[Elecraft] Question about Possible FL1 Problem

[Don Wilhelm]

Tom,
With the variable filter set to such a wide bandpass, the passband ripple
becomes a significant factor.  It is quite likely that the particular tone
that you were listening to occurred at a valley in the passband - you could
check that out on the Spectrogram display.

The 'fix' can be either 1) Narrow the passband for your filter to about 1.2
kHz, or 2) Set the BFO so that your sidetone frequency is aligned with a
peak somewhere on the passband.

As an additional note - with wide settings of the varaible filter (width
>1.8 times the sidetone frequency) there is the possibility that the BFO can
be adjusted so you can hear right through 'zero-beat' and up the other side.
This destroys the 'single signal' reception that we usually strive for.  To
prevent this from occurring, align the passband so the low frequency corner
is set at about 300 Hz rather than attempting to 'center the passband'.  You
will still be able to hear signals that are low pitched (down to the limits
of the K2 audio response and your hearing limits), even though the level may
be reduced, but you should hear no signals on the opposite sideband.

73,
Don W3FPR

----- Original Message ----- 
| SNIP...
| The filter settings are as follows:
|
| FL1  set to 2.25
| FL2 set to 0.70
| FL3 set to 0.40
| FL4 set to 0.10
|
| The good news is that on the Spectrogram the clock showed up at the same
| spot through each filter (i.e. it didn't "bounce around" as I switched
| filters.
|
|
| However, I noticed a very significant decrease in the audio level when
tuned
| to FL1.  - the widest filter!
|
|
| Here are the readings from Spectrogram  (a really super utility BTW!):
|
| The audio output readings were as follows:
|
| FL1  ( the 2.25 setting)   -20Db
| FL2 (the 0.70 setting)     -8 Db
| FL3  (the .40 setting)      -10Db
| FL4 (the .10 setting)       -13 Db
|
|
| I guess the slight loss of audio from FL2 through FL4 is OK, but I'm
| wondering why FL1, with a very wide bandwidth is so much weaker than the
| others.
|
...SNIP