PA transistor choice

[F6duk]

Dear all, as we want to use this in some Sota or anything like that. Antenna matching is not always garanteed. We do not want a blown RF PA in first seconds of activity. 3 BS170 are doing the job but what could replace them?
I tried some real RF MOS transistors like RD15HV1, PD55003 or PD85004 but I am near or beyond the max VDS specification. Using a 28V transistor MRF137, BLF244 limits efficiency.
So what could be the ideal undestroyable, efficient Transistor for class E ?
best 73s Hubert F6DUK

[dc8lz]

Hello Hubert,

1st: Guido and Manuel added swr an power measurement and it should not blown on open and short antenna connection. I did not test that at the moment but I worked outdoor with a hy end feed 2m over ground in the tree with no tuner. And even if I choosen a "wrong" band for my antenne where I got a SWR >= 3 nothing bad happened. Very impressive, perfect!

2nd: Did you looked on Manuels 8 Band RF board?

https://dl2man.de/8-band-rf-board/

There you can read "...It uses a single FET in SOT23 Package as PA. This can be various Types but I had best Results with IRLML2060...".

I have ordered some, too. Will see how they work. But as Manuel posted on the forum they both are working on a setup for higher bands. Stay tuned.

[DL2MAN]

Hi together,

changing the FET´s without accounting for that, ruined the chinese uSDRs, so I would not recommend to do that.
All the L and C Values on the RF Board are calculated and tested for 3xBS170.
They can take much more abuse than the IRLML2060 from the 8-Band Board, and this was the choice to go back to them. Safe thing.....
On top: There will be a software feature soon, reducing output power (or stopping TX) on high SWR to prevent PA Fet smoke totally. However this is not yet implemented in the software.

There are 2 additional Footprints on the Backside of the RF PCB for future experiments.
One SOT23 (for something like IRLML2060, which is no bad choice in Terms of highest efficiency - but that one needs software protection)
and one SOT223-4 for FDT86256 (which I have never tested, but looks very promising and I plan to play with as soon as I find some time....)

Bottom Line:
Changing the FETs ALWAYS requires changing the Coils and the Capacitors in the Class E Network !

73 Manuel; Dl2MAN

[dl8dtl]

A lot of the parts from the original BOM seem to fall under the current electronics parts availability crisis.
Even simple things like BS170 in SOT-23 appear to be unavailable.
Does anyone have L/C values for 2N7002? I've got plenty of those around.

[DL2MAN]

Again:
There are 2 additional Footprints on the Backside of the RF PCB for future experiments.
One SOT23 (for something like IRLML2060, which is no bad choice in Terms of highest efficiency - but that one needs software protection)
and one SOT223-4 for FDT86256 (which I have never tested, but looks very promising and I plan to play with as soon as I find some time....)

This means:
The 3x BS170 are on the Front and Through hole parts in TO92 Housing !!!. They still can be sourced anywhere from mouser, over Toroid King, over LCSC to Reichelt and even plenty on ebay....

73 Manuel; DL2MAN

[dl8dtl]

The 3x BS170 are on the Front and Through hole parts in TO92 Housing

Sorry, didn't realize that. Yes, the TO-92 version appears to be better available.

Anyway, as I've got 2N7002 around, it would be interesting how to optimize the L/C values for that one.

[dl8dtl]

Looking closer, I've got the 8-band RF board (someone sponsored mine , and it's only got the SOT-23 footprint. The schematics says it needs an IRLML2060 … so gotta try getting that one.

[G8RDI]

I've seen that the IRFI510G can be suitable to replace the BS170/2N7000 fets. Has anyone experimented with them?

Radio Club PSK posted this "Q1 transistor – you can follow various options on the forum mentioned above. I had BS170, 2N7000, IRF510, IRF540N and IRF610 at my disposal. The IRF540N worked best for me on the 80m and 40m bands, and 3 2N7000 connected in parallel on the 20m band." Transceiver uSDX with Arduino Nano | Radio Club PZK LAB-EL HF5L

73, Rob

[DL2MAN]

OK guys, this forum is exclusively about (tr)uSDX.

Older Developments and specifically other peoples designs are discussed here:
https://groups.io/g/ucx/topics

There´s 14300 Postings about uSDX.

73 Manuel; DL2MAN