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  1. Yaesu-FT-980
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Frequency Error

 

I am curious if there is an adjustment to correct the issue described below.

In CW or AM, according to my frequency counter, my carrier is the same frequency as the frequency display. However, in USB and LSB I must tune my FT-980 to 80 cycles higher than the frequency of a station I am talking to in order for said station to sound right and in order for me to sound right to someone who knows my voice. This is on any amateur band.

Thanks in advance for any advice you can render.

WA5UEK
 

The FT-980 clock structure is very elegant (w/ error canceling technique
s and such not) ... but also complicated. Fortunately you've identified some clues:

1. Happens in SSB (USB & LSB) but not CW/AM/FM. May or may not happen in FSK. Frequency is lower in both USB & LSB.
2. Happens in transmit & receive, but in the same direction
3. Offset is about 80Hz (between 2^6 and 2^7 in binary) Hz

Nothing jumps out right away based on the above clues:
a. The 30MHz ref oscillator would affect both receive & transmit ... but it affects all modes (not just SSB).
b. The BFO oscillator would affect would affect CW as well as SSB (and also FSK)
c. The width oscillator self-cancels error theoretically
d. The CW sidetone oscillator is only used in receive (not transmit) .. and AFSK
e. The FM modulator osciillator is only used in FM transmit
f. X4001 is used separately in rec and xmit, but error is supposed to cancel as it is fed also in the VCO chain.

I'm wondering if it isn't a xtal or oscillator, and is instead a digital FLL in the VCO. If you are losing one of the digital lines from the uC to Q4014 (DET/DIV), maybe this would account for the shift. But why just SSB? This theory is still not a clear match to the clues I'm afraid.


--
-Mat Breton, N8TW
 

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Thank you. I guess I’ll have to put on my engineering hat and dig deeper.?


On Aug 3, 2022, at 6:52 PM, Mat Breton N8TW <i.m.n8tw@...> wrote:

?The FT-980 clock structure is very elegant (w/ error canceling technique
s and such not) ... but also complicated. Fortunately you've identified some clues:

1. Happens in SSB (USB & LSB) but not CW/AM/FM. May or may not happen in FSK. Frequency is lower in both USB & LSB.
2. Happens in transmit & receive, but in the same direction
3. Offset is about 80Hz (between 2^6 and 2^7 in binary) Hz

Nothing jumps out right away based on the above clues:
a. The 30MHz ref oscillator would affect both receive & transmit ... but it affects all modes (not just SSB).
b. The BFO oscillator would affect would affect CW as well as SSB (and also FSK)
c. The width oscillator self-cancels error theoretically
d. The CW sidetone oscillator is only used in receive (not transmit) .. and AFSK
e. The FM modulator osciillator is only used in FM transmit
f. X4001 is used separately in rec and xmit, but error is supposed to cancel as it is fed also in the VCO chain.

I'm wondering if it isn't a xtal or oscillator, and is instead a digital FLL in the VCO. If you are losing one of the digital lines from the uC to Q4014 (DET/DIV), maybe this would account for the shift. But why just SSB? This theory is still not a clear match to the clues I'm afraid.


--
-Mat Breton, N8TW

 

I forgot: the base for the FLLs in the FT-980 is actually 10Hz, not 1Hz. So ... and 80Hz error would be 2^3 (= 8) * 10Hz. Could be a coincidence ... but maybe check out the drive and diode on the 3rd bit of PD2 (the VCO FLL setting)?

Just a thought ...


--
-Mat Breton, N8TW

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