[Yaesu] Re: FT-1000D 4th IF / Notch and Prod Det - Frequencies? Function?

[Chris Codella, W2PA]

Ok, Jeff, I've stared at the schematics some more (and gone hopelessly 
cross eyed), so here are some additional observations:

The 4th mixer, Q2019, is driven by a buffer stage, Q2028, which gets its 
455 kHz signal from the output of the selectable filters.

Q2019 also gets a 4th LO (12.635 MHz) signal from Q2050,51&53.  Huh?!  
What's going on?  12.635 - 0.455 = 12.18 MHz... is that the 4th IF?  
Something doesn't make sense.

But wait - there's more!
Q2051 didn't simply pass that 12.635 MHz signal on to Q2053 (and then 
4th mixer Q2019) unaltered.  It first mixed the signal with a signal 
coming from Q2056 and Q2055, which are supplying 12.280 or 12.283 MHz, 
depending on whether USB or LSB is selected, respectively.  Notice that 
12.635 - 12.280 = 355 kHz (in the case where USB is selected).  This 
looking better and better.

So, the 355 kHz signal coming from Q2051 is mixed with the 455 kHz 
signal in Q2019 to produce (wait for it...) 100 kHz, the fourth IF 
frequency, where the notch is applied.

The signal is then amplified by Q2023 and Q2024 and sent on to various 
places for detection.

I'll take a look next at the product detector.

73,
Chris, W2PA

KA9S - Jeff wrote:

>I would like to understand the frequency scheme of the 4th mixer, 4th 
>IF / notch filter, and product detector of my FT-1000D. 
>  
>