80M 350W GaN AM Transmitter

[VE3ELQ]

Based on lessons learned with FET failures, a new 350W 1.7KW PEP 4 GaN FET PWMod AM transmitter has been constructed and tested. It has survived extensive bench torture testing and recently several days of on air testing with about 20 QSOs.  Signal and audio reports have been great.  A recording made on QIX Steve's remote sdr receiver was valuable in assessing both. A few pics attached of this latest project. Please say hello if you hear me on 80M.

73s  Nigel

[ka1tdq]

That much power with 4 FETs is very impressive. Nice compact size too!

Which FETs did you use again (part number)?

Jon

[VE3ELQ]

Which FETs did you use again (part number)?

Jon

This rig uses four TPH3208PS  650V 20A GaNs. Peak drain current under modulation is about 12A leaving plenty of current headroom so it could be pushed harder. It should be good to 40A. Drain peaks are 600V so little room left for higher voltage.

My 40M D rig uses four of the slightly faster TPH3206PS 600V 17A GaNs. It runs at 400W carrier 1.8KW PEP since last winter with no issues.

73s  Nigel

[ka1tdq]

The TPH3206’s are about $11 each AND come in a TO-220 package. Very tempting!

(I’ve come to hate two-word sentences in the last couple years. Apologies if I offended anyone.)  

Jon

[KB2WIG]

No problem.

klc

[W2PFY]

I'm OK with just part of a sentence! It keeps me busy trying to figure out what someone meant?

Nice project Nigel!

[vk3alk]

Hi Nigel...

Yes all looks great.....
Its a nice feeling finishing a successful build...

Noticed the wood in the box...is chassis ground the rear aluminum sheet or is there a sheet underneath connecting to the front panel...
The SWR bridge is that for just Power / SWR or more perhaps like rollback etc:

Have you ever tried Current Mode CMCD ...... has advantages in restricting voltage levels that may have caused some of your blowups...




Wayne

[vk3alk]

There is another question too...

You said you have a regulated 150 volt supply...

How do you achieve that .... by SMPS ?


Wayne

[VE3ELQ]

Wayne,
Dont have the equipment or skills to make fancy metal enclosures so settled on 1/8 door skin wood with 7/16 corner stringers in all my projects. Front and rear panels are sheet aluminum cut with a metal blade jigsaw. I can do that.    The rear panel painted flat black is the ground plane and also provides what little cooling is required, no finned heat sinks.

The Bruene bridge senses reflected and forward RF voltage switch selectable for display as a bar graph on row 2 of the 20x4 LCD display. Row 1 is VFO freq and step size, row 3 is Drain current and row 4 shows modulator voltage with a diode cap resistor peak hold circuit.  These 3  are all high res bar graphs. There is also a comparator circuit set to trip at 148V, 2V below clipping, which flashes the blue LED on the front. This way modulation can be monitored and best mic gain can be set.  There is no fold back or any other protection except a 5A fuse into the modulator.

The power supply regulator is linear done with a IRFB4332 FET connected as a source follower. The drain is on the filter caps at about 165V ( rectified mains). The gate is supplied with 154V from a zener reference that has it own 200mfd filter cap fed by a diode from the 165V rail. Regulation is important for 3 reasons. It prevents voltage overshoot when un-keyed. It prevents voltage pulling down under modulation giving a more linear output. And it strips off the 120hz ripple so no hum is modulating the carrier. Hope that is clear enough, can hand scribble up a schematic if needed.

Well done down there with the Invictus games.

73s  Nigel

 

[vk3alk]

OK on everything...
Your box looks good and has a nice finish...
Have uploaded a photo of a 40M receiver that was finished a little while ago now....
Goes amazing well for a simple single conversion 455Khz IF...has an Infinite Impedance detector too and driving a reasonable speaker sounds fantastic...I'm slightly overcome by it sometimes....
Used primer undercoat and a finishing top coat and left it in the rear windows of my car for about 1 week...
The camera flash light shows some imperfections that aren't normally noticable  
All my stuff now will paint the front cover looks better than plain aluminum .....

OK too on your power supply...
120VAC can be handy ... ours is 240VAC and has to be respected  

I use a regulator board that has error amplifiers .... one that I use for overload shutdown and one for SWR rollback...
You can vary the output voltage too which makes it very handy .....
Can email this to you if interested....

Thats enough....


Wayne