After a year, I finally added a MeanWell DC-DC converter to eliminate the need for a second (-5Vdc) power supply.

Here it is tucked nicely underneath the improvised Arduino shield - in the only remaining space inside of the PeaShooter. 

Amateur radio just isn’t holding my interest these days.  I’ve abandoned plans for the 6146B “Tube Defined” Amplifier - primarily because the bands are just in poor shape.

I am building a tube-type amplifier for the iPOD instead.  You can follow my blog here:

http://tubeamp.tumblr.com/#

In the intervening months, I built my own CNC Router, that blog is here:

http://dustbot.tumblr.com/

The PowerMate didn’t last long in its virgin state - I’m after a real PTT solution.  Clicking on the MOX button in PowerSDR or tapping the space bar on my keyboard are not going to work for me. 

So,  I’ve hacked into the PowerMate with an interface that will allow me to electronically generate the TopHat press to toggle the MOX line over the USB interface.  I added an optoisolator in the base of the control to avoid level problems and brought the interface out over a 3.5mm stereo cable+plug which will connect to the back of the PeaShooter.

In the PeaShooter I’ll use a Microchip 12F675 which will be watching the PTT switch in the microphone connected to the front panel RJ-45.  When it sees the op hammer down on the PTT bar, it will generate the needed pulse to simulate the TopHat press to key the TX.  Likewise, when the TX is keyed and the op drops the PTT bar, the TopHat press will toggle again to unkey the TX.   It’s a lot of work for something as simple as PTT, but somethings are just more difficult in the SDR world!

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postscript…

12/16/2010 After adding this feature the PeaShooter feels more like a radio to me.  I can tune the transceiver with the PowerMate and, when I want to talk I simply push the PTT bar on the microphone and start yammering.  The laptop makes for a great front-panel but now I don’t feel so much like I’m using the computer.

I checked into the SouthCars net on 7.251MHz  this morning and got a resounding “welcome aboard” from many who were hearing me.  I’m continually amazed at what can be done with 5W on SSB with this software radio design!

South Coast Amateur Radio Service

http://southcars.com/main/

I added the Griffin Powermate and am using it primarily for tactile reasons.  It does make the tuning a bit more natural - plus it looks cool and feels pretty nice in my hand!  A push-down on the knob toggles the MOX which, for now, is still a bit awkward.  I am hoping to integrate a PTT interface from the microphone in the near future.

Q.  What’s uglier than a Software Defined Radio transceiver?

A.   A thoroughly modern amateur radio station.

I’m very fond of some of the latest transceivers on the market.  Ok, I don’t like any of the transceivers from the Big 3 (Yaesu, Kenwood, ICOM) that look more like a piece of furniture than communications equipment. But I do like the Kenwood TS-2000,  the ICOM IC-7200 (very much!), and the Yaesu FT-897D.  But an amateur radio station completely devoid of one or two “historical pieces”, to me at least, is a little bit dull.

I certainly want (need?) to add some new technology here - but the Yaesu FT-101ZD is staying!  As is this little meter that I picked up recently.  I’d hoped to use it in a 6146B amplifier that I want to build.  But when you’re shopping the flea markets sometimes you’re not quite sure of what you are getting.

And this meter movement is just not sensitive enough for the amplifier.  So, I’ve mounted it proudly atop the Peashooter so that I can watch the transceiver supply voltage and marvel at how far we’ve come in the last 100years of radio. 

Go buy something old and polish it up — You’ll be glad you did!

I finally figured out why my little MFJ SWR/Wattmeter was prone to give me odd readings occasionally.  Bless MFJs little heart, but rivets have no place in any piece of RF gear.  The four that were holding onto the SO-239 connectors had all but fallen out!

For over 30years of Amateur Radio - I’ve mostly been a listener.  So the whirring noise of a small fan to keep the 2x2N7000 PA finals below their melting point for the few occasions when I’m actually transmitting was more than I could take.

So, I decided to throw together a 12F675 PIC and a thermistor to do the work of keeping things cool when needed.  After frying a handful of transistors it finally dawned on me that a resistor in the base circuit might be a smart idea!

This morning I checked into every 40M net I was hearing.  And they were hearing me too.  The refrain was the same wherever I went, “you’re not very strong”  and then a bit later “wow, for only a few watts you sound pretty good!”

VERY satisfying!

These are my two new grandsons - yes there’s more to life than playing with toys!

The MIC preamp is in — built on a riser card as is my habit for afterthoughts! Tonite I’ll see if I can snag a contact or two and get a critical audio report.  Here it is, the IC amplifier laying on it’s back.

Shortly after my first SSB QSOs, while experimenting with some preamplification on the MIC-IN,  I “popped” the 2N7000s in the output stage of the PA.  So I thought I’d ~upgrade~ to the beefier BS170s.  I ordered 10 of them.

The most misbehaved transistor I’ve ever used.  I’m back to the 2N7000s!

Second SSB QSO was with Barry, K4BBL about 100miles to the east.  Barry was nice enough to appreciate the weight of the moment and sent me this QSL card.

I’m ready to declare victory.  The PA section, after many weeks of wrangling, looks like a winner.  I’m very pleased with the voice quality that it yields and the power level is adequate for most <100W linear amplifiers.

This has been a wonderful experience, every piece of the design challenging me in one way or another.  My new workspace is a joy and will be a year-round refuge from the heat and cold of the garage.

There are many pieces of this design that were not completed:

• the PA section is only good out to about 10MHz.
• there is no bandswitching on the RX bandpass filters or PA LPFs.
• it’s uncertain as to whether the RX works at all beyond 15M.
• …

So this is my SDR “baby”.  In a diminutive 5inx6inx2in package, absent any knobs or switches, and as ugly (in a very charming way) as any others I have seen.

But make no mistake, I am a convert to the technology!  This radio is constructed using point to point wiring and the performance is very respectable.  RX readability on very weak signals is quite remarkable in fact.  I can only imagine how much better it might be on a properly designed PCB. 

There are some things, however that don’t quite sit with me.  RX spurs top this very short list.  Although I saw a big improvement when I relocated the Si570 next to the I/Q demodulator, spurs are still an annoying phenomenon that disturb my sense of peace and well being as I tune across the bands.  I think they are a fatigue factor at a minimum and worse case can cover up some weak signals that may otherwise be copyable.  Spurs are evil.

The only other item on my list is that I just don’t feel like I’m driving a radio with that mouse in my hand.  It just hasn’t given any satisfaction from the operability perspective.  Perhaps the Griffin PowerMate or Contour ShuttlePro device could help with that.  I may have to give one of those a try.

The Peashooter will now take it’s place alongside my Small Wonder 40M QRP CW transceiver, and the grandaddy Yaesu FT-101ZD.  I’ll continue to collect parts for the 6146B Linear Amplifier project that I hope to complete in the not too far distant future.  

For those of you who have been following: thanks for showing an interest!  I think that it’s vitally important to be a creator - to create ideas, to create things, to create opportunities.  I think that when God created mankind in His image - He gave us all the ability and curiosity to carry on, in smaller ways, what He started! 

Keep creating!

Charlie

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p.s.  Nice way to finish up.  I had my first SSB contact this evening (10/6).  I received a 5x5, but Bruce mentioned I was nearly “armchair” copy towards the end of the QSO.  I think he was just being nice!

— p.s. 10/12/2010

I’ve decided that the Mic input needs a preamplifier stage before it is sent off to the LINE-IN input of the sound card.  The absence thereof can explain the poor signal to noise ratio that I’m experiencing on SSB.

In an attempt to create a reasonably linear 2-3W output, the 5th iteration of my PA design consists of three stages:  The first two are a direct lift from the SoftRock v6.3 TX and the third a pair of 2N7000s driving the output transformer. 

In a previous attempt I’d hacked this together across two interconnected boards and thought I was getting close to something workable.  I had the IRF510s as the final stage at one point but convinced myself that they were just not going to behave.

So, in the next day or so, I’ll go over the new PA (picture) with an eye loupe to make sure I’ve wired it correctly before I drop it into the Peashooter SDR for initial testing.

I’m hoping to wrap this up soon!

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p.s. very linear at first glance and willing to make 2-3W keydown easily.  The 2N7000s have very meager drain current capability so I’ve cranked the gate bias down to keep things happy.  Somehow I got Tx I/Q switched around again.  After switching those again,  the SSB voice quality seems pretty decent.  Any chance I could raise a QSO on 2W?