Hi Stefan,
DCF39 is more than 40 dB above the noise, but the problem is that
my FT897 only seems to have 40 dB dynamic range without the AGC. (range between
the receiver noise floor, and max LF output before the signal gets
distorted). With the AGC it is much
more of course, but then I cannot use the LF output to measure the dB’s between
the band noise and DCF39. I will need to calibrate my S-meter sometimes… But
based on what I know about the S-meter, I guestimate that DCF39 is more than 60
dB above the noise floor (but probably not by much).
Wrt to the Speclab settings: I have everything still
on the default settings (just installed it, selected QRSS3 and a suitable
frequency range). But the FFT tab says:
Effect of FFT settings with fs= 11.0250 kHz:
Width of one
FFT-bin: 336.456 mHz
Equiv. noise bandwidth: 504.684 mHz
Max freq range:
0.00000 Hz .. 5.51250 kHz
FFT window time: 2.972 s
Overlap from scroll
interval: 50.0 %
If you have suggestions for improved settings I am very interested.
I definitely need to read up on the math behind the FFT settings (and possibly
RTFM hi)
By the way, the noise (man-made QRM) is now much lower than it was
this afternoon. I saw – but could
not hear - your CQ an hour ago, see
attachment. Using the TS130 so the receiver is still a bit off.
Pity I can’t
TX … L
Regards,
Minto pa3bca
Hello
Minto,
Nice to read about your progress!
Am 07.08.2011 18:06,
schrieb Minto Witteveen:
Hi
Stefan,
I noticed I wrote ALC, but obviously this must be AGC….
I installed Speclab, and did some tests with the 879. With the ACG
off I adjusted the gain just to the threshold of (audible) distortion of the
DCF39 signal (500 Hz filter) and read-out the level in Speclab. Then I
dialed to 137.700 and read out the (average) noise level. This turned out to
be a 40 dB lower, however I could hear NO bandnoise at this setting of the
manual AGC… only the receiver noise.
So DCF-39 would just
be 40 dB above the noise? This is much to low. At least 30 dB would be missed i
estimate.
But what was the FFT setting "width of one FFT bin" in the FFT
register card?
From this I inferred two things:
A.
DCF39 is more than 40 dB above the noise (but how much I cannot measure with
this method)
B. The 879 is a really lousy receiver (But I already knew
that)
But: there is also good news! I did see (but not hear) your CQ
at 17:40 HR CET, see attached screenshot. My first RX on
137!
Congrats to your first LF reception! And it shows me
that my calls are not only for my pleasure :-) So here we may better estimate
how many dBs are missed. Looks like you choosed a relative broad BW for the FFT
settings. 488 (some use 366 mHz) mHz would be a better choice. And i assume you
don't use a noise blanker so far. This will improve thing too!
So
at least the receiver + software works.
In the screenshot you can see your
first CQ recorded with the FT897. At 17:32 I switched to the TS130. At first
glance the signal looks better on the TS130. Also notice that this trace is a
bit off-frequency and drifts visibly. The 130 has an analog VFO, and the
frequency readout is in 100 Hz steps. The drift might also be attributable to
the SA612 mixer I use (now with a 10 MHz xtal)
This proves that at
least QRSS3 QSO’s will be possible, so I have no excuse not finishing my PA
and variometer.
Yes! :-)
How do you go on improving the RX
system? Ah, i have an idea: Display the whole band, as broad as the SSB filter
permits. Use a slow scrolling spectrogram and make your local noise visible.
Normally local QRM sources disappear and appear from time to time. And they
could be band limited.
You should see the band noise ideally and its minimum
just after the local sunrise and a few hours later... If that all is on an equal
level, it must be covered by local noise!
Try to run the PA0RDT on batteries
and your TRX and PC as well (netbook). Do not change the antenna position and
see how and if the noise is changing and so on... :-)
73,
Stefan/DK7FC
