From: "'Joe Dzekevich' joedzekevich@charter.net [wsjtgroup]" <wsjtgroup-noreply@yahoogroups.com>
Date: Feb 10, 2018 7:31 AM
Subject: RE: [wsjtgroup] Re: MSK 144 question
To: 'Bob McGraw K4TAX' <RMcGraw@Blomand.net>,wsjtgroup@yahoogroups.com
Cc:
As a follow-up to Bob’s note on freq cal mode.....I have two rigs: a 3 year old TS-590SG and a 13 year old IC-746PRO. I ran the freq cal test on both, and the TS-590SG had warm-up freq drift issues and the IC-746PRO also had the drift issues. So, given that MSK144 needs to have frequency accuracy within 200 Hz, I dropped-in TCXO’s into each rig. A cheap TS-590SG TCXO got me within 4 Hz on WWV 20 MHz and I was able to adjust the IC-746PRO to within 1 Hz on WWV 20 Mhz. Both rigs were also now stable as a rock.
But....that does not mean that when you get up to 6M and 2M that you have the same frequency accuracy tolerance. Using a 200 Mhz counter, I could see that while things on 6M were very good on both rigs, when the IC-746PRO got up to 2M, it was further off frequency than I wanted. It was within the 200 Hz, but barely, meaning that if stations on MSK144 were off in the other direction, I would not decode them. To fix that, in the WSJT-X frequency tables, lower part, you can put-in a frequency offset, plus or minus, in Hz, for each band. For 6M I put-in a very slight offset and on 2M I put-in a slightly larger offset. The goal was to get the rigs within +/- 25 Hz so I could decode other stations should their offset be in the opposite direction as mine and be well within the 200 Hz for deep decoding.
In short – everything was a success. Basically with modes like FT8 you need very accurate time. With the fast modes like MSK144 for meteor scatter, you need very accurate frequency.
Joe, K1YOW
From: wsjtgroup@yahoogroups.com [mailto:wsjtgroup@yahoogroups.com] On Behalf Of Bob McGraw K4TAX RMcGraw@Blomand.net [wsjtgroup]
Sent: Friday, February 09, 2018 8:04 PM
To: wsjtgroup@yahoogroups.com
Subject: [wsjtgroup] Re: MSK 144 question
Joe made reference to the radio master oscillator accuracy which is where the display numbers on the radio originate.
To that end, the latest release of WSJT-X has a nice mode being FreqCal. If you have your radio and computer configured for CAT control, selecting this mode will step the receiver through various frequency standard broadcasts. Or you can manually select the frequencies of your choice.
The software automatically sets the radio via CAT control to the specific frequency, and then inserts a - 1500 Hz offset. The table will show as such as below. The column of values DF is the error in Hz.. From this table I presume my radio to be about -0.2 to -0.5 Hz low looking at the DF column.
UTC Freq Cal Offset Fmeas DF Level S/N
00:42:39 2500 1 1500 1499.797 -0.203 -4.6 47.8
00:42:41 2500 1 1500 1499.700 -0.300 -4.2 45.8
00:42:43 2500 1 1500 1499.644 -0.356 -6.2 47.9
00:42:49 2500 1 1500 1499.747 -0.253 -4.8 50.6
00:42:51 2500 1 1500 1499.661 -0.339 -0.7 45.4
00:42:54 2500 1 1500 1499.685 -0.315 -2.0 46.7
00:42:56 2500 1 1500 1499.745 -0.255 -2.0 47.0
00:42:58 2500 1 1500 1499.775 -0.225 -1.3 46.6
00:43:04 2500 1 1500 1499.497 -0.503 -3.9 49.2
00:43:06 2500 1 1500 1499.506 -0.494 -4.4 49.9
00:43:09 2500 1 1500 1499.551 -0.449 -2.9 48.5
00:43:11 2500 1 1500 1499.618 -0.382 -2.0 47.2
00:43:13 2500 1 1500 1499.655 -0.345 -2.6 47.5
00:43:19 2500 1 1500 1499.744 -0.256 -3.4 48.9
This has proven to be a good check regarding ones radio. I've use a high precision source to verify the results are quite accurate. Again this says to me the digital readout on your radio may or may not be as accurate as you might like to think and believe. In my case I've adjusted the reference oscillator in my radio to produce the least error on all frequencies checked between 2.5 MHz, 5.0 MHz, 10 MHz, 15 MHz and 25 MHz WWV signals.
73
Bob, K4TAX
Re: MSK 144 question
Fri Feb 9, 2018 6:31 am (PST) . Posted by:
"Joe Dzekevich" jdzekevich
Yes, the MSK144 Tx freq is 1500. Now, what you are seeing are folks being
off freq depending on the accuracy of their rig's freq osc. Most folks
running MSK144 meteor scatter are usually within +/- 25 Hz or so. If you
set your freq tol to 200 and deep decode, provided your CPU and memory can
handle that, you should decode folks on 50.260 with the 1500 Hz offset.
Then, add-in other frequencies to your table, like 50.255, 265, whatever.
That way you can do easy QSY's or call CQ on .260 and QSY to 255 or whatever
if crowded.
Basically, if your F Tol is 200, then you will decode stations that are
within 200 Hz of the 1500.
Joe, K1YOW__._,_.___
Posted by: "Joe Dzekevich" <joedzekevich@charter.net>
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