noise to signal ratio

[longhaireddwb]

I've been thru this over and over and over. I bet I've turned the RX with the sinad program 50+ times and this is all I can get out of it.

I'm about done!

I might just need to send this radio to someone for this as it is obvious that I just don't understand something. I've adjusted the generator and checked to see what tone it is putting out and have it set for the lowest amount of signal I can put out to make the sinad program work. (-99dbm) if I went as low as what radioman said then the program wouldn't work so I had to come up some.

I'll try to tune it another couple times but that's about the best I can get. It sure don't look anything like what Robb posted up!:angry:

BTW, I don't think I have ever said what radio this is.
Mirage 44 (signal final CB)

 

[Robb]

I can see that on the lower half of the SINAD's GUI that you have too much volume going into it DWB.

What radio are you using it on?

Your sig/gen may also be sending an off freq signal; did you check it with a freq counter?

 

[longhaireddwb]

Mirage 44
11 meter radio Robb. I had to put the volume of the radio at half just to make the sinad hear the signal.

What opinion or recommendations do you have?

 

[Robb]

If you can't hold a steady freq out of your sig/gen - testing it with a freq counter; then it won't cut the mustard . . .

 

[Robb]

Please notice the bottom half of the graphic user interface - where it says 'Spectrum'.

Now please notice the narrow, tall green line at 1khz; that is the signal w/o any distortion around it. That is because I turned down the volume on the radio low enough to get the noise around it to settle down. Experiment until you get a similar picture. If you can't; then either you are doing something wrong or your sig/gen is just too unstable or even generating too much internal noise to make the SINAD program work as designed.

 

[RADIOOMAN]

Before you give up please verify the frequency of the 1 kc tone.
If it is off by even a few cycles the SINAD meter will not work properly.
And also, the advice ROBB is giving you is spot on; I am on the same page with what ROBB is saying.

 

[G0HZU]

Before you give up please verify the frequency of the 1 kc tone.

I think the basic idea (for AM) is that you let the SINAD program generate the 1kHz modulation tone and feed this (from the soundcard) to the signal generator as external AM modulation.

That way the modulation tone should always be on the same frequency as the notch filter in the DSP in the computer.

 

[RADIOOMAN]

I think the basic idea (for AM) is that you let the SINAD program generate the 1kHz modulation tone and feed this (from the soundcard) to the signal generator as external AM modulation.

That way the modulation tone should always be on the same frequency as the notch filter in the DSP in the computer.

I just looked at the operation manual for the software and you are absolutley correct.
I guess I was assuming that you would use the 1 kc modulation tone as provided by the signal generator.
I had downloaded the software but have not let it install yet; I am waiting to find out how long the trial period is before I fool with it.

 

[Robb]

The SINAD picture above was receiving a signal from my Hp sig/gen through the radio under test.
Didn't need to use the reference sig from the SINAD program.

Those E200D B&K Precision sig/gen can be stable and have relatively low noise output. Owned one of them for a total of 2 days before I got my money back; it had a known issue with Q-9 and just didn't want to deal with it. It also uses a 400hz audio signal for the reference freq; not 1khz! But it can be modified to do 1khz. That may well be your problem. If so; then you may need to use the SINAD program's 1khz generator into your B&K - or use the 1khz mod below - to get you on the right road.

Be SURE to test the output FREQ (eg. 27.185mHz) of your gen to be sure that it is stable to +/-200hz on AM.

If there is a problem with yours - DWB, then check out all of these links:

Main page:

E-200D Info Page

VERY useful stuff to consider if you are going to keep/use this unit:

http://www.freeinfostuff.com/E200D/e-200d_bulletin.pdf

http://www.freeinfostuff.com/E200D/e-200d_attenuator.pdf

E-200D 1KHz Modulation

E-200D BNC Output

http://www.freeinfostuff.com/E200D/E-200D_Frequency_Counter.htm

Service Manual:

http://www.freeinfostuff.com/E200D/E-200D_Service.pdf

http://www.freeinfostuff.com/E200D/e-200d_alignment.pdf

 

[G0HZU]

I tried out the Commtek SW a year or so ago ((V1.1?) and I still have it installed on this PC but it expired after a couple of weeks.

It did work reasonably well but on all the PCs I tried it on it did seem a bit flakey in operation at times.

Maybe the later version is better or maybe I didn't spend enough time setting up the soundcard.

From memory it also didn't allow the audio filter to be changed or deselected as an option. At my place of work we once considered buying this software but I think we are in the process of upgrading a few 2023/2024 signal generators to fit the SINAD module as this allows the selection of several audio bandpass filter options in the DSP, eg CMES, CCITT or flat response.

 

[G0HZU]

The SINAD picture above was receiving a signal from my Hp sig/gen through the radio under test.
Didn't need to use the reference sig from the SINAD program.

Yes, some generators can generate the 1kHz quite accurately.

However, I have a couple of old Marconi 2019/A generators here and they weren't accurate enough when generating a 1kHz AF tone and this caused issues.

I had better results with external modulation or when using a Marconi 2024.

I think the only reliable way with the BK generator will be via external modulation unless the modulation was derived from dividing down a 10MHz crystal oscillator module to 1kHz using a couple of 74HC390 chips (and a suitable lowpass filter to remove harmonics) and fitting this inside the generator on a little PCB.

 

[Robb]

I think the only reliable way with the BK generator will be via external modulation unless the modulation was derived from dividing down a 10MHz crystal oscillator module to 1kHz using a couple of 74HC390 chips (and a suitable lowpass filter to remove harmonics) and fitting this inside the generator on a little PCB.

Think the B&K uses a tunable Colpitts osc - IIRC . . .

 

[longhaireddwb]

Been out for house duties. You know how it is when your gone all the time. As far as the tone, I listened to the tone the sinad program put out and listened to the one my generator puts out and they are really close to the same. So when I was injecting the tone into the radio then to the computer I adjusted the computer program a bit to the point that the meter on the program was at its highest reading. You will note the tone is 930hz I think on the picture.

I don't think I can put a tone into this generator. I have seen a way to do it just yet although there is a couple ports on the front that are marked as EXT MOD. I'll have to go back to the manual on this. I'll do that in just a minute.

As far as the volume, I will give it another try and see if I can turn the volume down some more but then I will need to make the signal stronger so that the program can see it in the green on the meter.

I hope this makes sense. Thanks for all the help guys. I got another day to give it a try before I go away for another week then when I get back the free time on the program will be over. I'd like to buy it but not if I cant get things to work right.

 

[RADIOOMAN]

Been out for house duties. You know how it is when your gone all the time. As far as the tone, I listened to the tone the sinad program put out and listened to the one my generator puts out and they are really close to the same. So when I was injecting the tone into the radio then to the computer I adjusted the computer program a bit to the point that the meter on the program was at its highest reading. You will note the tone is 930hz I think on the picture.

I don't think I can put a tone into this generator. I have seen a way to do it just yet although there is a couple ports on the front that are marked as EXT MOD. I'll have to go back to the manual on this. I'll do that in just a minute.

As far as the volume, I will give it another try and see if I can turn the volume down some more but then I will need to make the signal stronger so that the program can see it in the green on the meter.

I hope this makes sense. Thanks for all the help guys. I got another day to give it a try before I go away for another week then when I get back the free time on the program will be over. I'd like to buy it but not if I cant get things to work right.

I think you can inject a tone into the generator; "EXT" is for external modulation.
Put the tone from the output of the computer sound card into the EXT MOD Jacks on the generator and set the switch to "EXT" and then set the modulation percentage level with the "MOD LEVEL" control, and there you have it.
(approximately 1v rms for 50% modulation level)
(me thinks someone has not read the operators manual for their signal generator)

 

[longhaireddwb]

Your right. I didn't read it all. Just read what I thought I needed too. :redface:

I did this just a few minutes ago. Put the 1Khz signal from the program into the generator. Re adjusted everything and did this with the volume as low as I could make it on the radio. I had to go with -90dbm to get the sinad program to read enough to adjust. And still the spectrum is all over the place. This is picture #1.

I then turned the volume all the way down so no signal was making it to the program and I still had noise all over the spectrum. This is picture #2.

I dont understand why this is. I must have a noisy computer is all I can think of.