K2 freq stability

[lstavenhagen]

Hi all,
Here's an interesting finding, though I apologize if this is already in the past archives.

No matter how careful you are when installing L33 on the bottom of the board, it's so close to the bottom cover that any movement of it, say when you're picking up the rig or manipulating the bale, etc., will pull the BFO. On my 2nd K2 that I just completed it was so bad that I could pick up the rig, set it back down and the tone of signals was very slightly, but noticeably off.

So what I did was put a lockwasher between the cover and the standoff near L33 to raise the cover a little bit and get it the heck away from L33 as much as I could. It actually made a large improvement in the general frequency stability of the rig - which means before I was seeing more contributions in overall drift from the BFO in addition to the rest of the circuitry.

The washer is an ugly fix, since the cover bows out a little bit, but it's totally non-destructive and reversible. I did the same fix to my other K2 which didn't have the problem to the same degree, but it helped on that one too.

Fortunately the slightly bowed out bottom cover is under the rig and you never see it. But just in case you've been experiencing more drift in your K2 than you think you should get, or it pulls when you pick it up.... that's a fix that is working on mine.

73,
LS
W5QD

[Don Wilhelm]

LS,

That is not usually a problem if the rubber mounting stem has been cut
off as instructed and the 1/8 watt resistor is pushed down inside the
toroid core (so the core cannot move).

One does not usually manipulate the bottom cover during operation, so
the only time the BFO is liable to shift is when pressure is placed on
the bottom cover.
That is not 'drift' IMHO, but a change because of the physical proximity
of the bottom cover.

73,
Don W3FPR

On 4/24/2016 9:31 AM, lstavenhagen wrote:

> Hi all,
> Here's an interesting finding, though I apologize if this is already in the
> past archives.
>
> No matter how careful you are when installing L33 on the bottom of the
> board, it's so close to the bottom cover that any movement of it, say when
> you're picking up the rig or manipulating the bale, etc., will pull the BFO.
> On my 2nd K2 that I just completed it was so bad that I could pick up the
> rig, set it back down and the tone of signals was very slightly, but
> noticeably off.
>
> So what I did was put a lockwasher between the cover and the standoff near
> L33 to raise the cover a little bit and get it the heck away from L33 as
> much as I could. It actually made a large improvement in the general
> frequency stability of the rig - which means before I was seeing more
> contributions in overall drift from the BFO in addition to the rest of the
> circuitry.
>
> The washer is an ugly fix, since the cover bows out a little bit, but it's
> totally non-destructive and reversible. I did the same fix to my other K2
> which didn't have the problem to the same degree, but it helped on that one
> too.
>
> Fortunately the slightly bowed out bottom cover is under the rig and you
> never see it. But just in case you've been experiencing more drift in your
> K2 than you think you should get, or it pulls when you pick it up.... that's
> a fix that is working on mine.
>
>

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[lstavenhagen]

Agreed, though on my most recent K2, it was close enough to actually change the BFO freq slightly even after releasing the pressure of my hand on the cover, etc., when I picked it up and moved it around.

Course we're talking, like, fractions of a millimeter almost lol. I think just the small warp in the RF board and maybe in the bottom cover are just enough to get the panel close enough to the toroid and BFO area to make this happen on my recent K2. I was extremely careful with the bumper and positioning of the resistor and it was still mechanically too close to the panel (I could see the slight divet in the electrical tape when I'd take the cover off, but I never saw that on my first K2).

But even K2 #1 pulls the BFO a little when I handle it pressing on the bottom cover with the rig on. Just not nearly as bad as #2....

But just the thickness of a lockwasher was enough to spread things out for a great improvement...

Definitely not a "problem" problem, but, er,...How about a "very very close tolerance mechanical issue with L33 and the bottom cover", I'll put it that way lol.

73,
LS
W5QD