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RE: Time Machine....?
- Subject: RE: Time Machine....?
- Date: Mon, 6 Jan 2003 14:56:40 +0100
> > I suspect that when a strong
> >local signal is present and a very weak EME signal is desired in
> the same passband, the
> >Time Machine would not hold a candle to the 2.5 mhz I Q detector
> designed by Leif. The
> >assembled price is $170 and kit form is $135, making it a
> tempting project for a rural
> >EMEer or perhaps an Urban EMEer such as myself that does not
> normally experience
> >local signals at the low end any closer then 30 km away (10db
> over S9) and is somewhat
> >pocket book challenged. The big question then becomes, what is
> the dynamic range of the
> >Time Machine? 80 db perhaps?
Would be interesting to know. I am sure it is good enough for
the typical EME operator but not for 144MHz terrestrial work
when beaming into each others main lobes may cause much
stronger signals compared to an elevated EME antenna.
> I think that the dynamic range of your sound card and Linrad will likely
> be the determining factor rather than TTM hardware.
I do not think so. Linrad is certainly not the limiting factor
and I think even a low cost soundcard will be better than the
Time Machine. The problem is second order IM, a strong signal
near the center frequency. As long as there is no strong
signal within 50% of the passband the overtones come outside
the passband and then the Time Machine should be very good.
> The TUF-1 is not the limiting factor.
I think it is. (for second order IM)
> And if you are concerned about that, and have enough LO power,
> you can substitute a TUF-1H.
May be not so easy because you will also need a much better
LO. Ths schottky mixer also works as an AM detector so any
noise on the LO will reach the output as audio noise.
The Schottky mixer is also an FM detector so limiting the
amplitude to get rid of AM will not eliminate the problem.
The Time Machine is an easy way of getting started. I do
not know if calibration will work properly because of the
rather wide notch at the center frequency. (High pass
filters are used to avoid mains frequency interference.)
I think it will be ok but it has to be verified.
Leif / SM5BSZ