Panadapter shift when filter switched in

[Dave Scarfe]

Hi, I have a K3s with a 400hz filter.  I am using an SDRPlay (HDSDR)
connected to the IF out port.  When the 400Hz filter activated using the
xfil button or tuning the DSP), the signal on the panadapter shifts up
approximately 1.5khz.  It seems to happen on all bands/modes.

Any help very much appreciated!

73,
Dave
VE5UO
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[tomb18]

HiMany sdr packages do not present an accurate output based on mode and filters when fed from the if out. Hdsdr is one of them.73 tomva2fsq.com



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-------- Original message --------From: Dave Scarfe <[hidden email]> Date: 2018-08-05  11:15 PM  (GMT-05:00) To: [hidden email] Subject: [Elecraft] Panadapter shift when filter switched in
Hi, I have a K3s with a 400hz filter.  I am using an SDRPlay (HDSDR)
connected to the IF out port.  When the 400Hz filter activated using the
xfil button or tuning the DSP), the signal on the panadapter shifts up
approximately 1.5khz.  It seems to happen on all bands/modes.

Any help very much appreciated!

73,
Dave
VE5UO
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[Richard Ferch-2]

Do you have any 5-pole roofing filters? In particular, is your wide filter
a 5-pole 2.7 kHz filter or an 8-pole 2.8 kHz filter? The 5-pole filters
have an offset, which is written on the filter and which is entered into
the firmware with the CONFIG:FLx FRQ menu entry (or by using the K3
Utility). When a filter with an offset is selected, the IF changes by the
amount of the offset. For example, if you have a filter with an offset of
1.0 kHz, then when that filter is selected, the centre of the IF bandpass
is actually moved by 1 kHz relative to where it is when using a filter with
no offset. If your panadapter takes its input from the IF Out port, input
signals will move when you switch the receiver between filters whose
offsets are different from one another.

There is also a per-mode offset between SSB modes and CW, AM or FM. This is
not actually a change in IF frequency, but rather a change in the way the
radio's dial frequency is related to the receiver's bandpass. In CW, AM and
FM, the receiver's bandpass is centred on the dial frequency. In FSK D or
AFSK A, the receiver's bandpass is centred between the mark and space
tones, i.e. 85 Hz away from the dial frequency. In SSB or DATA A, the
receiver's bandpass is centred above (USB and DATA A) or below (LSB) the
dial frequency by approximately half the audio bandwidth (more accurately,
by the DSP filter Fc setting). If the panadapter uses the dial frequency to
label frequencies in the display, simply changing modes will result in a
shift in the displayed signal relative to the frequency markers.

There are a couple of other things that affect the relationship between the
IF Out signal and the frequency displayed on a panadapter. One is the
filter Shift control (or Hi-Cut and Lo-Cut controls) - when the filter Fc
is moved, so is the IF relative to the signal frequency. Another was
mentioned by Wayne in a recent post on another thread: in CW, with some
combinations of sidetone pitch (low) and DSP filter bandwidth (high), the
firmware moves the IF centre frequency to ensure that the low edge of the
audio bandpass stays away from zero. Both of these effects are usually
quite a bit smaller than the mode-to-mode or crystal filter offset
differences, but they can be seen easily enough when you zoom in the
panadapter display.

There is a radio control command specific to the K3/K3S that software and
the P3 can use in order to adjust the frequency display markings to
compensate for these offsets, but generic software like HDSDR doesn't use
that command.

73,
Rich VE3KI


VE5UO wrote:

Hi, I have a K3s with a 400hz filter.  I am using an SDRPlay (HDSDR)
connected to the IF out port.  When the 400Hz filter activated using the
xfil button or tuning the DSP), the signal on the panadapter shifts up
approximately 1.5khz.  It seems to happen on all bands/modes.
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