VK2BLQ Builds the High-School Direct Conversion Receiver

It is truly a thing of beauty.  Stephen VK2BLQ built it just as we designed it, so his build (like those of several others) serves as confirmation that this design is ready for the high school students. 

Stephen writes: 

Bill,

Don't worry, you are not alone out there.

Here is my build; sorry that the front panel is overexposed and hard to see, but it is plywood.

I did follow the schematic but due to the contents  of the junk box there have been some component changes.

The only thing that I had to buy was the 3/16 x 50 mm (2 inch) brass screw.

My calculations for the coils for the PTO and  BPF  were  a little  bit off necessitating padding down the PTO with a further 100 pF (easier than remaking the coil and mounting)  and removing a few turns from the T50-6 toroids.

Like other people have found: the audio takes off at full volume; I am thinking but not yet tried adding decoupling between R5 (15K) and C2(47 uF). It isn't the actual values of the electros as I had to use 100 uF so might be the audio output getting back into the earlier stage.

The tuning range I get is  our 7000 to 7200 KHz and some shortwave stations above and below, Turning the screw is a little bit fiddly, but once tuned the vfo is quite stable and the audio sounds good.

Best wishes,

Stephen

VK2BLQ

I really like the ruler near the tuning control.  Is that (I hope!) the frequency readout? 

Rick N3FJZ Completes Build of High-School Direct Conversion Receiver Project -- LISTEN!

Rick N3FJZ has completed his the direct conversion receiver that we will soon be building with students at a local high school.   See video above. 

We are hoping that a number of people will build the receiver as we designed it.  Some folks have sent us versions of the receiver that they have built, but these versions often include significant deviations from our design, rendering them less-than-useful in checking our work.  Rick built it just as we prescribed.  His build is very useful in confirming the validity of our design.  So if you are working on one of these receivers, I would encourage you to -- for the moment -- dispense with innovations and build it the way Rick did:  as per the design we have been using. 

We know that our design is not perfect.  But we have decided to stick with it because it is very simple and very easy to explain.  Examples:  We know there is an impedance mismatch between the mixer and the AF amp.  But fixing this would introduce complexity that we want to avoid.   And the receiver works fine with the imperfection.   We know that a push-pull AF amp would probably work better than the one we have.  But we do not want to have to explain push-pull amps, biasing schemes, and PNP transistors in this short introductory course.  So we stuck with three common-emitter AF amp circuits and an 1K-8ohm transformer. 

Rick did a really excellent job not only in building this receiver, but also in documenting it.   His diagrams and drawings are really superb.  We will probably use these in our presentations to the students: 

http://www.remmepark.com/circuit6040/SolderSmoke-DCR/SolderSmoke-DCR.html#AUDIO_AMP

We will keep all of you informed on the progress of this project.  We will begin this week.  But if you are still working on the receiver, please send us your work,  even if it comes in after we begin the course.  

Thanks Rick! 

To Re-Cap or Not to Re-Cap -- Curious Marc on the Electrolytic Controversy in Ham Radio

A while back I got some fairly acerbic feedback when I DARED to suggest that perhaps it would be a good idea to replace the old electrolytic capacitors in ham radio equipment.  It was as if I had attacked motherhood and apple pie!   

Yesterday I was looking at CuriousMarc's YouTube channel and I came across the above video.  While I had been in the preemptive replacement camp, Marc makes a good case for leaving some of the old caps in place.   The fact that the electrolytics usually are open when they fail, and that there are fuses in the power supply to protect the transformers,  are important points.  His admonition not to replace electrolytics with tantalum caps (which fail closed) was also very useful. 

OK, my flame-proof suit is on! 

CuriousMarc (AJ6JV) Goes to a Hamfest

Jean Shepherd once said that all of us at one point come to a cross-roads in our lives -- one road leads to success, the other to ham radio flea markets.  

As I watched this, I realized that CuriousMarc sounds like a ham.   Sure enough, some Googling revealed that his real name is Jean-Marc Verdiell and his ham radio callsign is AJ6JV. 

I knew Marc was one of us when, in the video, he opens up the teletype.  He says that the seller claimed that it still worked.  But Marc comments that he hopes that this is not true, so that they will be able to troubleshoot and fix the device.  FB.  That's the spirit.  

We are really lucky to have someone as successful and creative as Marc in the ranks of ham radio operators.  

Be careful with the high voltage Marc!  

Checking Into the Vienna Wireless Pow-Wow Net after 23 Years!

 

I used to check into this net with my HW-101 from 1996-2000.   Last night I fired up my uBITX, hookied it up to my CCI .1 kW amp, and tuned the 75 meter doublet for 10 meters.  Bill AF4LL (Mr. 10 Meters) was net control.   Mike AE4R was also on frequency -- he was there the last time I checked in too.   It was fun.   

The QSL card shows the transceiver with the LiPo battery that was powering it. 

Direct Conversion Receiver Bandscan -- 40 Meters early on a Thursday Morning -- With W1AW/4

I superglued a San Jian frequency counter to the front panel of my High School Direct Conversion receiver.  Then I tuned it through the 40 meter band.  You can hear the W1AW/4 station.  And several SSB stations.  

Hammarlund HQ-100 Misidentified in 1963 FCC Film

Oh the indignity!  It appears at 7 minutes 16 seconds in this FCC film.  It is clearly an HQ-100, but the FCC subtitles identify it at an HQ-110.  It is clearly an HQ-100 ( the model without the clock). 

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

As the owner and operator of what must be one of the few remaining HQ-100s, I feel obligated to defend the reputation of this fine piece of shortwave gear.   

How many of you have HQ-100s?  

Curious Marc's Lab and Workshop

This is the guy who has done all the amazing videos on the Apollo communications systems.  And a lot more. This look at his lab is inspirational.  

There is so much to see here.  But a couple of things really caught my attention: 

All of the RF electronics in the Apollo spacecraft was made with discrete components -- the only chips in the spacecraft were in the computer.  And in the Apollo systems, they welded the discrete components in.  No soldering.  Welding.  That's hardcore.  That is how they got to the Moon.  

Curious Marc's YouTube channel:  https://www.youtube.com/@CuriousMarc

Rick N3FJZ Builds the Mixer for the High School Direct Conversion Receiver

Wonderful progress from Rick N3FJZ.   Having completed the PTO,  Rick went on to build the diode ring mixer and diplexer.  (See video above.)  He then connected these to boards to a band pass filter and an AF amp from previous project.  And wow, the resulting receiver sounds really great!  I think it sounds better than the ones Dean and I have built.  

-- It will be interesting to see how Rick's receiver sounds with the very simple AF amplifier that we are using.  

-- We need to get Rick a coil form for the PTO variable inductor! And getting him the PTO form will allow him to dispense with the varactor circuit (which, I must say, is pretty cool). 

-- In the PTO, for the coupling capacitor (C15) , I now have a 260 pF NP0 cap.  But your .1 uF ceramic disc seems to be doing just fin.  So maybe we don't need the NP0. 

-- I'm glad that Rick grounded the brass screw.  Without that, the hand capacitance effect is bad. 

-- I think results will be much the same with the dual tuned circuit bandpass filter that we use.   But it will be interesting to see if Rick's triple tuned circuit helps with AM breakthrough (I think I heard Radio Marti when Rick tuned to the top of the band). 

-- I haven't had a hum problem and I don't think Dean has either.   Dean is running his on two 9V batteries.  Maybe that would take care of the hum.  Our PTOs are completely Al Fresco! 

-- The Traders Net sounds like fun!  

Thanks Rick!  73 

Hugo Gernsback -- Was he Like Wayne Green?

"The Electrical Experimenter" sent to me by Nick M0NTV reminded me of Hugo Gernsback.  Many of the radio books I have on my shelf have his name on them.  He played a big role in early radio and television, and in science fiction. Check out the Wikipedia article on Gernsback:  

https://en.wikipedia.org/wiki/Hugo_Gernsback

I see similarities between Hugo Gernsback and Wayne Green.  What do you guys think?   

Gernsback's TV goggles in 1963 

That's Gernsback watching TV in 1928

N3FJZ Builds PTO for High School DC Receiver

Rick N3FJZ has stepped forward and is building the direct conversion receiver that Dean and I have been working on.  This will be big help in our testing of the receiver.  See above for the video report on his build of the PTO stage. 

When I saw this, I found myself thinking two things: 

1) Those really are "rigs." 

and

2) I am not alone! 

Years ago, I was having a tough day on 40 meters.  The Waterfall Policemen were gleefully attacking my admitedly less-than-perfect SSB signal.   Unbeknownst to me, someone out there was listening, and listening with a homebrew receiver.  A receiver with a PTO.  It was Rick N3FJZ.  He made my day when he sent this video: 

https://soldersmoke.blogspot.com/2015/02/parasitic-anguish-on-40-then-homebrew.html

Here are the other blog posts on the amazing rigs of N3FJZ here: 

https://soldersmoke.blogspot.com/search?q=N3FJZ

More to follow, both on Rick's receiver and on the work of other intrepid builders. 

Thanks Rick. 

"The Electrical Experimenter" -- A Treasure Trove of Inspiration

Oh this is really phenomenal.  Nick "the Vic"  M0NTV is on the mend from some routine surgery.  While mending he found this 1915 issue of Hugo Gernsback's "The Electrical Experimenter."  I just spent a few minutes quickly going through it and I can see that this is a treasure trove that could keep us -- the modern day electrical experimenters -- busy for a long time.  

-- We see Signor Marconi in Italian military uniform (I never saw that before).  

-- There is mention of successful DX reception of the station in Arlington Va. (just down the road from me).  

-- There is a an article about the radio station of T.O.M -- Hiram Percy Maxim.  

-- There are detailed maps of Mars, complete with the canals. 

And there is a lot more.  

Above all, I think what stands out from this magazine is the homebrew spirit,  the notion that we can and should build our rigs ourselves, and seek to understand them. 

Below is the whole magazine.  Please take a look and use the comment section below to point us to passages of interest to the electrical experimenters of today.  

Thanks Nick.  Your e-mail came during a discouraging period filled with a few "tales of woe."  The magazine really lifted my spirits.  

Here it is: 

http://soldersmoke.com/EE-1915-10.pdf