Hi Andy,
I've got resevations about the suggestion in your last
paragraph.? Whilst it would certainly reduce the overal number of
turns in the winding it creates a single shorted turn in the
inductor? which might introduce other problems.? Better to
actually remove turns I feel.
73 Dave G3WUN
On 02/11/2017 12:40, Andy G0FTD via
Groups.Io wrote:
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On Thu, Nov 2, 2017
at 04:49 am, Hans Summers wrote:
If the power output is less than expected, and if
other test equipment is not available, then I suggest removing a
turn or two from each of the toroids,
I agree with Hans.
I think the LPF values are derived from the W3NQN designs for
standard value components, and are also reproduced by the GQRP
CLub literature.
I found that the design was just a tad too harsh, and these values
would often represent a 1.5db in band loss. (I think G4APB found
the same).
For the 30m and up designs, I personally knocked >1< turn
off each of the 3 coils and that was perfect.
(I don't have enough experience yet with the lower band LPF's to
offer any experience).
Two turns is probably too much, and the harmonic attenuation tends
to suffer in my opinion.
Users of U2/U3's might like do the same thing whilst we're on the
subject.
Perhaps one technique to this might be to scrap a bit of the
enamel off with a scalpel / sharpie knife on two adjacent
turns and place a blob of solder across them to to short them out.
The mod can easily be reversed if there are any issues.
73 de Andy
