Yes, there is a very strict rule for this, and it all comes down to how the RF Gain control physically interacts with the S-meter bridge circuit.
Here is the golden rule of thumb for the SX-28: **If you want the S-meter to tell you the truth, the RF Gain must be set to absolute maximum (fully clockwise).**
Here is exactly why that is, and how you should balance it for actual listening versus measuring.
## Why the RF Gain "Fakes" the S-Meter
On the SX-28, the RF Gain control is a variable resistor that changes the cathode bias on the RF and IF amplifier tubes.
* When you turn the RF Gain *down*, you are increasing the negative bias on those tubes, which throttles back their gain. * As their gain drops, their plate current drops. * Because the S-meter is nothing more than a bridge measuring that exact plate current, turning down the RF Gain manually swings the needle *upward*.
If you have the RF Gain backed off to 50%, the S-meter might read an "S9" even with no antenna connected. You are no longer reading the strength of the incoming radio wave; you are just reading the position of your own RF Gain knob.
## The Rules of Thumb for Operation
Because of this quirk, vintage radio operators generally follow two distinct modes of operation depending on what they are trying to achieve:
### 1. "Logging Mode" (Measuring Signal Strength)
If you are trying to accurately log a station's strength, test an antenna, or align the receiver:
* **RF Gain:** 100% Maximum (fully clockwise). * **AVC:** ON. * **Audio Gain:** Adjusted to a comfortable listening level. * *Result:* The S-meter is accurately calibrated. A massive local station will read S9+40, and a faint whisper will barely move the needle off zero.
### 2. "Listening Mode" (Chasing Weak Signals in Noise)
When you are actually trying to listen to a difficult signal in the presence of heavy atmospheric noise or a strong adjacent station, leaving the RF Gain at maximum often results in an exhausting, fatiguing roar in the speaker. The AVC tries to amplify the noise floor between words.
**Audio Gain:** Turn it up much higher than normal (e.g., 70% to 80%). **AVC:** OFF (often preferred by DXers to stop the noise floor from pumping up and down). **RF Gain:** Manually turn the RF Gain *down* until the background noise just drops away, leaving the target signal standing out cleanly above the hash. *Result:* You significantly improve the Signal-to-Noise Ratio (SNR) and make listening much more pleasant. However, your S-meter is now completely inaccurate and will be pinned high.
Page: /Alignment/Mix/Adjust/Gemini_1103.shtml
Last modified: Thursday, 23 Jul 2026