Valid point about the frequency change with increased inductance. I just happened to look at the Hartley and used that as an example but it certainly applies to LC circuits in general.
Thanks, Barry - N4BUQ > Hi > > *Any* L/C oscillator (VFO or whatever) goes down in frequency as you add > inductance to the tank. Indeed crystal oscillators work the same way. (add > series inductance and the frequency goes down). > > First step on linearity is to get the end point span so it’s near right. That > may > well involve a bit of electrical fiddling ahead of the mechanical stuff. Most > of > these PTO coils have shrunk a bit over the decades ... > > Bob > >> On Sep 16, 2024, at 9:45 AM, Barry Scott <[email protected]> wrote: >> >> Hi Larry, >> >> I remember seeing a lot of documentation for the repair and "linearization" >> of the R-390A PTOs from years ago. It's a good idea to go back and review >> those. The R-390's PTO has slight differences but I think the mechanical >> aspects are probably very similar to the R-390A's PTO. >> >> Other than a cursory test, I haven't done much to check the linearity but >> will probably get into that once I get the radio fully back together (which >> shouldn't be long now). >> >> Thanks again, >> Barry - N4BUQ >> >> >> On Mon, Sep 16, 2024 at 8:37 AM Larry Haney <[email protected]> wrote: >> >>> Hi Barry, I thought what you wrote makes sense and is correct. It's good >>> that you are understanding how it all works. It makes diagnosys so much >>> easier. Good going. >>> >>> If you're interested in more reading on the 390A PTO's, there are 3 docs >>> on our website in the repair tutorials section by Tom Marcotte, Jim >>> Miller and myself. >>> >>> Regards, Larry >>> >>> On Mon, Sep 16, 2024 at 5:51 AM Barry Scott <[email protected]> >>> wrote: >>> >>>> Okay, Larry. Thanks for the reply. >>>> >>>> On further reading, the VFO is a Hartley design and, given that the >>>> frequency formula for a Hartley is an inverse function of the LC values, >>>> presuming that at xx 000, the iron core is "out" of the coil and a >>>> clockwise turn of the KC knob causes the core to be pushed further inside >>>> the coil increasing the L, then the frequency would indeed drop with CW >>>> motion of the knob. Sorry for the awkward way of stating that but I think >>>> it makes sense to me. >>>> >>>> Thanks again, >>>> Barry - N4BUQ >>>> Thanks, >>>> Barry - N4BUQ >>>> >>>> >>>> On Sun, Sep 15, 2024 at 11:10 PM Larry Haney <[email protected]> >>>> wrote: >>>> >>>>> Hi Barry, You are absolutely correct in your deductions. When the KC >>>> is >>>>> at its lowest of 000, the vfo is at its highest (3.455 mh). >>>>> >>>>> Regards, Larry >>>>> >>>>> On Sun, Sep 15, 2024 at 7:23 PM Barry Scott <[email protected]> >>>>> wrote: >>>>> >>>>>> Looking at the simplified schematic for the 3rd mixer (V205), the >>>> output >>>>>> from the 2nd mixer (V204) tunes from 3 to 2 MC and the VFO tunes from >>>>>> 3.455 >>>>>> MC to 2.455 MC yielding a constant 455 kc mixer product. Is it >>>> correct to >>>>>> interpret those numbers to mean that if the counter starts at XX 000 >>>> and >>>>>> the KC control is rotated CW to XX +000 the VFO's output frequency >>>> starts >>>>>> at 3.455kc and falls 1000 kc for 10 turns CW on the KC knob? >>>>>> >>>>>> I'm asking because I want to know what the frequency of the VFO is >>>>>> supposed >>>>>> to be when the dial is at XX 000 and I presume it's 3.455 kc but >>>> wanting >>>>>> to make sure. >>>>>> >>>>>> Thanks, >>>>>> Barry - N4BUQ >>>>>> ______________________________________________________________ >>>>>> R-390 mailing list >>>>>> Home: http://mailman.qth.net/mailman/listinfo/r-390 >>>>>> Help: http://mailman.qth.net/mmfaq.htm >>>>>> Post: mailto:[email protected] >>>>>> >>>>>> This list hosted by: http://www.qsl.net >>>>>> Please help support this email list: http://www.qsl.net/donate.html >>>>>> >>>>> >>>> ______________________________________________________________ >>>> R-390 mailing list >>>> Home: http://mailman.qth.net/mailman/listinfo/r-390 >>>> Help: http://mailman.qth.net/mmfaq.htm >>>> Post: mailto:[email protected] >>>> >>>> This list hosted by: http://www.qsl.net >>>> Please help support this email list: http://www.qsl.net/donate.html >>> >>> >> ______________________________________________________________ >> R-390 mailing list >> Home: http://mailman.qth.net/mailman/listinfo/r-390 >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ > R-390 mailing list > Home: http://mailman.qth.net/mailman/listinfo/r-390 > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ R-390 mailing list Home: http://mailman.qth.net/mailman/listinfo/r-390 Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
