[TenTec] 509 IF Filter Replacement

[DSJKALLEN@aol.com]

Some of you may know Ten-Tec has no spares for the 2.4kHz 4-pole IF filter in
the 509.  When one fails (either due to out-of-spec passband ripple, increased
insertion loss, etc.), they replace it with the 8-pole 2.4kHz filter used in
the new Omnis.  According to Garland Jenkins at Ten-Tec, this is their only
option as repair or production of the 4-pole units is not cost effective.

The only problem is the new 8-pole filter is quite a bit longer and wider than
the original 4-pole.  Therefore, the filter doesn't fit well onto the SSB
generator board, requiring the filter's input/output to be hard-wired to the
land side of the board.  Because of this, the filter's ultimate rejection
(speced at greater than 80 dB) is not seen as installed in the 509.  But, Ten-
Tec's solution is still an improvement as the original 4-pole filter's
ultimate is typically only 45 to 50 dB.

Another option is to use the KVG XF-9B filter.  It's much smaller in size and
has an excellent shape factor, over 100 dB of ultimate, and only about 1 dB
greater insertion loss compared to the original 4-pole.  This filter can
easily be installed on an aluminum or copper stock riser  plate -- 1/4" to
1/2" above the SSB generator board -- using a center vertical shield
separating the input and output ports.  The plate is mounted via a short
threaded stud, 4-40 screws and lockwashers thru the board to the large ground
on the PC ground land of the SSB generator board.  The plate and its center
shield, the common ground point to the land, and the resultant vy short
connecting leads to the input and output of the board maintain the integrity
of the filters specs.  The overall footprint of this option is actually
smaller than the original 4-pole.  The only caveat is changing the Zin and
Zout terminations to 500 ohms and 37pf as required by the KVG filter.  When
done correctly, the filter and its mounting configuation looks like a factory
stock installation.

I hope this info helps anyone who may have a problem with the 509 stock
filter.

73,
Don Allen W9CW
Urbana, IL

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