[R-390] R-390 VFO Question
Barry Scott
72volkswagon at gmail.com
Thu Sep 19 09:49:43 EDT 2024
Okay, Larry. I thought that might be the case. I was able to make the
endpoint adjustment and it's tracking extremely close now - at least
end-to-end and I think points in between are quite good too. I need to do
some more checking on everything now that the PTO is reinstalled.
Thanks!
Barry - N4BUQ
On Thu, Sep 19, 2024 at 12:20 AM Larry Haney <larry41gm2 at gmail.com> wrote:
> OK Barry, That is certainly the right approach to take. I thought you
> were already planning on what to do if the screw driver adjustment was not
> enough. I hope it is.
>
> Regards, Larry
>
> On Wed, Sep 18, 2024 at 11:51 AM Barry <n4buq at knology.net> wrote:
>
> > Hi Larry,
> >
> > I'm sorry but I'm still a little confused. My intent of adjusting L701
> > would be by using a screwdriver on the endpoint adjusting core. If that
> > doesn't give me enough range, then I presume I'd need to start modifying
> > the C or L values but would start with just the core adjustment.
> >
> > Thanks again,
> > Barry - N4BUQ
> >
> > Hi Barry, I believe that the total range of adjustment of L701 is about
> > 7.5 kc (5 turns of wire). If you needed to only adjust it 1-2.5 kc to
> get
> > it back into range, I'd probably go the route of removing 1-2 turns, but
> at
> > about 1.5 kc per turn, you'd need to remove 3 turns and that makes the
> > adjusting range quite small after that. It's doable, but a little
> > restrictive.
> > Regards, Larry
> >
> > On Wed, Sep 18, 2024 at 10:52 AM Barry <n4buq at knology.net> wrote:
> >
> >> Hi Larry,
> >>
> >> I'm curious why changing out a cap would be the first line of effort.
> Is
> >> that because there may not be enough change available from L701 to
> correct
> >> for 4 kc?
> >>
> >> Thanks,
> >> Barry - N4BUQ
> >>
> >> > Hi Jim, Yes, I've done that and it works quite well.
> >> >
> >> > Barry, Since the EP is about 4kc off, I'd suggest using the capacitor
> >> > adjustment method because removing 1 turn off of the L701 is not going
> >> to
> >> > be enough. Removing 2 turns really limits its adjustment range. Be
> >> very
> >> > careful with those 10 pf caps inside the pto, they are very fragile.
> >> You
> >> > should be able to calculate fairly close as to the value to put in
> >> series
> >> > with a 10 pf, and give it a little wiggle room for adjustment.
> >> >
> >> > Regards, Larry
> >> >
> >> > On Wed, Sep 18, 2024 at 9:07 AM Jim Whartenby via R-390 <
> >> > r-390 at mailman.qth.net> wrote:
> >> >
> >> >> Since the trend is a reduced frequency range, something has obviously
> >> >> increased in value internal to the PTO. There are two inductors and
> >> three
> >> >> capacitors in the circuit. The inductors have two ferrite cores so
> >> there
> >> >> are seven components in total that determine frequency. I have the
> >> feeling
> >> >> that the ferrite permeability has increased over time perhaps due to
> >> >> shrinkage. I don't see how either coil can have increased in
> >> inductance
> >> >> without causing binding with their respective ferrite cores. Of
> >> course it
> >> >> is still possible that any or all of of the tank capacitors could
> have
> >> >> increased in value.
> >> >>
> >> >> I assume that the two 10 pF capacitors have either a positive or
> >> negative
> >> >> temperature coefficient of different slopes to compensate for the
> >> operating
> >> >> temperature of the PTO. Lifting one of the two 10pF caps and
> placing,
> >> for
> >> >> example, a 100 pF NPO in series with it will subtract 1 pF from the
> >> total
> >> >> tank capacitance and raise the operating frequency without
> >> significantly
> >> >> changing the temco. This should preserve the end point coil
> inductance
> >> >> range. Has anyone tried this instead of removing a turn on the
> >> endpoint
> >> >> coil?
> >> >>
> >> >> Jim
> >> >>
> >> >> Logic: Method used to arrive at the wrong conclusion, with
> confidence.
> >> >> Murphy
> >> >>
> >> >> On Wednesday, September 18, 2024 at 10:04:39 AM CDT, Barry <
> >> >> n4buq at knology.net> wrote:
> >> >>
> >> >> Sorry. The first line of that last paragraph had kc where it should
> >> have
> >> >> been MC (or Mc or MHz or...):
> >> >>
> >> >> I don't how the counter now shows 499.7 for the VFO set at 2.9550 MC
> >> and,
> >> >> conversely, the VFO frequency at 500.0 is now at 2.9548 MC.
> >> >>
> >> >> Thanks,
> >> >> Barry - N4BUQ
> >> >>
> >> >> > Previously, I mentioned I have the endpoint data.
> >> >> >
> >> >> > VR Counter VFO Frequency (in MC)
> >> >> > ---------- ---------------------
> >> >> > +001.4 2.4550
> >> >> > 499.7 2.9550
> >> >> > -997.4 3.4550
> >> >> >
> >> >> > That makes the counter span for 1000 kc of the VFO to be 1000 +
> 1.4 +
> >> >> 2.6 = 1004
> >> >> > kc.
> >> >> >
> >> >> > Switching to zeroing the VR counter at both ends:
> >> >> >
> >> >> > VR Counter VFO Frequency (in MC)
> >> >> > ---------- ---------------------
> >> >> > +000.0 2.4566
> >> >> > 500.0 2.9548
> >> >> > 000.0 3.4524
> >> >> >
> >> >> > That makes the VFO span for 1000 kc on the counter to be 3452.4 kc
> -
> >> >> 2456.6 kc =
> >> >> > 995.8 kc so 4.2 kc short. Hopefully the endpoint adjustment still
> >> has
> >> >> that
> >> >> > much left in it and I won't need to open the can and perform any
> >> surgery.
> >> >> >
> >> >> > I don't how the counter now shows 499.7 for the VFO set at 2.9550
> >> and,
> >> >> > conversely, the VFO frequency at 500.0 is now at 2.9548 kc.
> >> Something
> >> >> must've
> >> >> > moved just a tiny bit since I set it.
> >> >> >
> >> >> > Thanks,
> >> >> > Barry - N4BUQ
> >> >> >
> >> >> >> Hi
> >> >> >>
> >> >> >> Using a impossible extreme case to keep the math easy:
> >> >> >>
> >> >> >> If your PTO covers (say) 900KHz rather than 1000 KHz, there will
> be
> >> a
> >> >> 100KHz
> >> >> >> “gap” that you can not tune to.
> >> >> >>
> >> >> >> Any significantly “too small” range would have the same impact.
> >> (Yes,
> >> >> there is a
> >> >> >> bit of extra travel at the ends of the range so this does not get
> >> >> totally
> >> >> >> insane ….).
> >> >> >>
> >> >> >> Bob
> >> >> >>
> >> >> >>> On Sep 18, 2024, at 9:54 AM, Barry <n4buq at knology.net> wrote:
> >> >> >>>
> >> >> >>> Would a significant difference in span between bands be due to
> the
> >> >> first crystal
> >> >> >>> oscillator? Otherwise, I'm not sure how that would occur.
> >> >> >>>
> >> >> >>> Thanks,
> >> >> >>> Barry - N4BUQ
> >> >> >>>
> >> >> >>>> Hi
> >> >> >>>>
> >> >> >>>> As long as the end points still line up so you have a 1000 KHz
> >> span
> >> >> with one
> >> >> >>>> being at 2955, the radio should be in reasonable shape. Having a
> >> >> “gap” between
> >> >> >>>> bands ( = a < 1000 KHz span) would be a PIA …. Fortunately that
> >> >> rarely is the
> >> >> >>>> case.
> >> >> >>>>
> >> >> >>>> There are still piles of R-390A’s sitting here or there ….
> >> >> >>>>
> >> >> >>>> Bob
> >> >> >>>>
> >> >> >>>>> On Sep 18, 2024, at 9:39 AM, Barry <n4buq at knology.net> wrote:
> >> >> >>>>>
> >> >> >>>>> I set the PTO's frequency per the manual (i.e. set the VR
> >> counter to
> >> >> any 500.0
> >> >> >>>>> reading and adjust the PTO to 2955 kc. The endpoint on the low
> >> side
> >> >> is
> >> >> >>>>> different from the endpoint on the high side so I'm presuming I
> >> have
> >> >> just a bit
> >> >> >>>>> of non-linearity; however, I think if I get the endpoints set
> to
> >> an
> >> >> even 1000
> >> >> >>>>> kc, then any non-linearity will hopefully be minimal. I'm not
> >> all
> >> >> that
> >> >> >>>>> concerned if the minor divisions aren't exact and will live
> with
> >> it
> >> >> as long
> >> >> >>>>> it's not too much. The trouble to tweak that may be much more
> >> >> effort than it's
> >> >> >>>>> worth to me.
> >> >> >>>>>
> >> >> >>>>> I wish I could've seen some of those "mountains"! I've seen
> >> >> pictures of the
> >> >> >>>>> stacks of blue-striper R-390A/URRs that sat out in the rain.
> >> Sad.
> >> >> >>>>>
> >> >> >>>>> Thanks,
> >> >> >>>>> Barry
> >> >> >>>>>
> >> >> >>>>>> Hi
> >> >> >>>>>>
> >> >> >>>>>> The gotcah is that the internal adjust coil may not have
> enough
> >> >> range to get the
> >> >> >>>>>> PTO back to where it needs to be. You may need to get a bit
> >> >> creative. Better to
> >> >> >>>>>> do this *before* any of the other work.
> >> >> >>>>>>
> >> >> >>>>>> This is not a new issue. Back in the day, the military spent a
> >> lot
> >> >> of time and
> >> >> >>>>>> money swapping out PTO’s. It was cheaper / easier to do that
> >> than
> >> >> doing a full
> >> >> >>>>>> rebuild. There are stories of “small mountains” of PTO’s
> >> building
> >> >> up behind
> >> >> >>>>>> repair depots as a result. Like any story, the size of those
> >> >> mountains likely
> >> >> >>>>>> got bigger and bigger with each telling of the story :) :) :).
> >> >> >>>>>>
> >> >> >>>>>> Bob
> >> >> >>>>>>
> >> >> >>>>>>> On Sep 18, 2024, at 8:28 AM, Barry <n4buq at knology.net>
> wrote:
> >> >> >>>>>>>
> >> >> >>>>>>> Hi Bob,
> >> >> >>>>>>>
> >> >> >>>>>>> I see where the PTOs for the R-390/URR and R-390A/URR both
> have
> >> >> end point
> >> >> >>>>>>> adjustments. L701 performs that in both. The schematic I
> see
> >> for
> >> >> the
> >> >> >>>>>>> R-390A/URR conveniently labels that as such on the schematic.
> >> RM
> >> >> >>>>>>> 11-5820-357-35 calls it out on page 12, Paragraph 12-b
> defines
> >> the
> >> >> function of
> >> >> >>>>>>> that coil. I just wasn't seeing that last night. I sure
> wish
> >> I
> >> >> had a
> >> >> >>>>>>> searchable PDF for the R-390/URR's service manual.
> >> >> >>>>>>>
> >> >> >>>>>>> Thanks,
> >> >> >>>>>>> Barry - N4BUQ
> >> >> >>>>>>>
> >> >> >>>>>>>> Hi
> >> >> >>>>>>>>
> >> >> >>>>>>>> Motorola most certainly made their own PTO’s for the radios
> >> they
> >> >> supplied. Long
> >> >> >>>>>>>> ago I talked to the folks who did the linearity adjustments
> on
> >> >> them. They still
> >> >> >>>>>>>> had (not so) fond memories of doing those adjustments.
> >> >> >>>>>>>>
> >> >> >>>>>>>> Bob
> >> >> >>>>>>>>
> >> >> >>>>>>>>> On Sep 17, 2024, at 11:29 PM, Barry <n4buq at knology.net>
> >> wrote:
> >> >> >>>>>>>>>
> >> >> >>>>>>>>> Hi Larry,
> >> >> >>>>>>>>>
> >> >> >>>>>>>>> Regarding the tutorials, I'm wondering which might apply to
> >> the
> >> >> PTO in the
> >> >> >>>>>>>>> R-390A/URR. I see most(all?) of them are regarding the
> >> COSMOS
> >> >> units but am
> >> >> >>>>>>>>> wondering which PTO is in the R-390/URR and whether any of
> >> the
> >> >> >>>>>>>>> rebuild/linearity documents apply to that one. Were all
> the
> >> >> R-390/URR PTOs
> >> >> >>>>>>>>> made by Collins and no COSMOS in that version?
> >> >> >>>>>>>>>
> >> >> >>>>>>>>> Mine is running just a bit fat - maybe 1.5 kc end-to-end.
> I
> >> >> have the actual
> >> >> >>>>>>>>> numbers written down and can post that when I get back to
> the
> >> >> workbench. From
> >> >> >>>>>>>>> what I remember, removing a turn shortens the end-to-end
> but
> >> >> perhaps additional
> >> >> >>>>>>>>> C would work as well. I don't know what effect that might
> >> have
> >> >> on linearity
> >> >> >>>>>>>>> but I don't think it should.
> >> >> >>>>>>>>>
> >> >> >>>>>>>>> The R-390A/URR PTO has an endpoint adjustment. Does this
> >> exist
> >> >> for the PTO in
> >> >> >>>>>>>>> an R-390/URR?
> >> >> >>>>>>>>>
> >> >> >>>>>>>>> Thanks,
> >> >> >>>>>>>>> Barry - N4BUQ
> >> >> >>>>>>>>>
> >> >> >>>>>>>>>> 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 <
> >> >> 72volkswagon at gmail.com> 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 <
> >> >> larry41gm2 at gmail.com> 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 <
> >> >> 72volkswagon at gmail.com>
> >> >> >>>>>>>>>>>> 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
> >> >> >>>>>>>>>>>>>
> >> >> ______________________________________________________________
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> >> >> >>>>>>>>>>>>
> >> >> >>>>>>>>>>>
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