开云体育

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 ...

--- In softrock40@..., KD5NWA <KD5NWA@c...> wrote:

What I would need to know what is the maximum gain that the software
would use while listening to weak signals.

I think it is settable in the agc section of the setup screen.

73 de Phil N8VB

Thanks for the offer, it would be nice to compare.

I'm not going around buying sound cards for the fun of it, I own several sound cards (most free) and I would like to know how well they do in my setup. I bought the Delta-44 because that one is the card that is supposed to have really good qualities and can be used for both receive and transmit, which I intend to experiment with. I have the following cards;

5 SB1024I Pci 24 bits
4 SB Live Pci 16 bits
2 SB MP+ USB 16 bits
1 SB Live 24 Pci 24 bits
1 SB Live 24 USB 24 bits
1 SB Audigy 2 ZS Pci 24 bits
1 Delta-44 Pci 24 bits, on it's way
1 CHAINTECH AV-710 Pci 16/24 bits, just got it today.
1 iMic USB 16 bits? it's on my Mac but it can move
1 Philipps 7:1 Pci 24 bits, took me forever to find the right drivers.
1 Weirdo Brand Pci 32 bits 192KHz claims 129 dB range, eats CPU cycles like there is no tomorrow, if I can find the darn thing, it's in a box somewhere.
Various built in sound cards, most are AC97 based 20 bits

I'm sure if I look around in the garage I can find some additional models packed in boxes, but this gives you an idea.

The Delta-44 is going in the main Dell PC(2) on my workbench next to my radios, but I would like to play with SDR on the PC's I have in the den(4), and in the living room(2). I have a lot of PC's, that is not counting two MAC', nor my son's PC's(3). No! I don't have them all turned on at the same time, usually no more than three at a time.

Crazy huh?


At 04:25 PM 10/27/2005, you wrote:

If you are interested, Gerald may be willing to share info we have here
on several sound cards. I'm sure he has MDS numbers for at least a few
of them.

For what it's worth, you could probably just measure the MDS of the
SDR-1000 and use those numbers combined with MDS figures of soundcards
that are well documented. That might keep you from having to buying one
of each card for your tests.

Eric

-----Original Message-----
From: KD5NWA [mailto:kd5nwa@...]
Sent: Thursday, October 27, 2005 4:17 PM
To: eric@...
Subject: RE: [Flexradio] Turning off the AGC

That is precisely what I'm trying to measure, the MSD of the entire
system, when you listen to a signal you are using the entire system,
front end, sound card, PC and all. If I was designing a new front
end, I would be interested in the figures for it alone, but that is
for another day.

I can then compare the readings of various sound cards and see which
one makes the system as a whole behaves the best. I have a Delta-44
coming and hopefully will be here by Tuesday, hopefully it will get
the best numbers since it's the most expensive.

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 ...

I don't want any of my energy going outside the filter or coming in from outside. I would swap 1,2 and always do. It probably makes a tenth dB difference altogether but I don't want even that error.

Bob
N4HY



Gerald Youngblood wrote:

--
Laziness is the number one inspiration for ingenuity. Guilty as charged!

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@...

--
No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.1.362 / Virus Database: 267.12.5/150 - Release Date: 10/27/2005

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 ...