In the early days of our hobby some form of comparative signal reporting evolved. In those days signal reports were at the top of the list. Consider that the rigs were homebrewed often running 20 watts or less and literally all stations were using wire antennas and no beams.
The RST system became the standard with R being readability and S being signal strength and T for tone. I am not sure how the exact factors were derived but 599 was the best signal you could have. Mind you the Mode was CW for a period of time until phone was invented and then the T was dropped. The T component was there because many stations were using marginal power supplies and the Tone sounded like a Buzz saw.
With phone operation, the RS was modified so that a 5X9 was not the ne plus ultra and a certain signal level (S9) was accurately given a value, and soon very strong signals could be 5X9 + 20 for 20dB over S9, where S9 was a calculated numeric value. I marvel how in contests where a hardly heard signal is given a report 59. We now have S Meters to tell you your Signal Strength sucks!
Fast forward to the SSB era and SDR radios. Now several pieces of critical data. In a well-designed SSB transmitter there is an absence of carrier signal and many of the SDR radios can read signals to 1 Hertz using a GPS disciplined frequency standard.
Having a signal with a carrier it is easy to zero in on the carrier and there you have the exact frequency. In many homebrew type rigs using the Arduino and Si5351 there has to be an initial calibration run made to determine the software correction factor so that the frequency readings are dead nuts on!
A process I use for that calibration is to tune in my homebrew SDR rig to WWV and using the AM mode zero in on the carrier and note the frequency readout. A couple of runs usually lets me adjust the Si5351 correction factor to align the radio to WWV.
Now signal reports are no longer that the audio is of a good quality and you are very strong, but the dreaded off frequency report to values like 49 Hz high. Many hams with more money than brains even add a GPS Disciplined Frequency Standard as "show proof" they are on and you are off by as little as 30 Hz. Using headphones helps.
With SSB the computer between our ears is an excellent to tool to tell if a radio is not on frequency. Most of my rigs with digital LO's enable me to tune within 10 Hz. Most of the time the step tuning rate defaults to 100 Hz.
Tuning by ear lets me toggle between 100 Hz points and just like the eye doctor is A better than B. Using a comparative listening approach typically we can hear a difference with the 100 Hz settings. Now setting the step tuning rate to 10 Hertz puts us closer to a signal selection that sounds the best to us.
Let us back up a moment to the Arduino and S15351. Most of the time for a filter type SSB the combo is producing two outputs: the LO and BFO. There is but one correction factor and that affects both frequencies being generated.
My bent in a filter type rig is that the BFO is the more critical of the two. This is based not on just the frequency display, but the BFO is generating frequencies that impinge on the filter slope and what gets put through the filter pass band.
In a I/Q type SDR then we have no BFO signals and so the correction factor affects the actual operating frequency.
In SolderSmoke Podcast #252 there was a lively discussion about the value of the GPS locked frequency standard, and my two cohorts rejected the GPS disciplined frequency standard as a means of determining 49Hz low because of the absence of no carrier.
I have never fully embraced their view as I just do not know enough about the GPS disciplined frequency standard. The simple explanation of no carrier certainly has gravitas. But imagine someone suggesting you can generate an SSB signal without a BFO signal source. We know that is possible with SDR and therefore that original thought about the absence of a BFO is simply wrong.
In the usual where I don't know let's ask AI, this is what Copilot had to say.
How does a GPS disciplined frequency standard work with an SSB Signal that has no carrier frequency and just a sideband?
A GPS‑locked frequency standard and an SSB signal seem like they shouldn’t have anything to do with each other—one gives you an ultra‑stable reference frequency, and the other deliberately removes the carrier. But they actually fit together beautifully once you look at what each piece is really doing.
🛰️ How a GPS‑Locked Frequency Standard Helps With SSB
A GPS‑disciplined oscillator (GPSDO) does not recover or detect the missing carrier in an SSB signal. Instead, it solves a different problem:
⭐ It ensures that your own radio’s internal oscillators are on the correct frequency.
That’s the key. SSB doesn’t transmit a carrier, so the receiver must recreate the carrier locally. If your receiver’s local oscillator is off by even a few hertz, the recovered audio pitch will be wrong.
A GPSDO fixes that by making sure your radio’s internal reference is extremely accurate—typically within parts per billion.
📡 What Actually Happens in an SSB Receiver
Even though the SSB signal has no carrier, the receiver still needs one. It generates a Beat Frequency Oscillator (BFO) to replace the missing carrier.
Here’s the chain:
The incoming SSB signal contains only one sideband (USB or LSB).
The receiver mixes that sideband with a locally generated BFO.
The BFO must be at the exact suppressed‑carrier frequency.
Any error in the BFO frequency shifts the audio pitch.
🎧 Example
If the BFO is off by 20 Hz, every voice on the band sounds like it’s shifted up or down by 20 Hz.
🛰️ Where the GPSDO Fits In
A GPSDO provides a rock‑solid reference (often 10 MHz). The radio uses that reference to stabilize:
So the GPSDO ensures:
Your BFO is exactly where it should be.
Your LO is exactly where it should be.
Your tuning dial is accurate.
Your frequency doesn’t drift.
But it does not reconstruct the missing carrier from the SSB signal itself.
🔑 The Important Distinction
❌ The GPSDO does not extract a carrier from the SSB signal.
✔️ It ensures your radio generates the correct replacement carrier.
SSB depends entirely on the receiver’s ability to regenerate the suppressed carrier accurately. GPS locking simply makes that regeneration extremely precise.
🧠Why This Matters
Without a GPS‑locked reference:
With a GPSDO:
You stay exactly on frequency.
Your SSB audio sounds natural.
Other stations hear you exactly where you should be.
Digital modes (FT8, JT65, etc.) become far more reliable.
It seems a GPSDO might be a good thing as it approaches the problem from the standpoint of what signal frequency gives the right solution and then compares that to what is being actually being received. It indeed could tell you that you are 49 Hertz high.
Them that know can make things go.
73's
Pete N6QW
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