[Elecraft] noodling with K1 VFO range

Mon Dec 9 08:53:01 2002

Andy -
I cannot remember because I sold my first K1 and will be building another -
how many turns does the pot have and could you add a pot with more turns?
73/Tim NZ7C
----- Original Message -----
From: "Wallace, Andy" <[email protected]>
To: "'Elecraft'" <[email protected]>
Sent: Monday, December 09, 2002 6:08 AM
Subject: [Elecraft] noodling with K1 VFO range


> In the CQWW contest, I was hearing interesting DX at the limits
> of my K1 80 kHz VFO range. This past weekend, I decided to see
> how I liked the extended 150 kHz range by putting a bigger cap
> at C2 (68pF = 80 kHz, 120 pF = 150 kHz).
>
> I pulled the stock cap and saved it. I then installed a
> 68pF surface mount cap on the back of the board with a jumper
> wire to connect the other lead to the hole for C2.
>
> On the top of the board, I stuck a two-position jumper in one
> hole for C2, and ran a wire toward the other hole. Then, I experimented
> with cap values to use between the wire and the other C2 hole.
>
> It sounds confusing the way I am writing it but basically I have two
> caps in parallel (which adds), one on each side of the PC board.
>
> With a jumper installed, I get the pair paralleled. Without
> the jumper, I get just the bottom 68pF cap and the stock ~80 kHz
> range.
>
> I settled on a 47pF cap for the top side jumper. This gives
> enough overlap that I can calibrate things and still have about
> 150 kHz range.
>
> Now, remember if you change caps, you'll have to redo the VFO range
> (adjusting toroid spacing) to have the counter-clockwise end meet
> 3.100 MHz; redo the band OPF calibrations, and redo the OFS offset
> adjust. Your RIT range will change, also. My idea of using the
> jumper means that I will have to redo all these if I decide to
> change back to 80 kHz -- still, easier than getting the soldering
> iron and solder sucker out during a contest.
>
> NOTE: it's not necessary to change the 30m crystal if you had previously
> installed the one for 80 kHz range starting at 10.100 MHz. The only
> loss here will be that you'll be tuning 10.100 - 10.250, and won't get
> WWV at 10.0 MHz.
>
> How do I like it? Well, the jury is still out. I'm getting about 16 kHz
> per revolution on the VFO, which is not too bad. However, it is tougher
> to zero beat the other stations (but still possible). There are also some
> nonlinearity "jumps" at one end of the VFO but it may be because I have
> worn my pot down after months of steady band cruising. ;-)
>
> The activity up to the ~150 kHz range of the bands has not been
> overwhelming.
> I did hear an HK station on 21.135 the other night, and I still need
> Colombia, so I guess I'll leave it in for now. If I decide I like it
> overall, I'll pull my jumper setup out and just install the stock
> factory 120 pF polystyrene cap. Obviously the K1 was designed with
> this in mind and it IS perfectly usable, but the 80 kHz range
> makes things even smoother.
>
> -Andy
>
>
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