[ARC5] Drift in BC-453 - more

Wed Dec 13 14:08:54 EST 2017

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> 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>
> 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> <kgordon2006 at frontier.com> wrote:
>>
>>
>> On 12 Dec 2017 at 0:00, 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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