The personal website of Scott W Harden
February 12th, 2011

Wideband Receiver Works!

I demonstrated earlier this week that I can generate a wide range of frequencies using a tank circuit and the oscillator in a SA612. I added a little circuitry and hooked the receiver to my homemade indoor 20m/40m dipole antenna and vwa la, audio emerges! Endless improvements can be made, but it demonstrates the functionality of this simple circuit.

Markdown source code last modified on January 18th, 2021
---
title: Wideband Receiver Works!
date: 2011-02-12 23:28:56
tags: amateur radio, circuit, microcontroller, old
---

# Wideband Receiver Works!

__I demonstrated [earlier this week](http://www.swharden.com/blog/2011-02-09-minimal-radio-project-continues/) that I can generate a wide range of frequencies using a tank circuit and the oscillator in a SA612__. I added a little circuitry and hooked the receiver to my [homemade indoor 20m/40m dipole antenna](http://www.swharden.com/blog/2010-02-07-simple-diy-stealth-apartment-antenna-for-20m-and-40m/) and vwa la, audio emerges!  Endless improvements can be made, but it demonstrates the functionality of this simple circuit.

![](https://www.youtube.com/embed/FajGFEL-DDg)
February 9th, 2011

Minimal Radio Project Continues...

I got a big bag of fresh, new, copper clad PC board and I now wish I purchased a big pack months ago! Don't laugh at me, but I was buying 4''x6'' sheets of it at Radio Shack for about $5 a pop - ouch! I probably purchased 3 boards in my lifetime, but at that price you can imagine how careful I was not to use them. I soldered minimally to them, and only used them for the most important, established projects. Wake up Scott! If your experimental platform actually inhibits experimentation, there's something fundamentally wrong. Anyway, I got a stack of the stuff and I no longer hesitate to grab a fresh board and start working. I made some progress today simplifying my ultra-minimalist functional radio project. Here's what I came up with!

As you can see, it's running on 9V batteries! The frequency counter has its own 9V battery and a spiffy new hand-me-down case (originally used for a power supply I think, before which it was a watch case!). The IC is a SA602, SA612, or NE602 (all about the same) direct conversion receiver (Gilbert cell mixer).

I now have a small battery powered handheld frequency counter. SWEET! I need to contrive a spectacular case for it. I can't wait! It's probably the most impressive thing I've ever made with respect to the "cool factor". Does it look like a bomb? That probably makes it cooler! It just needs a big red on/off switch labeled "MISSILE LAUNCH", then it'll be the coolest thing on the planet! ... moving on ... <a <a="" href="http://www.SWHarden.com/blog/images/IMG_5261.JPG">

This is the receiver component. It's about as simple as it gets. No antenna or headphone connector is attached, but doing this is trivial! A resonant front-end filter might make it more sensitive, and add some complexity, so comparisons are needed to get a feel for how much better it really is with one attached.

For this board, I added a buffer chip (74HC240) to take the pretty sine wave and turn it into a higher-power square wave...

The quality of the oscillator is reflected in the smoothness of the sine wave (purity?) and its amplitude (indicating high Q?), though more investigation/research is required to fully understand what makes a good oscillator circuit for this chip. My strategy has been to throw components in the air, let them fall randomly, and eventually something happens and the thing starts oscillating...

Markdown source code last modified on January 18th, 2021
---
title: Minimal Radio Project Continues...
date: 2011-02-09 00:18:26
tags: circuit, amateur radio, old
---

# Minimal Radio Project Continues...

__I got a big bag of fresh, new, copper clad PC board__ and I now wish I purchased a big pack months ago! Don't laugh at me, but I was buying 4''x6'' sheets of it at Radio Shack for about $5 a pop - ouch! I probably purchased 3 boards in my lifetime, but at that price you can imagine how careful I was not to use them. I soldered minimally to them, and only used them for the most important, established projects.  Wake up Scott! If your _experimental platform_ actually _inhibits_ experimentation, there's something fundamentally wrong.  Anyway, I got a stack of the stuff and I no longer hesitate to grab a fresh board and start working. I made some progress today simplifying my ultra-minimalist functional radio project. Here's what I came up with!

![](https://www.youtube.com/embed/KTQZzNkMuC8)

<div class="text-center img-border">

[![](IMG_5278_thumb.jpg)](IMG_5278.jpg)

</div>

As you can see, it's running on 9V batteries! The frequency counter has its own 9V battery and a spiffy new hand-me-down case (originally used for a power supply I think, before which it was a watch case!). The IC is a SA602, SA612, or NE602 (all about the same) direct conversion receiver (Gilbert cell mixer). 

<div class="text-center img-border">

[![](IMG_5275_thumb.jpg)](IMG_5275.jpg)

</div>

I now have a small battery powered handheld frequency counter. SWEET! I need to contrive a spectacular case for it. I can't wait! It's probably the most impressive thing I've ever made with respect to the "cool factor". Does it look like a bomb? That probably makes it cooler! It just needs a big red on/off switch labeled "MISSILE LAUNCH", then it'll be the coolest thing on the planet! ... moving on ... <a <a="" href="http://www.SWHarden.com/blog/images/IMG_5261.JPG">

<div class="text-center img-border">

[![](IMG_5261_thumb.jpg)](IMG_5261.jpg)

</div>

This is the receiver component. It's about as simple as it gets. No antenna or headphone connector is attached, but doing this is trivial! A resonant front-end filter might make it more sensitive, and add some complexity, so comparisons are needed to get a feel for how much better it really is with one attached. 

<div class="text-center img-border">

[![](IMG_5263_thumb.jpg)](IMG_5263.jpg)

</div>

For this board, I added a buffer chip (74HC240) to take the pretty sine wave and turn it into a higher-power square wave...

<div class="text-center img-border">

[![](IMG_5284_thumb.jpg)](IMG_5284.jpg)

</div>

The quality of the oscillator is reflected in the smoothness of the sine wave (purity?) and its amplitude (indicating high Q?), though more investigation/research is required to fully understand what makes a good oscillator circuit for this chip. My strategy has been to throw components in the air, let them fall randomly, and eventually something happens and the thing starts oscillating...

<div class="text-center img-border">

[![](IMG_5282_thumb.jpg)](IMG_5282.jpg)

</div>
February 3rd, 2011

Prototype Radio Receiver Improving Daily

This is the current state of my receiver. Unlike earlier designs this one uses NO VARIABLE CAPACITORS! This helps because (a) it reduces cost, (b) makes it easier to build for anyone (it's hard to hunt down identical variable capacitors), and (c) allows it to be totally voltage controlled so microchip or PC control of frequency becomes trivial. Tuning over the entire 40m band is achieved with 3 LEDs reverse biased acting as varactors (wow!). The knobs are potentiometers. The whole circuit runs on 5v.

Markdown source code last modified on January 18th, 2021
---
title: Prototype Radio Receiver Improving Daily
date: 2011-02-03 23:16:55
tags: amateur radio, old
---

# Prototype Radio Receiver Improving Daily

__This is the current state__ of my receiver. Unlike earlier designs this one uses NO VARIABLE CAPACITORS! This helps because (a) it reduces cost, (b) makes it easier to build for anyone (it's hard to hunt down identical variable capacitors), and (c) allows it to be totally voltage controlled so microchip or PC control of frequency becomes trivial. Tuning over the _entire_ 40m band is achieved with 3 LEDs reverse biased acting as varactors (wow!). The knobs are potentiometers. The whole circuit runs on 5v.

![](https://www.youtube.com/embed/ikBk_HQ48hc)
January 28th, 2011

Home-Brew Transceiver Taking Shape!

In the spirit of furthering my knowledge of AC circuity, I'm trying to build a 100% homebrew transceiver. Yeah, QRSS and ultra-weak signal, ultra-narrowband communications is still fun, but it's not the same thrill as actually engaging in real time communication with somebody! My goal is a transmitter / receiver in a box. The basic features I desire are (1) multiple bands (at least 40m, 30m, 20m), (2) FULL-band coverage, (3) direct conversion receiver, (4) 10W transmitter, (5) digital frequency display, (6) common standard components (nothing mechanical, no air variable capacitors, everything must be easily obtainable on sites like Mouser and DigiKey), (7) SMT capability, (8) inexpensive ($20 is my goal, but that's a tough goal!). My designs are changing daily, so I'm not going to waste time posting schematics every time I write on this blog, but here are some photos and videos of the product in its current state.

(I just found that last video - it was one of my favorite songs as a teenager, performed live!)

UPDATE: I got a cool dual 16-bit counter IC made by TI, a SN74LV8154N - very cheap, and can be configured as a 32-bit counter. It seemed like a better option than multiple 8-bit counters, and this chip is about $0.60 so if I can make it work I'll be happy! I breadboarded it up (see circuit diagram) and it seemed to work. I started wiring it on the perf board, but haven't written software for it yet...

UPDATE - I just found this video on youtube I never posted on my blog, so this seems like an appropriate location for it:

Markdown source code last modified on January 18th, 2021
---
title: Home-Brew Transceiver Taking Shape!
date: 2011-01-28 14:13:33
tags: circuit, microcontroller, old, amateur radio
---

# Home-Brew Transceiver Taking Shape!

__In the spirit of furthering my knowledge of AC circuity,__ I'm trying to build a 100% homebrew transceiver.  Yeah, QRSS and ultra-weak signal, ultra-narrowband communications is still fun, but it's not the same thrill as actually engaging in real time communication with somebody!  My goal is a transmitter / receiver in a box. The basic features I desire are (1) multiple bands (at least 40m, 30m, 20m), (2) FULL-band coverage, (3) direct conversion receiver, (4) 10W transmitter, (5) digital frequency display, (6) common standard components (nothing mechanical, no air variable capacitors, everything must be easily obtainable on sites like Mouser and DigiKey), (7) SMT capability, (8) inexpensive ($20 is my goal, but that's a tough goal!). My designs are changing daily, so I'm not going to waste time posting schematics every time I write on this blog, but here are some photos and videos of the product in its current state.

![](https://www.youtube.com/embed/LACpR1vIwWM)

![](https://www.youtube.com/embed/Cq-lnMONUe4)

<div class="text-center img-border">

[![](IMG_4994_thumb.jpg)](IMG_4994.jpg)
[![](IMG_5013_thumb.jpg)](IMG_5013.jpg)

</div>

![](https://www.youtube.com/embed/B-klfgb125o)

(I just found that last video - it was one of my favorite songs as a teenager, performed live!)

__UPDATE:__ I got a cool dual 16-bit counter IC made by TI, a SN74LV8154N - very cheap, and can be configured as a 32-bit counter. It seemed like a better option than multiple 8-bit counters, and this chip is about $0.60 so if I can make it work I'll be happy! I breadboarded it up (see circuit diagram) and it seemed to work. I started wiring it on the perf board, but haven't written software for it yet...

<div class="text-center img-border">

[![](IMG_5042_thumb.jpg)](IMG_5042.jpg)
[![](IMG_5039_thumb.jpg)](IMG_5039.jpg)
[![](IMG_5041_thumb.jpg)](IMG_5041.jpg)

</div>

__UPDATE__ - I just found this video on youtube I never posted on my blog, so this seems like an appropriate location for it:

![](https://www.youtube.com/embed/w2MJQakqI0M)
January 16th, 2011

First Homebrew QSO Ever!

Today is a very special day, as it's the day I first made a contact with a radio transmitter I built completely on my own! The plans were copied from no where (although the concepts were obviously learned elsewhere), so it's somewhat of a unique design (likely because it's not very good!). I'll be the first to admit there is MUCH room for improvement, but my goal was to design and build a multi-band transmitter which would produce RF (not necessarily efficiently) at multiple bands by dropping in crystals of different frequencies.

My first QSO was with Bob, KC8MFF in West Virginia at 5pm today on 7MHz. He heard me calling CQ and replied! He gave me a 559 which made my happy. I was sending about 8 watts at the time into a Mosley Pro 67 Yagi at 180FT and receiving from a 40m dipole at 150FT at the W4DFU Gator Amateur Radio Club station in Gainesville, FL. Although he's was about 650 miles away, I hope to make a more significant contact as the band opens up later tonight. It's such an exciting feeling! The aluminum plate gets very hot (even with the fan) and there's a slight smell of smoke whenever I transmit, but it adds to the fun I guess! Here's some information about the build, though I'm confident it's less than optimal.

I'll preface this by stating that my goal was to produce an experimental platform which I could use to investigate construction techniques of small moderate-power transmitters. This is by no means a finished product! Much work (and some math) must be done to calculate the best number of turns on each coil for each band, including the RF choke on the power (resulting in class C amplifier behavior), the RF transformer, and the inductor/capacitor values of the low pass filter - all of which were determined empirically (watching output on an oscilloscope while adding/removing turns on a toroid). At 10W, it's not QRP, but it's easy to tone down to QRP (5W levels).

One of my desires was to create a transmitter which could be built at minimal cost (total value of this is probably about $10). The microcontroller (ATTiny2313) was what I had on hand ($2), the buffer chip acts as a small amplifier ($0.50), and the power amplifiers are IRF510 MOSFETs ($1). The rest of the components are junkbox, and their values aren't really significant! The power supply is a 19V 3.6A power supply from an old laptop - small, convenient, awesome! Hopefully with some tweaking I'll have a nice transmitter which I'm proud to share and have replicated...

The overall schematic represents a crystal clocking a microcontroller at the transmit frequency, where the CKOUT fuse has been set, producing 5PPV square waves. These trigger an inverting buffer which (a) amplifies the current of the signal and (b) provides an easy source of inverted signal. The two (inverse) signals then fire a pair of IRF510s in tandem, each acting as a Class C amplifier producing about 60PPV waves (not quite as square-ish). The output is low-pass filtered with a Pi filter (3 pole Chebyschev), then sent to an antenna. Nothing special has been done to match the output to the antenna, so SWR with a 50ohm load is currently a bit high, but I imagine a variable capacitor on the output LPF would give me something to adjust to improve this. I should probably go back to square 1 and re-do the math from start to finish and follow my impedance values more closely.

Future work will be invested into adding an iambic keyer property to the microcontroller, as well as a button to send CQ at various speeds. It may be interesting to clock this from a Si570 digital synthesizer, allowing me to transmit on any frequency and no longer be crystal-bound. Additionally, using the same oscillator source to power a direct conversion receiver would yield obvious benefit, allowing transmit/receive from a home-brew device at minimal cost. Currently, I'm locked into using a commercial rig as a receiver. We'll see how it goes...

Anyhow, that's that. I wanted to document this because I know I'll look back in the future and laugh at how poorly designed this project is. I'm just amazed it works, and for now this represents a gigantic step step in my learning and growth as an engineer. As poorly designed as it may be, it's something I'm very, very proud of!

Great inspiration has come from Wes Hayward's Experimental Methods in RF Design text. I've been checking it out from the library every few weeks (Interlibrary Loan, from Vanderbilt University to the University of Florida) but I finally got my own copy for Christmas. It's such a great resource! The IRF510 push-pull idea came from figure 2.101.

PS: The image below is of a MOSFET I exploded in the development process. Too much current... oops!

Markdown source code last modified on January 18th, 2021
---
title: First Homebrew QSO Ever!
date: 2011-01-16 18:39:32
tags: amateur radio, circuit, old
---

# First Homebrew QSO Ever!

__Today is a very special day,__ as it's the day I first made a contact with a radio transmitter I built completely on my own! The plans were copied from no where (although the concepts were obviously learned elsewhere), so it's somewhat of a unique design (likely because it's not very good!). I'll be the first to admit there is MUCH room for improvement, but my goal was to design and build a multi-band transmitter which would produce RF (not necessarily efficiently) at multiple bands by dropping in crystals of different frequencies.

![](https://www.youtube.com/embed/u4nI0cwSP0Q)

__My first QSO was with Bob, KC8MFF in West Virginia at 5pm today on 7MHz.__ He heard me calling CQ and replied! He gave me a 559 which made my happy. I was sending about 8 watts at the time into a Mosley Pro 67 Yagi at 180FT and receiving from a 40m dipole at 150FT at the W4DFU Gator Amateur Radio Club station in Gainesville, FL.  Although he's was about 650 miles away, I hope to make a more significant contact as the band opens up later tonight. It's such an exciting feeling! The aluminum plate gets very hot (even with the fan) and there's a slight smell of smoke whenever I transmit, but it adds to the fun I guess!  Here's some information about the build, though I'm confident it's less than optimal.

<div class="text-center img-border">

[![](IMG_4946_thumb.jpg)](IMG_4946.jpg)

</div>

__I'll preface this by stating__ that my goal was to produce an _experimental platform_ which I could use to _investigate_ construction techniques of small moderate-power transmitters. This is by no means a finished product! Much work (and some math) must be done to calculate the best number of turns on each coil for each band, including the RF choke on the power (resulting in class C amplifier behavior), the RF transformer, and the inductor/capacitor values of the low pass filter - all of which were determined empirically (watching output on an oscilloscope while adding/removing turns on a toroid). At 10W, it's not QRP, but it's easy to tone down to QRP (5W levels). 

<div class="text-center">

[![](30m_40m_80m_transmitter_10watt_aj4vd_thumb.jpg)](30m_40m_80m_transmitter_10watt_aj4vd.jpg)

</div>

One of my desires was to create a transmitter which could be built at minimal cost (total value of this is probably about $10). The microcontroller (ATTiny2313) was what I had on hand ($2), the buffer chip acts as a small amplifier ($0.50), and the power amplifiers are IRF510 MOSFETs ($1). The rest of the components are junkbox, and their values aren't really significant! The power supply is a 19V 3.6A power supply from an old laptop - small, convenient, awesome! Hopefully with some tweaking I'll have a nice transmitter which I'm proud to share and have replicated...

<div class="text-center img-border">

[![](IMG_4928_thumb.jpg)](IMG_4928.jpg)

</div>

__The overall schematic__ represents a crystal clocking a microcontroller at the transmit frequency, where the CKOUT fuse has been set, producing 5PPV square waves. These trigger an inverting buffer which (a) amplifies the current of the signal and (b) provides an easy source of inverted signal. The two (inverse) signals then fire a pair of IRF510s in tandem, each acting as a Class C amplifier producing about 60PPV waves (not quite as square-ish). The output is low-pass filtered with a Pi filter (3 pole Chebyschev), then sent to an antenna. Nothing special has been done to match the output to the antenna, so SWR with a 50ohm load is currently a bit high, but I imagine a variable capacitor on the output LPF would give me something to adjust to improve this. I should probably go back to square 1 and re-do the math from start to finish and follow my impedance values more closely.

<div class="text-center img-border">

[![](IMG_4939_thumb.jpg)](IMG_4939.jpg)

</div>

__Future work will be invested into__ adding an iambic keyer property to the microcontroller, as well as a button to send CQ at various speeds. It may be interesting to clock this from a Si570 digital synthesizer, allowing me to transmit on any frequency and no longer be crystal-bound. Additionally, using the same oscillator source to power a direct conversion receiver would yield obvious benefit, allowing transmit/receive from a home-brew device at minimal cost. Currently, I'm locked into using a commercial rig as a receiver. We'll see how it goes... 

<div class="text-center img-border">

[![](IMG_4940_thumb.jpg)](IMG_4940.jpg)

</div>

__Anyhow,__ that's that. I wanted to document this because I know I'll look back in the future and laugh at how poorly designed this project is. I'm just amazed it works, and for now this represents a gigantic step step in my learning and growth as an engineer. As poorly designed as it may be, it's something I'm very, very proud of!

__Great inspiration__ has come from Wes Hayward's [Experimental Methods in RF Design](http://www.amazon.com/Experimental-Methods-Design-Wes-Hayward/dp/087259923X/ref=sr_1_1?ie=UTF8&s=books&qid=1295289709&sr=8-1) text. I've been checking it out from the library every few weeks (Interlibrary Loan, from Vanderbilt University to the University of Florida) but I finally got my own copy for Christmas. It's such a great resource! The IRF510 push-pull idea came from figure 2.101.

__PS:__ The image below is of a MOSFET I exploded in the development process. Too much current... oops!

<div class="text-center img-border">

[![](mosfet_die_thumb.jpg)](mosfet_die.jpg)

</div>
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