The AM Forum

I repurposed an existing RF amplifier experimental project, and threw together a transmitter for 40 meters.  4 MOSFETs in the RF amplifier - runs 45 V @ about 6A.  I want to add 4 more MOSFETs to get things up to 400 watts or thereabouts.

The modulator is an old class H analog modulator.

The Antenna is an additional dipole on an existing "fan" dipole that is now 160, 80 and 40 meters.  Seems to work !!!

Nice getting on 40 meters after a *VERY* long absence from the band.

This is the RF amplifier:
(http://www.classeradio.com/40_meter_4_fet.jpg)


This is the modulator:
(http://www.classeradio.com/40_meter_class_h_modulator.jpg)

Nice work. Your breadboards look about as tangled as mine ;)
RIP to the HP power supply, but its body lives on!

What are those bits of styrofoam(?) on top of the modulator - spacer for a cable? It's hard to see clearly what's going on...

Nice work Steve

Underwriter's Lab is waiting to test and pass this set for the public

Fred

Oh, those are part of the support for the bank of filter capacitors.  Keeps some pressure on the entire bank (16 capacitors) and adds mechanical stability.

Heard you in my mobile in Westerly RI last night talking to Chuck, K1KW on 7295, along with some
8 landers right around sunset. You and Chuck were LOUD.  Great to hear short haul stations like that on 40.  Tried to give you a call but everyone was quick keying on the turn overs and don’t think anyone heard me.  I’ve noticed that on 40 AM most people quick key, as opposed to on 75 where most times people drag their feet a bit in case others are trying to join in.

Heard you on the air this afternoon, sounding very good!

I had trouble, not seeing the links or images until I removed the [img] bbcode. Had anyone else had trouble seeing the pictures or links? If so, was it a windows setting? seems I have troubles for some reason. No one has been able to sugest what.

no issues here with MS Edge, Firefox, SeaMonkey or Brave browsers.

Works FB here with Chrome as the browser.

--Shane
WP2ASS / ex KD6VXI

That says It's my fault. The computer is so gaslighted by my tweaks that it's become totally paranoid. OK done and and I abase myself for straying from topic.

I have a decent question about this cliplead special though - the Modulator. Is this the same one built a few months ago? I just remember the handsome front panel. h/p looking.

And on the RF chassis, that large copper coil looks a lot like the type that might be in a tube pi-network unit. I find it interesting, what is it used for?

This is actually a different modulator.  This particular modulator is _OLD_ - about 20 years old to be exact.  It is an analog (class H) modulator.  All of my other modulators are PWM.  I used the class H modulator because it will work into any load from 45V @ 10A to 45V @ 1A.  This rig is running at about 6A.

The plan is to add 4 more MOSFETs and then use my pulse width modulator with this rig as well as the other class E amplifiers I have in this power class.

The big copper coil, along with the variable capacitors that are mounted on the piece of copper clad board form the output network.  It is a standard class E output network, with the coil and larger capacitor forming a series resonant circuit, and the smaller capacitor serving as the loading capacitor.

The input is broadband, digital drive.

It's a very straight-forward RF amplifier.  The analog modulator is a bit more complex than a pulse width modulator, but it too is fairly straight-forward - a source follower output consisting of 6 IRFP260n MOSFETs handling the carrier and negative peaks, and another bank of 6 MOSFETs feeding more voltage to the lower set of MOSFETs for the positive peaks.