SB-620 "Pip" disappears at screen centre

[Stewart D Lyon]

Yes, this is normal. The input impedance of the 3395 filter is very low
at its center frequency and tends to "short out" the signal to the -620
at the center frequency. I have tried a series resistor of 1k or so
between the -620 takeoff and the filter and it did help some but it also
lowers the gain of the IF strip by 6db (about 1 Sunit) so I didn't think
it was worth it.

Too bad the fix of  N7BH's doesn't work on the SB-301 (no transformer).
Does gud on the SB-101 though.

Stu, W6CUX

On Thu, 11 May 2000 09:46:54 -0400 "Mark V. Johnson VE3DJU"
<mjohnson at CA.IBM.COM> writes:
> Hi everyone;
>
> Just got an SB-620 (wired for 3395 IF) and connected it to my
> SB-301. Seems
> to work OK, but when a signal is tuned in, the Pip moves to centre
> and
> disappears. Is this normal operation?? Also, I'm having trouble
> getting a
> nice symmetrical "Pip". Adjusting T2 & T3 as per the manual shrinks
> the
> "Pip" but won't shape it?? Ideas or comments appreciated.. I have
> attached
> a note I found in the archive but wondered if there was anything
> further.
>
> Thanks again Folks!
>
>
> From:         Robert Schlegel <N7BH at AOL.COM>
>  Subject:      SB 620 PIP
>  Content-Type: text/plain; charset="US-ASCII"
>
>  For those who are using the SB620 with an SB100-101-102 and wish to
> see
> the
>  PIP at center frequency try this.  Move the tap point from V!2A,
> pin 6 to
> the
>  unused seconday winding of  T201. The capacitor is eliminated.
> There may
>  still  be a slight reduction in PIP height , but the PIP will
> remain in
> view
>  as you tune across center frequency.
>
>  Bob  N7BH
>
> Mark V. Johnson
>

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