Gareth,
Since you are using DM780, yes you can see the 100 Hz subcarrier. I
usually use the Spectrogram 'scope display and that subcarrier is there
but it is a low amplitude and becomes "lost" in low frequency 'trash'
like any 60 Hz noise in the computer soundcard and the zero frequency spur.
73,
Don W3FPR
On 3/3/2015 2:29 AM, M5KVK - Gareth wrote:
Thanks Don
Since sending that email, I'd come across Wayne's article on the mechanics of
CAL FIL. That opened my eyes to something I'd read, but clearly not absorbed:
i.e. when a modified BFO is saved, the K2 re-calculates the value of VCO needed
to obtain the same AF tone as before. Although the audio moves moves when the
BFO is adjusted, once the BFO is saved, the tone goes back to where it was (or
within 20Hz anyway).
One thing though. Unless it's just my KSB2 filter, you can still see WWV's
100Hz sub-carrier on DM780 when the filter skirts are set as you suggest. It's
very low, but DM780 has a high dynamic range and the carrier is just visible.
Gareth, M5KVK
Sent from my iPad
On 3 Mar 2015, at 02:11, Don Wilhelm <w3...@embarqmail.com> wrote:
Gareth,
That is NOT correct.
You must do things in order and all will work out properly.
First, the 100 Hz WWV subcarrier should be outside the passband of the SSB
filters, so it will have a very low amplitude.
It is better to use the alternating 500 and 600 Hz as well as the 'on the
minute' tone at 1000Hz to determine the correct tuning of WWV. The tone at 2
minutes after the hour is 440Hz.
If your SSB OP1 (or FL1 if no KSB2) filter passbands are not properly aligned,
do an initial alignment of the LSB and USB filters so the filter passband low
frequency slope -5dB point is at 300 Hz (use Spectrogram to observe the
passband position).
Once the SSB FL1 filter is adjusted, then receive WWV and use the Spectrogram
(or other audio spectrum analyzer) to properly tune the WWV transmitted tones.
Once tuned properly, lock the VFO to prevent moving the VFO knob.
With WWV properly tuned, set to CAL FCTR and alternate the internal counter
probe between TP2 and TP1 while adjusting Control Board C22. Since all WWV
transmissions are on '000.000 kHz boundaries, all you need to do is observe the
4 low order digits in the CAL FCTR display and you do not have to do the
subtraction in every case.
Once C22 is properly adjusted, put the counter probe in TP1 and run CAL PLL.
When CAL PLL finishes, then go to CAL FIL.
Even though the FL1 passband has been previously set, you must still change the
BFO settings. Move them up one DAC count and back down to where they were
before.
Then adjust the BFOs for SSB FL2 thru FL4. I set the low frequency slope of
FL2 at 350Hz, FL3 at 400Hz, and FL4 at 500Hz.
Adjust the BFOs for the CW filters (and RTTY filters if you have them enabled)
to properly position the filter passbands. If they were set correctly before,
move them by one DAC step and back again - this is to force the BFO frequencies
to be recorded into EEPROM with the current 4MHz reference frequency.
After those steps, re-check the WWV tuning. It should be correct within 20 Hz.
The BFO DAC steps are approximately 20 Hz wide, so you may see a shift in the
tuning by that amount. If it is greater than 20 Hz, re-do the entire procedure
from the beginning.
I do this procedure more than 3 times a week on K2 repairs, and it always works.
73,
Don W3FPR
On 3/2/2015 11:11 AM, Gareth - M5KVK wrote:
I realise this is close to becoming an obsession, but I really want to
understand what's going on.
Once I'd gone through my modified version of Wayne's process for adjusting
the VCO (i.e. adjusting the VFO to have the WWV 100Hz sub-carrier on
100Hz), I realised that this applied only to LSB FIL1. As soon as I
switched to FIL2, the sub-carrier moved and I needed to use CAL FIL to
adjust it back.
Also, if you want to move the position of the filter in the audio spectrum
(e.g. to change where the skirts are), and thus change the BFO; you need to
run Wayne's process again.
Is that right?
73, Gareth - M5KVK
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