New Project

Hallicrafters SX-101A Communications Receiver

Saw this for sale on ebay and just could not resist. This is one of ham radio receivers I have always coveted. This one will need a little work (see dial pointer) but seems in very good cosmetic condition. No sign of rust and, for its age (over 50 years old), isn't as dirty as some similar aged electronic equipment I've seen. It is a true "Boat Anchor," weighing in at 75lbs. I've read that manufacturers at this time created these heavy weight behemoths to help with frequency stability.

There is a pic after it was removed from its cabinet:

It will need to have a number of the old electrolytic and paper capacitors replaced, as well as a general going over for out of spec components.

Swan 350C

I found this Swan transceiver from the 60's on eBay for an excellent price with free shipping! It is in excellent condition but lacks the necessary power supply, so that is my next quest. I'll replace some of the original electrolytic capacitors and it should be good to go.

 Heathkit Cheyenne Transceiver

Picked up a 60's transceiver at a ham swap meet. It needed some work, including replacing some of the electrolytic capacitors, rewiring it for 6.3VAC tube filaments and replacing the changeover relay. I also changed the microphone jack to be compatible with my Astatic D-104 8-pin connector. I 3D printed an adapter (blue plastic piece) to allow the smaller diameter jack to fit the larger original mic jack hole. Also, this transceiver requires an external power supply, so building one will be required.

Replaced the relay on left that was "chattering" with the one on the right.

3D printed adapter for 8-pin mic jack

Power Supply for Cheyenne Transceiver

Power supply provides 600VDC, 300VDC and 6.3VAC

I had some of the PS components on hand, but needed a transformer, the 20Watt resistors and the Cinch-Jones 6-pin connectors that the Cheyenne uses for power input. The voltage output is a little high with out a load but should be within specs with a load.

Found one of the tubes bad so I just ordered replacements for all the tubes except the 6146 power output tube. I have another on hand in case that one is bad.

Next steps are to get the Cheyenne aligned.

Yet Another 40 Meter Transceiver Project.... but this one seems to be working.... a bit

I found another transceiver project by someone who has inspired me over the past year. Dave Richards (AA7EE) has an amazing site that has quite a wide variety of his projects, including this 40 Meter transceiver. While I was using Dave's site for guidance, the transceiver circuit was originally inspired by Peter Parker, VK3YE. I've built several of Dave's projects and learned a lot from what he has done and the techniques he uses in electronic construction. 

The audio amp is in the upper center-left. The VFO is located lower left using a variactor with the 10-turn potentiometer in the lower right (blue) for tuning. Center right is the transmitter, along with band-pass filters. Upper right is the relay to switch both power and signal between receive and transmit.

A little better view of the audio amp (left) and the VFO (right). In the center is the microphone amp and 9 volt regulator supply for the LCD display. The red wire that doesn't seem to go anywhere is the pickup for the frequency display.

Volume control is upper left with the mic jack below. The toggle switch is receive/transmit. Large knob is tuning with the 10-turn pot.

The receiver works but doesn't produce adequate volume, so I'm still trying to figure out why. I know the transmit function works but I'm looking for a proper microphone so I don't know what the quality of the signal will be. It will probably need some work as well.

Yet Another Transceiver Project

Discouraged with my efforts to get the transceiver below working, I have embarked on a new transceiver project, thanks to the postings and helpful hints of Peter Juliano (N6QW) and his extensive website of transceiver projects. Some of these projects are just too challenging for me, at least until I have some successful outcomes with the transceiver projects I've been working on! Peter's projects are incredible!

In order to get acquainted with a circuit, I often redraw it, and in that way I have a better idea about how to tackle layout and the order in which I will complete the project. Below is my schematic of the transceiver. Some modules are not yet represented. I will build this part and attempt to get the receiver working before I move on to the transmitter. The shaded areas are what I have completed so far, along with the bottom portion with the Arduino, display and Si5351 signal generator module.

Here are pics of the central board and Arduino controller.

Got the Arduino programming to work after several days of troubleshooting. Some of the code protocols had been revised in the past couple of years and it took forever to figure out that the encoder (the thingy to the left of the display that controls the frequency that appears on the display) was faulty. Replacing the encoder solved the problem.

Still working on this project...

Code Practice Oscillator

I'm having only limited success with the 80 meter receiver project. Some of the modules work but I'm having problems with the mixer and product detector. I have built 5 VFOs trying to get one that is stable enough for reliable operation. While they all work to some degree, there seems to be too much frequency drift. So.... I've been working on a couple of other projects to take a break from that project.

I've been working on re-learning morse code, so I though I would build a code practice oscillator. Some pics of that project are below:

While there are many basic circuits for constructing a CPO, the sound that they make is very disappointing. So this was a circuit that creates a true sine wave signal so the sound is quite satisfying.

The finished CPO

With the CPO finished, it was time to start another project. I found a schematic for a 40 meter ham band receiver that uses varactors for tuning. Traditionally, radio tuning was accomplished with variable capacitors, sometimes large mechanical devices that are becoming more difficult to obtain and often expensive. Varactors are semiconductor diodes that change capacitance with a varying voltage.

Like a previous project, I found an interesting circuit on AA7EE's web blog that seemed to fit the bill. It is a regenerative 40 meter ham band receiver.

 

The finished project. And it works!

More radio projects!

I’ve been thinking for a while that I would like to build a more sophisticated ham band receiver. To date, I’ve been making regenerative receivers, some general coverage short wave and a couple of ham band. Regenerative radios are fairly simple, with the exception of active audio filters that can be added to limit the interference of stations close to the frequency you wish to isolate.

More sophisticated (read more stable and actually usable for ham radio) short wave receivers, such as those using superheterodyne circuits, can be quite complex, especially for someone (me) who has not had much experience with radio frequency circuits. I have often thought that what I would like to try is a project that involves a series of “modules” so I could build each subsystem and work out the kinks before tying all together into a working receiver.

Lo and behold, I found a publication by Frank W. Harris  (titled Crystal Sets To Sideband, 2002.

Harris describes a number of separate modules/circuits for each of the system boxes above.

VFO prototype works, but a neater and more stable one will be built eventually.

12/10/2020: Audio Amp is complete and works - although this is probably the easiest module because we're not dealing with high frequency signals.

Variable Frequency Oscillator (VFO) to be used as local oscillator in the receiver

I built a number of VFO circuits to try to get one that was as stable as possible. This last one seems to fit the bill. The two jacks in the upper right part of the enclosure lid are for the 5VDC input. The connector to the left of these is for the RF output (approx. 4.500 MHz to 5.500MHz). The variable air capacitor (15pF) on the right is for fine tuning the VFO frequency, while the one inside the enclosure is for rough tuning.

 

The Intermediate frequency (IF) Amp layout sketch and finished circuit

Assembling the modules for testing: Left to right... 5volt precision power supply for VFO; VFO with lid removed; Mixer (BFO is also in that module but unused right now); IF Amplifier; Product Detector and Audio Amplifier (without enclosure).

Testing Setup: Signal Generator (above oscilloscope) tuned to 4.00MHz feeds a signal with a tone into Mixer, along with 5.00MHz signal from VFO. The result should be a 9MHz output (along with a 1MHz signal we don't want). The IF Amplifier should increase the 9MHz signal and output it to the Product Detector that is supposed to detect the audible tone, which should output that tone signal to the Audio Amplifier then to the speaker so we can hear the tone.

VFO output is 5.00MHz (left) and Signal Generator output is 4.00Mhz (right)

Initial testing

I am getting as signal but the frequency doesn't add up. It's about 7MHz instead of the 9MHz expected from the Mixer. Back to the drawing board.

The switchable 9MHz Crystal Filter.

The output from the mixer is the sum and difference of the two input frequencies (5MHz and 4MHz). The crystal filter should attenuate all the frequencies but those very close to the 9MHz sum. Reading about others experience with these filters, and the suggestion to make the number of crystals switchable, I made the filter above. Each crystal added in series should narrow the bandwidth of the signal output. It will be mounted in an aluminum box to shield it from stray RF. Next, I'll see if this makes a difference in the output signal from the mixer.

Intermission...

This past spring, during pandemic lockdown, I started studying for the General Class amateur radio license - anything to keep busy and use the time for something constructive. I held a Novice (WV2LWW) and then a Technician Class license when I was in high school (WA2LWW). I let that license lapse during college, but took the Morse code and written theory test for the Technician Class license while teaching in the late 80's, some 20 years later. I had tried to test for the General license at that time but fell short of the ability to copy Morse code at 13 words per minute. As I remember it, the Technician and General Class theory tests were the same, with the difference being the Technician license only required that you copy code at  5 WPM as opposed the the 13 WPM required for the General. So I got the consolation prize of the Technician license.

In June, I took and passed both the Technician and General Class theory test. I applied to the FCC for the license call sign I had in the 80's and it was issued: N2IFV. The ability to read and send Morse code is no longer necessary to qualify for an Amateur Radio license. Not sure how I feel about that and evidently there is quite a bit of controversy within the ham radio community - at least with the older hams. I have started to re-learn the code but it is quite the challenge for me. The highest level I achieved once upon a time was 11 words per minute, but I would like to get up to the respectable 20 WPM to make it a useful method of communication. We'll see.

As of this writing, I haven't used the license. I guess I want to construct my own equipment. I'm not terribly interested in just "jawing" at people I don't know, but would rather have something to say about the equipment I am using, having built it myself. I still have some equipment from the 80's that seems to work, but would probably require replacing parts that tend to deteriorate over time to ensure that it would be reliable. Maybe some day.

Regenerative Short Wave Receiver - No. 23?

Wandering the intertubes, I found a website by Dave Richards (AA7EE), a ham radio enthusiast, who has built a number of amazing shortwave radios. His workmanship and skill were inspiring. One of his projects, the Sproutie MK II regenerative short wave radio (https://aa7ee.wordpress.com/2015/09/14/the-sproutie-mk-ii-hf-regen-receiver/) was about the best example of the genre I have ever seen. I just had to give it a try and attempt to make something that I was proud of, even though I was sure that I didn't have the experience (and probably skill) to come up to the level of Mr. Richards.

This is my attempt. I used the same circuits and a lot of Dave Richards ideas, so there isn't much new here. But the radio works quite well, although I am still making coils to try it on other shortwave bands.

Here are a few photos of the radio I built.

The case is quarter sawn white oak and the panels are standard 19" aluminum rack mount panels. The center knob is tuning and the large knob on the right is fine tuning (bandspead). To the left of the center dial is the regenerative control. It is the heart of a regen radio and was used for the very early radios in the early 20th century. The speaker is in the top panel.

Below is what the inside of the radio looks like.

Below is an example of an audio filter that removes some of the noise/static that is always present on the shortwave bands. It didn't make it into the final radio, although four others did.