Thanks, should not steps 1 and 2 be switched for maximum accuracy?
At 05:36 PM 10/27/2005, you wrote:
Measuring MDS is a simple procedure on the SDR-1000 with PowerSDR software.
The software calculates the RMS noise power within the 3dB bandwidth of the
filter so you can read it directly on the meter when the radio is connected
to a dummy load. You do have to accurately calibrate the radio with a known
signal source and the image rejection must be properly adjusted.
So do the following:
1) Calibrate the radio with a signal generator
2) Null the image
3) Set the filter bandwidth to 500 Hz
4) Attach a dummy load
5) Set the RX meter to Signal Avg
6) Read the meter and that is your MDS
There is NO AGC in these measurements because they are measured before AGC.
73,
Gerald
-----Original Message-----
From: FlexRadio-bounces@...
[mailto:FlexRadio-bounces@...] On Behalf Of KD5NWA
Sent: Thursday, October 27, 2005 3:20 PM
To: eric@...
Cc: softrock40@...; 'Flex Radio'
Subject: Re: [Flexradio] Turning off the AGC
I'm not trying to measure the noise floor, I'm trying to
measure the lowest discernible signal "MSD"
A voltage reading on a meter by itself means nothing since
it's not being compared to a known quantity.
The procedure is;
Run the radio at maximum gain with a 500 Hz filter Measure
the Audio output with a RMS meter, and a 1 micro-volt signal
in the pass-band, set for maximum audio output.
Remove the 1 microvolt signal and measure the Audio output
with the meter Do some simple math with the two figures and
you come up with MSD rating of the radio.
But for this to be accurate the radio must be running at
maximum gain, not minimum gain. Once you have that figure you
can figure out the noise floor in dB.
What I would need to know what is the maximum gain that the
software would use while listening to weak signals.
At 02:35 PM 10/27/2005, Eric Wachsmann - FlexRadio wrote:
Cecil,
If you are trying to measure the noise floor of the unit,
the easiest
thing to do is to just connect a dummy load, open the
software and put
it in 500Hz BW. Look at the multimeter (might help to put it in Sig
Avg. mode). This is the effective noise floor of the unit (assuming
that it is higher than the sound card noise floor).
To answer your question more specifically, turning the AGC
to Fixed and
setting the Fixed Gain on the Setup Form to 0dB will effectively set
the processed audio to have no gain, variable or otherwise. The
spectrum and multimeter are both before the AGC however.
Eric Wachsmann
FlexRadio Systems
-----Original Message-----
From: FlexRadio-bounces@...
[<mailto:FlexRadio-bounces@flex->mailto:FlexRadio-bounces@flex-
radio.biz] On Behalf Of KD5NWA
Sent: Thursday, October 27, 2005 12:50 PM
To: Flex Radio
Cc: softrock40@...
Subject: [Flexradio] Turning off the AGC
I want to try to measure the noise floor of my SR-40
setup and will
need to have the AGC completely turned off.
If I turn off the AGC of the Flex software will it really
completely
turn off all forms of variable gain?
Cecil Bayona
KD5NWA
www.qrpradio.com
I fail to see why doing the same thing over and over and
getting the
same results every time is insanity: I've almost proved it isn't;
only a few more tests now and I'm sure results will
differ this time
...
_______________________________________________
FlexRadio mailing list
FlexRadio@...
Cecil Bayona
KD5NWA
www.qrpradio.com
I fail to see why doing the same thing over and over and
getting the same results every time is insanity: I've almost
proved it isn't; only a few more tests now and I'm sure
results will differ this time ...
_______________________________________________
FlexRadio mailing list
FlexRadio@...
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Cecil Bayona
KD5NWA
www.qrpradio.com
I fail to see why doing the same thing over and over and getting the same results every time is insanity: I've almost proved it isn't; only a few more tests now and I'm sure results will differ this time ...
