thanks for taking the time to go through that!?

gordon

---

From: [email protected] <[email protected]> on behalf of Ashhar Farhan <farhanbox@...>
Sent: Wednesday, November 29, 2017 3:38 AM
To: [email protected]
Subject: Re: [BITX20] Help me understand the USB (upper side band) mod

?

Lets take a concrete example.

An lsb signal generated at 12 mhz carrier, now considee that it is modulated with a 500 hz carrier, it produces a signal at 11,999,500 hz. If the modulating carrier is at 1khz, the signal will shift further down to 11,999,000 hz.

Now, lets mix this with a? 5 mhz oscillator. The lsb signal will be subtracted from the 12 mhz signal. The 11,999,500 - 5,000,000 = 6999,500? mhz. The 1khz signal will be even lower at 11,999,000 - 5,000,000 = 6,999,000. Thus as the modulating tone moves up, the rf moves down, it is still LSB.

Now, consider the local oscillator at 19 mhz. Here, the signal is subtracted from the 12hz signal (the previous example had oscillator subtracted from the 12 mhz if). So, 19,000,000 - 11,999,500 = 7000,500 is the frequency of the signal at 500 hz is 700.5 khz. When the audio shifts to 1000 hz, the IF is at 11,999,000 and the rf is at 19,000,000 - 11,999,000 = 7001,000 hz. That is 7001 khz. Thus, the rf frequency moves up as the audio tone goes up. We are in USB!!

On 29 Nov 2017 1:33 pm, "Dale Brooks KG7SSB" <kg7ssb@...> wrote:

Can someone answer this question for me. The latest sketch 1-27-2 has switching for UPS and LSB by pressing the function button (VFO sel. a/b) if I remember right. How is this accomplished by the Raduino output acting only as a single output VFO? I could see it if it also controlled the BFO frequency but this is not the case for the BITX40.?

Dale

KG7SSB

On Tue, Nov 28, 2017 at 10:00 PM, John Backo via Groups.Io <iam74=rocketmail.com@...o> wrote:

But remember, Clark, that the "carrier" is the BFO frequency. We can
adjust that to be about anything we want within reason.

Changing the center frequency changes the position of the sidebands.
In a SSB rig, we actually change that to get the best response for the sidebands
from the filter. The filter itself doesn't change. How it is constructed will determine
the bandwidth, but not the actual frequencies that go through it. The position of
the BFO does that.

It also means that if a given filter allows the USB through, shifting the BFO will
allow the LSB through. BUT the position of the frequencies will be reversed
(inverted). So the LSB will come out "upside down". But that doesn't matter as
the transmitted frequency is determined by the mixer, not the BFO. And
the other receiver's mixer determines what is extracted -- it can extract that
"inverted" signal and set it "right side up" in its own crystal filter. So the
other side hears a regular audio signal.

That also means that any carrier that gets out of the mixer can go through the
filter if the BFO is positioned right. Ordinarily in SSB, any suppressed carrier
that gets out of the mixer is cut off by the filter. The sides of the filter are
designed to do this -- but one could, if one wanted, unbalance the mixer,
center the BFO on the mixer signal, and get a form of CW through the filter.
The result is indistinguishable from a true A1 CW signal.

So it's all about the BFO and the shape of the filter...

john
AD5YE

Hi
the problem is solved in an brutal amateur way : the solution with a resistor did`n work so I connected A2 dirctly to +5V. Now the ability of calibrating the offset is lost but that?s a thing I can live with, it?s better than buying somthing new.
I think the start of the problem was the other selfmade 6W- rig on my table : I tested both on a dummyload for outputpower separatly, all the cables of the BITX in originaly length wound to a smal ring, probably a fine coil with high induction ! I forgot all about the physics I once learned !
Thank?s for your help anyway, hope to meet you on the band one day

73 Gert DG3OQ

Can someone answer this question for me. The latest sketch 1-27-2 has switching for UPS and LSB by pressing the function button (VFO sel. a/b) if I remember right. How is this accomplished by the Raduino output acting only as a single output VFO? I could see it if it also controlled the BFO frequency but this is not the case for the BITX40.?

Dale

KG7SSB

On Tue, Nov 28, 2017 at 10:00 PM, John Backo via Groups.Io <iam74=rocketmail.com@groups.io> wrote:

But remember, Clark, that the "carrier" is the BFO frequency. We can
adjust that to be about anything we want within reason.

Changing the center frequency changes the position of the sidebands.
In a SSB rig, we actually change that to get the best response for the sidebands
from the filter. The filter itself doesn't change. How it is constructed will determine
the bandwidth, but not the actual frequencies that go through it. The position of
the BFO does that.

It also means that if a given filter allows the USB through, shifting the BFO will
allow the LSB through. BUT the position of the frequencies will be reversed
(inverted). So the LSB will come out "upside down". But that doesn't matter as
the transmitted frequency is determined by the mixer, not the BFO. And
the other receiver's mixer determines what is extracted -- it can extract that
"inverted" signal and set it "right side up" in its own crystal filter. So the
other side hears a regular audio signal.

That also means that any carrier that gets out of the mixer can go through the
filter if the BFO is positioned right. Ordinarily in SSB, any suppressed carrier
that gets out of the mixer is cut off by the filter. The sides of the filter are
designed to do this -- but one could, if one wanted, unbalance the mixer,
center the BFO on the mixer signal, and get a form of CW through the filter.
The result is indistinguishable from a true A1 CW signal.

So it's all about the BFO and the shape of the filter...

john
AD5YE

But remember, Clark, that the "carrier" is the BFO frequency. We can
adjust that to be about anything we want within reason.

Changing the center frequency changes the position of the sidebands.
In a SSB rig, we actually change that to get the best response for the sidebands
from the filter. The filter itself doesn't change. How it is constructed will determine
the bandwidth, but not the actual frequencies that go through it. The position of
the BFO does that.

It also means that if a given filter allows the USB through, shifting the BFO will
allow the LSB through. BUT the position of the frequencies will be reversed
(inverted). So the LSB will come out "upside down". But that doesn't matter as
the transmitted frequency is determined by the mixer, not the BFO. And
the other receiver's mixer determines what is extracted -- it can extract that
"inverted" signal and set it "right side up" in its own crystal filter. So the
other side hears a regular audio signal.

That also means that any carrier that gets out of the mixer can go through the
filter if the BFO is positioned right. Ordinarily in SSB, any suppressed carrier
that gets out of the mixer is cut off by the filter. The sides of the filter are
designed to do this -- but one could, if one wanted, unbalance the mixer,
center the BFO on the mixer signal, and get a form of CW through the filter.
The result is indistinguishable from a true A1 CW signal.

So it's all about the BFO and the shape of the filter...

john
AD5YE