NRG Pro 6 help

[jvok]

Looks like the same pll but with 10w pa instead of 6w and screen to set frequency instead of dip switches

[MiXiN]

the stereo encoder pilot causes deviation. should be set to 7-10%. to adjust the mpx level you will probably have to open the cover of the device.

OK, I altered the MPX input adjustment on the rear of the Pro 6 this evening, but the highest deviation I can get is 4Khz, 5%.

This setting is with no audio going into the stereo coder as you mentioned.

The mono/stereo switching is definitely working, as the stereo indicator lights up on the radio when the jumper is removed from the stereo coder - and this happens from anything from around 2.8Khz deviation onwards.

Do you know what the issue could be?

20230507_224445.jpg

[Albert H]

You could have a mismatch in the audio input, attenuating your audio (though that's unlikely - the output impedance of the stereo coder is pretty low), or the level meter on the NRG box is out of calibration.

[MiXiN]

You could have a mismatch in the audio input, attenuating your audio (though that's unlikely - the output impedance of the stereo coder is pretty low), or the level meter on the NRG box is out of calibration.

Thanks for the reply, Albert.

The MPX cable I'm using (phono to BNC) says 75 ohm impedance, but this wouldn't matter at audio frequencies & is just relevant for RF I thought. Is this right?

I did try a different NRG Pro 3 coder (I have 2 of them), and I couldn't even get that higher than 1Khz deviation - so I'm not sure what's going on with that one.

The audio sounds fine, though, considering I'm just feeding it from a CD source with no limiter, processing, etc.

Can you think of an alternative solution to setting this up correctly or am I just being picky?

[yellowbeard]

The guy who built that is a member here - he hasn't been on since April 10th mind you... I would PM him here or send him a message from his site:
https://nrgkits.co.nz/index.php/contact/
memberlist.php?mode=viewprofile&u=433

He is a good guy, and trust me - he wants that to work well for you for his own pride (and to make Sinus Trouble buy one )
If he had been on I am sure he woud have sorted it for you.

[MiXiN]

Hey Yellowbeard,

I'll send him a PM later today when I get a bit of time.

As I say, it's not the end of the world; the audio from it is fine. It just appears that it might be out of calibration.

It could even be the Pro 3 Stereo coder with insufficient output, who knows? As I already mentioned before - with one of the Pro 3 coders, I could only achieve 1Khz deviation with the MPX level maxed out, yet on the other I achieved 4Khz.

I'm not well versed on all this.

[Krakatoa]

I never trust built-in modulation indicators.
Use a real modulation meter like the Pira to find out your real levels of pilot tone, rds and peak deviation of the transmitted signal.

[nrgkits.nz]

Hi MiXiN
You've got an earlier revision of the board which requires a higher rms on the MPX input, as it was designed to be fed from a computer sound card running StereoTool which generally output a higher rms voltage. The stereo encoder you're using is likely a lot lower. To fix this, you can change R2 from 10K to 4K7 and will increase the sensitivity the MPX input. Then with only the stereocoder going in with pilot tone (no audio), adjust the pot through the back of case so you get around 6.7KHz deviation.

Also there is another change we made in the new revision of this board, R39 was changed from 330R to 470R to reduce the drive slightly to the output device. We had a couple instances where under certain conditions and customers reducing the power right down below 1W, the RD15HVF1 output device would fail after a few months of running. Output power is controlled by varying the bias voltage on the gate of the output device, and when wound right down so the output is less than 1W, this in turn results in a slightly higher peak to peak voltage measured at the gate. The gate to source maximum for the RD15HVF1 is -5v to +10v. So replacing R39 brings it back down to below 5v peak to peak. If you don't intend to run it at a very low power, then there won't be any issues.

[MiXiN]

Hi MiXiN
You've got an earlier revision of the board which requires a higher rms on the MPX input, as it was designed to be fed from a computer sound card running StereoTool which generally output a higher rms voltage. The stereo encoder you're using is likely a lot lower. To fix this, you can change R2 from 10K to 4K7 and will increase the sensitivity the MPX input. Then with only the stereocoder going in with pilot tone (no audio), adjust the pot through the back of case so you get around 6.7KHz deviation.

Also there is another change we made in the new revision of this board, R39 was changed from 330R to 470R to reduce the drive slightly to the output device. We had a couple instances where under certain conditions and customers reducing the power right down below 1W, the RD15HVF1 output device would fail after a few months of running. Output power is controlled by varying the bias voltage on the gate of the output device, and when wound right down so the output is less than 1W, this in turn results in a slightly higher peak to peak voltage measured at the gate. The gate to source maximum for the RD15HVF1 is -5v to +10v. So replacing R39 brings it back down to below 5v peak to peak. If you don't intend to run it at a very low power, then there won't be any issues.

Hello,

Many thanks for the informative reply & fast response to my message.

I'll go inside & have a look at R2. If it's a 0805 size or larger, I'll be OK swapping it out, but if it's a 0603 it might be a bit of a challenge unless there's good space around it - so I'll leave it. Those 0603 parts are tiny.

Is running it at its current maximum of 4Khz going to be of any detriment, or is it "essential" to achieve around 6.7Khz?

If anybody knows of any coders that output an higher RMS level, or know how to increase this from the Pro 3 that would be great as it would save me having to swap out R2?

I'll leave this set to full output power and don't intend reducing to 1W, so there's no problem with the final.

Thanks very much for your help.

[nrgkits.nz]

Hi MiXiN
You've got an earlier revision of the board which requires a higher rms on the MPX input, as it was designed to be fed from a computer sound card running StereoTool which generally output a higher rms voltage. The stereo encoder you're using is likely a lot lower. To fix this, you can change R2 from 10K to 4K7 and will increase the sensitivity the MPX input. Then with only the stereocoder going in with pilot tone (no audio), adjust the pot through the back of case so you get around 6.7KHz deviation.

Also there is another change we made in the new revision of this board, R39 was changed from 330R to 470R to reduce the drive slightly to the output device. We had a couple instances where under certain conditions and customers reducing the power right down below 1W, the RD15HVF1 output device would fail after a few months of running. Output power is controlled by varying the bias voltage on the gate of the output device, and when wound right down so the output is less than 1W, this in turn results in a slightly higher peak to peak voltage measured at the gate. The gate to source maximum for the RD15HVF1 is -5v to +10v. So replacing R39 brings it back down to below 5v peak to peak. If you don't intend to run it at a very low power, then there won't be any issues.

Hello,

Many thanks for the informative reply & fast response to my message.

I'll go inside & have a look at R2. If it's a 0805 size or larger, I'll be OK swapping it out, but if it's a 0603 it might be a bit of a challenge unless there's good space around it - so I'll leave it. Those 0603 parts are tiny.

Is running it at its current maximum of 4Khz going to be of any detriment, or is it "essential" to achieve around 6.7Khz?

If anybody knows of any coders that output an higher RMS level, or know how to increase this from the Pro 3 that would be great as it would save me having to swap out R2?

I'll leave this set to full output power and don't intend reducing to 1W, so there's no problem with the final.

Thanks very much for your help.

The resistors are all 0603, I usually use a fine pair of tweezers and hot air. An easier way to do this, just use a 10K through hole resistor, bend one lead around 180deg so its parallel to the other, trim both down to same size and then solder across the existing 0603 10K resistor, you'll get 5K then which is close enough to 4K7. Alternatively, running the pilot tone at 4KHz isn't going to cause any major problems, if anything it will improve reception slightly in fringe areas as receivers will drop to mono sooner due to less pilot tone.

[MiXiN]

Hi MiXiN
You've got an earlier revision of the board which requires a higher rms on the MPX input, as it was designed to be fed from a computer sound card running StereoTool which generally output a higher rms voltage. The stereo encoder you're using is likely a lot lower. To fix this, you can change R2 from 10K to 4K7 and will increase the sensitivity the MPX input. Then with only the stereocoder going in with pilot tone (no audio), adjust the pot through the back of case so you get around 6.7KHz deviation.

Also there is another change we made in the new revision of this board, R39 was changed from 330R to 470R to reduce the drive slightly to the output device. We had a couple instances where under certain conditions and customers reducing the power right down below 1W, the RD15HVF1 output device would fail after a few months of running. Output power is controlled by varying the bias voltage on the gate of the output device, and when wound right down so the output is less than 1W, this in turn results in a slightly higher peak to peak voltage measured at the gate. The gate to source maximum for the RD15HVF1 is -5v to +10v. So replacing R39 brings it back down to below 5v peak to peak. If you don't intend to run it at a very low power, then there won't be any issues.

Hello,

Many thanks for the informative reply & fast response to my message.

I'll go inside & have a look at R2. If it's a 0805 size or larger, I'll be OK swapping it out, but if it's a 0603 it might be a bit of a challenge unless there's good space around it - so I'll leave it. Those 0603 parts are tiny.

Is running it at its current maximum of 4Khz going to be of any detriment, or is it "essential" to achieve around 6.7Khz?

If anybody knows of any coders that output an higher RMS level, or know how to increase this from the Pro 3 that would be great as it would save me having to swap out R2?

I'll leave this set to full output power and don't intend reducing to 1W, so there's no problem with the final.

Thanks very much for your help.

The resistors are all 0603, I usually use a fine pair of tweezers and hot air. An easier way to do this, just use a 10K through hole resistor, bend one lead around 180deg so its parallel to the other, trim both down to same size and then solder across the existing 0603 10K resistor, you'll get 5K then which is close enough to 4K7. Alternatively, running the pilot tone at 4KHz isn't going to cause any major problems, if anything it will improve reception slightly in fringe areas as receivers will drop to mono sooner due to less pilot tone.

Thanks again for the reply.

When I get a bit of free time, I'll open it up & either remove it or parallel a 1/8W Resistor over it like you suggest.