Alan Melia wrote:
[snip]
But that is maybe a useful thought , you could set the default dependent
upon the mode setting, as that defines the screen width. A value slightly
less than a screen width would allow accurate 'pasting' of successive
windows. This would be useful as it is not all that obvious, when you begin
a slow scan, how much time it will take to fill a screen width. Anyone
wanting odd periods between saves to align with transmissions like Jacks
could over type it.
Hi Alan,
suggestion accepted, I will add an 'Auto' choice for the capture interval,
that will change accordingly with the mode setting.
I am interested to see it suggested that the '2 Hz LF' is a common error on
all the cards. Maybe this is a divide error like Bill had to deal with on
Africa.
I think it is higly dependent on the brand, the model and the batch of the
sound card.
I use an old ISA AWE32 SB card, and, as far as I can tell, this error is not
present.
I haven't checked on my laptop, a Thinkpad with a Crystal Sound chip, yet.
While we are at this, I take this opportunity to answer to a private message of
David, G0MRF, who signalled me a frequency error on the 3 and 10 sec/dot modes,
but not on the full band view mode. I think that the problem is that the 5512
S/s sampling
rate is not a standard one, and is implemented differently by the various
manufacturers.
In Argo all modes, except the full band view, use this sampling rate. On my
sound card,
I see no frequency errors when using this sampling rate, but maybe this is not
true for
every card model. It would be useful to have reports on tests done on many
sound cards.
I used the Magnitude Squared estimator and left the AGC on. Calibration by a
sig-gen coupling into the aerial and being measured to 0.1Hz resolution on a
counter referenced to Droitwich. The interesting thing is that there is
little sign of drift over two nights. The RX has a TCXO and has been ON
continuously for four months, but the soundcard seems to perform adequately
considering that the usual 'computer grade' crystals are not usually very
good quality..... and the computer does get switched on an off.
Assuming an overly optimistic stability of 10 ppm over the whole temperature
excursion range
for that crystal, this means a deviation of 0.01 Hertz for an audio signal of
1 kHz.
At this frequencies, even cheap crystals can prove adequate.
Thanks for your tests Alan,
73 Alberto I2PHD
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