The personal website of Scott W Harden
January 10th, 2011

40m Junkbox QRP Transmitter

I decided to sit down and build something last night, and I'm surprised by how functional it is! Nothing about it is extraordinarily complex, and it's extremely flexible, accommodating almost any crystal you want to drop in. Although I doubt I'll use this exact design for a permanent transmitter, it was fun to build and I'll post photos hoping to inspire others to tinker with RF circuitry as well! The final device worked on 7.000MHz and had 3 components: power supply, oscillator/amplifier (making 20mW), and amplifier (making 1.5W).

First, I needed an oscillator. I had an easy source of one because I had a pile of ATTiny25 microcontrollers. Often I run a microcontroller at my transmit frequency with a crystal (applied to XTAL1 and XTAL2 pins) and collect the convenient 5V square wave on the CKOUT pin (after the appropriate fuse setting is applied). However, although the ATTiny25 has both XTAL and CKOUT pins, they overlap! This means that CKOUT cannot be obtained when using a crystal. This complicates things slightly...

I ended-up getting a nice sine wave from the XTAL1 pin, although it was less than 1PPV. I tried having this signal directly switch an N-channel MOSFET as an amplifier, but it didn't work that well (a transformer might help increase PPV, but that complicates things). I instead used a 74HC240 (8 inverting buffers on one chip) to help boost the signal. However, 1PPV wasn't enough to get the buffer oscillating. I therefore added a 2 resisters and a capacitor to the first inverting output, such that a persistent low would slowly raise the voltage of a wire, and I attached that wire to the input of the buffer chip. This way, although 1ppv wasn't enough to start oscillations, a few milliseconds of time allowed the inverting output (high when the input is low) to raise voltage of the input until it was enough to fire the buffers. Once it starts, it starts! I'm trilled, because a voltage divider or a potentiometer would have been a pain, and required specific parts.

The result is about 20mW of power with no tuned circuit! This means it will work on pretty much any crystal you can pop in the micro-controller. This may be suitable for a QRSS transmitter, and since we're not pushing any of the components very little heat is produced, should it should be thermostable and easy to regulate. Modulation is achieved by a reverse-biased LED varactor diode varying crystal capacitance to ground, discussed elsewhere on my site so I won't go there again.

Power supply is one I built a while back and had available. 5V for the microcontroller, and 12V for the amplifier. Simple!

Amplifying the signal was pretty easy as well. The 5V signal output of the buffer goes from 0V to 5V, which was enough to trigger an IRF510 N-channel MOSFET with a convenient packaging that I screwed into a huge heatsink. I push the MOSFET a lot, and a lot of heat is produced, but as long as I keep it separate from the oscillator the heat shouldn't affect frequency too much. Although on my workbench I use exposed wires connecting components, this is prone to getting RFI so obviously use shielded cable of some sort, or use extremely short leads. The MOSFET is arranged as a class C amplifier, with a RFC inductor at the drain.

In retrospect I'm doubting that 5V is enough to fully activate the IRF510. I should probably use some method to bring voltage just below firing threshold, so the 5V can more fully open the gate. I'll try that later! The output is filtered with a PI lowpass filter. I use two 1nF capacitors and a coil which I wind until the output on the scope looks acceptable. I know there are more exacting ways. Anyhow, I had fun, so I thought I'd post. I'm just tinkering at this point!

It's putting out about a watt and a half into 50 ohms. How cool? Adding a code key is trivial, as the 74hc240 has "gate enable" pins for easy on/off control - even from a microcontroller! Food for thought... 73!

UPDATE - I decided to slap a 10.140MHz (QRSS window) crystal in there and see what happened. I saw my signal locally (AJ4VD/W4DFU grabber), but not elsewhere, so I left it up for about a day. [Vince Adams, N9VN]() spotted it in IL (about 1,000 miles away) and made a post on a mailing list asking who it was. Awesome! Note that for QRSS I used a lower-current power supply, so I don't actually know what power output was, but I'd estimate it to be about 500mW.

(It's the "V-shape" at the bottom)

Markdown source code last modified on January 18th, 2021
---
title: 40m Junkbox QRP Transmitter
date: 2011-01-10 09:01:20
tags: qrss, amateur radio, circuit, old
---

# 40m Junkbox QRP Transmitter

__I decided to sit down and build something last night__, and I'm surprised by how functional it is!  Nothing about it is extraordinarily complex, and it's extremely flexible, accommodating almost any crystal you want to drop in.  Although I doubt I'll use this exact design for a permanent transmitter, it was fun to build and I'll post photos hoping to inspire others to tinker with RF circuitry as well! The final device worked on 7.000MHz and had 3 components: power supply, oscillator/amplifier (making 20mW), and amplifier (making 1.5W). 

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

[![](IMG_4916_thumb.jpg)](IMG_4916.jpg)

</div>

__First, I needed an oscillator.__ I had an easy source of one because I had a pile of ATTiny25 microcontrollers.  Often I run a microcontroller at my transmit frequency with a crystal (applied to XTAL1 and XTAL2 pins) and collect the convenient 5V square wave on the CKOUT pin (after the appropriate fuse setting is applied).  However, although the ATTiny25 has both XTAL and CKOUT pins, they overlap! This means that CKOUT cannot be obtained when using a crystal. This complicates things slightly... 

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

[![](IMG_4906_thumb.jpg)](IMG_4906.jpg)

</div>

__I ended-up getting a nice sine wave from the XTAL1 pin__, although it was less than 1PPV.  I tried having this signal directly switch an N-channel MOSFET as an amplifier, but it didn't work that well (a transformer might help increase PPV, but that complicates things).  I instead used a 74HC240 (8 inverting buffers on one chip) to help boost the signal. However, 1PPV wasn't enough to get the buffer oscillating.  I therefore added a 2 resisters and a capacitor to the first inverting output, such that a persistent low would slowly raise the voltage of a wire, and I attached that wire to the input of the buffer chip.  This way, although 1ppv wasn't enough to start oscillations, a few milliseconds of time allowed the inverting output (high when the input is low) to raise voltage of the input until it was enough to fire the buffers.  Once it starts, it starts!  I'm trilled, because a voltage divider or a potentiometer would have been a pain, and required specific parts. 

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

[![](IMG_4908_thumb.jpg)](IMG_4908.jpg)

</div>

__The result is about 20mW of power with no tuned circuit!__ This means it will work on pretty much any crystal you can pop in the micro-controller. This may be suitable for a QRSS transmitter, and since we're not pushing any of the components very little heat is produced, should it should be thermostable and easy to regulate.  Modulation is achieved by a reverse-biased LED varactor diode varying crystal capacitance to ground, discussed elsewhere on my site so I won't go there again. 

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

[![](IMG_4910_thumb.jpg)](IMG_4910.jpg)

</div>

__Power supply__ is one I built a while back and had available.  5V for the microcontroller, and 12V for the amplifier.  Simple!

__Amplifying the signal was pretty easy as well.__ The 5V signal output of the buffer goes from 0V to 5V, which was enough to trigger an IRF510 N-channel MOSFET with a convenient packaging that I screwed into a huge heatsink. I push the MOSFET a lot, and a lot of heat is produced, but as long as I keep it separate from the oscillator the heat shouldn't affect frequency too much. Although on my workbench I use exposed wires connecting components, this is prone to getting RFI so obviously use shielded cable of some sort, or use extremely short leads. The MOSFET is arranged as a class C amplifier, with a RFC inductor at the drain.

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

[![](IMG_4911_thumb.jpg)](IMG_4911.jpg)

</div>

__In retrospect__ I'm doubting that 5V is enough to fully activate the IRF510. I should probably use some method to bring voltage just below firing threshold, so the 5V can more fully open the gate. I'll try that later!  The output is filtered with a PI lowpass filter. I use two 1nF capacitors and a coil which I wind until the output on the scope looks acceptable.  I know there are more exacting ways.  Anyhow, I had fun, so I thought I'd post. I'm just tinkering at this point!

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

[![](IMG_4917_thumb.jpg)](IMG_4917.jpg)

</div>

It's putting out about a watt and a half into 50 ohms. How cool? Adding a code key is trivial, as the 74hc240 has "gate enable" pins for easy on/off control - even from a microcontroller! Food for thought... 73!

`` UPDATE `` - I decided to slap a 10.140MHz (QRSS window) crystal in there and see what happened. I saw my signal locally (AJ4VD/W4DFU grabber), but not elsewhere, so I left it up for about a day. [Vince Adams, N9VN]() spotted it in IL (about 1,000 miles away) and made a post on a mailing list asking who it was. Awesome! Note that for QRSS I used a lower-current power supply, so I don't actually know what power output was, but I'd estimate it to be about 500mW.

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

[![](n9vn_thumb.jpg)](n9vn.jpg)

</div>

(It's the "V-shape" at the bottom)
January 9th, 2009

RF Circuitry Links

PSK-31 receiver - sports a crystal filter front-end and active receiver

Neophyte Receiver - old article based around an NE602 / SA602 / SA612.

602 Primer - old document but very good about SA602, includes method to estimate capacitor values for Colpitts oscillator mode.

Hans' 30m receiver where he used an inverting gate buffer oscillator to generate 5v square waves which he fed into a SA602

Making Friends with the SA602 - an attempt at a write-up of the circuitry behind the Ramsey receiver kits (which only do 1 band each), although the manuals (example for 40m) may be useful

3.5-10MHz receiver - around a few SA602s, uses IF transformers too

30m receiver design - "The Limerick Sudden 30m Receiver Kit" based around a SA602/LM386 very simple and pretty

Sudden Storm Receiver - tuna tun style, check out schem a few pages in... sa602 + LM386 + crystal

Etching PCBs with hydrogen peroxide, vinegar, and table salt (wow!)

Morse.exe - A good way to learn Morse code!

High Altitude Balloon

Oscillator page which has a section mentioning that the 7th overtone can be used in an oscillator. The 7th overtone of 18mhz (17m) is 144mhz (2m) smack dab in the CW region. Nice!

Path prediction - note that UF is 29.642276 latitude and -82.344949 longitude

Icarus - a HAB project run on advertising revenue that seems successful and has launched many balloons with some awesome photos. Robert Harrison knows his stuff!

Project Space Planes - launches paper airplanes from 30km above the earth which glide down and land all over the world!

HALO project - very well documented HAB with pictures/video

JBOT - An SSB linear amplifier made from Just a Bunch of Transistors. It's pretty straightforward, cheap, and converts 1mW input to 5W output.

harmonic oscillator

tuned oscillator example

overtone oscillator

amplifier design walk-through

Lessons in Electric Circuits - A very good (free) textbook. Anyone starting to learn about electronics should start by skimming over relevant chapters of this text!

1W CW transmitter kit - Although I don't own one, I appreciate the kit and love the schematic. This guy uses a buffer chip (a 74HC04n, similar to a 74HC240 often used in QRP too) to act as an oscillator and small amplifier. The output is then further amplified by a 2n3866 transistor.

30M Solar QRSS transmitter - such an inspiring project! This guy uses a buffer chip (74hc245) to amplify the output of CKOUT of a microcontroller clocked at the transmit frequency. The thing is solar powered, and has a unique temperature compensation mechanism which uses the chip's built-in thermosensor to adjust its offset. I haven't seen this technique used anywhere else in a QRP transmitter!

HansSummers.com - Everything this man does is impressive! His QRSS section is wonderful, and I won't detract from it by trying to describe it here. He also has a simple QRSS receiver circuit based upon a SA602, something I replicated (tuned front-end not shown) to operate my W4DFU QRSS Grabber at the University of Florida.

MOSFET "Switched Mode" Amplifiers - a wonderful document, read it multiple times! Transistors are traditionally used in many QRP circuits as amplifiers, but MOSFETs have some unique qualities which in many ways makes them easier to work with in simple circuits. I found this guide EXTREMELY helpful!

Amplifier design - a cool walk-through of the design of an amplifier with the math described every step of the way

IRF-510 QRP transmitter design which looks pretty interesting... Note that increasing efficiency lets the MOSFET run cool!

Similar IRF-510 transmitter I like as well....

SA602 as an oscillator - clever, clock with tank, mix with nothing, output (mixed?) is clock only!

JFET Rainglasz/Colpitts Oscillator Design which looks interesting

Misc

Battery info - useful for calculating life of batteries under load

Battery tests - tests common batteries at different loads to determine real (not optimal) amp hour ratings!

Filter design software I use for low pass filter design

Mini ring and core calculator very convenient for designing inductors with toroids or calculating resonance of LC networks

Knights QRSS Compendium - Live image feeds of QRSS grabbers all around the world, often situated at the QRSS watering hole of 10.140MHz

Knights QRSS Mailing List - Sign up for this mailing list to see who's transmitting what on which frequency. People also often post photos of their transmitters, and interesting captures from grabbers that you may have missed!

Experimental Methods in RF Design - Only $32 on Amazon.com right now, this book is an amazing resource for anyone interested in building RF circuits. It goes from extremely simple transmitters, receivers, and amplifiers all the way through advanced topics, modulation methods, etc. It even describes how to build your own test equipment, and even how to use an oscilloscope and assess various stages of your transmitter designs. Flipping through the pages of this book gives me new ideas every time! I requested it many times from my university library (interlibrary loan, often came from Vanderbilt University) before I broke down and got it. I highly recommend this book!

Markdown source code last modified on January 18th, 2021
---
title: RF Circuitry Links
date: 2009-01-09 15:30:00
tags: circuit, amateur radio
---

# RF Circuitry Links

<a href="http://www.nutsvolts.com/media-files/A_Universal_Direct_Conversion_Receiver_For_PSK-31.pdf">PSK-31 receiver</a> - sports a crystal filter front-end and active receiver

<a href="http://www.arrl.org/files/file/Technology/tis/info/pdf/28814.pdf">Neophyte Receiver</a> - old article based around an NE602 / SA602 / SA612.

<a href="http://techdoc.kvindesland.no/radio/b1/20051213190607573.pdf">602 Primer</a> - old document but very good about SA602, includes method to estimate capacitor values for Colpitts oscillator mode.

<a href="http://www.hanssummers.com/30m.html">Hans' 30m receiver</a> where he used an inverting gate buffer oscillator to generate 5v square waves which he fed into a SA602

<a href="http://frrl.wordpress.com/2008/11/15/direct-conversion-receiver-making-friends-with-the-signetics-sa602/">Making Friends with the SA602</a> - an attempt at a write-up of the circuitry behind the <a href="http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&amp;key=HR-SERIES">Ramsey receiver kits</a> (which only do 1 band each), although the manuals (<a href="http://www.ramseyelectronics.com/downloads/manuals/HR40.pdf">example for 40m</a>) may be useful

<a href="http://www.seekic.com/forum/22_circuit_diagram/25644_35_TO_10_MHz_SIMPLE_SUPERHETERODYNE_RECEIVER.html">3.5-10MHz receiver</a> - around a few SA602s, uses IF transformers too

<a href="http://www.gqrp.com/suddenbuildingyourkitbooklet30m.pdf">30m receiver design</a> - "The Limerick Sudden 30m Receiver Kit" based around a SA602/LM386 very simple and pretty

<a href="http://www.qrpme.com/docs/ORIGINAL%20SS%20Instructions.pdf">Sudden Storm Receiver</a> - tuna tun style, check out schem a few pages in... sa602 + LM386 + crystal

<a href="http://www.stephenhobley.com/blog/2011/03/02/still-messing-with-forces-i-dont-understand-the-formula/">Etching PCBs</a> with hydrogen peroxide, vinegar, and table salt (wow!)

<a href="http://swharden.com/qrssvd/files/morse.exe">Morse.exe</a> - A good way to learn Morse code!

## High Altitude Balloon

<a href="http://www.ve7zsa.net/technical/advsgtxt/c7oscillator_r00.htm ">Oscillator page</a> which has a section mentioning that the 7th overtone can be used in an oscillator. The 7th overtone of 18mhz (17m) is 144mhz (2m) smack dab in the CW region. Nice!

<a href="http://habhub.org/predict/#!/uuid=6f0e725b992a00555d7b2e65b0bae1ade0d38fae">Path prediction</a> - note that UF is 29.642276 latitude and -82.344949 longitude

<a href="http://www.robertharrison.org/icarus/wordpress/">Icarus</a> - a HAB project run on advertising revenue that seems successful and has launched many balloons with some awesome photos. <a href="http://www.robertharrison.org/index.php?option=com_content&amp;task=view&amp;id=25&amp;Itemid=78">Robert Harrison</a> knows his stuff!

<a href="http://projectspaceplanes.com/">Project Space Planes</a> - launches paper airplanes from 30km above the earth which glide down and land all over the world!

<a href="http://natrium42.com/halo/flight2/">HALO project</a> - very well documented HAB with pictures/video

<a href="http://www.phonestack.com/farhan/jbot.html">JBOT</a> - An SSB linear amplifier made from Just a Bunch of Transistors. It's pretty straightforward, cheap, and converts 1mW input to 5W output.

<a href="http://oz2oe.dk/radio/interference/xtalgen/xtalgen.html">harmonic oscillator</a>

<a href="http://www.radiosparks.com/images_d/OSBA1078.jpg">tuned oscillator example</a>

<a href="http://www.radiosparks.com/images_d/OSCR941.jpg">overtone oscillator</a>

<a href="http://my.integritynet.com.au/purdic/rf-amplifier-with-feedback.htm">amplifier design walk-through</a>

<a href="http://openbookproject.net/electricCircuits/">Lessons in Electric Circuits</a> - A very good (free) textbook. Anyone starting to learn about electronics should start by skimming over relevant chapters of this text!

<a href="http://www.genesisradio.com.au/Q5/">1W CW transmitter kit</a> - Although I don't own one, I appreciate the kit and love the <a href="http://genesisradio.com.au/Q5/q5_20.gif">schematic</a>. This guy uses a buffer chip (a 74HC04n, similar to a 74HC240 often used in QRP too) to act as an oscillator and small amplifier. The output is then further amplified by a 2n3866 transistor.

<a href="http://clayton.isnotcrazy.com/mept_v1">30M Solar QRSS transmitter</a> - such an inspiring project! This guy uses a buffer chip (74hc245) to amplify the output of CKOUT of a microcontroller clocked at the transmit frequency. The thing is solar powered, and has a unique temperature compensation mechanism which uses the chip's built-in thermosensor to adjust its offset. I haven't seen this technique used anywhere else in a QRP transmitter!

<a href="http://www.hanssummers.com/">HansSummers.com</a> - Everything this man does is impressive! His QRSS section is wonderful, and I won't detract from it by trying to describe it here. He also has a simple QRSS receiver circuit based upon a SA602, <a href="http://www.swharden.com/blog/2010-06-09-minimalist-radio-receiver/">something I replicated</a> (tuned front-end not shown) to operate my <a href="http://ham.w4dfu.ufl.edu:8080/">W4DFU QRSS Grabber</a> at the University of Florida.

<a href="http://www.aoc.nrao.edu/~pharden/hobby/_ClassDEF1.pdf">MOSFET "Switched Mode" Amplifiers</a> - a wonderful document, read it multiple times! Transistors are traditionally used in many QRP circuits as amplifiers, but MOSFETs have some unique qualities which in many ways makes them easier to work with in simple circuits. I found this guide EXTREMELY helpful!

<a href="http://my.integritynet.com.au/purdic/rf-amplifier-with-feedback.htm">Amplifier design</a> - a cool walk-through of the design of an amplifier with the math described every step of the way

<a href="http://www.ham.se/en/27939-post26.html">IRF-510 QRP transmitter</a> design which looks pretty interesting... Note that increasing efficiency lets the MOSFET run cool!

<a href="http://www.rason.org/Projects/transmit/transmit.htm">Similar IRF-510 transmitter</a> I like as well....

<a href="http://www.pan-tex.net/usr/r/receivers/svfo.htm">SA602 as an oscillator</a> - clever, clock with tank, mix with nothing, output (mixed?) is clock only!

<a href="http://en.wikipedia.org/wiki/User:Rainglasz/Colpitts-Oscillator">JFET Rainglasz/Colpitts Oscillator Design</a> which looks interesting

## Misc

<a href="http://www.gizmology.net/batteries.htm">Battery info</a> - useful for calculating life of batteries under load

<a href="http://www.powerstream.com/AA-tests.htm">Battery tests</a> - tests common batteries at different loads to determine real (not optimal) amp hour ratings!

<a href="http://www.aade.com/filter32/download.htm">Filter design software</a> I use for low pass filter design

<a href="http://www.dl5swb.de/html/mini_ring_core_calculator.htm">Mini ring and core calculator</a> very convenient for designing inductors with toroids or calculating resonance of LC networks

<a href="http://digilander.libero.it/i2ndt/grabber/grabber-compendium.htm">Knights QRSS Compendium</a> - Live image feeds of QRSS grabbers all around the world, often situated at the QRSS watering hole of 10.140MHz

<a href="http://cnts.be/mailman/listinfo/knightsqrss_cnts.be">Knights QRSS Mailing List</a> - Sign up for this mailing list to see who's transmitting what on which frequency. People also often post photos of their transmitters, and interesting captures from grabbers that you may have missed!

<a href="http://www.amazon.com/Experimental-Methods-Design-Amateurs-Library/dp/0872598799">Experimental Methods in RF Design</a> - Only $32 on Amazon.com right now, this book is an amazing resource for anyone interested in building RF circuits. It goes from extremely simple transmitters, receivers, and amplifiers all the way through advanced topics, modulation methods, etc. It even describes how to build your own test equipment, and even how to use an oscilloscope and assess various stages of your transmitter designs. Flipping through the pages of this book gives me new ideas every time! I requested it many times from my university library (interlibrary loan, often came from Vanderbilt University) before I broke down and got it. I highly recommend this book!
November 29th, 2010

My Simple Balcony Antenna

I've been using a new HF antenna recently with surprisingly good results. Hopefully this page will be encouraging to those in apartments with severe antenna restrictions. I used to operate an indoor dipole mounted on my ceiling which was virtually invisible, but ever since solar panels were added to my apartment roof this antenna is picking up a huge amount of noise. In the past I played with a base-loaded vertical antenna made from copper pipe and it worked okay, especially when on my balcony, but it was bulkier than needed and awkward to store. My most recent antenna is made from 24AWG wire helically wrapped around the top element of a 3-element cane pole. My dad found a 15ft cane pole for $4 and it's working pretty well for me. I guess the best description of this antenna is a "fully-loaded vertical" similar to a DIY hamstick. Here are some photos.

Notice that I only wrapped the highest element with wire. (The arrows in the above image depict where the helical element begins and finishes.) My logic is geared toward trying to get as much of the functional antenna above my apartment roof as possible. While it might not be a high-gain antenna, the level of noise reduction I experienced by raising the majority of the antenna above the roof is astounding.

I can hear stations nearly full quieting that I cannot even detect with my indoor dipole. Also, I hate reports like this, but I've only made a few SSB contacts ever with my indoor setup, and always local US stations. The very first contact I made with this vertical antenna was Slovenia! He was calling CQ, I responded, and it picked me up on the first try.

THIS ANTENNA IS UGLY and a certain violation of my lease agreement which specifically states no outdoor antennas are allowed. Therefore, this is something I can only set up at night. Notice the PVC fitting at the base of the antenna - it makes it easy to set up and break down. Maximum setup / breakdown time is 30 seconds. On the floor of my balcony I have wire running up and down the wooden boards which forms a makeshift mesh ground plane. It's not optimal, but I'm limited and it's what I came up with. When I feel ambitious, I have quarter-wavelength radials that I toss off the balcony and in the bushes to improve grounding. Although I'm sure I could have tap points and gator clips to select the antenna's resonant frequency, currently I run the antenna right into a MAC-200 antenna tuner. I've used it on 17m, 20m, 30m, 40m, and 80m. Again, this antenna is far from optimal, it should represent the last resort for extreme cases, but when you're faced with not being able to operate at all this little quick and dirty setup has been a godsend!

I'm sure a lot of people will read this and be angry or argue as to why this doesn't make a good antenna. I'm not claiming it's awesome, but for me it's the best I could come up with in my limited situation. That's my $0.02!

Markdown source code last modified on January 18th, 2021
---
title: My Simple Balcony Antenna
date: 2010-11-29 14:04:54
tags: amateur radio
---

# My Simple Balcony Antenna

__I've been using a new HF antenna recently__ with surprisingly good results. Hopefully this page will be encouraging to those in apartments with severe antenna restrictions. I used to operate an [indoor dipole mounted on my ceiling](http://www.swharden.com/blog/images/dipole_apartment_2.png) which was [virtually invisible](http://www.swharden.com/blog/images/dipole_apartment_1.JPG), but ever since solar panels were added to my apartment roof this antenna is picking up a huge amount of noise.  In the past I played with a [base-loaded vertical antenna made from copper pipe](http://www.swharden.com/blog/2010-01-30-rainy-mornings-and-boring-bicuspids/) and it worked okay, especially when on my balcony, but it was bulkier than needed and awkward to store. My most recent antenna is made from 24AWG wire helically wrapped around the top element of a 3-element cane pole. My dad found a 15ft cane pole for $4 and it's working pretty well for me. __I guess the best description of this antenna is a "fully-loaded vertical" similar to a DIY hamstick.__ Here are some photos.

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

[![](IMG_4631_thumb.jpg)](IMG_4631.jpg)
[![](IMG_4632_thumb.jpg)](IMG_4632.jpg)
[![](arrows_thumb.jpg)](arrows.jpg)

</div>

__Notice that I only wrapped the highest element with wire.__ (The arrows in the above image depict where the helical element begins and finishes.) My logic is geared toward trying to get as much of the functional antenna above my apartment roof as possible.  While it might not be a high-gain antenna, the level of noise reduction I experienced by raising the majority of the antenna above the roof is astounding.  

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

[![](antenna-stitched_thumb.jpg)](antenna-stitched.jpg)

</div>

I can hear stations nearly full quieting that I cannot even detect with my indoor dipole. Also, I hate reports like this, but I've only made a few SSB contacts ever with my indoor setup, and always local US stations. The very first contact I made with this vertical antenna was Slovenia! He was calling CQ, I responded, and it picked me up on the first try.

__THIS ANTENNA IS UGLY__ and a certain violation of my lease agreement which specifically states no outdoor antennas are allowed.  Therefore, this is something I can only set up at night.  Notice the PVC fitting at the base of the antenna - it makes it easy to set up and break down. Maximum setup / breakdown time is 30 seconds. On the floor of my balcony I have wire running up and down the wooden boards which forms a makeshift mesh ground plane.  It's not optimal, but I'm limited and it's what I came up with.  When I feel ambitious, I have quarter-wavelength radials that I toss off the balcony and in the bushes to improve grounding.  Although I'm sure I could have tap points and gator clips to select the antenna's resonant frequency, currently I run the antenna right into a MAC-200 antenna tuner.  I've used it on 17m, 20m, 30m, 40m, and 80m. Again, this antenna is far from optimal, it should represent the last resort for extreme cases, but when you're faced with not being able to operate at all this little quick and dirty setup has been a godsend!

__I'm sure a lot of people will read this and be angry or argue__ as to why this doesn't make a good antenna. I'm not claiming it's awesome, but for me it's the best I could come up with in my limited situation. __That's my $0.02!__
November 14th, 2010

Improved MEPT Enclosure

I've been pretty busy lately, but I drip to the hardware store with the XYL produced a PVC enclosure that looked perfect for my ongoing MEPT (manned experimental propagation transmitter) projects. I didn't want to buy it (it was a little pricey by my standards, at $6 USD, which is about the total cost of the transmitter!) but the wife convinced me and I'm glad she did! I intended it to replace the styrofoam enclosure I had been using, but I wasn't thinking clearly and drilled holes in the box and mounted screws through them. While electrically this is a wonderful way to add antenna connections, thermally it was a bad idea. The main point of the enclosure was to be temperature stable! Oh well. I put the whole thing in the Styrofoam and as a test, I'm leaving it outside tonight. I can't wait to see how it goes! Here are some photos of the project.

Update: Even when being housed outdoors when temperature fluctuations vary greatly between day and night, this MEPT is surprisingly stable! When I open the box, it's very warm inside, so I am thinking that the voltage regulators and the MOSTFETs of the PA are heating the device nicely. Here's a capture spanning about 2 hours. The vertical height of each "V" is about 10Hz, so I estimate that for this span of time, drift is <1Hz. However, I do believe that long term (day to day) frequency stability is still not optimal, but only time will tell.

Signal report: briefly, this is my signal in Alaska courtesy of KL7UK. My signal is the V-shaped one near the bottom:

Markdown source code last modified on January 18th, 2021
---
title: Improved MEPT Enclosure
date: 2010-11-14 20:22:38
tags: qrss, amateur radio, circuit
---

# Improved MEPT Enclosure

__I've been pretty busy lately__, but I drip to the hardware store with the XYL produced a PVC enclosure that looked perfect for my ongoing MEPT (manned experimental propagation transmitter) projects. I didn't want to buy it (it was a little pricey by my standards, at $6 USD, which is about the total cost of the transmitter!) but the wife convinced me and I'm glad she did!  I intended it to replace the styrofoam enclosure I had been using, but I wasn't thinking clearly and drilled holes in the box and mounted screws through them.  While electrically this is a wonderful way to add antenna connections, thermally it was a bad idea.  The main point of the enclosure was to be temperature stable! Oh well. I put the whole thing in the Styrofoam and as a test, I'm leaving it outside tonight. I can't wait to see how it goes!  Here are some photos of the project.

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

[![](IMG_4526_thumb.jpg)](IMG_4526.jpg)
[![](IMG_4534_thumb.jpg)](IMG_4534.jpg)
[![](IMG_4547_thumb.jpg)](IMG_4547.jpg)
[![](IMG_4548_thumb.jpg)](IMG_4548.jpg)

</div>

__Update:__ Even when being housed outdoors when temperature fluctuations vary greatly between day and night, this MEPT is surprisingly stable! When I open the box, it's very warm inside, so I am thinking that the voltage regulators and the MOSTFETs of the PA are heating the device nicely.  Here's a capture spanning about 2 hours. The vertical height of each "V" is about 10Hz, so I estimate that for this span of time, drift is <1Hz.  However, I do believe that long term (day to day) frequency stability is still not optimal, but only time will tell.

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

[![](qrss_stable_thumb.jpg)](qrss_stable.jpg)

</div>

__Signal report__: briefly, this is my signal in Alaska courtesy of KL7UK. My signal is the V-shaped one near the bottom: 

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

[![](KL7UK_alaska_thumb.jpg)](KL7UK_alaska.jpg)

</div>
November 11th, 2010

Deciphering QR Code from Radio Spectrogram

Although I've been ridiculously busy the last few weeks, I've been eying some posts circulating around the Knights QRSS mailing list regarding mysterious signals in the 40m band. They recognized it as a QR Code and tried decoding it with phones and such, but the signal wasn't strong enough above the noise to be automatically deciphered.

That's the original spectrograph as captured by ON5EX in Belgium. It's a pretty good capture, it's just not great enough to be automatically decoded. The first thing I did was pop it open in ImageJ, separate the channels, and use the most useful one (red, I believe). When adjusted for brightness and contrast, I was already at a pretty good starting point.

I tried using an automated decoder at this point (http://zxing.org/w/decode.jspx) but it wasn't able to recognize the QR code. I don't blame it! It was pretty rough. I decided to manually recreate one, so I slapped the image into InkScape, add a grid, and align the image with the grid. From there, it was as easy as drawing a single grid-square-sized rectangle and copy/pasting it in all the right places.

However problems came when working on those last few rows. The static was pretty serious, so I tried a lot of different filters / adjustments. One of the greatest benefits was when I stretched the image super-wide and performed a "rolling ball" background subtraction, then revered it to its original size. That greatly helped reduce the effect of the vertical striping, and let me visually determine where to place the last few squares by squinting a bit.

Once it was all done, I saved the output as orange, then later converted it to black and white for web-detection via the ZXing Decoder.

The final result:

which when decoded reads:

WELL DONE / F4GKA QSL PSE 73

Yay! I did it. Although my call sign is AJ4VD, I'm spending the afternoon at the University of Florida Gator Amateur Radio Club station and am using their computers, so I might QSL as W4DFU. Also, there's a lot to be said for ON5EX for capturing/reporting the QR code in the first place. After a bit of research, it turns out that F4GKA is one of the Knights! I should have known it =o)

Thanks for the fun challenge!

Markdown source code last modified on January 18th, 2021
---
title: Deciphering QR Code from Radio Spectrogram
date: 2010-11-11 15:13:29
tags: qrss, amateur radio
---

# Deciphering QR Code from Radio Spectrogram

__Although I've been ridiculously busy the last few weeks,__ I've been eying some posts circulating around the [Knights QRSS mailing list](http://cnts.be/mailman/listinfo/knightsqrss_cnts.be) regarding mysterious signals in the 40m band.  They recognized it as a [QR Code](http://en.wikipedia.org/wiki/QR_Code) and tried decoding it with phones and such, but the signal wasn't strong enough above the noise to be automatically deciphered.

<dev class="center border medium">

[![](on5ex-odd_thumb.jpg)](on5ex-odd.jpg)

</dev>

__That's the original spectrograph__ as captured by ON5EX in Belgium. It's a pretty good capture, it's just not great enough to be automatically decoded.  The first thing I did was pop it open in ImageJ, separate the channels, and use the most useful one (red, I believe).  When adjusted for brightness and contrast, I was already at a pretty good starting point.

<dev class="center border medium">

![](better.jpg)

</dev>

__I tried using an automated decoder__ at this point (<http://zxing.org/w/decode.jspx>) but it wasn't able to recognize the QR code. I don't blame it! It was pretty rough.  I decided to manually recreate one, so I slapped the image into [InkScape](http://inkscape.org/), add a grid, and align the image with the grid.  From there, it was as easy as drawing a single grid-square-sized rectangle and copy/pasting it in all the right places.

<dev class="center border medium">

[![](building_thumb.jpg)](building.jpg)

</dev>

__However problems came__ when working on those last few rows.  The static was pretty serious, so I tried a lot of different filters / adjustments.  One of the greatest benefits was when I stretched the image super-wide and performed a "rolling ball" background subtraction, then revered it to its original size. That greatly helped reduce the effect of the vertical striping, and let me visually determine where to place the last few squares by squinting a bit.

<dev class="center border medium">

[![](building3_thumb.jpg)](building3.jpg)

</dev>

__Once it was all done,__ I saved the output as orange, then later converted it to black and white for web-detection via [the ZXing Decoder](http://zxing.org/w/decode.jspx).

<dev class="center border medium">

[![](building2_thumb.jpg)](building2.jpg)

</dev>

__The final result:__

<dev class="center">

![](finished.jpg)

</dev>

__which when decoded reads:__

`WELL DONE / F4GKA QSL PSE 73`

__Yay!__ I did it.  Although my call sign is AJ4VD, I'm spending the afternoon at the University of Florida Gator Amateur Radio Club station and am using their computers, so I might QSL as W4DFU.  Also, there's a lot to be said for ON5EX for capturing/reporting the QR code in the first place. After a bit of research, it turns out that F4GKA is one of the Knights! I should have known it =o)

Thanks for the fun challenge!
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