Big mistake

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nrgkits.nz
no manz can test innit
no manz can test innit
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Big mistake

Post by nrgkits.nz » Fri Aug 03, 2018 10:32 am

I forgot to enable the ground plane on my new amp before sending in the files to get a sample, luckily it was only a sample I ordered and not 100 boards!

Any ideas for a quick fix? I'm thinking silver conductive varnish https://www.jaycar.co.nz/silver-conduct ... h/p/NS3030

I got 2 sample boards, decided to build one anyway and just as I thought, output power is dropping due to the bad earth even though i've bolted it down to an aluminium heat-sink, current draw is less also with efficiency still at around 75%, it really needs that copper ground plane on the bottom of board!
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s2000
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Re: Big mistake

Post by s2000 » Fri Aug 03, 2018 5:57 pm

Maybe something like this...

http://www.agarscientific.com/copper-sp ... eMEALw_wcB

I saw something similiar to this used on a job once a while back... The electricians were spraying the inside of plastic office dado trunking and making little wire links where the dado was couplered together. When I asked the spark why he was doing it, he said the firm couldn't afford to use screened cable! lol That was on a mod job too :lol: :whistle

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yellowbeard
no manz can test innit
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Re: Big mistake

Post by yellowbeard » Fri Aug 03, 2018 6:28 pm

No matter what you do you wil lose the benefit of the plated thru holes. You could maybe try a blank sheet of single side copper clad, sand 50% of the substrate off both it and the circuit board and epoxy them together - a belt sander would be the tool to use. You would need to use a handful of rivets or Harwin pins for a decent ground plane contact. I don't know about the silver paint, I imagine it would oxidise and you'd get all sorts of stray, weird sprog inducing currents flowing on the ground plane after a while - but it may last long enough to confirm the design.

nrgkits.nz
no manz can test innit
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Re: Big mistake

Post by nrgkits.nz » Tue Aug 07, 2018 9:11 am

I managed to get this sorted out in the end, found out it was indeed my output matching although it could still do a little better with the ground plane. This new PCB is basically a copy of the board from the MRFE6VP5150N datasheet with a some slight modifications for testing. https://www.nxp.com/docs/en/data-sheet/MRFE6VP5150N.pdf

So far so good, down the low end of the band i'm getting 200watts out, and the top end 180watts with 1.5watts drive and the bias set at around 2.6v, 1/2 wave length of coax into a 50ohm load.

Output power can also change slightly depending on the length of coax being a multiple of either 1/4 or 1/2 wave length and load and source impedance's. Adding another 1/2 wave length of coax can either increase or decrease the output power by upto 1.5dB i've found. It's well documented by this guy, and it affects any power level.

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