Hi Gary and thanks for the quick reply. I guess what I don't
understand is why the FSK tab was deleted from the late model C-line
PTOs like I have.
Oh well, just a thought for another project in the queue of
hundreds! ;-)
73 -- Dino
On 10Dec2009, at 3:59 PM, Garey Barrell wrote:
Hi Dino -
The FSK tab was present in all the 4 Series PTOs, with the
exception of the TR-4CwRIT where that same tab was rewired to serve
as the RIT port.
The early 4 Series PTOs, with the Bipolar oscillator, had a very
simple pair of capacitors that were connected across the oscillator
voltage divider and the Buffer input. An external capacitor of ~
259 pF was connected from the terminal through a diode switch to
ground. When the diode was reverse biased, the PTO was "on
frequency" and when the diode was forward biased the PTO was
shifted ~850 Hz. Less capacity was required for 170 Hz shift when
that was developed.
The later 4 Series PTOs with the FET oscillator, required a second
tap on the PTO linear inductor along with the capacitor across the
Buffer input to effect the shift at the higher impedance of the FET
oscillator. So to answer your question, I suspect it would be
difficult (adding the tap to the coil, linearity effects?,) to
modify the RIT and/or 7 Series PTOs for FSK.
Effective with the TR-4CwRIT, the RTTY shift terminal was re-tasked
to be the RIT terminal, and an internal varactor circuit was added
to give the large shifts required for the RIT function.
According to Bill Frost, there was some concern at the time about
losing the FSK capability, but it was determined that by that time
most everyone was using AFSK and the FSK function was no longer
needed.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Dino Papas wrote:
When I first got my twins in 1979 I wanted to use FSK....the
manual described the FSK tab on the PTO but it appears that in the
very late models towards the end of the run Drake deleted the
tab. Not a big deal I just ran AFSK for many years.
With all the talk about the RIT tab on the TR7 PTOs I wonder if it
would be possible to mod these late PTOs to add the FSK
capability? This isn't a big deal either but I've always wondered
and someday may put together my old RTTY TU and it would be nice
to at least have the capability.
Anyone ever done it???
Dino KL0S
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