[linrad] QEX Sept/Oct 2003

[<wb9uwa@xxxxxxxxxxx>]

Hi All,

In Leifs article in QEX, September/October 2003 issue, titled
Linrad: New Possibilities for the Communications Experimenter, Part 4,
I believe Leif is still talking about the noise blanker when he states:
"I do not know how the IC-706MKIIG compares to other receivers, but
I believe the results for the IC-706 are typical."
I have compared several VHF radios in actual use and can compare
the built in noise blanker. I have used the Kenwood TS700A, Icom
IC202, Icom IC271A, Yeasu FT736R, Yeasu FT621B, Icom 706MKII and
most recently a Yeasu FT100D. In short, the Icom 706MKII noise blanker
is the worst one I have used by far. The 706 has a high threashold
before any blanking will happen. It blanks very few line noise
sources effectively. Even when it does a good job on ignition noise,
nearby S-9 signals will completely turn it off. It also has an
annoying clicking sound on S-9 signals. This is more evident on
the AM mode. I made mine less annoying by reducing the value of the
time constant capacitor on the noise blanker AGC loop. I was
unable to make the noise blanker work properly on this rig and
Icom was not interested in improving it. It acts like there is
an unwanted feedback path in the noise blanker but I could not
isolate it. Other then the poor noise blanker, the Icom 706 series
is superior in every other way to comparibly priced radios.

All of this being said, Leifs article is well thought out and easy
to follow. It looks like Linrad should be a valuable addition to
any station even if only used to process SSB bandwidth audio. It
would be interesting to see what it could do with a wider IF filter.

I am still stumped on selecting an effective low cost PC for wide
band Linrad use. It seems there are many potential "gotchas"
to avoid but they are not well defined. There are a large number of
$250 PCs that would seem to qualify, but it is difficult to
predict which one might work. I have a Monitor, a Delta44, 
Mandrake 8.0 and $250 earmarked for the PC, but have not made 
my selection yet. Potential trouble spots seem to be built in
sound cards and built in video cards and the ability to use
external sound cards and video cards and having the ability to
turn off the internal cards if they are incompatible. Then when
external cards are needed, there is a potential problem of running
out of PCI slots. Hmmmm.... I think I would have rather dealt with
just getting a DOS machine with the right hardware for compatibility.
I have been comparing PC prices on Pricewatch.com and looking
at PCs that have no operating system. If you know of one that should
work, please let me know.

Jim Shaffer, WB9UWA EN50
4 X UWA12 (18.5DBD XPOL)
2 X GU74B by LZ2US.




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