Modulator Output

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Modulator Output

Postby K9ACT » Sat Sep 18, 2010 11:42 am

I have my Class D RF deck upgraded to the 200W level and it worked well for a time but I blew one of the finals in the testing process. Hopefully, no big deal but it was my last spare and hopefully Steve will get out the ones I just ordered ASAP.

In looking at the mod board schematic, I am again wondering what that C and D limit are for and how they work. The connections are a bit confusing to me. Is this something I need or part of the overload board which is still just a bag of parts?

Jack
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Re: Modulator Output

Postby kf1z » Sat Sep 18, 2010 3:45 pm

The D and C limit are not included with Steve's "on-board parts" ... as far as I know.
And are not mounted on any board (neither the pwm generator nor the overload board).

If you need the diode ( DSEI30-06) or any other spare parts, let me know....
I'd stick them in the priority mail box on Monday......

In a nutshell, these 2 parts are supposed to keep any voltage 'spikes' created in the pwm filter to the limit
of the power supply voltage...
"dumping" any higher voltage back into the PS I suppose.

I'd suggest installing them.....


Wondering if you have installed any transorbs in the RF deck?
Just curious..


Bruce
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Re: Modulator Output

Postby K9ACT » Sat Sep 18, 2010 11:49 pm

>If you need the diode ( DSEI30-06) or any other spare parts, let me know....
I'd stick them in the priority mail box on Monday......

Thanks but that's one part I have lots of. Do you have any 11N90's to spare?


>In a nutshell, these 2 parts are supposed to keep any voltage 'spikes' created in the pwm filter to the limit
of the power supply voltage...
"dumping" any higher voltage back into the PS I suppose.

Sounds like the solution to most of my problems thus far.


>I'd suggest installing them.....

I put the diode in but the cap right next to another just like it didn't make much sense so I left it out.

Don't know if it is just a coincidence but I ran it for several hours this afternoon with no problems.

However, it did seem like there was something preventing it from modulating beyond 100% and I wonder if the diode is doing that. Until I get some spare 11N90's, I will leave it as it is.

Wondering if you have installed any transorbs in the RF deck?
Just curious..

No but I have some left from the modulator but I am not sure what value I need or where to put them on a Class D.

>Bruce kf1z

I hear you checked into the NTF streaming on my day off. Sorry I missed you.

js
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Re: Modulator Output

Postby kf1z » Sun Sep 19, 2010 7:11 am

What is your power suplly total voltage?

And what voltage at carrier OUT of the modulator?



Yes I still have 11n90 's left.
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Re: Modulator Output

Postby K9ACT » Sun Sep 19, 2010 8:00 am

[quote="kf1z"]What is your power suplly total voltage?

And what voltage at carrier OUT of the modulator?

Max voltage is 120 and carrier is 33.

>Yes I still have 11n90 's left

I will contact you off line on this.

Thanks,

js
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Re: Modulator Output

Postby kf1z » Sun Sep 19, 2010 9:16 am

Well, obviously you have plenty of voltage for more than 100% modulation...

I don't see how the limit diode could cause low modulation.
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Re: Modulator Output

Postby steve_qix » Sun Sep 19, 2010 7:01 pm

Hi !

The D-limit and C-limit (as Bruce pointed out) prevent any possible high voltage spikes that may develop in the PWM filter, if it were not properly terminated (like, during an overload and/or NO load, or transient load) from reaching a voltage higher than the high voltage power supply voltage.

The Capacitor (c-limit) is necessary as a "sink" for high frequency spikes, as the length of the wiring between the limit diode (d-limit) and the power supply is mostly likely long enough to have sufficient inductance to either "ring", or allow short spikes to get through. Also, a differentiation of the input spike can occur due to the inductance of the wiring. So, the capacitor, applied directly at the diode's cathode, will absorb even the highest frequency spike.

This diode/capacitor pair will have NO effect whatsoever on the modulation, because the high limit is the high voltage power supply voltage, and the modulator's output should NEVER exceed the power supply voltage under any conditions.

Regards,

Steve
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http://www.classeradio.com
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