Use of a Sinadder 3 and sinad measurement

[Lkaskel]

Good Day Everyone,
So, I have now a Sinadder 3 that was calibrated in 2020. I have a few questions on aligning a receiver with it. I understand the fundamental operations of sending a 1KHz tone through the receiver and the notch filter is allowing that signal through "listening for" or measuring that tone. Sinad would be the comparison of the noise outside of the 1KHz tone and the tone itself. The lower the noise the quieter the receive. We make adjustments to the radio to maximize that reading/signal. While in the Sinad mode as you make those adjustments there is a scenario where you are lowering the noise and distortion but you are also taking the radio out of alignment therefore lowering the reading as well. How would you suggest or explain the logic of making the adjustment for the lowest sinad but maximizing the receive strength? The only factor that I can see with this device is the audio tone that you can hear. If the volume of the tone begins to decrease then the radio alignment is getting worse.

Any thoughts here?

 

[Pez]

They are a really nice meter. Have you seen this video?



It might help with the question and some fundamentals on it's operation. The short answer is that is the signal to noise and distortion components are constantly working together to give you the SINAD readings, so if you made any of these things "worse" the meter should reflect this in its reading.

Another point, is that you need to ensure you have enough RX audio drive from the radio into the meter (at all times) to allow it to see the "noise" when a signal is reduced, or the distortion is increased, etc. If you don't give it enough audio level to work with, this can also impact its readings.

 

[brandon7861]

Been quietly reading the mail for a while, but this thread interests me and I too would like to learn more about it.

 

[Lkaskel]

They are a really nice meter. Have you seen this video?



It might help with the question and some fundamentals on it's operation. The short answer is that is the signal to noise and distortion components are constantly working together to give you the SINAD readings, so if you made any of these things "worse" the meter should reflect this in its reading.

Another point, is that you need to ensure you have enough RX audio drive from the radio into the meter (at all times) to allow it to see the "noise" when a signal is reduced, or the distortion is increased, etc. If you don't give it enough audio level to work with, this can also impact its readings.

Hi Pez,
I did watch his video. He is VERY good at explaining things and seems like a good guy!!! When I used my meter, this is the scenario. I was aligning a mint Cobra 29 XLR that is100% stock except for a re-cap. The alignment guide states to hook a VTVM to the speaker and make your adjustments for max reading. In other words, for the loudest not for sinad. So, I used the Sinadder 3 in AC Volts mode and aligned the receive (per the alignment guide) for a max reading at 1KHz tone @ -100dB on 27.185 MHz hoping to avoid the RF Gain circuit kicking in and affecting the reading. I then switched the meter to sinad. It was reading about -8 to -9 and I knew that the desired reading would be -12 and lower (towards -20). At that point I have 2 measurements happening with this meter. The sinad meter measurement and the sound (volume) of the 1KHz tone and static coming from the speaker in the meter. As I tried to tweak the coils for a better sinad, both the static and the 1KHz tone volumes were dropping as well as the sinad measurement. That is unlike what the video shows. It was at that point that I realized that I might be de-tuning the radio instead of making the alignment better. That is where the question comes from. As I was de-tuning it the sinad was dropping to -12 towards -20 but that is because the overall receive sensitivity was dropping not just the sinad. How do I know that I am actually making the receive better and not de-tuning it? I was thinking that I would see the sinad measurement drop but hear the 1KHz tone stay at the same level. Am I wrong here?

Thanks everyone for reading through these posts and giving your input!!! It is things like this that should seem easy to me but the truth is, I just can't seem to get it.....

As a reference to the overall question, I attached a pic of my signal generator and frequency counter as well as 2 different alignment guides that I used.

 

[SuperLid]

Good Day Everyone,
So, I have now a Sinadder 3 that was calibrated in 2020. I have a few questions on aligning a receiver with it. I understand the fundamental operations of sending a 1KHz tone through the receiver and the notch filter is allowing that signal through "listening for" or measuring that tone. Sinad would be the comparison of the noise outside of the 1KHz tone and the tone itself. The lower the noise the quieter the receive. We make adjustments to the radio to maximize that reading/signal. While in the Sinad mode as you make those adjustments there is a scenario where you are lowering the noise and distortion but you are also taking the radio out of alignment therefore lowering the reading as well. How would you suggest or explain the logic of making the adjustment for the lowest sinad but maximizing the receive strength? The only factor that I can see with this device is the audio tone that you can hear. If the volume of the tone begins to decrease then the radio alignment is getting worse.

Any thoughts here?

A few things to add here. The audio level, either too high or too low, can measure an inaccurate reading. Also, the load must be 8 ohms. If you are using a speaker, check the impedance. AF Gen, AM mod should be 30%, FM Deviation 4.5 KHz (15 KHz BW) @ 1000 Hz.

SL

 

[staticcity2]

A few things to add here. The audio level, either too high or too low, can measure an inaccurate reading. Also, the load must be 8 ohms. If you are using a speaker, check the impedance. AF Gen, AM mod should be 30%, FM Deviation 4.5 KHz (15 KHz BW) @ 1000 Hz.

SL

I would recap the sinader check the power supply in it and realign the sinader and try again. In some cases lower the receiver gain for better sinad is ok. Example would be if the radio has a lot of background noise. If the signal is weak your not going to hear it through the noise floor any. Try and find a happy medium. You can also lower the generator output to say -110db or even lower and retune the radio again both ways, best sinad or best audio volts and see if it's any better or worse.

Joe
BBT RADIO
AKA MTNMAN
UPSTATE NY

 

[brandon7861]

I hesitated sharing my thoughts on this yesterday because I don't know much about it, but here it goes.

FM does not change amplitude. Therefore, when the signal is near the noise floor, the noise begins to cause phase errors in the entirety of the signal. AM varies in amplitude, so when the voice peaks, the signal climbs out of that noise. And when that signal is in the noise, it is a sum of a smaller noise voltage on a big signal, rather than the continuous mixing of the two at nearly constant levels in the case of FM. I think that is why people suggest 30% modulation when using a sinad meter in AM, to keep the amplitude variation small.

The BFPs in AM radios will pass less signal and less noise simultaneously when it is detuned with respect to the next filter down the line, so that might explain your observation.

Since FM signals don't vary in amplitude, as they approach the noise floor, there is a point when the noise degrades the entirety of the signal, meaning there is a fairly specific signal level that the limiter and detector needs to see to reproduce the information sent. With a mode that varies in amplitude, the effects the noise has on the signal is less apparent with a less distinct transition into the weeds because it is varying in strength with respect to the average noise voltage.

 

[Lkaskel]

A few things to add here. The audio level, either too high or too low, can measure an inaccurate reading. Also, the load must be 8 ohms. If you are using a speaker, check the impedance. AF Gen, AM mod should be 30%, FM Deviation 4.5 KHz (15 KHz BW) @ 1000 Hz.

SL

Thx SuperLid!!
Regarding the 8 ohm load, I made a breakout box with an 8 ohm 25 watt resistor. I use a cable with an 1/8" mono jack on each end, plug one end into the ext spkr jack on the radio and the other into the breakout box. The sinadder leads connect onto jacks on the breakout box. That way I get a consistant 8 ohm load.