Re: #uBITX Firmware KD8CEC - IF-Shift etc. #ubitx

Tim Gorman


If you are listening to a CW signal then moving the IF Shift doesn't
change the tone of the CW signal at all. You are just moving the
passband. That can change the sound of a SSB signal because you are
removing some of the received audio along with the interfering signal.
Just like cutting the highs or lows with a treble/bass tone control.

tim ab0wr

On Sat, 10 Mar 2018 21:07:17 -0500
"Vince Vielhaber" <vev@...> wrote:

IF Shift is supposed to shift the signal thru the passband without
changing the frequency. So if you're listening to 3930 and there are
signals on 3928 (it happens daily) at the same time, you can use the
IF Shift to move the signals on 3928 out of the passband. If affects
the sound of the desired signal like a tone control but that's a side
effect of the action.


On 03/10/2018 09:02 PM, Ronald Pfeiffer via Groups.Io wrote:
Yes I was confused a while back when Ian announced his IF shift.
The code looked just like our RIT. Our RIT displays the freq on
bottom line and the line above displays the plus/minus offset as
you move the encoder.


*From:* Tim Gorman <tgorman2@...>
*Sent:* Saturday, March 10, 2018 8:24 PM
*Subject:* Re: [BITX20] #uBITX Firmware KD8CEC - IF-Shift etc.

I wonder if we need to define some terms here. Passband tuning and
IF Shift typically move the *filter*, not the carrier. The carrier
will remained tuned to the same frequency when adjusting this. For
instance, if you use IF Shift when listening to a CW signal the
tone of the CW signal should not change. You can move the filter
bandwidth up or down to eliminate an interfering carrier that is
close to the desired frequency.

What you are describing is more like an Incremental Tuning, e.g.
RIT or XIT. When you move the BFO you move the carrier frequency,
not the filter bandwidth.

Ideally the BFO would be set to replicate the suppressed carrier
frequency. The filter then determines what is heard.

The ubitx uses a 12Mhz crystal filter. I don't know its bandwidth or
what the actual absolute frequencies are. I haven't had a chance to
run a spectrum analyzer against mine. Let's assume it has a 2400hz
bandwidth and goes from 12,000,300hz to 12,002,700hz.

If you want to listen to a signal at 10Mhz then CLK2 should be
tuned to 55Mhz to generate the 45Mhz signal the first IF needs.

CLK1 should then be set to generate a 12Mhz signal, i.e. 33Mhz. For
an USB signal we should then see frequencies of 12Mhz to 12.003Mhz
(or whatever the transmitted bandwidth is, e.g. 0-3000hz). You will
then see frequencies of 12.0003Mhz to 12.0027Mhz out of the filter.

This is how an ideal receiver would work.

When you are talking about adjusting the BFO I assume you are
talking about adjusting CLK1. If you adjust CLK1 to move the actual
suppressed carrier frequency somewhere else in the filter bandwidth
then your frequency indication is going to be off. What should be a
10Mhz signal is going to look like something else.

This will cause an asymmetric USB and LSB response and frequency

If you want to change the BFO frequency on the fly then it should be
understood as being an incremental tuning so you can remember what
the base frequency should be.

Now each filter is probably going to have a different actual
physical, absolute bandpass. The BFO will have to be adjusted to
allow for this but the frequency indication needs to be adjusted as
well to match. It should be a fixed reference, not a variable one.

Your transmitted frequency has to be offset from the CW-tone if it
is to be zero beat with the received signal. If it isn't then
you'll never be zero beat. I'm assuming that the CWL and CWU
frequencies are indicating a frequency CW-tone away from the actual
transmitting frequency. That may be because your receive BFO
frequency isn't set to indicate actual carrier frequency.

I didn't mean for this to get so complicated but it isn't an easy

tim ab0wr

On Sun, 11 Mar 2018 01:08:55 +0100
"ge_clipboard" <clipboard@... <mailto:clipboard@...>>
Hi All

Many thanks for all the response concerning the BFO adjustement and
about using the IF-shift. I have been playing around with the BFO
setting while monitoring myself on another transceiver but as I’m
not getting there where I really would like to, I returned to the
factory settings. Leastening to the transmitted LSB and USB on
another transceiver was never symetric, maybe the steps to set the
bfo are not fine enough to do this or I am making something wrong.

Yes, the IF-shift is often a very helpfull feature within crowded
bands and as Mike pointed out, it is also nice to be able to adjust
the sound of a ssb signal on receive. So, if this could be
corrected in the software would be very fine.

Another point I’ve noticed today while using CW, dx-cluster and CAT
to jump to a anounced station... When the CWL-, CWU-feature is
enabled, then the frequency is not spot on but offset by the amount
of the CW-Tone.

Nevertheless, this little rig is a joy to play with, especially
with all the added features by Ian‘s software.

Vy 73, Gerald - HB9CEY

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