SB-301/SB-620 connection

[Stu Lyon]

> > > Hello,
{clip}
Does adding the 620 scanalyzer further load
down the IF, and do I have to change the coupling cap to feed both
units simultaneously?  Thanks.
--Ed--

> > From: Stewart D. Lyon [mailto:slyon at pacificnet.net]
> > Sent: Thursday, April 05, 2001 8:39 PM
> > To: Ed Goss
{clip}
> > One problem with the SB-620 / SB-301 combination is "suck-out" of the
> > crystal filter at the center frequency. As you tune toward a signal, its
> > display height decreases to near zero as the signal approaches the
passband
> > of the filter. A way to lessen this effect is to install a transformer
in
> > the plate circuit of the mixer. I used a "T201" transformer from a junk
> > SB-100 with has a low-Z link as a secondary. The co-ax from the SB-620
> > connects directly to this link with no capacitor.

----- Original Message -----
From: "Goss, Ed" <Ed.Goss at jhuapl.edu>
To: "'Stewart D. Lyon'" <slyon at pacificnet.net>
> Hi Stewart,
>      Yes I would like to see your schematic -- whenever you get to it and
> it's convenient
> Ed Goss

Hi Ed,
There are three transformers on a SB-100(1,2) that are suitable -- T1, T103
& T201, all p/n 52-79. Before you remove the transformers, be sure to mark
the terminal numbers.

I mounted the transformer under the SB-301 chassis just in front of the RF
circuit board using 1/2 of a 3M mounting pad. The transformer primary
connects across the plate resistor of the second mixer R23, 2K. Pin 1 goes
to pin 5 of  V3 and pin 4 goes to the junction of R23, R22, R24. Use any
hookup wire. Leave R23 in place -- it broadens the responce of the
transformer. Using RG-174, connect pins 2 & 3 (either polarity) to the spare
RCA connector on the rear panel near the converter socket. You are going to
need a long tuning wand to tune the transformer. I used a antenna bridge as
a noise generator and tuned the transformer for a uniform signal across the
display of the -620.

Actually the idea is not mine. It came from the below posting of N7BH.

++++++++++++++++++++++++++++++++++++++++++++++++
Date:         Mon, 27 Mar 2000 13:03:37 EST
From:         Robert Schlegel <N7BH at AOL.COM>
Subject:      SB 620 PIP
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
++++++++++++++++++++++++++++++++++++++++++

Once you get this all done, I think you will find that the SB-620 is a lot
less useful than the SB-610. I hardly ever turn my -620 on anymore. (!!)

73, Stu W6CUX
Winnetka, CA
slyon at pacificnet.net

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