[linrad] Linrad and the EME contest

[w3sz <w3sz@xxxxxxxxxxx>]

Hello, All!

This is just a brief report on my experience with Linrad in the EME  
contest this past weekend.  I have used Linrad each year beginning in 2000  
for the annual ARRL EME contest.  For the last several years it was my  
primary receiver.  But this weekend, the first leg of the 2004 ARRL EME  
Contest, was the first time that I used it for EME with the  
Antennspecialisten Linrad hardware.  Like last year, I did not even have a  
conventional receiver online.  Linrad was it and nothing else was needed.

I was very pleased and impressed.  I worked only CW for the contest, but I  
did take some time out to go up above 144.100 and listen to some EME JT65b  
using Linrad and the Antennspecialisten hardware as the front end for  
WSJT.  What were the advantages of using Linrad in this manner?  [1] I  
could immediately see any JT65b station that came on the air over a 96 KHz  
frequency span, [2] I could take advantage of Linrad's noise reduction [3]  
the Linrad waterfall was  superior to Spectran's in my hands for seeing  
the stations [4] using Linrad's click and point frequency control, I was  
able to set, immediately and with no trouble, the receive frequency so  
that there was zero frequency offset for WSJT to deal with [5] the  
receiver seemed very sensitive and I had no dynamic range problems.

On cw, I found [as before] that quite a number of stations that I heard  
very clearly with Linrad replied with 'QRZ' for a long time [sometimes  
forever] to my calls.  That tells me that Linrad with the  
Antennspecialisten hardware hears very well.  I also found that when I  
called CQ, I was able to work the station calling me every time.  So I  
believe I heard everyone who called me, but not everyone whom I heard  
clearly was able to copy me.  I was running 1500 watts, and my 2 x 2  
2mxp32 array has a theorerical gain of 21.8 dBd, so I had a reasonable  
ERP.  I could see and hear my own echoes with no problem.  Using Linrad, I  
was clearly 'transmitter limited' in terms of making contacts.  This is  
where I want to be.

I kept the 'smart' and 'dumb' noise blankers on [manual] nearly the whole  
time, and I was not bothered by noise.  When I turned them off I was  
reminded that when my rotors are rotating they generate a lot of noise,  
totally obliterating the EME signals.  Their noise had been totally  
eliminated by the noise blankersa and as I was never looking at the  
wideband spectrum while operating the rotors, I had been oblivious to the  
noise.

My cw parameters gave me a 5.3 second receive delay, which was not a  
problem for me.  I learned to watch the wideband spectrum as 'the end of  
the minute' approached, and to start transmitting when the spectral peak  
of the station I was working disappeared.  These parameters were:

First FFT bandwidth (Hz) [100]
First FFT window (power of sin) [3]
First forward FFT version [5]
First FFT storage time (s) [20]
First FFT amplitude [1000]
Enable second FFT [1]
First backward FFT version [1]
Sellim maxlevel [6000]
First backward FFT att. N [6]
Second FFT bandwidth factor in powers of 2 [5]
Second FFT window (power of sin) [2]
Second forward FFT version [2]
Second forward FFT att. N [10]
Second FFT storage time (s) [20]
Enable AFC/SPUR/DECODE [1]
AFC lock range Hz [150]
AFC max drift Hz/minute [100]
Enable Morse decoding [0]
Max no of spurs to cancel [0]
Spur timeconstant (0.1sek) [5]
First mixer bandwidth reduction in powers of 2 [4]
First mixer no of channels [1]
Baseband storage time (s) [100]
Output delay margin (0.1sek) [5]
Output sampling speed (Hz) [6000]
Default output mode [1]
Audio expander exponent [3]
A/D speed [96000]
Check [1110107]



My parameters for JT65b [ssb mode] were:

First FFT bandwidth (Hz) [83]
First FFT window (power of sin) [2]
First forward FFT version [5]
First FFT storage time (s) [10]
First FFT amplitude [1000]
Enable second FFT [1]
First backward FFT version [1]
Sellim maxlevel [6000]
First backward FFT att. N [6]
Second FFT bandwidth factor in powers of 2 [2]
Second FFT window (power of sin) [2]
Second forward FFT version [2]
Second forward FFT att. N [7]
Second FFT storage time (s) [10]
Enable AFC/SPUR/DECODE [1]
AFC lock range Hz [150]
AFC max drift Hz/minute [100]
Enable Morse decoding [0]
Max no of spurs to cancel [100]
Spur timeconstant (0.1sek) [5]
First mixer bandwidth reduction in powers of 2 [4]
First mixer no of channels [1]
Baseband storage time (s) [10]
Output delay margin (0.1sek) [5]
Output sampling speed (Hz) [10000]
Default output mode [1]
Audio expander exponent [3]
A/D speed [96000]
Check [1110107]

The delay using these parameters was less than one second.

I played around with the CW parameters to get good performance with  
reasonable delay times, but I did not play around with the SSB parameters  
as I didn't need to do so.

For the second leg of the contest I am going to actually hook up a  
conventional receiver, so that I can again directly compare the Linrad  
software and hardware to the conventional receiver, much as I did in 2000  
and 2001 when using my own front end.  I am doing this out of curiosity,  
not because I need anything besides Linrad.  I will be using an SSB  
Electronics LT2S-Mk V along with either my Elecraft K2 or my FT1000MP.  If  
I get the narrow roofing filter for the MP in time, it will be the one I  
use.

I can't wait for the second leg of the contest.  The combination of the  
Linrad hardware and software made this EME contest the most enjoyable one  
I've had since my first getting on EME in 1998, and I can't wait to spend  
another EME contest weekend with the combination.

The Lin-2-1000MP add-on to make a Linrad transceiver out of my FT1000MP  
and Linrad worked fine except for those occasions when I forgot to type  
'q' to bring the MP on-frequency before transmitting.

73,

Roger Rehr
W3SZ

-- 
Roger Rehr
W3SZ
http://www.qsl.net/w3sz

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