{"id":420,"date":"2025-10-21T00:54:49","date_gmt":"2025-10-21T00:54:49","guid":{"rendered":"https:\/\/lance.conryclan.com\/home\/?p=420"},"modified":"2025-10-21T00:56:58","modified_gmt":"2025-10-21T00:56:58","slug":"exploring-the-ts-520s-frequency-chain","status":"publish","type":"post","link":"https:\/\/lance.conryclan.com\/home\/exploring-the-ts-520s-frequency-chain\/","title":{"rendered":"Exploring the TS-520s’ CW frequency chain."},"content":{"rendered":"\n

There were some peculiarities with my TS-520s CW operation, and not knowing exactly where the issue lay, I have tried to understand the different factors at play. This post will attempt to demystify the CW signal chain’s frequency transformation.<\/p>\n\n\n\n\n\n\n\n

Note that I’ve named the components based on a combination of user\/service manual terms, and the role they perform. As such, the block diagrams later in the discussion are labelled for clarity of understanding, rather than consistency with traditional block diagrams. I’ll kick off the discussion by exploring some of the key components, and then later bring it all together.<\/p>\n\n\n\n

The Local Oscillator<\/strong><\/p>\n\n\n\n

Known my many names, including the Local Oscillator (LO), Carrier Generator, and Beat Frequency Oscillator (BFO), this section generates a frequency used to demodulate the signal during receive, or the carrier wave for transmission.<\/p>\n\n\n\n

In the TS-520s, there are four distinct LO frequencies for use depending on mode.<\/p>\n\n\n\n

MODE<\/strong><\/td>Receive<\/strong><\/td>Transmit<\/strong><\/td><\/tr>
LSB<\/td>3.3935 MHz<\/td>3.3935 MHz<\/td><\/tr>
USB<\/td>3.3965 MHz<\/td>3.3965 MHz<\/td><\/tr>
CW<\/td>3.3943 MHz<\/td>3.3950 MHz<\/td><\/tr><\/tbody><\/table>
TABLE 1, Carrier Frequencies. Source: TS-520s User Manual, p25.<\/figcaption><\/figure>\n\n\n\n

Note that for both LSB and USB, the RX and TX frequencies are the same, whilst CW has a 700 Hz offset between TX and RX. The need for different TX and RX frequencies on CW will be explored in more detail later.<\/p>\n\n\n\n

As can be seen from the carrier circuit below, each mode has its own crystal oscillator, with the CW RX bypassing the inline capacitor (C2), resulting in a lower frequency.<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n

Heterodyne Mixer<\/strong><\/p>\n\n\n\n

The heterodyne mixer converts between the on-air frequency at the antenna, and a heterodyne frequency to generate an intermediate frequency (IF) in the range of 8.295 and 8.895<\/strong> MHz<\/strong>. We’ll call this IF-1<\/strong>. To do this the on-air frequency must be mixed with a different frequency per band, as per the table below. The frequency is determined by the band selection switch.<\/p>\n\n\n\n

Band<\/strong><\/td>Freq.<\/strong><\/td>Band<\/strong><\/td>Freq.<\/strong><\/td><\/tr>
1.8 MHz<\/td>10.695 MHz<\/td>21 MHz<\/td>29.895 MHz<\/td><\/tr>
3.5 MHz<\/td>12.395 MHz<\/td>28 MHz<\/td>36.895 MHz<\/td><\/tr>
7 MHz<\/td>15.895 MHz<\/td>28.5 MHz<\/td>37.395 MHz<\/td><\/tr>
14 MHz<\/td>22.895 MHz<\/td>29.1 MHz<\/td>39.995 MHz<\/td><\/tr><\/tbody><\/table>
Table 2, Heterodyne frequency. Source: TS-520s user manual, p25.<\/figcaption><\/figure>\n\n\n\n

As you can see, mixing any on-air frequency with its band’s heterodyne frequency will put it in the IF range during RX, and vice versa for TX. e.g.<\/p>\n\n\n\n