Snoopy come home...

Well.. decided to try out the BeagleBoard-XM finally.  You know what?  Once you realize that a 5V 1A supply isn't going to cut it no matter what the beagleboard.org instructions say and you move up to a 3A (15W) supply.. then you are fine..  Otherwise it's fun watching the device reboot itself endlessly!

Note the Meanwell supply that I use with the Trimble Thunderbolt GPS Disciplined Oscillator.  It's rated at 3A at 5V (15W) which is what you want to run with the BB-xM.  I hear you can use 2A supplies.. but 3A is guaranteed to run everything.  1A will not work.  No matter what you read.

Here is a picture of the BB-xm running the TI (arowboat) image of Android Froyo 2.2 .. It's cool.

The graphics on the flat panel (big) monitor there is a 3D demo that TI put on the image.  It ain't too bad.. it does show what the device is capable of.  The Android distro though thinks it's on a phone screen so the resolution is a bit limited.

I'm a little disappointed that video tends to crash the thing under the Android native apps.  A sure bet is to try to watch a YouTube video.. Ironic isn't it?  After about 15 seconds it crashes the system fairly hard.

So even though I'd still like to learn how to write an "Android app" I'm thinking that I may be looking for a different Linux distro for Ham Radio and/or SDR use.  (Maybe Angstrom.  Ubuntu is reported to be sick with the Beagle-xM unless you do a kernel patch...)

Interestingly enough a certain ARRL Midwest Division Convention probably will have a class on the BeagleBoard XM on August 5th (Friday)... at the Clarion Hotel in CR.  look at http://convention2011.cvarc.rf.org for details...  We hope to push this as a ham SDR embedded platform-- it has a lot of potential for little financial outlay.

Tomorrow is the ND and OK QSO parties.. I need both confirmed for WAS (and ND on eQSL for eWAS)... so I need to get to bed and work at least five stations from each state this weekend.

I worked OK last weekend but I suspect I'll need to turn a card around to get confirmed from that station.  I'm cheap, I try to avoid spending the $0.10 for the envelope, $0.40 for postage and $0.20 for the card or thereabouts.  I'll save that for DX.  So ND and OK stations.. use LOTW and eQSL.. please?!?

QTU

I have been really active on the air this weekend..  I decided to try to fill holes in my WAS (and DXCC) paperwork.. I decided 25 years I'd do that.  I got the eQSL DX "25" award too.. I figured "why not"?

It's been harder than DXCC on LoTW is (so far)... so "so much" for the "ultra secure" LoTW being the "harder" system.  There are times the ARRL really irks me off (tho I support them greatly).  LoTW is so obtuse that 25% of the DX stations that WOULD participate on it say "hell with it!"  eQSL is "not legitimate" to many.  I look at is as a different award, like CQ awards are.

I did work a 3905 Century Club net, a whole bunch of DX and the Wisconsin and Idaho QSO parties this weekend.  I hope with 10+ Idaho and 100+ Wisconsin that those will get confirmed in eQSL.cc and LoTW.
It is rare that I do 100+ contacts on a non-field day or DX contest weekend.. but I did.  I'll pay for it.  The XYL is already mad at me.

"QTU" is the problem though this weekend... Something is hosed on the shack PC (I'm hoping a dead battery on the Real Time Clock on the motherboard) of the old PC.  Last night I just thought it was Daylight time and the fact that the HRD logbook (but not DM780 oddly enough) has issues with Daylight time transitions.   I probably blew some DX by having the stupid computer changing time on hour boundaries randomly.  I'll replace the CMOS battery and hope it fixes...otherwise it'll have to be replaced.  I've never seen a computer change time by itself.. but it's doing it every hour now.. I don't quite get it.

I also bought on a whim and took delivery of $213 of telescoping Aluminum ordered from DX Engineering.  I'm going to replace my 40m half square (on which I worked South Africa on last night) with a hopefully better performing phased array of two (maybe eventually four) elevated radial verticals on 40m.  If it works I'm thinking I'll need to do a 66 foot vertical too with a pulley on it so I can use it for 80m and 160m.  I'm starting to like the low bands.  In the winter I can do beverages so that should work next fall/winter.

Need to have the ground thaw for a week or two first...

I've not forgotten about the SDR Cube and the AMP projects.. I just wanted to so some spring stuff and operate.. if I never operate what is the point of all of this?

I'm really tired.

TTFN.

Still ticking

This is a time of year for me that tends to get chaotic.. so the ham projects naturally slow down.

I'm also been too lazy to take pictures in the last few weeks too.

Lets see.. I started building up a PIC32MX795 .. but am short the 8 MHz crystal I will need to bring it up for USB use which.. well I might as well.  I did get the boards from Hong Kong to prototype the 0.5mm "PF" center PICs and I've built two up.  I actually, for the first time in a long time damaged one of the boards and PIC trying to fix the damaged pin.  So one of those two are missing Pin 74.. which for my use I do not think will matter.

The boards I used for PIC32 prototyping are about $2 on e-bay and are by "ETT-Team" in Thailand.  They are decent for the price but are a bit heat sensitive.  The one I damaged was one I tried to reflow skillet solder.. I think I overheated the board and that plus having a slightly bent pin on the device that I didn't notice from the sample pack had me do a dreaded bent and shorted pin.  I should have done better with it but I did it in a hurry.

The second one I just hand soldered down and it's perfect.  So.. on those 0.5mm PICs I think I will hand solder.  The 0.4mm leads, even though are smaller.. seems to be of a "tougher" material and actually to me are easier to solder.  If I finish this and then lay out a board, I'm going to go with the PT 0.4mm package.  I had no issues reflow soldering the 0.4mm PT's,,,

I worked the first 9 hours of the ARRL SSB DX contest from the club station at work, under my callsign. I got to use the Alpha 87A and I can see why people pay the bux for those amps.  I was just looking for DX for DXCC (and Alaska for WAS) so I was only "hunting and pecking".  Still on 20m (for about 1 hour), 40m and 80m I worked 86 contacts and 59 different countries (including AK & HI).  Not bad.. was fun too.  I wanted to get back on 20m the next day, but our local NWS spotter training was on Saturday and I had to do or I would have lost the credentials.  I bet I could have done 25 more countries the next day.

I want to get back and finish the amplifier.. I suppose I ought to.

I also have a BeagleBoard-xm coming still and I'll use that as a distraction on my other projects too.  There is interest in using that as a basis for a self-contained (including Latency) SDR within the W0CXX club.  We will see if we have time to take that on also.

I also found a deal on a HD Radio to play with..$19.99.. so far, I can see why it's a dead end technology.  In Cedar Rapids, only one commercial FM station (KZIA) has HD (hybrid digital, not "high-def" by the way).. and supposedly two AM's do 1450 KMRY and 600 WMT.   I got the HD signal to lock on KMRY for about a second and it sound surprisingly good.. but it's not usable.  I'm only about 20 mi away from the transmitters too!  600 WMT is very strong here, and I'm wondering if they turned off the HD signal?  On FM, KZIA's HD subchannel 2, a classic rock station, is very good.  The non-commercial stations, three, are all very good though.. there are additional subchannels that have NPR programming on them.. and in one case the NWS weather radio-- that sounds better than over the FM weather radio.

I was hoping to try DXing digital AM.. I like in the country and have put up beverages in the past, and EWE's Flags, K9AY loops are no issue either.  But I doubt if the signal levels I'm feeding the radio with on 600 and 1450 aren't cutting it for HD AM.. neither will a DXed station from a Beverage.

So I'd say when I replace my failing factory head unit in my car I'll spend the extra $15 difference just to get the WX radio off of KCCK...well that and the very good HD2 channel of KZIA.

But when the difference was $100-$200?  Who'd ever buy that?  It's one of these technologies that could have been very good if it wasn't implemented in such a "half-fast" way.

Anyway.. that's all I've been doing lately for "fun stuff"...  When I make progress on any of my open projects, I'll let you know...

Busy... and all the stuff since last time!

I didn't want anyone to think I've dropped off the face of the earth being more than a week since I posted..

I've not felt overly well.. something is going around Cedar Rapids that everyone I know feels dead tired all the time.. I have it too no doubt.. all I want to do is sleep... even more so than normal!  That makes it harder to force yourself to work on projects until midnight when you get home at 8:30 PM from work! :O)

I showed off the SDR-Cube to the Collins ARC, ordered a TFT display from China (touch screen $29 bux delivered)  on e-bay and got some PIC32MX's to play with sampled.. I want to port the DSP-Cube GPL'ed software to that platform... that'll take me a while to get the stuff and to hack it together and to then get something running.  I sampled and got some PHY's from National Semiconductor (thanks NS and Microchip) and will make the PIC32MX795's I have do Ethernet as well.  I'd like to lay out a board with a PIC32MX, a National PHY and magnetics, with the interface to a CODEC and the TFT module... maybe in calendar 2011.. we will see.  It takes a lot of time to do this and I'm thinking Kicad instead of Eagle this time.. so I need to learn that as well...  In the meantime it will be protoboards and point to point.. but that's fun too...

Being that I am a masochist I also ordered off a BeagleBoard-xm.  I think that could be a higher end SDR platform than the DSPic and PIC32MX.   My talk at the Collins ARC convinced me to pull the trigger on this.

I fixed up the shack PC on Saturday (yesterday)-- windows update, etc.  I worked the Feld-Hell sprint... it was unusually fun.., and also later that night decided to load, dual boot Ubuntu on to the PC, while listening to the AM guys on the Antique Radio QSO Party.  I did this all on the old Kenwood because I didn't want to futz with the temperamental Flex-1500 and only run QRP 5W... maybe when the AN-762 is done...

I am a Linux advocate, but for God's sake, people-- will you ever just get a distribution done that works out of the freakin' box?  The Ubuntu 10.10 ran off the CD okay but crashed big time when I installed it dual boot with Windows.  This has happened for the last three years/attempts (once a year) at installing Ubuntu.  What happened this time is that the computer I put it on (the shack PC) is a dual Pentium-D "mini" PC that I added a "small form factor" (it's a SFF machine) Nvidia card to...  I wanted dual monitors and no ATI I could find would fit!

Well.. the install set "X" up the Ubuntu boot for the proprietary NVIDIA drivers but never installed them!  Huh?  What?   CANONICAL:  NO FRICKIN' EXCUSE!  NONE.  NADA.  Next time: Fedora! You bunch of Commies!  (That's another issue I don't like about Ubuntu.. but I won't make this political except for hints of my ideas...)

No "NORMAL" person wants a four hour @#$@#ing debug session after the install.  I'm a freak, and I don't want it.  Last three times I've had it and it's always been because of my "weird" hardware.  You know what?  It's not weird and that is an excuse whether you like it or not!!  And all three of my computers being weird?  Nope it's Ubuntu thats weird.. sorry...  It's been video 2/3 times too..

I installed the NVIDIA proprietary driver directly.. it worked fine after that.  But that was hours later...Once I finally updated half the CD (over 400 MB!)  from my slow satellite internet (why the hell did I get the CD image on the fast connection at work in the first place?  You suck Canonical...Sorry no other way to say it!)  and then got the thing to finally come up in recovery mode in console mode and typed "startx" and saw the error... uugh...

Got on the net and found how to install the NVIDIA "horrible proprietary" driver manually.. did it, rebooted it and it just worked.  Hmm.. how bad is proprietary software?  Maybe a lot.. but in this case it made the system usable.. which is more than it was from the Canonical Ubuntu stock install!   !!!! 

Really.. I don't want to hear that crap that Windows is harder to install than Linux.. Ubuntu is supposed to be the desktop Linux "for everyone" (Commies... sorry I did it again...).. and I'm a software engineer who at one time submitted stuff for the Kernel.. and because of this was able to debug a basic install that I shouldn't have.  What?  15 years after the first Linux install I did?  NO EXCUSE.. NONE...  I got it but it was insane to have to debug the install on such common hardware!

If I want to be serious about running Android on the BeagleBoard-xm I needed to get a decent i386 Linux running again.. so I am there.  And I'll be happy to run Linux again.. but it's the last Ubuntu I'll ever do.

I do have an image of Android for the TI ARM based Beagle ready... hopefully Mouser will ship 3/8/11 like they estimate.  I figure that board will be a good learning experience for me.. maybe I can get my nine-year old to program that.  I have to say that I plan on teaching my children programming the way I learned it... that is from small "embedded" (I did 8080's and Z-80s starting in 1977 and back then that wasn't embedded... but that is the power of current "embedded")...8-bit to 16-bit to 32-bit to doing the BeagleBoard to VisualStudio.  If I can teach them that way I'd feel good about doing that so the kids can actually understand low level...

I operated the FeldHell contest this weekend plus some random PSK.. so I finally got on the air again too.. I need to get my CW up so I can do some.. but, my god.. 40 WPM+ on the DX contest.. I'll never get there.. I'm too retarded when it comes to "automatic" responses to learn Morse that way... hopefully I'll get on the weekend of 3/5.. I really want to get those 25 countries I need for DXCC and those 15 states to finish up WAS...

Again, being  licensed for 25 years I'm trying to make up for lost time on the radio front.. I'll get there eventually...

I did build up the filter bank on the K5OOR board.. but haven't had time to tweak on a VNA on work yet.. I will post details when I get there... until I do... Sayonara...

This week in W0FMS Amateur Radio

Getting busy... hopefully no one missed me too much.  I'm probably the tree falling with this 'blog anyway..

First of all I prepared for the CVARC (local ham club) "show-n-tell" and got totally outclassed by Dave Cripe NM0S... well someday I'll get to his "QRP" greatness.. I think I might have took second place there.. but nice thing about CR is that there was at least two other tables of good projects there.

Lets see.. Had "issues" with the 5W class-A RD15HHF driver amplifier.  The issues really were the 0.1 uF "SURE" 0.1 uF "50V" (really 16V) 0805 capacitors.  Once I got them to smoke .. and replaced them with surplus Kemet mil 100V leaded (chips inside the package tho) caps... well the amp is as designed.

I think probably more cheap Chinese 0.1 uF's are in my future, though (since I ordered a full roll of 4000 of them off of e-bay this week....!)  The solution for that is to parallel a bunch of them.  Everywhere in the circuit I had three or more worked/survived..  Two or less...*POOF*  (NO MORE POOFTERS!).   Weird low pass filters got created on the +12V supply to the FET and then smoke "on the bypass.. fire in the cap" when I got fed up and pushed them.  Kemets fixed the situation.  More than three cheap Chinese caps seem to about = one good American cap.  One American cap $ = 5-6 Chinese.  Solution: 4 or more Chinese..

New board (post capacitor fire) looks like this:

New Schematic...

Puts out 7W.. 5W somewhat clean at 700 mA Quiescent (yeah this isn't efficient but could be used at 2-3W *without* low passes and is flat from about 1 MHz to 60 MHz)  At 5W about +20 dBm is needed clean it drive it.  Gain is 18-19.5 dB across all of HF and into 6 meters.

[C8, C9 were the caps that decided they really rather be LED's.. if you were wondering...  they were also the source of my mysterious loss of Drain current with drive and all sorts of other nasty things...]

So that's getting there.  I might just do two of these in series for the driver for the AN-762.  It'd be a bit of a waste of 24W from the power supply but the "Barack Obama" green police are not after me yet.  It's simple and clean.  At 100mW out or less it's so clean you wouldn't believe it (2nd harmonic is down like -50 dBc at +20 out).

Also got the X-Tronic "fix and concession goodies" in.  What can I say.. hot air unit was less than perfect when I got it.  Seller probably knew this.  But seller gives out good amounts of freebies to compensate, buyer is okay with that.

New standoffs in place in X-Tronic 4000 "Hot air + Soldering".  Guess what?  They have only a hot air unit now.. I could have saved $50!   UGH!

But I did get a good amount of freebies and the soldering iron with that unit is decent.  For most the X-Tronic 4000 + soldering iron is recommended..  Freebies follow:

Nozzles.. this time with the correct set of them.  Yes the one I was missing prior to this was the "perfect" one for IC SMT rework.  But I do have a whole new set.  I got a couple of free replacement heaters.  I can't say for sure.. but they are "Gordak" (I think from planet "Ork") replacements for .. well Gordak... and ... well.. Aoyue model numbers.. 850A for example is very Aoyue-ish.  Not saying the Aoyue and Gordak are the same.. but they might be?

If so the X-tronic is a better deal, no doubt.  X-Tronic is "no doubt" made by Gordak.

I got a schematic leaked to me of the X-Tronic 4000 back board.  It's completely analog.. no computer controls the heaters.. so it's safer than I thought to leave it plugged in.. but I still wouldn't because all of the DC supplies are always on to the tune of 12-15W AC.  Unplug it after cool-down when not in use!  The heat gun and iron both use "K" type thermocouples and LM368 Quad Op-Amp comparitor circuits to control the solder heat; the air gun heat and the fan motor on the heat gun.  A second loop shorts off the air gun heat TRIAC but keeps the fan on until the secondary loop says otherwise.. factory cal'ed at 55C on my unit.

The display on the front has some sort of "K" thermocouple to deg C multimeter circuit.  I should dig on the part number and find the jumper on it that will change it to deg F.  $5 says it has one.  (Ok.. I'll not bet.. but it probably does.)

Lastly..

I've needed an impedance bridge for "L" at least for awhile.  I'm cheap I don't want to spend $100+shipping on the AADE unit.  So I won't.  Really, I refuse to.  I had all of the parts in my junk box, so I was so cheap I didn't even get the PCB board.  But it's probably a good thing as my USB sound card (Chinese, of course) for my netbook has R&L channels wired backwards from WB6DHW's board and the original article's Soundblaster Live! card.  That took me a few hours to figure out and fix too.

Anyway.. it's good enough that I can wind my Toroids on it and not bother with the HP LCR bridge at work.. but the HP bridge DID calibrate my loads for this bridge!  :O)

 I'll give WB6DHW credit.  The ICL7660D chip for the negative bias off of the USB 5V (regulated to 3.3V and then made -/+ 3.3V for the LM358 Dual Op-amp by the ICL 7660) was rather clever.  Especially since I "stock" that part (and ordered more from e-bay since I'm getting "low".)    The +/-3.3V is claimed to be safe for the sound card.  Since accidentally disconnecting the Rm load puts +2.0V DC on to one of the channels with no ill effects.. I think that putting the ST 78L33 regulator first wasn't a bad idea after all-- instead of having probably +4.5V DC, +2.0V on a screwup is better on the sound card.  The circuit overdrives the heck out of the card as it is.. but if you follow the author's instructions that is alleviated pretty well.

The negative voltage generator is needed since the Op-Amp is being used as a one to one High-Z to Low-Z device (a "power follower") and attempting to do the voltage divider for the + input doesn't work well in this configuration.  The ICL7660D does though.

The bridge at 4 KHz is good down to about 50 pF.. L seems to be good to about 100 uH or so.. R.. probably several hundred K ish.  Not a bad unit.. very accurate too if you pay attention to the proper impedance of what you are measuring and balance the bridge to 10:1 or better for what your are measuring by adjusting Rm.

Verifying level with a scope makes it more accurate as does taking care to balance the bridge out and set the various "tare" points.

Anyway.. fun stuff this week.. plus I worked to exhaustion at work..  But we are getting that much close to the 100% home brew HF.

Oh, yeah.. I ordered off a 320x240 color TFT panel from China to hook to one of the PIC32MX's I sampled and otherwise have floating around (I very well might interface it to the CUI32 I Have that I *bought*).  Note: If you want one, buy a UBW32 instead.. I didn't find out about that one until later.. I don't get the purpose of Sparkfun selling both...   Ideally I want to take my "PF" 0.5mm sized PIC32MX795F's with CAN/USB and Ethernet, put them on the 0.5mm Proto's I have coming from (e-bay) Thailand (previously I ordered 0.4mm ones only.. because I didn't realize that PIC32MX's come in both sizes.. well... at least the 7XX's do).  This, USB hardware a PHY and Ethernet... hooked to the TFT touch screen.. will be the next logical step for the SDR-Cube Software evolution...

I almost bought a STM32 board (to port SDR-Cube to also) for about $15 more and then I realized that I'd need a $80 JTAG to move to that plus another tool set and learning another tool set.  I don't like Microchip and their "stealing" GCC for profit (which they'll deny I am sure, but in my humble opinion is so as long as the are selling "optimized" versions).. but the tools are integrated.. cheaper and more available in the West than the ARM stuff is.. so for now I'm going to remain MIPS/PIC32MX but use the TFT LCD 320x200 module off of the ARM kit (which is in the $50 range.. the display was $30 shipped and has support in the Microchip Graphics Lib...).. It should be a cool project.  SDR-Cube in living color.

The SDR-Cube port to that will happen eventually.  Support Juha and George in the meantime.. it's a good project and they deserve your support.

If my hacked together version works.. then a port to the Mikroelektronkia $175 (shipped) unit is certainly possible as well.. that could be the "new platform".

I'm thinking the BeagleBoard-xm after than.. with the real DSP... Why not?

TTFN..

Beginning to make it legal...

Well.. I suppose if next week sometime I will take toroids and toroid winding stuff into work to hook to a L/C meter and a VNA when done to tweak, that I should have the rest of the board ready to go.

Except for getting the 12 pf Silvered Mica (marked, of course "120") swapped for the 120 pF (marked "120 pF").. no issues here either.  Switching out the 120 for the 12 pF and putting the 12 pF in the right place was uneventful as well.. but I did have to fire up the solder sucker to clear out the plated though holes.  No biggie.  Yeah the connectors are mounted on the opposite side of this board than K5OOR recommends, but all connections will have to come off the top because of the way I'm mounting it.

Maybe I should bring this in every evening and try to do a band a night?  We will see...  Some of the toroids are wound differently than "standard" and really should be "tuned" before placed in the filter board and verified on the VNA after for a perfectionist like me.

I'm getting curious about putting RF into that MOSFET amp and seeing how it does, too.  That could be an evening project this week also.  The stuff is starting to come together.  I might have my completely homebrew HF transceiver done by spring.. we will see...

AN762 Bias test & The beginnings of a 5W driver amp for the SDR-Cube...

This weekend I applied power to the AN-762 Amplifier for the first time prior to installing the final transistors (MRF454's) to verify that the bias regulator (the LM723H and bias diode circuit).  CCI stated that a 15 to 100 Ohm load needed to be applied B-E on one of the two MRF454 junctions for some load to the linear regulator/pass transistor circuit.  Then the adjustment range should be 0.5 to 1.0V across the resistor.

I did two 100 Ohm 1/4W resistors in parallel (50 Ohm load) and saw that the range was from 0.41V to 1.11V or so.  So it looks good.  That range is supposedly safe for the PA transistors.  As CCI suggested, the bias was preset to 0.50V.  Nominal operating voltage to the base should be 0.68V or so for class AB but starting off low is a safety margin.

Eventually, the correct way to bias the amplifier with the MRF454's installed is to adjust the bias voltage (really current on a RF Bipolar Junction transistor like the MRF454) so that the supply current drawn with no RF drive is, in the case of the MRF454's, 100mA (minumum) per device, or 200 mA total in Class AB push-pull service.  This can be adjusted up a small amount for IMD improvements, but will end up being in this general ballpark.

I still need to build the K5OOR switched filter module.  I really need access to a L/C meter when winding so many toroids (uuuughhhhh.. necessary here for many reasons though) , so I'm thinking of bringing the board in to work next weekend Sunday or after work several nights to do this.  I need a decent LC meter (or at least "L") some day... it is on the list.  The one by AADE seems to be the best hobbyist priced unit, and likely that is what I'll eventually get.

In the meantime, I decided to start experimenting with the Mitsubishi RD16HHF1 RF MOSFET that is readily available from RF Parts and the "Toroid King W8DIZ" (Kits and Parts.Com)

It's a single device, Class-A design.  I suspect that the part is intended for use in CB radios, so a singe device at 4-6W.. seems about right for that service.. :O)

Mike Collins KF4BQ has spent a lot of time playing around with this device in the requisite power range (5W ish) needed to drive the CCI / AN762 Amplifier to full power (on the "Mobo" project) and it seems it is capable of this with low-IMD output in a single device configuration if one is willing to trade off efficiency and run the device in Class-A.  What do I mean by this?  KF4BQ recommends 400-600 mA of bias to run these in Class A... the 100W AN-762 in Class-AB only needs 200 mA quiescent!  So there is a definite efficiency trade off.  This means for fixed station use, it's probably fine.  For battery, AB with worse IMD on the 5W driver might be a better design.  (Or of course Class-C for CW folks and maybe someday class-E and the more esoteric efficient amps...)

Class A is a good way to start experimenting with a device, obviously, for linear service.   I decided to take one of my 10 RD16HHF1's and built a prototype testbed for this.  If it is sufficiently clean to drive the AN762 with 400 mA of Bias, I can live with that for fixed station or even 12V mobile use for ICAS amateur service.  The circuit is simple enough.

Here is a drawing of the first version prototype.  It's meant to be driven initally on 20m with the TXPA (PAF-3) at about 750mW (I can drive it down now with the 1.01 SW).

The circuit is more or less stolen from Mike who in turn stole it from the "box.de" group.  However there are not many different ways of doing a N-Channel MOSFET class A amp, anyway.  The only clever thing about these amps are the "balun" designs which...effectively are RF Autotransformers instead of the normal transformers with two unconnected windings for broadband transformation.

The input impedance is set by R3/R4 to 50 Ohms (which will likely change if another driver stage is used).  There is roughly 8 dB of attenuation shown here so I can run it with the 750 mW or so that I'll put out of the SDR-Cube.  I'm guessing about 17dB of gain once I get the feedback tweaked.. maybe I can lower that to 15 dB or so for better IMD.  We will see in several weeks.  It took me quite a while to draw this up and build it because it took me a long time to re-learn Eagle (light) but the advantage to this is that once I get the amp working.. I'll have a few PCB's made up at Batch PCB (or elsewhere)...it's easy to do if you start in the PCB layout software from the beginning.

I intend on putting a small driver in front of this amp.  I am guessing that the drive at the gate needs to be right about +20 dBm (100 mW) so I really want to make a broadband amp (probably another class-A device -- smaller).  I am thinking that the 2N5109 at kitsandparts.com is ideal, but I have a lot of surplus 2N2219A's in the drawer of junque.

So likely there will be a 2N2219A amp built in front of this for the 100 mW ish drive for this driver in the next version of the amp.

Anyway, the one above looks like this when hacked together of old parts:

The bias circuitry on a MOSFET is voltage controlled.  I assumed that 5V would be enough.  It would in Class-AB push-pull.  To get this comfortably into Class-A range, apparently 400 mA of quiescent drain current is needed.  This was at about 4.82V on my device.  Many of KF4BQ's data seems to make me think that up to 600 mA might bee needed for good IMD.  That's at about 5.11V with my device. Not going to get there with 5.00V.  

I solved this by putting a "cheater" diode in between the 78L05 ground connection and real ground.  This raises the maximum bias voltage to 5.71V or so which is probably still safe for the device and allows up to 675 mA (on my device) to be "dialed" in with the bias pot.  Also I added a 8.6K resistor in series (on the "low side") so the overall adjustment rate of the 5K pot (13.6K total.. okay since the gate has such a high impedance and low bias current draw.. it's a MOSFET remember).. is more in the "actively biased" range.. rather than having all of the action at the last 15% of the pot travel it's now more like 65% of travel.... it's good.

I have my amp adjusted to 400 mA.  I will next feed in RF from a sig gen without the 8 dB atten, or the SDR-Cube with.. see first what RF power output we get and verify nothing starts smoking.  If it looks right then a directional coupler, attenuator and the Spectrum Analyzer will come out and I'll independently verify Mike Collins' results.

Then the 0 dBM to +20 dBM BJT amp would be next.. and then.. well the 100W amp.  I should finally at that point be able to go from 1 mW to 100W with the solid state and then 800W with tube amp.. all with home built equipment.

It'll still be awhile but I'm headed there.

One immediate change to the amp is that some sort of PNP or P-channel device, in a "high-side switch" configuration,  will be needed to turn on/off the regulator for bias.  With the bias off the device draws almost no current, so switching the entire amp off with a relay is not needed.

I've done this all the time with P-channel Enhancement mode MOSFET's... but I'd like to use something smaller and cheaper.  I'm wondering if the J176's I have would work.. that or 2N3906's.  The 3906's would but an additional NPN stage is needed for the safety of the 3.3V or 5V microcontroller.

I still need to think that one through.