[Elecraft] On the trail of 30m flat topping

[peter barville]

You may recall that a week or so ago I reported that my K2/100 flat tops
(at about 65-70 watts), but ONLY on 30m. One or two others reported
similar findings, but K2/100's tested by Elecraft were okay. 

I had a couple of hours spare today and decided to investigate further.
A prime suspect, of course, is the LPF.

A visual inspection of the 40/30m LPF (on the PA board) reveals that L4,
L5 and L6 each has the correct number of turns (on the correct toroid).
It also reveals that the C3x capacitors are correct - according to their
markings, and I do tend to check component values with a meter before
installation. So, nothing obviously wrong there.

I also checked that the LPF's were switching as they should.

Finally, I decided to look at the swr of the 40/30m LPF by using my
Autek RF1 Antenna Analyser. I terminated the PA output with a 50 ohm
dummy load, and fed the Autek into the input of the PA board. With the
PA board powered, but disabled in the menu, I was able to switch LPF's
by changing bands on the K2. I think the results may give a clue as to
why the rig is flat topping on 30m:

        MHz             Indicated SWR
         7.05                   1.2
         7.80                   1.1
         8.00                   1.1
         8.40                   1.1
         8.80                   1.2
         9.10                   1.3
         9.60                   1.4
        10.00                   1.5
        10.20                   1.6
        10.30                   1.7
        10.40                   1.8
        10.59                   1.9
        10.65                   2.0

I suspect these figures suggest that the filter *is* rolling off too low
in frequency. Maybe removing a turn from one (or more) of L4/5/6 would
help?

I would be grateful if Team Elecraft could comment, and also let me know
what value inductance L4 and L5/6 should be? It would be fairly easy to
remove them from the board to check their values, and possibly remove a
turn.
-- 
72, peter g3xjs