Tim
I've made this suggestion before on this reflector.
I can suggest a completely independent way of measuring the frequency of a RTTY
signal received by your radio and AFSK system.
You will need "Digipan" PSK software (because the waterfall is calibrated in
fractions of Hz), and a soundcard connected to you radio.
Set the rig to upper SSB, start Digipan as if you were going to operate PSK31.
Let's "measure" the frequency of a RTTY signal...
If you are looking for a station reported on, say, on 3589.100 kHz, set the
radio dial to 3588.100 kHz, (exactly 1 kHz lower).
The 3589.100 kHz MARK frequency should show up at 1000.0 Hz on the Digipan
waterfall if your radio is in calibration.
Click on the actual MARK trace and read the exact frequency in the Rx window
below the waterfall. The SPACE frequency will be
170 Hz lower.
Of course, Digipan will NOT decode RTTY, but you WILL be able to reliably
measure the MARK
frequency (1000.0 Hz), which you would then add to the radio dial frequency
(3588.100 kHz) to get 3589.100 kHz.
Now let's calibrate your radio to WWV...
For completeness, measure the frequency of WWV 5 MHz carrier exactly the same
way. Set the radio dial to
4999.00000 kHz, and observe the WWV carrier which should be exactly 1000.0 Hz on
the waterfall if the radio is exactly
calibrated correctly. 4999.00000 kHz + 1000 Hz = 5.000000 MHz.
If you notice a calibration error, just calculate that error in parts per
milloin, then apply this parts per million correction to the actual
frequency you are measuring.
I use this technique in the Frequency Measuring Tests and get within 1 Hz of the
right answer.
Cheers and 73
Kai, KE4PT
On 2/10/2014 3:56 PM, Shoppa, Tim wrote:
Here's my little Monday morning quarterbacking on Skimmer performance this past
weekend. I was wondering if maybe my VFO or frequency math (when doing AFSK)
was out of whack, because skimmer spots were most often 200-400Hz low. Pretty
soon I got in the habit of just clicking about 300Hz or so above any skimmer
spot and most often found this to handle the skew, but I also began to notice
that not all skimmers were offset by the same amount, sometimes clicking 400Hz
high was a bit better. Manually entered spots, while they had more callsign
busts than the skimmer busts, seemed to have less of a systematic offset in
frequency. So I also thought to myself, how can I check what other guys and the
skimmer thought my frequency was?
I looked at the peak of my most prolific run in the contest, 3589.9/3590.0kc in
the 03:55 to 04:28 timeframe the first night (hint, my station is most
effective on 80M, wow is 80M a joy). Many of these QSO's are already confirmed
in LOTW (hint, RTTY contesting has extremely high confirmation rates in LOTW).
If they are confirmed in LOTW, I can often see the frequency of the other guys
VFO too (not all ADIF's have to contain this frequency but for
computer-connected rigs it will be very common). Here's my QSO's, with my VFO
dial and the other guy's VFO dial where I know it. You can see I slide up about
100Hz in this run to minimize close-in QRM.
N3QE S57UX 2014-02-09 03:55:58 80M RTTY 3.58991 his VFO 3.58982
N3QE W5EW 2014-02-09 03:57:11 80M RTTY 3.58991 his VFO 3.5899
N3QE AB4SF 2014-02-09 03:57:36 80M RTTY 3.58991 his VFO 3.58989
N3QE KS4L 2014-02-09 03:59:37 80M RTTY 3.58991 his VFO 3.5899
N3QE N0EKM 2014-02-09 04:00:14 80M RTTY 3.58991 his VFO 3.5899
N3QE LZ2ZG 2014-02-09 04:01:04 80M RTTY 3.58991 his VFO 3.58983
N3QE VE6SQ 2014-02-09 04:02:48 80M RTTY 3.58991 his VFO 3.58988
N3QE K8MU 2014-02-09 04:03:30 80M RTTY 3.58991 his VFO 3.58988
N3QE AA0AW 2014-02-09 04:04:30 80M RTTY 3.58991 his VFO 3.59105
N3QE KD2A 2014-02-09 04:06:00 80M RTTY 3.58991 his VFO 3.58988
N3QE N3PPH 2014-02-09 04:06:22 80M RTTY 3.58991 his VFO 3.5887
N3QE N2QT 2014-02-09 04:13:29 80M RTTY 3.58991 his VFO 3.58989
N3QE VE3KI 2014-02-09 04:14:07 80M RTTY 3.58991 his VFO 3.58988
N3QE WB2SXY 2014-02-09 04:16:27 80M RTTY 3.58991 his VFO 3.58838
N3QE W4EE 2014-02-09 04:17:10 80M RTTY 3.58991 his VFO 3.58892
N3QE EA2KU 2014-02-09 04:20:20 80M RTTY 3.59000 his VFO 3.590
N3QE KA9MOM 2014-02-09 04:27:21 80M RTTY 3.59000 his VFO 3.58999
N3QE K6UFO 2014-02-09 04:28:35 80M RTTY 3.59000 his VFO 3.590
N3QE KN3A 2014-02-09 04:28:55 80M RTTY 3.59000 his VFO 3.58997
If you look at "my VFO" vs "his VFO" where both are known, maybe my VFO reads
like 30Hz high. There's obviously some with random offsets of up to a kc or more out there.
Now look at the RCKSkimmer spots in this same timeframe (fetched from downloads at
reversebeacon.net<http://reversebeacon.net/>):
20140209.csv:DL9GTB,DL,EU,3589.7,80m,N3QE,K,NA,CQ,17,2014-02-09 03:47:05,45,RTTY
20140209.csv:WZ7I,K,NA,3589.5,80m,N3QE,K,NA,CQ,26,2014-02-09 03:49:05,45,RTTY
20140209.csv:KB9AMG,K,NA,3589.7,80m,N3QE,K,NA,CQ,25,2014-02-09 03:49:53,45,RTTY
20140209.csv:WZ7I,K,NA,3589.6,80m,N3QE,K,NA,CQ,22,2014-02-09 03:54:10,45,RTTY
20140209.csv:WZ7I,K,NA,3589.6,80m,N3QE,K,NA,CQ,22,2014-02-09 03:59:24,45,RTTY
20140209.csv:N2QT,K,NA,3589.8,80m,N3QE,K,NA,CQ,20,2014-02-09 04:03:50,45,RTTY
20140209.csv:WZ7I,K,NA,3589.6,80m,N3QE,K,NA,CQ,25,2014-02-09 04:04:15,45,RTTY
20140209.csv:DL9GTB,DL,EU,3589.8,80m,N3QE,K,NA,CQ,23,2014-02-09 04:10:32,45,RTTY
20140209.csv:KB9AMG,K,NA,3589.8,80m,N3QE,K,NA,CQ,27,2014-02-09 04:12:38,45,RTTY
20140209.csv:KB9AMG,K,NA,3589.9,80m,N3QE,K,NA,CQ,26,2014-02-09 04:19:23,45,RTTY
20140209.csv:N2QT,K,NA,3589.9,80m,N3QE,K,NA,CQ,27,2014-02-09 04:24:05,45,RTTY
20140209.csv:WZ7I,K,NA,3589.7,80m,N3QE,K,NA,CQ,22,2014-02-09 04:25:05,45,RTTY
20140209.csv:KB9AMG,K,NA,3589.9,80m,N3QE,K,NA,CQ,26,2014-02-09 04:26:18,45,RTTY
20140209.csv:HA6M,HA,EU,3593.7,80m,N3QE,K,NA,CQ,12,2014-02-09 04:28:47,45,RTTY
Note that several skimmers are systematically low by 100-200Hz and one by
closer to 300-400Hz. That last one is way out in left field. The systematics
seemed to change from band to band.
None of this means that the skimmers are broken. It just means that we have to
apply a little observation when using them to increase our band awareness.
Tim N3QE
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