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

W2CTX
 

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.

rOn




From: Tim Gorman <tgorman2@...>
To: BITX20@groups.io
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
indication.

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
subject.

tim ab0wr


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

> 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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