VFO Tuning Noise, still some there after modification

[DaveL G3TJP]

After implementing Elecraft's VFO tuning hash modification, there was still hash to be heard on my K3, most notably in the bottom 40kHz of 10 metres.

 

The problem was finally eased by replacement of the two silicon diodes used in the modification.  Although no fault could be found with the original diodes - they were a couple from a large bandolier of 1N4148 purchased from a major retailer some time ago - their replacement with a couple of 1N4148 diodes recycled from redundant equipment reduced the hash level to below the received antenna noise level on 10m.

 

The only difference I could find between the two pairs of diodes was that the Vf on the original diodes was higher than that of the replacement diodes.  Original diode Vf 0.75v, replacement diode Vf 0.71v, all measurements taken at 5mA.

 

If anyone is still experiencing VFO tuning hash after making the modification, it might be worth trying a swap out of the diodes.  Perhaps using Schottky barrier diodes might be even better?

 

Hats off to Gary of Elecraft support for his patience and for always being there when needed.  Also to Dale, who could hear my K3's hash over 8,000 miles of landline.

 

73  DaveL  G3TJP
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[Jan Erik Holm]

David Lankshear wrote:

> After implementing Elecraft's VFO tuning hash modification, there was still hash to be heard on my K3, most notably in the bottom 40kHz of 10 metres.
>
>  
>
> The problem was finally eased by replacement of the two silicon diodes used in the modification.  Although no fault could be found with the original diodes - they were a couple from a large bandolier of 1N4148 purchased from a major retailer some time ago - their replacement with a couple of 1N4148 diodes recycled from redundant equipment reduced the hash level to below the received antenna noise level on 10m.
>
>  
>
> The only difference I could find between the two pairs of diodes was that the Vf on the original diodes was higher than that of the replacement diodes.  Original diode Vf 0.75v, replacement diode Vf 0.71v, all measurements taken at 5mA.
>
>  
>
> If anyone is still experiencing VFO tuning hash after making the modification, it might be worth trying a swap out of the diodes.  Perhaps using Schottky barrier diodes might be even better?
>
>  
>
> Hats off to Gary of Elecraft support for his patience and for always being there when needed.  Also to Dale, who could hear my K3's hash over 8,000 miles of landline.
>
>  
>
> 73  DaveL  G3TJP

Has anyone tried Schottky diodes? I will myself but haven´t
had time to deal with it yet, too busy with other things
in life right now.

Jim SM2EKM

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