[HBR] Homebrew string dial

[G4IZS]

Hi Marvin,

    Aha, I think you have caught me out, or at least, one half so!

    The aim always has to be the minimum number of pulleys, and yes, all the 
"front panel" stuff has to be in one plane. There is one "hidden" pulley 
that allows a change of string direction - and that is the tuning shaft. You 
do however, as you have correctly pointed out, need a third pulley to return 
the string off the large drum on the tuning capacitor back to the "top" of 
the tuning dial itself. All three pulleys sit in one plane, shared with the 
groove in the tuning shaft.

    An advantage of the tuning capacitor shaft being "vertical" - up or down 
as you say - (and hence the associated large diameter pulley horizontal) is 
that the height of the front panel (in a conventional set-up) is not defined 
by the large pulley diameter and there is more freedom to ensure an 
ergonomic layout of the front panel and associated dial.

    I have always found pulleys of about 0.5 inch diameter are the minimum 
to provide a smooth control action. Larger pulleys are better.

    Sorry I mislead you .....

        73
            Ron, G4IZS


----- Original Message ----- 
From: <match at ece.utah.edu>
To: <hbr at mailman.qth.net>
Sent: Friday, February 20, 2009 12:19 AM
Subject: [HBR] Homebrew string dial


> On 19 Feb 2009 at 18:34, Ron wrote:
>
>>     Now, the capacitor is mounted on your chassis. It goes in with the 
>> shaft
>> VERTICAL and in such a position that the string track around the rim of 
>> the
>> large pulley is asymptotic to the line of string across the top of the 
>> dial.
>> The pulley should be at the height of the control shaft. This means the
>> position of the capacitor is fully defined in 2 dimensions, you can 
>> choose
>> where you want it "left to right" so long as it is within the width
>> of the
>> proposed dial "window".
>
> Vertical meaning the shaft points either up or down?
>
> And here you lost me...
>
> So, the two brass pulleys, the  panel-mounted tuning shaft, and the 
> slide-rule
> dial itself are all in one plane, but the large pulley on the tuning cap 
> is in a
> different plane, perpendicular to the first?
>
> I cannot visualize how the string gets from one plane to the other without 
> two
> more pulleys.
>
> Marvin
> KA7TPH
>
> ______________________________________________________________
> HBR mailing list
> Home: http://mailman.qth.net/mailman/listinfo/hbr
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:HBR at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>