A 1941 Simplified Superhet

 

One of my favorite homebrew receivers is the one I built  based on the "Two Tube Superhet Receiver" shown in the 1941 ARRL Handbook. This one has a regenerative detector running at 1700KHz with a tunable convertor stage (covering 80 and 40) and a single stage of audio.

After few minutes of playing with the two tube superhet on 40 meters I decided that a BFO was needed for reasonable CW and SSB reception. The two tube superhet became a three tuber. The regenerative IF remained. It is not typically run into regeneration but just below to improve IF gain and selectivity. As a modern safety measure I RC coupled the headphones into the plate circuit of audio stage rather than directly connecting them. Read about this project here.

I then decided to make a major improvement by adding a crystal filter. This gives this simple receiver almost single signal selectivity. At 6dB down, the bandwidth is only 250Hz. Inserting the crystal into the middle of the regenerative IF stage feedback loop allowed regeneration to make up for crystal insertion loss without adding an extra tube. Also modified from the original was changing the regenerative detector from 1/2 of a 6C8 to a 6J7, adding better bandspread and a front panel BFO adjustment. The attenuator on the antenna input was added after experiencing problems from strong signals overloading the receiver. This version is described here.

The single AF stage really did drive a speaker very well. As built this is a headphone radio. In addition it needed an external power supply. I built another AF stage (with a speaker) and a power supply into an external box. In addition I added a toggle / Transmit-Receive switch.

I typically use this receiver with my 6J5-6L6 Transmitter.

QRP in the Park

It's 60 degrees and sunny today. After a "Minnesota Nice" winter and playing with Boat Anchors in the Basement it is turning into time to take my KX3 to a local park.

Last night I gave a "QRP in the Park" talk at the meeting of the Rochester Amateur Radio Club. I covered many possible objectives  of portable operating, how these might affect equipment/operating plans and then looked at some of today's options and my specific equipment and antenna choices.

Download a pdf version of my talk here:  http://wiegandfamily.org/QRP/QRPInTheParkTalk_10Apr2024.pdf

See a video showing me setting up my 20 mtr C-Pole vertical here: https://youtu.be/nYn-GnwcSoE

See a video showing how to get an antenna wire over a tree limb here: https://youtu.be/zibrXtaG_Ro

WN6ULH / WA5VLZ / W0VLZ Through the Years

 Here is a look at my stations through the years: http://wiegandfamily.org/shack_tours/shacks.html

 Some entries on this blog link to information on prismnet.com may be broken. If so, try going to https://web.archive.org/web/20220604005204/https://www.prismnet.com/~nielw/wa5vlz.htm

QRPKits / Pacific Antenna 40 mtr EZRcvr

Looking over my shack I see a lot of two tube homebrew receivers, mostly regeneratives.  It's time for a two IC receiver. 

 I've been a fan of direct conversion receivers for some time. Unfortunately most of them have left the market but recently my search found the QRPKits / Pacific Antenna 40 mtr Easy Rcvr. While only covering 75KHz of 40 meters the $25 price tag made it sound interesting. If I don't actually use it on the air maybe I can recommend it to a friend of mine as a learning tool and cheap way to listen in to ham QSOs.

My $25 (plus tax and shipping) got me a small plastic bag with all of the parts plus knobs, antenna connector and a 9V battery connector. A battery, antenna and ear phones/buds were all that was needed to put it to use.

I really liked the available on-line manual. It had check-off steps taking you though construction component by component along with construction tips and a troubleshooting guide. It reminded me of some of the Heathkit projects I've built in the long past.

The first step was to inventory the parts. Many of the parts, while discrete pin-in-hole, are really small. In some cases I had to use my phone's camera to blow up part markings in order to read them. I also made use of my digital multimeter to confirm what I was reading.

 

While an "Easy" receiver, this one still takes care in building. The component locations are all clearly marked but the solder pads are pretty close together in order to all fit on the 3.5" x 2" printed circuit board. I needed to get a sharper tip for my solder iron before I felt I could do a good job without any solder bridges. On the plus side the solder mask was effective. 

 

 

My Easy Receiver worked when I first powered it up. All I needed to do was set which part of 40 mtrs I wanted to cover. While marketed as half of a QRP CW station I found it works fine as a SSB phone receiver, not as good as a modern transceiver but certainly usable. 

The final Easy Receiver packaging is left up to the creativity of the builder. The QRPKits website mentions stacking it with the matching transmitter for a complete 40 mtr QRP station. For now I wanted more of a stand-alone receiver for listening to SSB.

For the "enclosure" I used a scrap of 4x1 as the base with a piece of aluminum attached to it for the front panel. Next, the stock Easy Receiver comes with no power switch. I added one to avoid wear and tear on the 9V battery connector. I also changed out the small knobs provided by QRPKits in order to make it easier to tune SSB signals. Finally, I added a more generic antenna connection. I wish I could have added some sort of bandspread, vernier tuning or a 10 turn pot as suggested by QRPKits. As it is now tuning SSB takes patience and a steady hand.

 

I've uploaded a demo to you tube. View it here.

I'm pretty happy with my 40 mtr Easy Receiver. It makes a good loaner that allows someone to get a feel for ham radio. It is also easy to shift down to the CW band so that I can pair it with a similar transmitter and head for a park.