K1 tuning range issue.

[Gil G.]

Hello,

After selling my K1, what a mistake, I just had to buy another one...
This one was built already. It has the following tuning ranges:

6098.2 - 7077.5
10092.2 - 10170.7
13092.6 - 14071.1
20990.5 - 21069.1

I want to bring the frequency up to the bottom of each band. I wonder
though, why the disparity between the 1.8kHz below bottom on 40m and the
other bands, the worst being 15m at 9.5kHz below band bottom?

When I built my first K1 I remember all four bands were pretty close to
each other as far as range is concerned.

What do I do?

Thanks,

Gil.

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[Don Wilhelm-4]

Gil,

Move the VFO frequency (L1 turns spacing) so the VFO frequency is closer
to 3.090 kHz.  That will raise the frequency of the output signal a bit.
See page 38 of the manual "VFO Range Adjustment".

There does have to be some "wiggle room" at the bottom of each band
because of the variance  in the 'real' frequency of the crystals on the
band board.
If one were to replace those crystals with custom made precision
crystals, you could get the bottom of each band to line up with the
bottom of the other bands, but that would be expensive.  I don't know
what the frequency tolerance is on the stock crystals, but the 'wiggle
room' is necessary with crystals at a price point that is affordable for
most hams.

73,
Don W3FPR

On 6/18/2015 12:28 PM, Gil G. wrote:

> Hello,
>
> After selling my K1, what a mistake, I just had to buy another one...
> This one was built already. It has the following tuning ranges:
>
> 6098.2 - 7077.5
> 10092.2 - 10170.7
> 13092.6 - 14071.1
> 20990.5 - 21069.1
>
> I want to bring the frequency up to the bottom of each band. I wonder
> though, why the disparity between the 1.8kHz below bottom on 40m and the
> other bands, the worst being 15m at 9.5kHz below band bottom?
>
> When I built my first K1 I remember all four bands were pretty close to
> each other as far as range is concerned.
>
> What do I do?
>
> Thanks,
>
> Gil.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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[Mike Morrow-3]

Gil wrote of his K1:

> This one was built already. It has the following tuning ranges:
>
>  6098.2 - 7077.5

Doubtless you meant 6998.2 low end.

> 10092.2 - 10170.7
> 13092.6 - 14071.1
> 20990.5 - 21069.1
>
>> I want to bring the frequency up to the bottom of each band. I wonder
>> though, why the disparity between the 1.8kHz below bottom on 40m and the
>> other bands, the worst being 15m at 9.5kHz below band bottom?

The variation in each band's low end for your K1 is better than the typical K1s that I have seen since I got mine in 2000.  The disparity results because the ACTUAL oscillation frequency of each of the four heterodyne crystals on the filter board does NOT vary by the exact same number of kHz from the nominal crystal frequency.  To get all four bands starting at the same offset in kHz from the low end of the bands, you do NOT need the filter board crystals to be exactly on their nominal frequency, but you do need the same kHz difference from nominal frequency for ALL four crystals.  That is most unlikely unless there are temperature stable trimmer capacitors for each crystal to allow adjustment.  There are no such trimmers on the filter board.

>> What do I do?

Do NOTHING!  Lowering the VFO frequency by compress turn on RF board L1 will raise the low end frequency of *all four bands* by the same number of kHz.  All that you can tolerate is an increase of about 1.0 kHz which will start your 40m low end at 6999.2 kHz...uncomfortably tight especially since temperature changes will at times move the low end closer or even above 7000 kHz.

I think your 6998.2 kHz low end is ideal for a K1 40m low end.  As for the other three bands, it is *impossible* to bring them in closer to the band's nominal low end without upsetting the 40m low end by the same amount.

These minor uncorrectible variations are mainly cosmetic.  If you need more coverage at any band's high end, consider adopting the wider "150 kHz" VFO option (you will actually get a VFO span of about 180 kHz, and you might want to change the 30m heterodyne crystal to start the coverage near 10000 kHz.)

Mike / KK5F



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[David Brown]

Gil,

My K1 is a two band (40/20) model purchased in 2001.  I too was concerned
with the lost "wiggle room" at the bottom of the bands, not to mention
different values on the two bands.  The 150 kHz VFO range ( I got 177 kHz)
was a bit too touchy for me yet the lower range was nice for smooth tuning
but a little limited on band coverage.  I decided a tuning range of 100 kHz
on 40 would be a nice trade off between band coverage and smooth tuning.
Experimentally I got this by changing C2 from 68 pF to 78 pF, then adding
14.1 pF across L1 to adjust the VFO range.  Silvered mica capacitors were
used for the mods.  I wound up with:

    104 kHz band coverage
    1.1 kHz lost wiggle room below 7.0 mHz
    7.4 kHz lost wiggle room below 14.0 kHz

73, Dave K8AX
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