20 meters and digital drive

[ka1tdq]

While I'm waiting on parts for my class E modulator, I've come up with this...

It's a 20 meter CW rig.  The FET is an IRF510 with a gate capacitance of about 300pf.  Is that low enough for an IXDD to drive it? 

If it won't work, I can at this point easily use a crystal for 40 meters and change out the cores to red. 

...or, I could make it a QRP 40 meter AM rig for use with a linear. 

It's really neat looking, so I want to do something with it.

Jon
KA1TDQ

[W3RSW]

Looks like fun.  Shine that copper.
The "Tinker Toy Special"

(I've seen those toroid mounts somewhere before.)

What voltage do you plan on using ; Impedance in and out?

http://www.vishay.com/docs/91015/sihf510.pdf

[ka1tdq]

I plan on using 13.8vdc for both the IXDD and FET.  It makes things easier.  I really haven't thought about impedance matching, other than to just hook it up and see what I get.  The transformer will use a 1:2 ratio.

Just to see if it works, I'm going to use my DDS VFO to input a 5.0 volt wave to the IXDD.  If it work, I'll hook up a keyed crystal oscillator.

It's a nice neat paperweight that'll have stories.  "I've talked to Africa on that thing..."

Jon

[W3RSW]

Id vs Ids curve has a 5.0 volt static, (roughly peak of pep,) line showing about 1 amp on the drain.
At 13.8 volts supply, output may be 13.8 *(1)* (say .6 eff) or about 8 1/2 watts pep if your impedances are ok.  Wonder if hard switching transients will back into your DDS or does it have a buffer.  If so A tuned input (trap to all but desired freq.) would help.

Not used to thinking of freq. in nS but should work on 40 meters OK.
How's that for a confusion of application and units.

Switcharoo Tinker Toy Limited.

Find a 28 to 32 volt supply for fun.

[ka1tdq]

I didn't notice it until after the fact, but there were some tiny copper shavings shorting the FET drain to the heat sink.  I applied 12 volts and noticed that my power supply was working especially hard.  Before I could react, the FET exploded like a fire cracker and blew across the room.

Eh, it's just a Tinker Toy project.  I had everything soldered just perfectly too.  I'll table this one for a little bit.  My inductors for my class E modulator come in Monday.  I'll play with that.

Jon

[ka1tdq]

Ok, so I soldered on a new FET.  This time, I put a 1k resistor from the IXDD input to ground.  This should ensure that the output is low when no oscillator drive is applied.  I'm thinking the output was high before causing the FET to conduct straight DC voltage, thus causing it to fly across the room. 

It seems to work now.  I put a 50 ohm resistor across the secondary transformer to act as a load. The waveform wasn't pretty, but a filter on the output should make a nice sine wave.  The output of 20 meters was less than the output on 40 meters.  20 meters does work, so I'm going to stick to my original plan and make this a CW rig for 20.

The thought did cross my mind however to make this a miniature class E 20 meter rig for AM.  Supply it with 48 volts and have the carrier run around 15 volts. 

Jon

[ka1tdq]

Well, 2.3 watts...  I like it though!

Jon

[K4RT]

Nice xmtr, Jon. What does the keyed waveform look like, make/break?

[ka1tdq]

The output at the antenna jack is a nice sine wave.  I don't notice any key clicks in the keyed audio.

The gate waveform looks to be over 50% duty cycle, and I think that's where my loss is.

The keying circuit I used is the oscillator circuit from the SoftRock Lite II receiver.  That circuit uses a crystal oscillator to drive the clock of a flip flop.  I replaced the flip flop with the IXDD chip input.

I've called CQ a few times, but no response.  I did find myself though on the reverse beacon CW site though in Reno, NV.  So, I am being heard.

Jon

[steve_qix]

I do not believe the IXDD chip will function (at least very well) on 20 meters.  The documentation for the IXDD414 does not look good above about 7.5 mHz.

[ka1tdq]

Yeah, so I found out. It's my 2.3 watt brick. 

I'm still going to keep it though. As inefficient as it is, it's still more efficient than tubes! 

Jon

[ka1tdq]

...one more quick note...

I just had my first QSO with this rig.  It was with WC7C in Washington state, and he gave me a 599!  I was checking the reverse beacon website and my signal was heard from many location in the US and Canada. 

I'm not a QRP convert, especially with AM (where 300 watts carrier or less is considered QRP), but that was fun!  So, if you want another spark in your hobby, whip out the ole' IXDD614 and run it on 20 meters...

Jon

[ka1tdq]

Not to beat a dead horse, but WA and now Carmel, NY!  He was QRP too.

But enough of that... I just finished ordering all the major components for my 8 FET 40 meter class E RF deck. 

https://www.youtube.com/watch?v=WZcqkTIOZRU

Jon

[ka1tdq]

For the record, the IXDD blew up and the FET caught fire when I put 48 volts to the drain.  I had to tear it apart and rebuild it.  This time, I put 3 turns on the secondary winding and now I'm getting 5.5 watts output. 

Jon

[KD6VXI]

If you're using an irf520, those are good to about 45 watts,  pep,  at 'ten'  meters.   The CBers have been using those as a 2sc1969 replacement for years.   About 8 to 10 watts carrier,  max.

They also have a sine to pseudo digital drive converter with a diode and couple resistors.   Squares off the sinewave.   Can't imagine what it does to the spectrum though....

--Shane
KD6VXI

[K4RT]

For the record, the IXDD blew up and the FET caught fire when I put 48 volts to the drain.

What with the fires & explosions, your shack must be a fun and interesting place.    

As they say, nothing ventured, nothing gained.

[ka1tdq]

My wife happened to be in the shack when I was testing it.  When I went key down, everything went pop/sizzle/flame.  The flame caught the wire insulation on one of the output toroids on fire and I had to blow it out.  She said that she wished she was recording the event because it'd get a lot of hits on YouTube. 

Then she brought up the time when I got zapped by HV on my linear, and that would've had lots of YouTube hits as well. 

Jon