[linrad] Linrad Experience

["w3sz" <w3sz@xxxxxxxxxxxxxxx]

Hello, All!

Following up on Joe K1JT's request for notes on people's experiences with
Linrad, this is a brief note of my listening experiences with Linrad at
W3SZ.

For those of you who have been doing Linrad for a long time who have read my
posts before, there is nothing new here, so feel free to delete this
for-you-unnecessary bandwidth.  I haven't posted much in quite some time
[given the excellent quality of the posts you guys are making, I really
couldn't add anything worthwhile from a technical standpoint; but a
description of my experiences may be helpful to those who haven't read my
by-now-moldy posts from the distant past].

I started using Linrad [before it was called Linrad] in 2001, and that year
I used it during the ARRL EME contest as my primary receiver.  It has been
my primary EME receiver ever since.

My EME station location was so noise-filled that little EME was audible with
conventional receivers even with their noise blankers and narrow filters.  I
could hear W5UN and KB8RQ and that was about it, even with 4 x 2xmp20 array
and 0.2 dB NF preamps on the tower.

With DSP-Blaster and its noise reduction, I could pull quite a few more
signals out of the noise, but it was still tough.

The other software solutions that were [and still are] available were not
really very helpful.  See

http://www.qsl.net/w3sz/w3szdspnew.htm and

http://www.qsl.net/w3sz/linrademe2001.htm

for a general discussion of things I tried, and a description of my first
EME contest with Linrad, if you are interested in such things.

Linrad was like a miracle for me in my high-pulse-noise environment.  Leif's
software noise blanker did an unbelieveable job of removing the noise at my
receive station, and I have found ever since that when a two way qso doesn't
occur now, it is nearly always now THE OTHER GUY who can't hear me, even
though I am running 1500 Watts out to 4 m2 2mxp20's.  Most of my time during
EME contests, after I have worked the first layer, is spent answering very
Q5 [on Linrad] stations who only seem able to send 'QRZ' in response to my
calls.  Note that you must CALIBRATE Linrad to make full use of both the
'smart' and 'dumb' noise blankers.  The use of both is necessary for the
best results, but even the use of the 'dumb' noise blanker alone [that can
be done without calibration] produces very good results.  I needed both
here.  Leif's pages show just how to calibrate Linrad.

So I have been very very happy with Linrad.

It has been implemented here from the first with dual polarity.  At first I
had only a moderately wideband system, allowing me to see 30-40 KHz of
spectrum.  For a couple of years or so [I think] I have had wideband
capability with about 90 MHz of bandwidth.

The front end is homebrew, with two parallel channels using TUF-1H mixers.
I have used PTS synthesizers as the LO's, as they have good phase noise for
a non-crystal source, and they are frequency agile and I can control their
frequencies from within Linrad via a patch that was added to the Linrad
program [see http://www.qsl.net/w3sz/lin2ft.htm ] .  This patch also
controls from within Linrad the frequency of my FT1000 MP, which is used as
the transmit section of the Linrad Transceiver here.  Just a keystroke
within Linrad sets the FT1000 to the Linrad receive frequency.

Initially I mixed 144 MHz down to 40 MHz and then to baseband.

When the RX2500 became available I mixed down from 144 MHz to 2.5 MHz and
used it.

Now I have just gotten around to installing the RX10700 and the RX70 and I
mix down to 70 MHz.  When the RX144 becomes available, I will get rid of my
trusty, simple, old front end and use it and all of my old hardware will
then be out of the system.

I have never used any commercial transverter / IF combination that has come
close to Linrad and my simple homebrew hardware in my particular
environment.

For me the advantages of Linrad have been:

1.  The noise blanker

2.  Automatic received polarization angle control that follows the angle of
the incoming signal

3.  The wideband waterfall that lets me see the whole useful cw eme band

4.  The graphically controlled filters

5.  The AFC that keeps the signal in the very narrow [usually 20-25 Hz]
filter in spite of [the other guy's] drift

I have also played with Linrad on HF, and for fun used it in the Frequency
Measuring Test the first year it was resurrected by the ARRL.  It of course
did superbly, as I had all the oscillators GPS locked.  See
http://www.qsl.net/w3sz/arrlfmt.htm
For that test I used 'The Time Machine" as my front end.

I have also played with Linrad and my homebrew hardware as the 'IF rig' for
2304 MHz and up, but haven't done any serious investigations there yet.

My Linrad computer software setup is pretty much as I detailed long ago on
Rein's pages.  I use RedHat and never had any major software issues in any
respect using it and the OSS drivers.  Those minor problems I had Leif
helped me thru.  He has always been extremely instructive and patient, and I
view him as an extraordinary 'natural resource' for us.

There may be some other tidbits on http://www.qsl.net/w3sz/start.htm that
some will find interesting or useful.

For me Linrad has meant the difference between being able to do a reasonable
amount of EME from a noisy QTH, and not being able to do it at all.

For all of this I thank Leif greatly.

I hope the above has been of some interest and help.

If it was boring and just a rehash too soon after my last post, please let
me know [privately  ;)  ].

And now to get back to getting that new USB printer working with Redhat 8.0
;)

73,

Roger Rehr
W3SZ




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