The AM Forum

Hi I am wanting an AM transmitter.  Wondering how hard a class E is to build?  I am a mechanic by trade.  Built my first electronics kit back in hs.  I have soldering equipment multimeters,frequency counters,tools for metal working but no scope or spectrum analyser.  I might be able to take the project to a friend who has the last two items for testing if that is required.  On a scale of 1 to 10 how hard is it to build one of these.  Or should I just try to find an old boat anchor?

From the N1 call - are you in New England?  If so, this project is realistic even for a "first time" build because there are so many experienced class E builders in the N.E. area.

The rigs are not that bad to build at all.  The hardest part is the metal work.  But, it will be advantageous to have class E "Elmers" around to help out, answer questions, and perhaps be there when you get ready to test circuits and fire up for the first time.

I would start out with an 8 MOSFET rig on 75 meters or possibly 75/160 meters.  This design has been reproduced many times, and is quite stable and reliable.

I did both.

I bought a Viking II.   

I built a PWM and then built various rf decks.

I haven't had the Viking on in almost 2 and a half years.   It's been between my pwm Homebrew and a fairly modified TS 440 Kenwood for me.

I think the stuff I have more of my heart in,  I get more enjoyment out of.

My two cents worth.   Honestly,  I'd be happy with just my viking or my pwm rig.   But,  I haven't sold the viking even tho it's a shelf drag queen.

--Shane
KD6VXI

As the old saying goes you climb a mountain one step at a time.
First buy a scope.  You absolutely cannot do this project without one.  The new DSOs are inexpensive and very versatile.
Read up on whats out there and decide on your objectives.  Then start somewhere, probably the power supply, build it test it and when its done build the modulator.  Start by making a dummy load for it, wind some lock wire around a brick to match the deck impedance, then the rest of it, and send some triangle waves into it and see how good it looks on the scope, clip a speaker with coupling cap to it at the bottom turn and play some MP3s and marvel at how great it sounds.  Then do the rest of it one step at a time. Ask questions when you are stuck, someone will have the answer.  You get the idea.  Persist until you reach the summit. Its a great journey.  Have fun.

73s  Nigel

What mhz scope should I be looking for?  Not just to build this but to have for general ham radio use?

The fastest you can afford but a 70mhz will do a good job for this application.  Many brands are available, Hantek and Rigol make good ones. Go for the extra memory if you can.  Post your choice before you buy and standby for lots of differing opinions on this one.

73s  Nigel

I use a Tektronix 475A, which can be had very reasonably these days.  And it's a really good scope (250mHz).

It looks like you're a fellow Maine-iac.  I'm from the Calais area originally.

I built a single MOSFET transmitter just to get the concept down.  Once I found out how to drive and tune one of these beasts, I felt more comfortable building the 8-FET version. 

I'm now in the process of building a 24-FET model. 

If I hadn't started small, chances are that I wouldn't have been able to build a bigger one.  I'm no engineer, so I had to figure things out step-by-step.

Jon

Fwiw, used TEK 'scopes are all over the place now. Almost all of them are really excellent.
You can find them used on ebay. At NEARFEST too. Of course you want one that actually works, so
the ebay purchases range from incredible bargains to having one or more functions broken. So,
you have to look carefully. Usually sellers with good scopes will show you pix with the trace
or preferably a signal. ESS in New Hampshire also sells scopes on ebay and their website and
their store too. AL, W1VTP lives a stone's throw away...

A 100mHz scope will likely suffice for most things. Higher freq is better...

I personally do not like the inexpensive digital scopes - can't stand "jaggies" on the trace.

              _-_-

The plans are to make it to nearfest.  Looking for a scope,amp parts,tubes and maybe an old am rig.

There are likely to be some H.B. class E rigs there, too.  You can check them out and see the construction for yourself.

Dale,

With the board kits that Steve offers, you should have little difficulty building a Class E rig.  A lot of the build is mechanical with good electrical layout.  With the digital gate drive its even simpler than before!
Layout is critical in some areas, but once you understand what needs to be where, you should not have any issues.  You have a very large support group out there to answer your questions. 

I am going to tackle the task of building one myself very soon. 

You will learn a lot and have tons of fun in the process, so just do it!

73,
Joe-W3GMS   

Will you have your boards there?

Also a mech by trade. I would like to know more about Jon,s first single mosfet rig.  Including a schematic.
Don

Ah man, I don't keep schematics!   :)

That's ok, I drew one up.  I don't have CAD software.  There's more "stuff" in the picture with the drive circuit, but I was experimenting to get the app. 5vpp sine wave.  Basically I just used a logic buffer, but the IC is glued to the board and I can't remember what I used.  

It helps to have a variable amplitude sine wave to drive the IXDD chip because you'll need to vary the duty cycle for best efficiency.  As I remember, about a 43% duty cycle works best.  So, I used a cheap Chinese DDS VFO to create the sine wave and my buffer squares it up.  

The rest of the schematic comes from the class E website.  I just halved the values Steve posted for his 75 meter deck since this transmitter is for 40 meters.  

The 150pf doorknob shunt capacitor is just what I had and it seems to work.  The value isn't perfect though.  

It's a good "local" rig for 50 watts carrier.

Jon

** I saw this after I posted the schematic, but a square wave goes into the IXDD chip at about a 43% duty cycle.  I use a sine wave into a buffer to square it up.  Also, the drain choke uses an FB43-1020 core with what looks like 7 turns.

Tnx. Thst is a big help to.me. I understand it. So turn on osc begore applying drsin voltage and kill drain voltge begote turning off isc so mosfet should never run without osc signal present, correct?
Don

That's it!

One more thing. The drain should have a Transzorb diode on it to protect it from over voltages, should they occur. The part number is on Steve's schematic. It's like a dollar part.

Jon