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[linrad] Time Machine....?
I subscribed to QEX after hearing about Leifs article. I found it to be well written.
I found an interesting ad in the back of the Jan/Feb 2003 issue about the Time Machine.
It is an I Q receiver with 80khz bandwidth. It is crystal controlled and can tune the popular
HF bands, so it seems the 10 Mhz version might be the logical choice to fit Leifs mixing
plan for down conversion. As well, the 28 mhz version could be built and used with a
standard 2m/10m converter.
The target use is for HF reception which aparently is less demanding then EME, as Leif
has defined it. It uses TUF-1 mixers and ordinary crystal oscillators. There is no mention of
any attempt at reducing phase noise or any mention of using an advanced sound card such
as the Delta 44. I Q detection is balanced on board. Since a 6db NF at HF is perfectly
ok and most signals tend to be similar in signal level, the TUF-1 mixers probably have
sufficient dynamic range most of the time on HF. A 20db attenuator (26db noise figure) on
the PCB is made available for setting the noise floor on HF. 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?
Incidently the Time Machine converts the sound from the sound card to the IF frequency,
so it can be used to transmit not yet thought of wide band emissions if a transverter were
used instead of a receive converter.
Here is an excerpt from the web sit:
'Whether you are using LINRAD or some other program the Time Machine makes
software radios a reality.'
Here is the Web site address.
For the price, it seems that this might be a reasonable way to go for those people wishing
to stop just short of a full blown 100db dynamic range, 95khz bandwidth system.
Perhaps a good notch filter could be substituted for the 20db attenuator to handle infrequent
local signals? Perhaps different bandwith options could be placed in line to improve strong
signal handling by forcing the undersired signal to be outside of the passband.
Since I plan to also use Linrad to do battle on the SSB calling frequency, I will have to weigh
any comprimizes carefully.
My latest thought on PC selection is to use my current Compaq Presario 5441 (475Mhz PIII),
strictly for Linrad and find a good bargan 1.7 gig PC to run Win98SE. My 475 Mhz PC today
is still fast enough, but in 2 years time, perhaps it wont be. Hmmm. Anything but an E-
73, Jim Shaffer, WB9UWA.