Re: 40-40 bandwidth mod...

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From: Allen Jones (ajones@niia.net)
Date: Tue Aug 08 1995 - 15:52:51 EDT


>Has anyone tried putting a switch on the toroid to make the 40-40 band-width
>larger? If it will tune any 50KHz portion, why not a switch at taps for
>7.000 -> 7.050, 7.050 -> 7.100, 7.100 -> 7.150 ? Cover *all* of 40, or at
>least *more* of it... (?)
>Matt N0XEU
>MK2331@STLMAIL7.SBC.COM

Matt . . .

Trying to tap a small toroid inductor and the associated switching rats nest
wouldn't be very practical plus I believe it would add quite a bit of
instability to the LO circuit.

On page 6 of the SW-40 instruction manual NN1G notes that greater frequency
coverage can be had by increasing the value of the 68pf cap at C9. With the
original cap I was able to cover about 35 KHz. I increased the value to
100pF and now have about 47 KHz of coverage. According to Dave's info the
upper limit is about 1000 pF using an NPO or Silver Mica cap. The more
spread you have the more difficult it will be to tune in stations in the 270
or so degrees of rotation available from R1. I was able to get a nice
10-turn pot and turn counting dial from Hosfelt Electronics that is very
small and really slows down the tuning rate, in my case < 5 KHz per turn.
My total investment was about $20.

72/73 . . . Allen
====================================
Allen Jones K9DZE ajones@niia.net
Michigan City, Indiana EN61nq
ARCI #8797 G-QRP #8812 NorCal #1061
SWOT #1368 SMIRK #5403
====================================


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