Re: [Drakelist] C-Line PTO FSK Tab
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 FSKthe 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 ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] C-Line PTO FSK Tab
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 FSKthe 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 ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] C-Line PTO FSK Tab
Hi Garey, Oh well, can't have it all, and I do like the RIT feature too. 73, Don, WB5HAK ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
