RF24zx mosfet thread

[Uncle Ronnie 336]

scored 10 off of ebay for $14 from a seller 6star
claimed better RF than IRF520
so curiosity got the best of me
the test bed radio is a taiwan cobra 29gtl so here are my findings so far:
a homemade arrangement of EKL layout (470-1n4148 and 3.3k) and the first thing i noticed is low dead key. this is partly because there is more gate capacitance im assuming. i changed the 3.3k to a 5.6k. now have 4.5 watts swinging around 25. so far it runs like a normal 520 with a lower dk. might have to build a hard-bias circuit.

if anyone else has messed with them post about it here, maybe it can become a sticky if theres enough of that juicy info in there

 

[Eldorado828]

Are they just rebadged irfz24npbf or rt1 as ranger calls them?

 

[Uncle Ronnie 336]

i dont think so. seems the gate capacitance is a bit high. idk though

 

[Handy Andy]

Yes, the Gate capacitance is quite high, nothing big but makes it harder to find the "Sweet spot" the RF wave to linear amplification takes place - so the choice of the 5.6K got you into a working value of power input - only to the lower side of the "gate change to charge" transition region or where the gate turns on the substrate like a potentiometer than the switch.

When you get into this region - the amount of capacitance needed will by dynamic - meaning the issue of putting two caps in parallel across each other to add or sub in capacitance to raise or lower the dead key will change the way the charge change works - but then lowering the resistor - then trying again to find that right sweet spot level - works but each radio even amongst the same chassis is different - it needs different values.

 

[Eldorado828]

I wonder if these are what Lester claims as his lc z6 and z7 or whatever he calls them.

 

[Uncle Ronnie 336]

had to hard-bias the one in the 29gtl. 3.9k to gnd, 4.7 k to 8vtx. bridged c62 with additional 300pf. left 470r-diode in place. now getting 8 swingin 30+ according to my mfj meter

 

[Handy Andy]

Sometimes there is not enough energy to convert the Driver's RF output to EKL-DC values to make them turn on.

 

[Uncle Ronnie 336]

yea this is one of those times. i haven't done anything else to it yet and these finding are with vr4 open, no r/c and i havent changed c71. im happy with the readings it's giving and the heat on the sink does get pretty warm but not alarming for the output, so it's gonna be getting a 2-pot TIP120 module so there will be a face switch for high and low set at 1 and 5w to take some of that heat away and allow for some real long winded jabberjawing.