Rig frequency calibration ― 2024年08月31日 10時17分52秒
The first important step when operating in digital modes is to adjust the PC’s time. Since FT8 is a synchronous communication protocol, having the PC’s time set accurately is crucial. Methods for adjusting PC time are covered in various sources, so I will not go into detail here.
The next important step is to adjust the rig’s frequency. If your rig allows setting a reference frequency, the frequency is unlikely to drift. However, rigs with this feature are usually high-end models.
Super Fox (SF) mode has been used in recent DXpeditions. There have been several posts to X and other forums from operators reporting that signals are strong but cannot be decoded properly.
One possible cause is a frequency mismatch in the receiving rig.
In SSB or CW operation, small frequency discrepancies are usually not a concern. However, in FT8 operation, even a slight discrepancy can cause the range displayed in the waterfall to differ from the actual signal range.
Even if the discrepancy is not extreme, some operators may be off by several Hz up to a few hundred Hz.
The reference frequency (DF) for SF mode is 750 Hz. If you receive a station operating in SF mode, and the decoded DF of the other station is different from 750 Hz, this indicates that the other station’s rig frequency differs from yours.
This does not necessarily mean the other station’s rig is perfectly calibrated, but in most cases, rigs off by several hundred Hz are uncommon.
If decoding failures occur, the cause may be a frequency deviation in your own rig.
From my observations:
- On WSJT-X RC5, decoding was successful within +/- 200 Hz.
- On RC6, decoding improved to +/- 100 Hz relative to the 750 Hz reference signal.
This suggests that frequency discrepancy should ideally be kept below 100 Hz.
For example, the ICOM IC-7300 — a very popular rig with over 100,000 units sold worldwide — unfortunately does not have a built-in reference frequency. The instruction manual explains how to adjust it while receiving standard frequencies such as 10 MHz or 20 MHz. However, I would like to show a method to adjust the frequency visually using software, rather than by listening and estimating by ear.
Although I will provide an example for the IC-7300, similar procedures can be applied to other ICOM and YAESU rigs that allow reference frequency adjustments. Please read the instruction manual carefully, and perform these adjustments at your own risk.
The software used is the familiar WSJT-X, and the mode used is **FreqCal**.
It is best to perform this procedure after the rig has warmed up sufficiently — in my case, about two hours after powering on.
Please read **WSJT-X USER GUIDE 13.1** first.
Then, launch WSJT-X and go to **Settings > Frequencies**.
Click **Mode** under Working Frequencies and scroll down to **FreqCal**.
You will see 5 MHz, 10 MHz, 15 MHz, and 20 MHz listed, but you can also add any local AM broadcast frequencies that you are able to receive.
If there is a value in the Frequency Calibration field, set it to 0.
Then click on “Execute frequency calibration cycle” from the menu Tools.
On the main screen, check the “Measure” checkbox in the fourth row under “Monitor”.
Leave it for a few minutes, and WSJT‑X will automatically change the frequency every 30 seconds.
You will see a line at 1500 Hz. However, if the rig’s reference frequency is off, this line will shift progressively with each band change.
In this state, try adjusting the rig’s reference frequency. Set it to a value that minimizes the DF reading at any frequency. This should nearly eliminate the frequency deviation.
On the IC‑7300, go to **FUNCTION** from the **SET** screen, and you will find **REF Adjust** on the last page.
-----------------------------------------------------
From here, we can further refine the settings. Even if your rig does not have a reference frequency adjustment function, you can still achieve accurate calibration by following the steps below.
1. Restart WSJT‑X and go to **Settings > Frequencies**.
2. Click **Mode** under Working Frequencies and scroll down to **FreqCal**.
3. Go to **File** in the menu, select **Open Log Directory**, and delete the file **fmt.all** if it exists.
4. From the **Tools** menu, click **Execute Frequency Calibration Cycle**.
5. On the main screen, check the **Measure** checkbox in the fourth row under **Monitor**.
6. Leave it for a few minutes; WSJT‑X will automatically change the frequency every 30 seconds.
7. After a few minutes, the calibration parameters will be calculated via the **Tools** menu.
If the measurement results are satisfactory, the message “Good Calibration Solution” will appear. Click **Apply**.
Then go to the **Settings** menu, select **Frequencies**, and note the values for **Slope** and **Intercept** in the **Frequency Calibration** section.
If you have strange data, you will get a message like this and the calculation will not work. Please refer to the items explained later.
JTDX users can also set these values from the menu: go to **Frequency**, enter the same values, and you’re done.
This ensures that even if the rig’s frequency is slightly off, the correct DF will be displayed.
If the frequency calibration does not work, open **fmt.all** in the log directory with a text editor.
Delete the lines marked with an asterisk, save the file, and recalculate the parameters.
Also delete any lines with extremely misaligned values.
コメント
トラックバック
このエントリのトラックバックURL: http://jp1lrt.asablo.jp/blog/2024/08/31/9713282/tb
※なお、送られたトラックバックはブログの管理者が確認するまで公開されません。
コメントをどうぞ
※メールアドレスとURLの入力は必須ではありません。 入力されたメールアドレスは記事に反映されず、ブログの管理者のみが参照できます。
※なお、送られたコメントはブログの管理者が確認するまで公開されません。
※投稿には管理者が設定した質問に答える必要があります。