RE: [linrad] Tuning RX2500

[Leif Asbrink <leif.asbrink@xxxxxxxxxxxxxxxxxxxx]

Hello Stan,

> I have had success! I can see and hear test signals applied to the RX2500.
> 
> 1.) Where do I begin tuning. I see lots of images in the center of the 
> display?
What to do depends on what you want. If you want to listen at 2.5 MHz
you just have to run the calibration procedures. You can also skip
them and accept the image spur and loss of the smart blanker.

> 2.) Do I need to begin with the "linrad support: Testing and tuning the 
> RX2500" or has that already been done at Antennspecialisten?
No. All units are carefully tuned. I have tuned the first batch 
of 25 units myself to verify the design and tuning procedures.
There is no guarantee there will be a continued production, it
depends on what time it takes to sell those 25 units.

> 3.) I must be not setting the Delta44 correctly It is set for +4 
> and a signal 
> of -20 makes the noise floor go crazy.

Look at the "linrad support: Testing and tuning the RX2500"
Table 1 at the bottom of the page. 
http://antennspecialisten.se/~sm5bsz/linuxdsp/rxiq/test.htm

For a -30 dBm signal the margin to saturation should be 17.5 dB.
It means the Delta44 will go crazy for an input level of -22.5 dBm.

The noise floor should be 148 dB/Hz below the level you see
with a near saturating signal. This is for a modified Delta44.
In the original shape the Delta44 noise floor should be in the
range -143 to -145dBc/Hz.

You can set the baseband filter to 1 kHz rectangular and use 
the S-meter. The reading on the signal should be 118 dB above
the reading you get without any signal. (or 113 to 115 with
an unmodified Delta44 if you avoid the spurs the unmodified 
board has)


73

Leif / SM5BSZ




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