OP1 and CW filter gain difference?

[Marteinn Sverrisson]

Hi All

I was measuring the gain difference of the OP1 x-tal filter and the
CW filter on my K2.

It seems that the OP1 filter has +10dB more gain than the CW filter
I have the 2.5kHz OP1 filter mod and the stock CW filter on 2.4kHz.
Measurements are done on 7 MHz band on LSB.

I did the measurements with AGC off, using noise gen and audio
spectrum analyzer.

Is this normal?

Should I look for some bad X-tals or varicaps in the CW filter?

73 de TF3MA

PS. same results if I unmodule the KSB2, the gain is still low.
--
   Marteinn Sverrisson    TF3MA
          Langitangi 2    Internet: tf3ma [at] raunvis [dot] hi [dot] is
        270 Mosfellsbær   http://www.raunvis.hi.is/~tf3ma
               Iceland
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[Vic K2VCO]

Marteinn Sverrisson wrote:

> I was measuring the gain difference of the OP1 x-tal filter and the
> CW filter on my K2.
>
> It seems that the OP1 filter has +10dB more gain than the CW filter
> I have the 2.5kHz OP1 filter mod and the stock CW filter on 2.4kHz.
> Measurements are done on 7 MHz band on LSB.

The CW filter has a large amount of ripple when it is adjusted to more than
about 1.5 KHz bandwidth, although the gain should be more or less the same.  How
does your CW filter work at narrower bandwidths, for example 1 KHz, 800 Hz, 400
Hz and 200 Hz?

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco

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[Stewart Baker]

Marteinn,

The CW filter has a greater signal loss than the OP1 filter mainly because of
it's varicap variable bandwidth design. My K2 has about a 6dB loss relative to
the OP1. Your CW filter loss of 10dB may be a bit high. I would check the
varicap lead orientation.

73
Stewart G3RXQ

On Fri, 8 Apr 2005 15:49:53 +0000, Marteinn Sverrisson wrote:

> Hi All
>
> I was measuring the gain difference of the OP1 x-tal filter and the
> CW filter on my K2.
>
> It seems that the OP1 filter has +10dB more gain than the CW filter
> I have the 2.5kHz OP1 filter mod and the stock CW filter on 2.4kHz.
> Measurements are done on 7 MHz band on LSB.
>
> I did the measurements with AGC off, using noise gen and audio
> spectrum analyzer.
>
> Is this normal?
>
> Should I look for some bad X-tals or varicaps in the CW filter?
>
> 73 de TF3MA
>
> PS. same results if I unmodule the KSB2, the gain is still low.

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[Marteinn Sverrisson]

Vic and Stewart, Tanks for answering

well, the ripple on the CW filter at 2kHz BW is abt 8db p-p.

the gain difference when the CW filter is offset to 1.2kHz
(for digital modes) and its BW is 1kHz is abt -3dB relative to
the OP1 filter (not bad?).

with the same at 200Hz BW the gain is -10dB relative to the OP1.

Maybe this is normal,

73 de TF3MA
--
   Marteinn Sverrisson    TF3MA
          Langitangi 2    Internet: tf3ma [at] raunvis [dot] hi [dot] is
        270 Mosfellsbær   http://www.raunvis.hi.is/~tf3ma
               Iceland
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[Vic K2VCO]

Marteinn Sverrisson wrote:

> Vic and Stewart, Tanks for answering
>
> well, the ripple on the CW filter at 2kHz BW is abt 8db p-p.
>
> the gain difference when the CW filter is offset to 1.2kHz
> (for digital modes) and its BW is 1kHz is abt -3dB relative to
> the OP1 filter (not bad?).
>
> with the same at 200Hz BW the gain is -10dB relative to the OP1.
>
> Maybe this is normal,

It seems more or less so.  Some people have less attenuation when moving from 1
KHz to 200 Hz.  It wouldn't hurt to make sure the toroid T7 is wound with the
proper number of primary and secondary turns.

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco

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[Don Wilhelm-3]

Marteinn,

The CW filter design point is for a bandwidth of 400 to 600 Hz, and it may
be that what you are seeing is normal - the high ripple with a bandwidth
greater than about 1.2 kHz is quite normal.  Greater attenuation does appear
at narrow bandwidth, but if that area is important to you, you may want to
experiment by changing the turns ratio of T7 a bit to see if it improves.

73,
Don W3FPR

> -----Original Message-----
>
>
> Vic and Stewart, Tanks for answering
>
> well, the ripple on the CW filter at 2kHz BW is abt 8db p-p.
>
> the gain difference when the CW filter is offset to 1.2kHz
> (for digital modes) and its BW is 1kHz is abt -3dB relative to
> the OP1 filter (not bad?).
>
> with the same at 200Hz BW the gain is -10dB relative to the OP1.
>
> Maybe this is normal,
>
> 73 de TF3MA
> --
>

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