[Heathkit] Heathkit Seneca

[Glen Zook]

CW is fine if you use crystal control.  Using the VFO
the Seneca sounds like a canary!  AM is controlled
carrier which was popular back in the late 1950s and
early 1960s.  It is OK, but you really need to have a
good microphone to get really decent sounding audio. 
This is the same modulation that Heath used in the
DX-35, DX-40, DX-60, MT-1, Johnson in the Challenger,
etc.

Basically controlled carrier modulation is clamp tube
modulation which is a variation on screen modulation. 
But, the resting carrier power (when nothing is being
said into the microphone) is relatively low.  The
power increases greatly with modulation more like SSB.
 In fact, on the lower bands (80 - 10), some users of
controlled carrier rigs used to zero-beat SSB stations
and the SSB stations often didn't know that AM was
actually being used.  Sometimes the SSB station would
make a comment like the carrier wasn't "nulled" as
much as it could be.  They never looked at the
unwanted sideband, for it was there as well.

For CW I use an external VXO which allows a fair
amount of moving around.  This particular homebrew VXO
has 5 crystals in it which move around 30 to 50 KHz at
2 meters.  It is possible to create a dial on a VXO
that is very accurate for frequency excursions.  I
also use the Seneca as an exciter for a varactor
tripler for 432 MHz CW.  Works great.  But, if I try
to use the internal VFO, by the time it gets to 432
MHz the signal chirps so bad that it is well over 1
KHz wide.

Heath did not allow for the use of a plate modulator
on the Seneca like Knight did on the T-150 / T-150A
rig which also used controlled carrier modulation.  It
will be necessary to modify the transmitter slightly
to use an external plate modulator.

Glen, K9STH



--- "James M. Walker" <chejmw@acsu.buffalo.edu> wrote:
AM work ok but cw is the best, might want to consider
a plate modulator if going for the AM mode.

=====
Glen, K9STH

Web sites

http://home.attbi.com/~k9sth
http://home.attbi.com/~zcomco

__________________________________________________
Do you Yahoo!?
Y! Web Hosting - Let the expert host your web site
http://webhosting.yahoo.com/