Linrad timf output to MAP65

[Conrad PA5Y]

Hello all.

I know that Linrad timf2 output is 16bit.

There is some information here:
https://www.sm5bsz.com/lir/map65/map65.htm

There is mention of 16bit MMX instructions and how to set the digital levels correctly. I assume that MMX is no longer relevant? We have lots of excess horsepower these days. However I the statement that 16bit data does not allow much dynamic range is still true and so setting digital levels correctly is still important for MAP65.

As there are still lots of users of Linrad with MAP65 it would be good if this page could be revised.

I tried some of the tests using the internal generator using F11 but as soon as I use it the screen goes blank and the level goes to zero. Is this SETLIM? I tried using F8 to reduce the amplitude of the internal generator but still I have a blank screen. Does this function still work properly?

Regards

Conrad PA5Y

[Earl Shaffer]

Hi Conrad

This looks like a good exercise to maximize dynamic range. When my LNA is connected to its dummy load at its input, my Map65 shows 20db. Perhaps this wastes dynamic range. I get about 3 or 4 when the IQ+ is muted. A long standing problem is observed here and perhaps proper settings would solve this.

I monitor noise from my neighborhood so my array is often pointed at the strongest noise source when I turn on the preamp. I leave the noise blanker on. This noise source is usually something like +30db above the level that my dummy load presents to my LNA and of course the noise level from the dummy load is already elevated by the LNA by some 15 or 20 db. That's a big increase in noise when I turn on the LNA and the Linrad noise blanker will always show 99% when I turn on the LNA. I have to cycle through turning both noise blankers off then back on to restore normal operation.  I have not been able to adjust the limiter in a way that solves the problem. Perhaps a better gain distribution in Linrad would help.  If I happen to be monitoring a noise level that is more like 15db over the level of the dummy load, then the problem usually does not show up, so it is a level issue. When the noise blanker gets stuck in the 99% mode, there is no reception and removing the noise source does not fix it. Only turning the blankers off (and back on) fixes it.

I use default settings if I recall correctly but I did reset first FFT amplitude to get that 20 db noise floor reading on Map65. That's a convenient level to monitor the noise floor of the array. In that case a +25db reading means I have 5db of antenna array noise.

There is a lot of text in that link and frankly I easily get lost in it. It would really take some study and hands on experience to go through it. Lately leif has been doing some videos and I have found them helpful. At times he may make assumptions that we know more than we do, but the videos are good. I would like to see a video done on proper level setup for Map65 and making the noise blanker work properly to avoid the glitch that I see.

WB9UWA.

--
There is an excellent Linrad User Guide by Gaetan, ON4KHG, at:
http://w3sz.com/Linrad%20Installation%20&%20Configuration%20User%20Guide%20-%20V1-0.pdf
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Earl Shaffer,  WB9UWA

 

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[Leif Asbrink]

The timf2 output from Linrad comes as 16 bit integers or
as 32 bit float depending on what version you have selected for
the backwards first fft. Only when MMX routines are selected
timf2 comes with 16 bit. MAP65 knows the difference:-)

73

Leif