Hi Ed, I have read the info again and it's a bit confusing. In the -26 variant the IC700 reference is 539-00010-55 and the standard is 539-00010-50. But there were different devices used under the 539-00010-50 number an 'old' one by NDK and a 'new' one made by Rakon. The 'new' one only uses 3 pins and the FM pin is not fitted or needed. So if the 2.5V is varied to pull the resonance and still have full adjustment swing it would not work. The variance is only by fitting another value resistor on the divider, not applying anything from external. As you say it can still swing on the adjustment alone. Sorry for leading you astray. I'll have to stop answering Emails at 2AM and get some sleep instead.
Al --- In [email protected], Ed Yoho <w6yj_ya...@...> wrote: > > niteviser wrote: > > OK Ed, > > > > I have 2 files showing the PCB details with -26 variant info. They > > frequency reference is still kept totally internal. If higher stability or > > external reference is available, the internal is removed and a mini coax > > socket fitted to have a cable connected to have an input on the rear panel. > > I will put the pdf files in the files section. Look for T857 > > 220-01398-02_-04.zip. > > > > Al (niteviser) > > > > Al, > > Thanks for the PDFs. > > Can you tell me where/how the "FM" (tuning voltage) is brought out on > the -26? I looked and both the -02 and -04 variants show the FM pin on > the VCXO tied to 2.5V and AC coupled to REF-MOD. For the life of me, I > cannot find a DC path that would allow for external frequency shifting. > If the -26 still has the resistive divider and nothing else loading the > FM pin, just ignoring the tuning voltage path should work fine (as a -20). > > Other than that, it appears only a few resistor and capacitors are > different from a -25 to comply with frequency mask compliance and these > would need to be changed anyway to make it a -20. > > Ed Yoho > W6YJ >
