Topics

Turn of BFO mod

Jeff Debes
 

Is there a way/mod to turn off the bfo to listen to AM signals?


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*jeff.debes@...*

Reed N
 


You should be able to listen to AM even with the BFO. However, if you want to get rid of it completely for some reason, you'll need to jumper C211 to C40 to remove the BFO crystal filter stage, then modify the code to get the correct mixing products on the audio side. I don't think I'd recommend this.


Reed

Jeff Debes
 

Thank you Reed , you’re always very helpful!


On May 28, 2020, at 12:14 PM, Reed N <greenkid336600+groupsio@...> wrote:


You should be able to listen to AM even with the BFO. However, if you want to get rid of it completely for some reason, you'll need to jumper C211 to C40 to remove the BFO crystal filter stage, then modify the code to get the correct mixing products on the audio side. I don't think I'd recommend this.


Reed

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jeff.debes@...

Dale Parfitt
 

Hi Reed,

I cannot see how a signal  will be present at the output of the product detector if you remove the BFO signal. Isn’t that equivalent to multiplying by zero (0)? And then any residual that  does remain (extremely low level) would require an envelope detector for AM demod.

 

Dale W4OP

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Jeff Debes
Sent: Thursday, May 28, 2020 1:52 PM
To: BITX20@groups.io
Subject: Re: [BITX20] Turn of BFO mod

 

Thank you Reed , you’re always very helpful!



On May 28, 2020, at 12:14 PM, Reed N <greenkid336600+groupsio@...> wrote:


You should be able to listen to AM even with the BFO. However, if you want to get rid of it completely for some reason, you'll need to jumper C211 to C40 to remove the BFO crystal filter stage, then modify the code to get the correct mixing products on the audio side. I don't think I'd recommend this.


Reed


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jeff.debes@...

Reed N
 

I described how to skip the BFO stage, but didn't put any thought into if it would actually work for AM. It may actually be that the audio mixing stage ended up becoming the BFO, sans filter, or perhaps there would be no output at all, like you speculate.


Reed

Curt
 

Jeff

we get the framework of your question - its in relation to BFO action on 'ancient' typically general conversion receivers, that lacked a proper product detector. 

an AM signal off course is 2X or more wider than SSB, especially if we want more spectrum into our headphones.  the 2nd xtal filter is too narrow for AM signals - for both sidebands to pass through.  but some may have added a product detector after the first 45 MHz xtal filter.  try a search engine to see who has reported results adding an envelope detector -- uBITX envelope detector or AM detection.  BTW, an envelope detector is pretty much a simple diode - but it has to have appropriate gain in front of it (but it might not take much for huge 41m AM signals.  others add a SDR at 45 MHz that would also be a good AM receiver. 

I appreciate your inquisitiveness.  Too easy for us to miss context of your question, not presuming product detector behavior.

73 curt

Evan Hand
 

Maybe a diode detector (like an RF probe) between CW-1 pin 1 and TP 20 might work to receive.  The selectivity is then defined by the 45 MHz roofing filter, which is 15 kHz wide.  You would need to turn off the BFO.  It would require a switching circuit for the diode to be able to back to SSB/CW with the crystal filter.

Just speculation on my part.

73
Evan
AC9TU

Arv Evans
 

Jeff

This is an SSB radio.  It requires the BFO to heterodyne the IF frequency to audio.

It might be possible to convert it to an AM radio by building a non-SSB detector to 
connect ahead of the heterodyne style detector circuit.  Why stop at AM?  Might 
also be interesting to add an FM style IF section and FM detector!

Another possibility is something like the rather old "Q-5'er" which would be an AM 
receiver tuned to the IF frequency and connected ahead of the SSB detector.
This might work, or might be plagued with BFO leak-through, unless the BFO were 
set way off the IF frequency or even turned off for AM mode.

All desires for the SSB transceiver to do something that it was not designed to do 
may be possible, and many on this group have dome some of these mods.  What 
is required to successfully modify the original circuit and original software is a good 
knowledge of how the system actually works, and how to design suitable 
modifications.

Arv
_._


On Thu, May 28, 2020 at 5:28 AM Jeff Debes <jeff.debes@...> wrote:
Is there a way/mod  to turn off the bfo to listen to AM signals?


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*jeff.debes@...*



ajparent1/kb1gmx
 

Jeff,

No, no and no.

Reasons the filter is less than 2.5Khz wide so even with a diode detector it would
sound really muddy.  AM really wants AGC, no got.   FM wants a wider filter as
well though its mostly a 10M thing.

Or you can tune in the AM and zero beat the carrier and listen to AM.
The digital VFO is stable enough to stay within a few HZ for days.

Allison
---------------------------------
No direct email, it goes to bit bucket due address harvesting in groups.IO

Jeff Debes
 

Not  tuning AM
Largely defeats the need /advantage / joy of general a coverage receiver that can’t receive AM.
But I bought the rig for use on the ham bands so I don’t  mind.
Jeff


On May 28, 2020, at 5:25 PM, ajparent1/kb1gmx <kb1gmx@...> wrote:

Jeff,

No, no and no.

Reasons the filter is less than 2.5Khz wide so even with a diode detector it would
sound really muddy.  AM really wants AGC, no got.   FM wants a wider filter as
well though its mostly a 10M thing.

Or you can tune in the AM and zero beat the carrier and listen to AM.
The digital VFO is stable enough to stay within a few HZ for days.

Allison
---------------------------------
No direct email, it goes to bit bucket due address harvesting in groups.IO

--
jeff.debes@...

Reed N
 

There are two things being said, but let me hopefully make the distinction clear.

The stock uBiTX does not have an AM receiving mode, that decodes AM signals "properly", using an amplitude detector.

However, SSB mode can be used to listen to AM signals just fine, since ignoring the existing carrier and half of the bandwidth doesn't prevent the SSB from correctly decoding the half that it does use. I used my local AM 1000kHz station a lot to initially calibrate, and the talk radio is perfectly intelligible.


Reed

Gordon Gibby
 

My car makes a really poor boat, also.    Maybe they should have designed it better?   (grin)
Gordon


On Thu, May 28, 2020 at 8:44 PM Reed N <greenkid336600+groupsio@...> wrote:
There are two things being said, but let me hopefully make the distinction clear.

The stock uBiTX does not have an AM receiving mode, that decodes AM signals "properly", using an amplitude detector.

However, SSB mode can be used to listen to AM signals just fine, since ignoring the existing carrier and half of the bandwidth doesn't prevent the SSB from correctly decoding the half that it does use. I used my local AM 1000kHz station a lot to initially calibrate, and the talk radio is perfectly intelligible.


Reed

Jeff Debes
 

Just saying. 
General coverage of shortwave.
And for Ham band use such as on 75 meters:
It would be nice to have a real AM capability on both receive and transmit.
HF Sigs future project?
Hope so, but maybe it would spoil the brew.
Jeff



On May 28, 2020, at 1:51 PM, Jeff Debes via groups.io <jeff.debes@...> wrote:

Thank you Reed , you’re always very helpful!


On May 28, 2020, at 12:14 PM, Reed N <greenkid336600+groupsio@...> wrote:


You should be able to listen to AM even with the BFO. However, if you want to get rid of it completely for some reason, you'll need to jumper C211 to C40 to remove the BFO crystal filter stage, then modify the code to get the correct mixing products on the audio side. I don't think I'd recommend this.


Reed

--
jeff.debes@...

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jeff.debes@...

Arv Evans
 

Jeff

Probably would spoil the simple elegance of the design.  

A simple receiver for AM from KHz through 30 MHz is 
fairly easy to do but probably not with the uBITX layout.
Think wider, or variable, IF filter bandwidth, and having 
built in noise blanker, AGC/AVC More audio gain, and 
manually adjustable input RF tuning.  Maybe even a 
roofing filter to help shape the IF.  Higher power audio 
output would also be nice.  For higher frequency coverage
a series of down-converters could be added ahead of 
the RF input.  Same thing for VLF and below if the user 
was interested in that.

But that is not what the BITX20 discussion group is for.

There are on-line groups that specialize in this.




Arv
_._


On Fri, May 29, 2020 at 3:26 PM Jeff Debes <jeff.debes@...> wrote:
Just saying. 
General coverage of shortwave.
And for Ham band use such as on 75 meters:
It would be nice to have a real AM capability on both receive and transmit.
HF Sigs future project?
Hope so, but maybe it would spoil the brew.
Jeff



On May 28, 2020, at 1:51 PM, Jeff Debes via groups.io <jeff.debes=gmail.com@groups.io> wrote:

Thank you Reed , you’re always very helpful!


On May 28, 2020, at 12:14 PM, Reed N <greenkid336600+groupsio@...> wrote:


You should be able to listen to AM even with the BFO. However, if you want to get rid of it completely for some reason, you'll need to jumper C211 to C40 to remove the BFO crystal filter stage, then modify the code to get the correct mixing products on the audio side. I don't think I'd recommend this.


Reed

--
jeff.debes@...

--
jeff.debes@...

Jeff Debes
 

Arv, others who kept after me to tune the BFO to the correct passband spot. I did it, It worked!
Thanks for the help and explanations.

Jeff



On May 29, 2020, at 9:27 PM, Arv Evans <arvid.evans@...> wrote:


Jeff

Probably would spoil the simple elegance of the design.  

A simple receiver for AM from KHz through 30 MHz is 
fairly easy to do but probably not with the uBITX layout.
Think wider, or variable, IF filter bandwidth, and having 
built in noise blanker, AGC/AVC More audio gain, and 
manually adjustable input RF tuning.  Maybe even a 
roofing filter to help shape the IF.  Higher power audio 
output would also be nice.  For higher frequency coverage
a series of down-converters could be added ahead of 
the RF input.  Same thing for VLF and below if the user 
was interested in that.

But that is not what the BITX20 discussion group is for.

There are on-line groups that specialize in this.




Arv
_._


On Fri, May 29, 2020 at 3:26 PM Jeff Debes <jeff.debes@...> wrote:
Just saying. 
General coverage of shortwave.
And for Ham band use such as on 75 meters:
It would be nice to have a real AM capability on both receive and transmit.
HF Sigs future project?
Hope so, but maybe it would spoil the brew.
Jeff



On May 28, 2020, at 1:51 PM, Jeff Debes via groups.io <jeff.debes=gmail.com@groups.io> wrote:

Thank you Reed , you’re always very helpful!


On May 28, 2020, at 12:14 PM, Reed N <greenkid336600+groupsio@...> wrote:


You should be able to listen to AM even with the BFO. However, if you want to get rid of it completely for some reason, you'll need to jumper C211 to C40 to remove the BFO crystal filter stage, then modify the code to get the correct mixing products on the audio side. I don't think I'd recommend this.


Reed

--
jeff.debes@...

--
jeff.debes@...


--
jeff.debes@...

Arv Evans
 

Jeff

Thanks for the feedback and update.   Congratulations on getting the BFO tamed.

Arv



On Fri, May 29, 2020, 10:15 PM Jeff Debes <jeff.debes@...> wrote:
Arv, others who kept after me to tune the BFO to the correct passband spot. I did it, It worked!
Thanks for the help and explanations.

Jeff



On May 29, 2020, at 9:27 PM, Arv Evans <arvid.evans@...> wrote:


Jeff

Probably would spoil the simple elegance of the design.  

A simple receiver for AM from KHz through 30 MHz is 
fairly easy to do but probably not with the uBITX layout.
Think wider, or variable, IF filter bandwidth, and having 
built in noise blanker, AGC/AVC More audio gain, and 
manually adjustable input RF tuning.  Maybe even a 
roofing filter to help shape the IF.  Higher power audio 
output would also be nice.  For higher frequency coverage
a series of down-converters could be added ahead of 
the RF input.  Same thing for VLF and below if the user 
was interested in that.

But that is not what the BITX20 discussion group is for.

There are on-line groups that specialize in this.




Arv
_._


On Fri, May 29, 2020 at 3:26 PM Jeff Debes <jeff.debes@...> wrote:
Just saying. 
General coverage of shortwave.
And for Ham band use such as on 75 meters:
It would be nice to have a real AM capability on both receive and transmit.
HF Sigs future project?
Hope so, but maybe it would spoil the brew.
Jeff



On May 28, 2020, at 1:51 PM, Jeff Debes via groups.io <jeff.debes=gmail.com@groups.io> wrote:

Thank you Reed , you’re always very helpful!


On May 28, 2020, at 12:14 PM, Reed N <greenkid336600+groupsio@...> wrote:


You should be able to listen to AM even with the BFO. However, if you want to get rid of it completely for some reason, you'll need to jumper C211 to C40 to remove the BFO crystal filter stage, then modify the code to get the correct mixing products on the audio side. I don't think I'd recommend this.


Reed

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jeff.debes@...

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jeff.debes@...


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jeff.debes@...