[ARC5] Drift in BC-453 - more

Wed Dec 13 15:50:08 EST 2017

I second Dennis's advocacy of Huff-and-Puff. It's the frequency-locking 
method used with great success in the HP8640B sig gen, just as one 
famous example.

Tom

-- 
Prof. Thomas H. Lee
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On 12/13/2017 11:08 AM, Dennis Monticelli wrote:
> For this application I think applying the Huff-and-Puff technique 
> would work best.  The concept is to inject a little corrective voltage 
> to a varactor in widely time spaced brief espisodes after comparing 
> the locally generated freq to a stable reference like a 
> crystal-derived source.  After many such corrective steps (of which 
> the cum voltage gets stored on a capacitor) the frequencies will 
> eventually match.  Think of it as turning on a frequency locked loop 
> for a brief period and then not turning it on again until the 
> frequency of your LC oscillator has slowly walked beyond a 
> pre-established amount.
>
> You can purchase a solid state board that does this in a manner that 
> is overkill for the BC-453.  The X-Lock has many features and it will 
> track a manually tuned VFO.  The latter is its big attraction to 
> drifty older rigs.
>
> http://www.eham.net/reviews/detail/8437
>
> Dennis AE6C
>
>
>
>
>
> On Wed, Dec 13, 2017 at 10:11 AM, Ian Wilson <ianmwilson73 at gmail.com 
> <mailto:ianmwilson73 at gmail.com>> wrote:
>
>     1MHz / 200 -> 5kHz (pair of cascaded 74LS90's); pick off 17th
>     harmonic with an LC.
>
>     A rather better idea would be to use a DDS. Good accuracy but not
>     sure about the jitter.
>
>     73, ian K3IMW
>
>
>
>     On Wed, Dec 13, 2017 at 9:02 AM, John Hutchins
>     <jphutch60bj at gmail.com <mailto:jphutch60bj at gmail.com>> wrote:
>
>         Watching the conversation take shape over time:
>
>         If the tube is the culprit in MO drift,  I may have miss
>         remembered,  I read some where that regulating the filament
>         voltage to the M.O. 6J7 ... , and the Detector (12,6)K8 may
>         help in subduing the tube drift, do to changes in temperature
>         do to voltage swing.   True or not true?
>
>         Thanks
>         Hutch
>
>
>         On 12/13/2017 9:54 AM, J Mcvey via ARC5 wrote:
>>         I have been musing about the "why" of VT oscillator
>>         instability. OK,  there's definitely a thermal element, but
>>         what parameters of the tube are most affected?
>>         I checked the spec on the resonating cap for the BFO and it
>>         is +/- 2 pf ! So the tube must be the culprit.
>>         Not being from the vacuum circuit design era, I took a look
>>         at some texts on the subject. It looks like the solution can
>>         become quite complex if one desires tight VT stability specs.
>>
>>         I'm going to put a cheezy Cmos LC oscillator together and let
>>         it run a while to see what kind of drift it produces.
>>         There were some 1 Mhz clock modules in the junk box, but
>>         there is no clean integer divide down that will arrive at
>>         85Khz...dang!
>>         Maybe a 455 Khz resonator oscillator can be padded down to
>>         425 Khz so it can be divided by 5? Or will that cause
>>         instability- on not work at all?
>>         Has anyone here tried heavy padding of a resonator? Did it
>>         work Ok?
>>
>>
>>
>>         On Tuesday, December 12, 2017 8:56 PM, Kenneth G. Gordon
>>         <kgordon2006 at frontier.com> <mailto:kgordon2006 at frontier.com>
>>         wrote:
>>
>>
>>         On 12 Dec 2017 at 0:00, spr at earthlink.net
>>         <mailto:spr at earthlink.net> wrote:
>>
>>         > Yes, but it doesn't have the truly horrible AVC LO frequency
>>         pulling that 6A7and 6A8 have.
>>
>>         True, but both of those were early tubes that the 'K8 was
>>         supposed to supplant.
>>         > >
>>         > >6/12K8 is the absolutely noisest "converter" tube in Terman's entire long list. I hate the thing
>>         > >for that, but it does work well enough in the "ARC-5" receivers....
>>         > >
>>         > >Ken W7EKB 
>>         >
>>
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