2m MRF300 PA

[PE5PVB]

Anyone ever build this one for DATV?

https://nl.aliexpress.com/item/1005002353128865.html

[g0mjw]

Not that one, but a similar design. I would not trust the Ali-Express board to handle high power for long CW transmissions. If you keep the power very low, which you may have to for linearity, it might be OK. Experience says you will not get much more than 100W of good spectrum DVB-T out of a pair of MRF300s, possibly less, so running at that level may be OK. You might be better off with the MRF300AN-START kit. Only one device but narrow band design and a bit more out, typically 100W DVB-S, 25W DVB-T

Mike

[radiogareth]

That design layout has been available for a long time with recycled MFR186 (IIRC) and worked fine at the 100W level. As Mike suggests, unless the board and parts are specced for the higher power level, 'buyer beware'.
Gareth

[VK5YYY]

Hi PE5PVB

I built one, but they sent random used components
You have to reverse engineer from the snippets you can find on the internet
Then go through stage by stage and tune it up and change components because it doesn’t work well
There is no RC feedback, which was recommended by the NXP rep, you could add it after

I ended up getting the Greek one on EBay
Don’t forget to scrape the paint off, if you use a black painted heat sink
Crank the bias to just before smoke comes out for a nice clean output, which means lots of heat
Copper heat sink with that conductornaught indium stuff is good

Good luck Roger VK5YYY

[VK5YYY]

Here’s a pic
You can see the black heatsink lol

download/file.php?id=4723

Here is the original post

viewtopic.php?f=76&t=7483

[PE5PVB]

I ended up getting the Greek one on EBay

Do you have a link for that item?

[SkyVision]

Hi Sjef

eBay item number:165048247132

Claims Class AB (opinions may vary), just crank up the bias (carefully)
Need a good power supply, heatsink, fan, fire extingisher, smoke alarm (hi hi)
Razvan Fatu's idea of Thermal Grizzly Conductonaut with copper heat spreader is the go (don't use it with Aluminium though)
https://qrpblog.com/2019/10/a-600w-broa ... s-devices/

The NXP data sheet says the MRF300 is good for VHF TV broadcast, so what little tricks can be done to help improve IM for us
The RC feedback could be played with, using 90 degree hybrids is common in broadcast amps, what driver amp is best...Mitsubishi module?
I dearly hope that someone smarter than me can improve MRF300 designs for DATV, as the device is quite cost effective
My attempts at DVB-T with MRF300/100s on 2M and 6M work, but are very low efficiency, DVB-S obviously better

Cheers Roger VK5YYY