51236Re: [softrock40] Softrock frequency for 10.680 MHz
- Jan 4, 2011Hi Neil,
The 14.089 MHz crystal provided in the Lite II Combined kit may be used to give a 1/3 sub-harmonic sampled center frequency of about 10.56 MHz. With 96kHz soundcard sampling the band coverage would be from about 10.51 MHz to 10.61 MHz. Not sure, but would this cover your IF band?
The QSD circuit is sensitive to odd harmonic signals and the response to the 3rd harmonic of its clocking frequency is only down about 4 dB from the fundamental response.
Tony Parks kb9yig@... http://www.kb9yig.com
On Tue, 2011-01-04 at 09:24 +0000, G3RIR wrote:
I have just completed a Softrock Lite II and used the band specific
components for 30m but I intend to use it on the IF of my TS2000. The IF is
10.695 MHz but an article I have found by K4DSP suggests setting the
Softrock at 10.680 MHz to avoid a "DC hump".
I have left one turn off the band-pass filter coil in the Softrock so that
the band pass moves up a little from 10.1 MHz (30m band). I have also built
a QRP2000 which has an Si570. I intend to disable the xtal oscillator in the
Softrock and inject the QRP2000 signal into the divider of the Softrock.
I understand that the way that the Softrock works "normally" for 30m is that
the xtal is on 13.5 MHz which when divided by 4 in the divider is 3.375 MHz
but this is rich in harmonics so the 3rd harmonic at 10.125 MHz is available
which of course is in the 30m band and this is injected into the mixer.
Now my question; the QRP2000 is capable of a very wide range of frequencies
and before I go "chasing my tail" which frequency should I use?
One possibility is to set it to 14.240 MHz so that dividing by 4 and
multiplying by 3 gives me 10.68 and this would be very similar to the
"basic" 30m setup. But it would seem to me better to set the QRP2000 to
42.72 MHz and this gives 10.68 from the divider and not relying on the
presence of harmonics.
One significant problem with the 14.24 MHz setting is that is well inside
the 20m band and the divided by 4 frequency of 3.56 MHz is within the 80m
band. I know that I will not use an antenna on the Softrock as it be
connected (via a buffer) to the IF of the TS2000 but I still suspect big 20m
signals to be picked up.
So what do the gurus think?
I have already built a Softrock for 80m and it is outstandingly good.
HNY to Tony Parks and to all
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