Re: [HCDX] Drake R8 Passband Tuning

[Djaci Franklin <djaci@xxxxxxxxxxxxx>]

At 05:09 14/07/00, you wrote:
> Hi:
>
> Does anyone know if there is an adjustment inside the R8 to adjust the
> passband tuning, so it can be centered?
> Mine seems to have drifted off in the past few years where the center of
> the frequency is off. If there is such an adjustment, where is it
> located or is it labelled on the chassis? Any help would be appreciated.
> Thanks!

This was compiled from the Drake R8-B Service Manual, pg. 33.

2nd LO/PBT (Pass Band Tuning)

The 2nd LO is a 45.05 MHz signal that is sent to the Front End
board and digital mixer circuit. The 2nd LO frequency
actually varies depending on mode and front panel PBT
adjustment, thus providing IF shifting. The 45.05 MHz signal
is produced by doubling a varactor tuned, crystal controlled
22.525 MHz oscillator. The oscillator consists of a 22.525 MHz
crystal (Y3), transistor Q28 and associated components.
It is not referenced back to the 35 MHz reference  signal thus
requiring its own temperature compensation.
Capactor C243 has a N1500 temperature coefficient and
provides the major temperature compensation. Variable coil
L32 provides the frequency tuning adjustment. Varactor CR30
provides a fine tune frequency adjustment. Fine tuning can be accomplished 
in two ways.

1) Front Panel PBT ajustment
2) uP controlled DAC

73s

Djaci
 

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