MRF24300N performance at high power

Latest News and Discussion about the use of the DATV transponder on Es'hail-2
G4WIM
Posts: 257
Joined: Thu Jan 29, 2015 8:36 pm

MRF24300N performance at high power

Post by G4WIM » Wed Jul 24, 2019 12:26 pm

Hi Guys,

just finished building and testing my 13cm PA - using a Pyro Joe PA as a driver to an MRF24300N powered from a 600 watt Meanwell PSU.

Max CW power was 350W but I've only tested IMD up to 180 Watts.

Surprising how warm LMR400 gets at 180 watts !

I've attached a few pictures of the 'guts' including the two large cooling fans to force air in and out.

Testing in the shack where the ambient temp was 29.9C resulting i the PA reaching 60C after about 15 minutes at 120 watts out put.

The remote control telemetry works on 868MHz and is designed to shut the PA down if it gets up to 70C. It monitors Vdd, Idd, Vbias and temp it also provides a fan hang timer when going to rx.

The bias control is temp compensated and after 1 hour of high power use the quiescent current was still a 1 Amp.

Tweaking the quiescent current up a tad didn't seem to after IMD significantly.

Now to install at the dish.
Attachments
13cm PA MT.jpg
13cm PA MT.jpg (378.27 KiB) Viewed 529 times
13cm PA internal.jpg
13cm PA internal.jpg (265.97 KiB) Viewed 529 times
13cm PA close up.jpg
13cm PA close up.jpg (284.07 KiB) Viewed 529 times
13cm PA IMD 120watts.jpg
13cm PA IMD 120watts.jpg (213.99 KiB) Viewed 529 times
13cm PA at 180 watts.jpg
13cm PA at 180 watts.jpg (228.44 KiB) Viewed 529 times

radiogareth
Posts: 312
Joined: Wed Jan 06, 2016 9:46 am

Re: MRF24300N performance at high power

Post by radiogareth » Wed Jul 24, 2019 1:18 pm

Very nice. Hope you're pleased with the performance too :-)
Gareth

g0mjw
Posts: 887
Joined: Sat Sep 20, 2014 9:15 am

Re: MRF24300N performance at high power

Post by g0mjw » Wed Jul 24, 2019 1:39 pm

I am not sure -25dB shoulders are good enough, so perhaps limited to 120W or less - but that's surely enough. Did you try messing about with the bias at all?

I don't know what antenna you are planning to use, but it will need to be resilient.

Mike

G4WIM
Posts: 257
Joined: Thu Jan 29, 2015 8:36 pm

Re: MRF24300N performance at high power

Post by G4WIM » Wed Jul 24, 2019 3:16 pm

Hi Mike,

just tried it on air and it is plenty powerful enough to get the 'over power warning' (oops) when running at 2MS.

The shoulders at -25dB was at nearly 200 watts, but looks much nicer at 120W as you can see above.

Output was about 120W into a 1.2M dish, so at this level -32dB shoulders should be fine.

Using about 0.8M of LMR400 from PA to one of your feeds and the coax gets warm to the touch. Connector is N type on the patch and made from stout copper so hopefully will handle the power ok.

Per my previous post - I did have a fiddle with the bias but no major reduction in shoulders -just more gain and heat !

Seems to be working ok remotely with the telemetry plus the air outside is a bit cooler than here in the shack, so fingers crossed all good so far !

g0mjw
Posts: 887
Joined: Sat Sep 20, 2014 9:15 am

Re: MRF24300N performance at high power

Post by g0mjw » Wed Jul 24, 2019 4:26 pm

If you can overpower at 2MS with a 1.2m dish then it's going to have to be backed off much more for the lower symbol rates. It will be interesting to see what 120W to a 2.4m dish can achieve...

Mike

G4GUO
Posts: 625
Joined: Tue Feb 16, 2010 12:51 pm

Re: MRF24300N performance at high power

Post by G4GUO » Thu Jul 25, 2019 9:00 am

I am curious to know whether you had to modify the PyroJoe driver amp. Above 2.4 GHz the output of mine drops off considerably
and I seem to remember that adding a tab on the transmission line at the corner of the output significantly increases the output
above 2.4 GHz.

- Charles

G4WIM
Posts: 257
Joined: Thu Jan 29, 2015 8:36 pm

Re: MRF24300N performance at high power

Post by G4WIM » Thu Jul 25, 2019 11:44 am

Hi Charles,

using the PJ amp by itself unmodified produced 25 watts with good IMD, adding a small snow flake increased this to 30 watts at 2406MHz.

However with the new final stage I only need about 4 watts of drive so the PJ 'driver' is very clean and grossly under run.

Regards Tim

G4GUO
Posts: 625
Joined: Tue Feb 16, 2010 12:51 pm

Re: MRF24300N performance at high power

Post by G4GUO » Thu Jul 25, 2019 12:14 pm

Thanks Tim,
I am getting much less than that at 2.405 GHz. I can't remeber the actual amount, I will have to measure it again when it gets a bit cooler
and all the flying ants in my shed have gone away, it is not very pleasant in there at the moment.

- Charles

G4WIM
Posts: 257
Joined: Thu Jan 29, 2015 8:36 pm

Re: MRF24300N performance at high power

Post by G4WIM » Thu Jul 25, 2019 5:55 pm

Interestingly I was checking to determine what contribution each stage in the tx chain made to the IMD - expecting the PA to be dominant which it is at powers greater than about 120 watts.

However at 120 watts the shoulders match those of the Lime exciter !

Looks like the Lime is not as clean as I was expecting - see my other post on this topic.

Could have implications for pre-distortion using the Lime ?

g7ntg
Posts: 24
Joined: Sat Feb 17, 2018 7:07 pm

Re: MRF24300N performance at high power

Post by g7ntg » Thu Jul 25, 2019 7:12 pm

very nice job!
Are spectral regrowth shoulders going to be very important when transmitting through the satellite because you only see the top 8dB of the signal above the noise floor? Some operators have plainly visible shoulders that must be only 10DB down or so and their signals seem perfectly ok.
Any thoughts please?

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