,

""the filter can't tell and doesn't care whether the spectrum going through it is upper or lower sideband"

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?the filter can tell and doesn't care whether the spectrum going through it is upper or lower sideband.....

What makes it upper or lower sideband is the relative relationships between the radio frequencies that resulted from low- or high-frequency audio waveforms.

In upper sideband, the higher audio frequencies cause higher RF frequencies.

In lower sideband, the reverse occurs.

The Receiver must provide the carrier back on the proper SIDE of the received spectrum in order to mix (demodoulae) to a recognizable voice signal.

Gordon

Hey David,

I figured this out last year when I could never resolve SSB in any superhet that I built. I got a copy of EMRFD and it all came together. Here is my attempt at explaining it. First, the crystal filter should have a pass band that’s only wide enough for one sideband (about 3,000 hertz). The BFO frequency positions you on the side band you want to hear. To be in the middle of the pass band, the two BFO frequencies must be 1,500 + - from the center of the filter, which is 3,000 from each other. I hope that helps.

Hi Allard
at A2 I measure 2V and can not find any short to ground.
Next thing I will try to wire a resitor from A2 to +5V and see what happens - comming back.
Thanks
Gert

So, as I understand it, a SSB signal is where half of an AM signal and the carrier are suppressed. For illustrative purposes, I'll draw a full AM signal like ..::||::.., where || is the carrier and the dots are the upper and lower parts of the signal envelope.?

Ok, so a normal LSB signal should look like "..:: " and USB should look like " ::..".

The USB mod for the Raduino appears to simply change the output frequency be 1500 hz lower. So really, we're transmitting a LSB signal at an offset, which means instead of " ::.." we get "..:: " in the air. Wouldn't this cause problems on the receivers end? I'm assuming their RX filtering would be expecting most of the signal near the carrier, not on the other end.?

For a "true" USB mode, would we need a different filter circuit to suppress the lower side band? I'm still pretty new to this and learning more everyday, please spare no detail in any explanation :)

-David

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?Getting it to do upper side band isn't that terribly difficult, a small mod or two in the raduino sketch will do it ---- but it is just as easy to upload one of Allards' sketches and then it handles the calibration much better and everything else.? ?

I am kinda using his 1.24 sketch and happily modifying that for my purposes.? ?

Btw, we are building it inside a Hello Kitty or Frozen lunchbox for her

Yes. She's 9. We just want a pushbutton to switch from LSB to USB and back again.

So, that's what I'd like to figure out how to do. I've got a heatsink for the final and removed C91 and c92