[Boatanchors] VFO Drift

[J. Forster]

> That is what Tony indicated to me.
>
> Even if one were to dry the board in an oven, the dielectric properties
> are
> no doubt still irreversible.

I'm by no means sure of that. I'm just guessing, but I think Bakelite is
sort of like a sponge and the water gets into it. Now water has a
dielectric constant of about 80, compared to vacuum at 1, so if the matrix
has a bunch of water in it, the dielectric constant goes up.

I'd suspect if the stuff were dried out, the dielectric constant would
revert to the original.

FWIW,

-John

=========
>
> Collins Radio in their early, early KWM-380, (below 50 serial numbers)
> had
> to change to a different circuit board material, probably, due to the
> changes in dielectric properties.
>
> Thanks
>
> David Knepper, W3ST/W3CRA
> Publisher of the Collins Journal
> Secretary of the Collins Radio Association
> www.collinsra.com
> Join today
> Nets: 14.263 Mhz, 1900Z, Sundays
> 3.805 Mhz, 2300Z, Mondays
>
> ----- Original Message -----
> From: "J. Forster" <jfor at quik.com>
> To: "David Knepper" <collinsradio at comcast.net>
> Cc: <boatanchors at qth.net>
> Sent: Friday, July 09, 2010 1:37 PM
> Subject: Re: [Boatanchors] VFO Drift
>
>
>> FWIW, the board material had likely absorbed water, changing its
>> dielectric constant, hence the frequency.
>>
>> Best,
>>
>> -John
>>
>> =============
>>
>>> I thought that I would pass this on for what it is worth.
>>>
>>> A friend of mine was utilizing the solid-state PTO board from a WRL
>>> Glaxy
>>> V,
>>> Mark II for his new homebrew transceiver project.
>>>
>>> Tony told me today that the problem was not the components mounted on
>>> the
>>> board but the board itself.  When he mounted the components on a new
>>> board
>>> made of plexiglass material, the drift problem went away.  It seems
>>> that
>>> the
>>> original board was the problem since it was made of some kind of
>>> phenolic
>>> material.  When he even blew on the board, the frequency would begin to
>>> take
>>> off.
>>>
>>> The new PTO drifts less than 200 cycles over a period of an hours and
>>> then
>>> settles down.
>>>
>>> Has anyone experienced a similar occurrence?
>>>
>>> That original material that WRL used for the PTO evidentally had lost
>>> its
>>> insulation properties.
>>>
>>> He thought sure that it was not a component failure since he had
>>> replaced
>>> everything on the old board.
>>>
>>> Thank you
>>>
>>>
>>> David Knepper, W3ST/W3CRA
>>> Publisher of the Collins Journal
>>> Secretary of the Collins Radio Association
>>> www.collinsra.com
>>> Join today
>>> Nets: 14.263 Mhz, 1900Z, Sundays
>>> 3.805 Mhz, 2300Z, Mondays
>>>
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>>
>>
>>
>
>