The Dummyloads

Where ham brains come to fry

Where ham brains come to fry

Archives for April 2018

Local Oscillator and Connecting the Chips

If you remember from last post we had the power rail all wired up to the sockets.  The next step is to connect the chips with the various capacitors, finish the audio out and start the Local Oscillator.  You will see in the picture that I have fixed the power wire for the LM386 and it is now wired to pin 6 which is the proper V+ pin rather than pin 7.  You will also note that indeed the power jumper created a small issue jumping from pin 6 and 7 of the NE602 over to the start of the local oscillator.  A good foot note for future builds to think about that a little more.  Other noteworthy lessons on this section are:  1.  My canonical tip for my Weller soldering station is not a great choice for melting the Krylon and getting a good ground solder bead.  Nor is my wet pad a satisfactory device for cleaning my tip.  There is a significant delay in having a clean tip and being able to melt solder that is sufficiently annoying.  As a result I went to Fry’s in Arlington, Tx and purchase an ST2 and ST3 soldering iron tip as well as a Hakko tip cleaning bucket.  This definitively made the soldering process better!

The only other notable step from this section was that I purchased a bunch of alleged NP0 caps on eBay.  They were shipped on the slow boat from China.  When they arrived they looked like ordinary ceramic capacitors and in no way looked C0G or NP0.  So I decided to try to test these out.  I took out a 680pF capacitor and put it on my AADE meter.  It was within tolerance of expected C value.  I then pulled out my YL’s (wife for non-amateurs) hair dryer.  I then kicked it on low and started heating up the cap.  It went from a cool room to hot enough I preferred not to touch it.  Total change is capacitance.  1 pF.  I’m still learning, but that seems to be well within tolerance for an NP0 capacitor.

The audio chain only needs the actual 3.5mm jack.  The LO only needs toroids and the final variable capacitors.  Then I will start on the front end.  This project is getting real!!  Hope to have it make noise soon!  When I do get it to make noise I will try to post video!

Hiking With Radio

The title is slightly misleading. While I did go hiking and I did take a radio, each night when I got to camp I was so wiped out I never set it up. I just didn’t have the energy to do it. I did take my GoPro and I thought you might enjoy the story.

More building next week!

Touching the Front End

Since I was using a different gauge wire, I checked my result

At the point I left off last time I nearly had the LO complete.  Winding a toroid and connecting all the pads was the last step to close that stage out.  For this step I opted to go ahead and do the toroids first.  I don’t understand why people dislike toroids so much, it really isn’t that hard.  This build was a T-37-6 with 21 turns of #28 wire.  (The schematic calls for 26, but I didn’t have any.  I did the calculation for what the inductance should be and measured my result.  They matched.)  Every time you go through the center of the toroid, count 1. Easy!

If your wondering about my L/C Meter.  They are unfortunately unavailable.  Its a really sad story. . .

This is the front end nearing completion

Since I already had the pads laid out for the local oscillator I finished up that section.  I still hadn’t decided how I wanted to do the tuning capacitors for this receiver.  I really am not in the mood to use 2-80pF variable capacitors.  I opted to go with a 0-50 variable cap that you need a screwdriver to tune for the band spread and a 20-107 pF air variable for the regular tuning knob.  With that decided and done, laying out the pads for the front end began.

The front end is a pretty simple circuit.  A toroid that matches the local oscillator, an on the board capacitor and a couple of trim caps.  The tricky part of this stage was making sure everything would fit.  The particular variable cap I had chosen was pretty big relative to the remainder of the board.

A picture of the board with all of its hardware and a 9V battery for a size comparison.

The particular day I was working on this the family had a variety of activities planned and I had to stop a couple of times and then start back up.  About 5p I had finished everything.  I decided to go through and double-check all the solder joints.  Then I realized that I had forgotten the 3.5mm jack for a speaker or headphones!  OK fixed that.  I double checked all the solder joints and all looked well.  I installed the ICs.  When installing ICs you will need to bend the leads ever so slightly inward so that they fit in the socket.  It is easiest to do when they are IN the socket.  Lightly press one edge of leads into the socket to bend them ever so slightly inward.  Then gently set the IC into the socket from the back and roll it forward.

 

Feeling very good about my progress and nervous about the next steps.  It’s time to apply power.  More to come!

How To Set Up a Park Portable Doublet

We had our park outing and I took some time to make a video on how to set up the park portable doublet.  If you have any questions on how to set it up or make your own, let me know in the comments below.