Re: True Received Frequency


Bill Garwood
 

I believe most of the popular sound card software programs have a built in procedure for sound card frequency calibration for your radio and computer.  You may want to check this out.


What might be fun sometime is to have 070 Club members meet on say 20 meters at the same time and all dial up 14.070 +1000 and then we all take turns seeing what we are getting from each other on transmit and receive.  Might be something we could get a sticker for.  I've been calibrated by Rolo?


I installed the TCXO in my TS590SG and adjusted it after several hours with WWV on 10 MHz.  I'm fairly confident that my rig is within a couple of Hertz at 10 MHz and on the the other WWV HF frequencies.  What I do not know is if there are errors in the radio on different bands or modes.  Also, there could be some errors added by the sound card in digital modes.


When will the next frequency measurement tests be done?


When you get into precision frequency measurement, you are not using the dial frequency on the typical radio but you can use a reference oscillator, an o'scope and other means to measure the frequency.  (I think there are some big dollar receivers that can measure frequencies very accurately but they are not available to the public).  When I was working in avionics repair, we originally used a 10 MHz rubidium precision oscillator that was fed all over the shop via a distribution amplifier to various items of test equipment such as comms analyzers and "professional" Hewlett Packard, Rohde and Schwarz, Fluke and similar signal generators.  This test equipment had a 10 MHz input for an external standard frequency.  The rubidium unit required an occasional calibration check and was eventually replaced by a GPS standard that was even more accurate.  It depended on the accuracy of the GPS "atomic clock" signal in the sky.  If there was any problem with the GPS, there would be an alarm.  There was a GPS antenna on top of the building feeding the GPS standard.  For a ham radio frequency measurement contest, you could zero beat the W5CM frequency under test with the output of a precision signal generator that is under tight frequency control and use a scope or monitor to get them synced up exactly.  If your test equipment is all in good alignment and in proper calibration, then the received frequency is the same as what is shown on the precision signal generator readout down to a very small margin of error.  There's some great surplus precision test equipment for sale on line and at hamfests for pennies on the dollar.


Us old-timers will remember the crystal calibrators that you could use on the receiver(s) in your shack to keep your station sort of on frequency.  The better receivers came with them installed.   There were several add on units.  They were good to maybe 2,000 Hz real world accuracy.  If you used one properly, it kept you from operating outside the limits of your band / license parameters.  The analog dials on most equipment were not but so accurate and some of the older transmit VFOs would drift.  Affordable digital frequency counters and better radios put the calibrators on the shelf.  (here's a picture from the internet)


 Happy Radio!


Bill N4GBK #1688






From: 070Club@groups.io <070Club@groups.io> on behalf of Steve R via Groups.Io <oldjavadrinker@...>
Sent: Tuesday, April 10, 2018 2:53:18 AM
To: 070Club@groups.io
Subject: Re: [070Club] True Received Frequency
 
OK guys that helps. I have the TS590SG and I do not have the SO-3 TCXO, which is supposed to be more accurate. I suppose 23 and 57 Hz off is certainly satisfactory, if it were several 100, then I would be concerned. Steve that does answer my question about the USB, thanks. 

I see these guys with results of <.1 hertz, that is some very accurate calibration for sure.

Steve
2301

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