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QIX PWM Board

PostPosted: Mon Aug 08, 2011 10:49 am
by W3FJJ
Hi, I am currently building a QIX PWM board, and wondering where the Feed Forward Pin should go to. What is the purpose of this pin?
I did read doc on ucc25701 and see it shuts chip down if voltage is low or too high.. How should the feed voltage pot (r400)be adjusted.

Thanks-Chuck

Re: QIX PWM Board

PostPosted: Tue Aug 09, 2011 5:52 am
by W3FJJ
I found the answer on this board reading some past threads, the feed forward pin is connected to the power supply. Well I sorta knew that, but
wasn't sure why it wasn't automatically hooked to power supply on the board. Seems the purpose of it to
sample ripple voltage of supply , and eliminate it on the PWM signal. QIX said he was not using it on his board, so don't think I going to worry about it..

Re: QIX PWM Board

PostPosted: Fri Aug 12, 2011 9:18 pm
by Gilly
Hi Chuck

Have always connected the Feed Forward Pin to the HV supply .... and have never had any problems with ripple etc: so if I was to build more would continue to do so ....
In all my PWMs the PWM generator board is close to the Current Meter so its easy to connect using a 47Kohm resistor etc:

In adjusting R400 to be honest it doesn't seem to do much other then to cause some Carrier Voltage swing....so I tend to leave it alone really.....


Wayne

VK3ALK

Re: QIX PWM Board

PostPosted: Sat Aug 13, 2011 5:03 pm
by W3FJJ
Thanks Wayne, I probably fool around with it and see what it does. I was real confused at first, thinking it
hooked to the power supply on the Generator board, but now I realize it goes to the power supply that supplies power
to the mod mosfets/rf deck.. I'm getting close to firing up the modulator into a resistor dummy load, this has been a fun project.
Thanks to QIX on FB Kit...

Re: QIX PWM Board

PostPosted: Tue Aug 16, 2011 7:52 am
by kf1z
IF you use a LOT of filter caps in your HV DC supply, you may not need the feed-forward.

However, if you do have some ripple, then the feed-forward will eliminate it.

Bruce
kf1z

Re: QIX PWM Board

PostPosted: Wed Aug 17, 2011 5:55 am
by Gilly
Hi Chuck

On another matter I bookmarked a WEB site that interested me a little while ago now...

http://www.eecis.udel.edu/~hanavin/chuc ... /synch.htm

Is this yours and if so how did it go.....and are you still using it ?
Are making a 40M Receiver at the moment and found a Sync Detector in QST using a couple of NE602's and a NE604.....
I have all the parts available and have designed the outlay so probably will built it...

Thanks


Wayne

Re: QIX PWM Board

PostPosted: Thu Aug 18, 2011 11:54 am
by W3FJJ
Hi Wayne, yes that's my synch detector. It works ok, but as description on web page, it has some hiss.
I don't use the lm-386 amp chip shown as schematic, it's not much of an amp ,so I just run line out from the
all pass filter in to exteranal Hi-Fi amp.. The selectable sideband function works great.
I haven't used the detector it in awhile,but I plan on building a homebrew receiver also, and that will be the detector for it.

Lately for synch detection, I built a soft rock 455kc down converter , and been using the flex software.

I be interested in what month/yr that synch detector is in QST, I like to check it out...

Thanks-Chuck

Re: QIX PWM Board

PostPosted: Fri Aug 19, 2011 1:31 am
by Gilly
Hi Chuck


Here is the link......

http://www.jogis-roehrenbude.de/Leserbr ... r_ARRL.pdf

July 1993 so its a quite a long time ago now.....
Have never built one so will see how it goes...not all that complex....


Wayne

Re: QIX PWM Board

PostPosted: Fri Aug 19, 2011 3:40 pm
by W3FJJ
Hi Wayne, Thanks for pdf link! Looks good, that article came out right after I built mine..
You'll like the synch detector, sometimes they make a dramatic difference, other times not so much..

Let me know how ya make out.. Chuck