Home / how to measure your frequency / Checking Frequency Calibration Of Your Transceiver
Checking Frequency Calibration Of
Using WWV and Computer Sound Card
WWV 15 Mhz Antennas
Documented by VK6JI
This document briefly describes a quick and easy method of checking your HF
receiver/transceiver end to end frequency calibration using WWV and your soundcard in
your PC. This process will enable you to determine if the transceiver has a problem or not
and should confirm any suspected error observed by operating the transceiver on air. It is
NOT to perform Laboratory type calibrations.
The carrier of a calibrated frequency reference such as WWV is used by your transceiver in
the CW mode to produce a tone which should correspond in frequency to the CW side tone
set in your transceiver. The tone is then measured by software such as "Spectrum Lab"
using the sound card to determine the transceiver's calibration. In the method described
here, it is assumed that sound card and software are roughly correct. When more accurate
measurements are required, you will need to calibrate "Spectrum Lab" and your sound card
using an external calibrated tone source which is not described here.
This method was shown to me by Andy (VK6OX) when netting my TS2000 onto approx.
Steps To Check Frequency Calibration
Confirm or measure the CW sidetone frequency used in the transceiver.
Determine the approx. freq error of transceiver.
Connect Transceiver To Soundcard.
Tune transceiver to WWV.
Adjust "Spectrum Lab" to enable resolution of audio side tone to within 2Hz.
Confirm measured results are approx. the error you estimated at the start.
Confirm CW Sidetone Frequency
As we are going to place the transceiver in the CW mode and use the CW sidetone offset to
beat with WWV carrier on 15Mhz or 10Mhz and measure the resulting beat frequency, it's
important to know what the CW sidetone is set to. In my case the CW sidetone was set to
800Hz. This is either determined in a menu setting on modern transceivers or fixed in older
transceivers by hardware. To determine the CW sidetone frequency you will need to check
the menu setting or user manual for your transceiver if this is unknown. If your CW sidetone
is continuously variable, you will need to set and measure it, which we will describe later.
Determine The Approx. Freq Error Of Transceiver
It is always good practice to have a rough idea of the current calibration error so you can
validate the results of the measurements you are about to make. Checking the transceiver
against other stations on air should give you a feel for any error. Using the higher bands
normally highlights any error more quickly. In my case I suspected the transceiver was
about 130Hz low in frequency on the 2m band based on the amount of RIT I had to apply
to correct the audio tone when in SSB for most stations. Should the measurements to
follow produce results that indicated results that are widely different to this, it would cause
you to question and check the measurement setup - in short this is a sanity check of your
Connect Transceiver to Soundcard
You now need to connect the audio output of the transceiver to the audio input of the
sound card in your PC or any external sound card such as SignaLink or Rigblaster for
example. This is the same set up you use when working any of the digital modes that use
the PC sound card that provide the required audio coupling and DC isolation to ensure good
audio coupling without introducing any DC loops that could possibly cause hum etc.
Tune Transceiver To WWV
With a suitable antenna connected to the transceiver, tune the transceiver to one of the
WWV time and frequency reference sources such as the WWV signal found on 15.000 Mhz.
It's important that you set your dial on the nominated frequency without any offsets or RIT
activated. With the mode now set to CW, you should now be hearing an audio tone at
approx. the frequency of the transceivers CW sidetone frequency you determined earlier.
Adjust "Spectrum Lab" Resolution To Measure Tone
Before you can begin to measure the resulting tone from the WWV carrier you first need to
setup Spectrum Lab or the programme of your choice so it's able to resolve the frequency
measurement of the tone to within 1 or 2 Hz. To achieve this you will need to adjust things
Centre Frequency of display
Frequency spread of the display
Sampling Rate of the sound card
Level Input to sound card
Before we show you some examples of these settings it's important that you understand the
main aim in making these adjustments is to setup Spectrum Lab to focus on the tone in such
a manner to allow you to resolve its frequency in your environment. To this end you may
find you need set these differently in your environment to achieve this goal.
Spectrum Lab Components window
which is good for showing all active
components currently being used.
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