Manual Antenna Tuner

Manual Tuner (10)Manual Tuner (9) Automatic antenna tuners are incredibly handy devices. They also require power, interface cables, feature many points of failure and have a limited impedance matching range. Manual tuners, on the other hand, feature a simple design and can have a very wide matching range.

Manual Tuner (6)Manual Tuner (4)After deciding that I wanted to build a T match type of tuner, I needed to find some high voltage air variable capacitors. I looked around at what was available and found this great pre-made assembly that features two 22-360pF variable capacitors (rated for 1kV) and a 12 position rotary switch (rated for 5A). This should be able to handle 100W when properly matched. After deciding on this component I selected an 8″ x 6″ x 3.5″ aluminum enclosure for the tuner.

Manual Tuner (2)The next part of the tuner is the inductor. In order to make use of the 12 position rotary switch I needed to make a coil with taps. I also had to keep the coil relatively small so that it would fit in the enclosure I was using. After doing some research I found that an inductance of 30-40uH is typical for a T match antenna tuner and should be able to match a good range of impedances from 160M – 10M. K7MEM has a great single layer air core inductor calculator that uses common PVC pipe as a coil form. For the coil I decided to use 18AWG teflon insulated wire since it should be large enough to handle 100W and the teflon insulation is both easy to work with and very heat resistant. Using the calculator I found that 46 turns of wire on a 1.25 inch PVC pipe resulted in a 35uH inductor that would fit nicely in the enclosure.

Manual Tuner (5)To wind the coil I used a ring terminal to secure the starting end and started winding. At every tap point I separated the insulation and soldered a jumper to the exposed wire. Then I continued winding until the next tap point and so on until I finished the coil with another ring terminal. I tapped the coil at turns 2, 4, 6, 8, 12, 16, 20, 24, 30, 36, and 42. The finished coil was then bolted on top of nylon spacers to the enclosure.

Manual Tuner (3)Manual Tuner (1)To finish the tuner I wired the taps in the order they were wound to the rotary switch. The start of the coil should be wired to the point where the variable capacitor rotors are connected together. The end of the coil should be grounded to the enclosure along with the common point on the rotary switch. Each variable capacitor stator is wired directly to the center of a SO-239 connector, one to the input and one to the output of the tuner. Finally, I added a ground stud to the enclosure.

Manual Tuner (8)Manual Tuner (7)When using a tuner of this design it is good to keep in mind that the most efficient match occurs when the capacitance is at a maximum and the inductance is at a minimum. Therefore when adjusting the tuner I always start with the capacitors at close to their maximum setting (fully meshed) and the inductor on the first tap. I then click through the inductor taps until I see a dip on the SWR meter and adjust the capacitors to achieve the lowest SWR I can.

I have used this tuner with a couple different antenna designs and it performs fairly well. When used with various dipoles and other wire antennas I have been able to achieve matches the majority of the time. However, I may need to adjust the design of the coil since it seems that I never make use of the later taps and may not require such a large coil.

Ham Radio EMCOMM Go Kit – Antennas

This is the fourth part of my emergency communications system. The system I am building is intended to be modular. When complete I will have a VHF/UHF station, an HF station, a battery box, an antenna system, and a computer system. Having a bunch of hardware and the power to run it is all fine and good, but if your antennas aren’t capable of getting the signal out all of those radios are useless.

Mast System

Like with my go kits, my first priority was to have a good VHF/UHF antenna system. A magmount on the roof of your car is OK, but for local line-of-sight communications the gain and height of your antenna are very important. I also wanted something that I could easily transport and erect by myself.

Antenna Mast (2)After some investigations I decided to aim for a simple lightweight mast system that I could mount to the trailer hitch on my car. The base for this setup is a hitch mount flagpole mount. For the mast I chose the MFJ 1904H. This mast solves a lot of potential problems for a portable mast system:  it is 5 feet long when collapsed making it easily transportable in my car, it is non conductive and will not interfere with any antennas mounted on it, and despite being made of fiberglass it is fairly sturdy (each tube wall is 1/8″ thick). I don’t intend to heavily load this mast so this should serve my needs well. In order to achieve a tight fit between the flagpole mount and the mast I used a section of 2″ PVC pipe as a spacer. When fully extended the top of the mast is about 21 feet high.

I also purchased a 33 foot version of this mast design from Max-Gain Systems. While this version requires some guying, it allows for considerable more antenna height and consequently performance.

VHF/UHF

Antenna Mast (3)Antenna Mast (1)For the VHF/UHF antenna I chose the Two Way Electronix Dual Band Slim Jim. As someone who uses a J-Pole antenna as my base VHF antenna, I am very familiar with how well these antennas perform. The Slim Jim is a J-Pole made from 450 Ohm ladder line so that it can be rolled up for easy storage and transport. I mount the antenna to the mast using a nylon bolt and wingnut the passes through the insulation at the top of the antenna and a hole drilled in the top fiberglass section. This setup is very light weight and has virtually no wind loading which makes guying the mast unnecessary (under average wind conditions).

HF

For HF I did considerable research regarding what type of antenna is appropriate for emergency communications. A lot of ham radio is focused on making contacts at great distances (DX). This necessitates a low angle of radiation from the antennas being used. For a dipole this means that the antenna should be at least a half wavelength above ground. The most common HF EMCOMM bands are 40 & 80 meters (one half wavelength on 40 meters is about 66 feet, double that for 80 meters). For EMCOMM purposes, however, we only want to communicate within a couple hundred mile radius of our location. This requires a Near Vertical Incident Skywave (NVIS) propagation path. It turns out that this makes our lives a lot easier since a dipole can be used for NVIS when it is mounted much lower than it would typically be. Instead of trying to get a dipole very high, mounting it at 15 feet is ideal for this application. Another benefit of this approach is that at this height the dipole loses almost all of its directionality and is essentially omnidirectional.

Hamsticks

Antenna Mast (4)In an effort to maximize portability and reduce both setup time the footprint of the EMCOMM station I decided to try MFJ’s hamstick dipoles (MFJ-2240, MFJ-2275). These are loaded antennas that use a base section coil wound on a fiberglass rod with a stainless steel whip on the top. While a small loaded antenna will not have the efficiency, or the bandwidth of a full size antenna, it is considerably smaller (15 feet vs 66 & 133 feet). The hamstick dipoles actually perform fairly well. I was able to tune them for the digital portion of the bands and using the antenna tuner in my Icom 703 I can tune either dipole across their entire respective band. The dipoles are also fairly light weight and my fiberglass mast seemed plenty strong enough to support their weight. I would still like to try stacking the dipoles on the mast simultaneously in a cross configuration and seeing if that effects anything.

Folded Skeleton Sleeve Dipole

Field Setup (1)Field Setup (2)After exploring a few different designs I think that my 75/40 meter Folded Skeleton Sleeve Dipole will make an excellent EMCOMM antenna. It is resonant on both bands, making it easy to tune up and operate on the two most common HF bands used during emergencies. It is also over 20 feet shorter than a typical 80 meter dipole, making it somewhat more space efficient.

Performance

While I haven’t done much operating with the Hamsticks, I have done a fair amount of testing with the Folded Skeleton Sleeve Dipole and it is a very competent antenna. My Ham Radio club used it during Field Day and made over 350 contacts with this antenna.

Ham Radio EMCOMM Go Kit – HF – Update

After using my HF Go Kit for a few months I decided that I wanted to treat this as more of a HF Field Kit than a true Go Kit. Part of this evolution was my desire to have a dedicated 100W HF field radio and consequently I decided to disassemble my Go Kit.

HF Kit (1)The Icom 703 is a great little radio, it is also somewhat long in the tooth at this point and can only output 10W maximum. I had heard good things about the Yaesu FT-450D and after seeing sale prices and mail-in rebates drop the price to $600 I decided to buy one. The Yaesu (9”W x 3.3”H x 8.5”D, 8.8 lbs) is larger and heavier than the Icom (6.6″W × 2.3″H × 7.9″D, 4.4 lbs) but is nowhere near as unwieldy as my Kenwood TS-590SG  (10.6″W × 3.8″H × 11.5″D, 16.3 lbs) which serves as my main HF transceiver in my station. For such a compact radio it contains many comparable features to my larger and considerably more expensive Kenwood.

Features

The Yaesu 450D is an entry level transceiver, however, it includes a lot of features that give you considerable bang for your buck.

  • HF/6M Coverage
  • 100W Transmitter
  • IF DSP Filtering (Width, Shift, Contour, Notch, Noise Reduction, etc.)
  • Backlit Buttons (perfect for field use at night)
  • Voice Keyer (perfect for contesting and Field Day)
  • Built-in Antenna Tuner

Field Case

HF Kit (2)To house the Yaesu I used the same Monoprice Weatherproof case I used in the previous HF Go Kit, however, this time I made use of the foam padding. This was mainly done in the name of simplicity and to keep the radio and other equipment secure. Less damage prone items like the power cable can be transported in my backpack. For power I will rely on my Go Kit Battery Box or depending on the event I will also bring a 22A switching power supply separately from the radio. I think that this setup will prove to be much more versatile than my previous one due mainly to the increased capability of the Yaesu 450D which provides many modern conveniences as well as 100W output.

Ham Radio EMCOMM Go Kit – Laptop & Software – Update

Asus (1)After using my Acer Cloudbook for a few months I came to the conclusion that it didn’t quite match with my requirements for a Go Kit laptop. The main reason for this was it’s inability to act as my main station computer due to it’s low performance running Windows 10. The low resolution screen was also a limitation. After some investigating I came across the Asus VivoBook E403A-US21 which looked like a good upgrade in performance, while maintaining the low price and power usage that were the Cloudbook’s main advantages.

Asus (2)Specs

  • CPU – Intel Pentium N3700 (Quad-Core, 1.6 GHz)
  • RAM – 4GB
  • SSD – 128GB
  • Display – 14″ (1920 x 1080)
  • Wireless – Wifi (AC), Bluetooth (v4.0)
  • Ports – USB 3.1 Type C, USB 3.0, USB 2.0, HDMI, Audio
  • SD Card Reader, Webcam, Microphone
  • Battery – 57 Wh
  • Weight – 3.3 lbs
  • Price – $400

Asus (4)Performance

With the extra CPU power and double the RAM of the Cloudbook, the Asus VivoBook easily runs Windows 10 and all of the ham radio applications that I need (N3FJP log, FLDIGI, FLWRAP, FLMSG, FLAMP, WJST-X, etc), which allows me to use it as my main station computer. Consequently, if I need to grab my equipment and hit the road I can just disconnect a couple of cables and take my laptop with me, armed with the knowledge that it is up to date, functional, and that the battery is fully charged. By using one laptop for everything it allows me to not worry about maintaining a secondary machine just for my Go Kit.

Asus (5)Power Usage

The extra power of the VivoBook comes at the expense of power usage when compared to the Cloudbook. Even so this machine is still fairly miserly when it comes to power usage compared to higher powered laptops and is well suited to field use.

  • Idle Maximum Brightness – 8W
  • Idle Minimum Brightness – 6W
  • FLDIGI, FLMSG, FLAMP, File Browser Open, Maximum Brightness – 11W
  • FLDIGI, FLMSG, FLAMP, File Browser Open, Minimum Brightness – 9W
  • Charging Battery – 33W

Overview

Asus (3)The VivoBook is thin and light and the keyboard and touchpad are excellent. It has a good selection of ports and the build quality is very solid for such an inexpensive machine. The increased display resolution is also a huge upgrade over the Cloudbook. The display quality, while better than the Cloudbook is still not very good as was expected for this price range. I was, however, able to improve the color reproduction using my Datacolor Spyder screen calibration tool. Overall this is a fantastic laptop for the money and I am very pleased with how it allows me to simplify my Go Kit setup.

Folded Skeleton Sleeve Antennas

Skeleton Sleeve Dipoles (4)I am always interested in trying different antenna designs, especially if they are simple to construct and provide increased functionality. While perusing some old issues of QST magazine online I found a series of articles that discuss a design called the Folded Skeleton Sleeve. The design is a unique way to build a dual-band resonant dipole or groundplane vertical. The articles appear in the May 2011, October 2011, October 2012, December 2013, and March 2015 issues of QST magazine.

I was particularly interested in this antenna design because a simple resonant dual-band antenna could be very useful for deployment at Field Day or for EMCOMM purposes. Other multi-band antenna designs exist and can perform quite well (windoms, off-center-fed dipoles, G5RVs, non resonant end feds, dipoles fed with window line, etc.), however, these require an antenna tuner to achieve a decent SWR. Other designs, such as trap dipoles, can be heavy and cumbersome with multiple points of failure. The folded skeleton sleeve design exhibits non of these limitations.

Design

Folded Skeleton Sleeve AntennaThe folded skeleton sleeve at first looks like a standard folded dipole, however, the top radiator is not continuous. Two notches are cut along the top of the window line to create the parasitic element that allows for operation on the higher frequency band.

A 75M / 40M antenna should be perfect for both EMCOMM (these are the most common HF bands used for emergency communications) and Field Day. A 40M / 20M antenna is equally perfect for Field Day and the combination of the two provides a lot of operating versatility from two simple antennas that cover the three busiest Field Day bands. I also decided to construct a 40M / 30M antenna for use as a portable antenna for digital communications.

Construction

Skeleton Sleeve Dipoles (2)Skeleton Sleeve Dipoles (3)I built the antennas using 18AWG stranded copper-weld 450 Ohm window line (Wireman #553) and folded dipole insulator kits (Wireman #804) which make fantastic strain reliefs for securing the window line. I also made my own 1:1 baluns in a similar design to what I have done before, except this time I used FT-150A-K toroids and 18AWG wire which allowed me to make the baluns smaller in size while still being adequate to handle 100W. To house the baluns I used Bud Industries PN-1322-DGMB NEMA 4X enclosures. These are well made boxes and they feature convenient mounting tabs that are easily bolted to the center insulator.

75/40 Bandwidth

75 Meter Band

  • 2:1 SWR:  3.68-3.785
  • 3:1 SWR:  3.63-3.86

40 Meter Band

  • 2:1 SWR:  7.18-7.238
  • 3:1 SWR:  7.1-7.3

While the bandwidth of this antenna is not particularly wide, it is easily matched to the radio’s 50 ohm output with practically any antenna tuner.

My ham radio club used the 75/40 at our Field Day site for the duration of the event. While obviously intended for use on 75 & 40 meters, the antenna was used on the higher bands as well with the help of a wide range antenna tuner. Over the course of field day this setup resulted in over 350 CW contacts.

40/30 Bandwidth

40 Meter Band

  • 2:1 SWR:  7.158-7.33
  • 3:1 SWR:  7.073-7.448

30 Meter Band

  • 2:1 SWR:  9.93-10.24

This antenna exhibits better bandwidth than the 75/40 and even reaches an SWR of 1.1:1 on 30 meters.

40/20 Bandwidth

This antenna is by far the best design of the bunch. This configuration results in an SWR of under 2:1 across the entirety of both the 40 and 20 meter bands.

Antenna Winders

Skeleton Sleeve Dipoles (5)Since ladder line can be annoying to work with since it doesn’t coil easily, I decided to build some winders from 1/2 inch PVC pipe to keep the finished antennas organized. I built a larger one for the 75/40 antenna and smaller ones for the 40/20 and 40/30 antennas. I am really pleased with how these turned out and plan to build more for use with other antennas; they are a fantastic way to avoid a tangled mess.

 

6 Meter Quad Turnstile Antenna

6M Quad Turnstile (2)After my less than successful attempts on 6 meters with my collinear array, I decided to try another design that I had been looking at for some time. A quad turnstile consists of two cubical quad loops oriented in a diamond configuration and angled 90 degrees apart from one another with both diamonds sharing the same top and bottom points. The advantage of this design over a single quad loop is that when phased 1/4 wavelength (90 degrees) apart the combination of the two antennas creates an omnidirectional radiation pattern. This type of antenna can also be made from two crossed dipoles, however, using full wave loops instead of half wave dipoles provides about 1 dB additional gain at low elevation angles (there is a great article about building a 6 meter quad turnstile written by L. B. Cebik, W4RNL in the May 2002 QST magazine that goes into further detail about the performance and advantages of this antenna design).

Another advantage, from a construction perspective, is that the spreaders required for a dipole turnstile would have to be 10 feet across. The spreaders for quads only need to be 7 feet across meaning that the use of lightweight pvc is that much more practical. The quad configuration is also perfect for being suspended by a push up fiberglass mast since the antenna is very light weight and virtually all of the loads are directed vertically down the center of the antenna which is also the center of the mast. This results in very little flexing and stress on the light duty fiberglass section at the top of the mast. I built my antenna using the Max Gain Systems MK-6-Standard fiberglass mast which stands 32 feet tall when fully extended.

From previous experiments with 6 meter loops I have found that 20 feet of insulated 14 AWG wire is resonant at the bottom of the 6 meter band (just above 50 MHz) where the SSB activity is concentrated.

6M Quad Turnstile (5)6M Quad Turnstile (6)The feed point is the most complex component in the entire antenna. It consists of a piece of 1/4″ thick Lexan with three SO-239 connectors (one for the feedline and one for each end of the phasing line) and four #10-32 stainless bolts (one for each loop end) mounted to it. The SO-239s and bolts are then wired together such that the feedline is wired directly to one loop and one end of the phasing line and the other end of the phasing line feeds the second loop. I used red and yellow electrical tape to mark which bolts attach to which loop. I also notched the Lexan sheet to fit around the mast so that I could wire tie it in place.

6M Quad Turnstile (7)6M Quad Turnstile (8)The phasing line is made using RG-63 coax which has an impedance of 125 Ohms. This is required because the feedpoint impedance of each of the loops is also about 125 Ohms. When fed together via the phasing line the final antenna impedance is approximately 62 Ohms which matches well with the standard 50 Ohm feedline (for this antenna I used a run of 100 feet of LMR400 coax). I purchased my RG-63 coax from The Wireman. The phasing line needs to be 1/4 wavelength long at the bottom of the 6 meter band. To calculate this you can use the formula (246/frequency) = quarter wavelength in feet. Therefore 246/50.5 = 4.871 feet = 58.46 inches. Next we take into account the velocity factor of the RG-63 coax, in this case 84%. Therefore 58.46*0.84 = 49.1 inches which is the length that the phasing light should be including the connectors on each end.

6M Quad Turnstile (11)6M Quad Turnstile (10)The PVC spreaders are made using 3/4″ PVC conduit glued into a 4-way junction box. By drilling a 3/4″ hole in the center of the junction box it allows the spreader assembly to slide down the top mast section and rest on top of the 1″ section of the mast. This is left to float in place and is not attached to the mast in any other way.

6M Quad Turnstile (9)The key to the construction of my version of a quad turnstile is that the entire antenna hangs from the top of the mast. To accomplish this I used a 1/2″ PVC cross with a nylon bolt running through the center. The bolt slides in the end of the 3/4″ fiberglass mast section and prevents the PVC cross from sliding off the top of the mast. I then fed the antenna wires through the cross such that the wires intersect at 90 degree angles. This method serves to secure the wires to the peak of the mast as 6M Quad Turnstile (12)well as providing some strain relief for the antenna wires. I then splayed out the wires and ran them through notches cut at the end of the PVC spreaders. I then centered the wires relative to the top of the mast and taped the wires to the end of the spreaders to keep them in place until they are attached to the feed point. The wires were then attached to the feedpoint using ring terminals that were soldered to the ends of the wires. The ring terminals make it easy to connect the wires to the bolts mounted on the feedpoint.

6M Quad Turnstile (3)6M Quad Turnstile (1)To erect the antenna I first raised the top 3/4″ section of the mast until the top wires became taught. This only requires about 3 feet of the top section to be extended such that the spreader assembly is not lifted off of the lower mast section. I then locked the top mast section in place. Next I raised the 1″ section of mast until the lower wires were taught and secured the feedpoint in place with a wire tie and taped the feed line and phasing line to the mast for strain relief. Then I continued raising each mast section until the mast was completely raised, resulting in a peak height of nearly 30 feet. I then finished guying the mast. For this antenna I only guyed the mast at 3 intervals, the bottom, the middle, and the top since the antenna is not heavy and is very evenly loaded on the mast. Three guy lines per 6M Quad Turnstile (4)interval were used made from UV resistant rope anchored using 10″ spiral ground anchors. This resulted in a very stable mast and the antenna that has held up well, even on breezy days. A tautline hitch is a great knot to know for tensioning guy ropes for masts as well as tents when camping.

After erecting the antenna I checked the SWR and found it to be 1:1 at the bottom of the 6 meter band. I also found that the 2:1 SWR bandwidth was quite large and easily covered the SSB portion of the band. I also noticed that a nearby 6 meter beacon station that was typically an S3 on my collinear array was now an S7 on my quad turnstile, which is a huge improvement.

The following day after getting the antenna on the air there was sporadic E band opening in North America and I was able to hear several stations. During this opening I worked my first 6 meter contacts, receiving good reports from stations in Oklahoma, Arkansas, Alabama, Tennessee, and Manitoba. Not too bad for 100W into an omnidirectional antenna in western Pennsylvania.

I also worked about four hours of the June 2016 ARRL VHF Contest and made 20 contacts with stations in 14 grid squares. Like a lot of antenna systems, this one allowed me to contact most of the stations that I was able to hear. I have, however, gained an appreciation for why most people use directional antennas for VHF work. While the extra gain directional antennas provide would definitely be a positive, I can see now how favoring one direction over another can be especially advantageous on 6 meters. More than once I could hear multiple strong stations on the same frequency and with a directional antenna I could have significantly nulled out one of those stations in order to make it easier to hear and work one station at a time. Another advantage would be the ability to focus your signal in the direction in which the band is open, instead of broadcasting in all directions.

With all of that said I am very pleased with how this antenna project worked out. This design is an inexpensive and effective way to get on 6 meters and make contacts which was my goal in the first place. It is also a good all around lesson in antenna design, construction, and phasing lines.

mcHF SDR Transceiver Kit

A huge part of the history of ham radio involves people building their own equipment. In fact that is how things started since at the beginnings of radio no commercial hardware was available. Over the years various companies and organizations have sold transceiver kits, but in recent years most of these have consisted of basic morse code only or single frequency single side band devices intended for digital communications. With the increased development of software defined radio (SDR), however, this is changing. Earlier this year I came across the mcHF SDR transceiver project and decided to purchase one of the kits. Unlike other basic transceiver kits the mcHF is a full featured radio with 80M-10M coverage, multi-mode support, variable bandwidth filtering, DSP (noise reduction, notch filtering, etc.), sound card interface, rig control, and band scope / waterfall capability. Not bad for a $388 kit.

mcHF (1)mcHF (2)The project was originated by Chris, M0NKA in the UK about 2 years ago and the design has gone through a number of revisions resulting in the current v0.5, which is what I purchased. One of the major reasons I was willing to undertake this project was that the kit offered by Chris includes the circuit boards already populated with about 95% of the surface-mount parts, including all of the tricky to solder chips and super tiny resistors and capacitors. The only remaining parts to install are larger, and therefore easier to solder, surface-mount parts and standard through-hole components. The builder also has to hand wind several toroid inductors and transformers. You also have to provide your own final power amplifier MOSFETs, shielding plate between the boards, and case for the radio. These requirements go along with the way this kit is sold, which is to say bare bones. The kit includes zero instructions. The builder is responsible for sorting through the mcHF downloads page, the mcHF Yahoo group, and the Github Wiki to find the details regarding how to wind the toroids and transformers as well as details on any recommended mods and instructions for how to use the radio.

Since this project is open source, both the hardware and firmware have undergone considerable development. In fact, from the time I started building the board to when when I completed the project a large firmware update was released which revised the main screen and menu layout as well as added a number of fixes and features, including the ability to control the transceiver via the usb port and detect the transceiver as a sound card device with a PC.

mcHF (3)The mcHF consists of two circuit boards called the UI board and the RF board. I built the UI board first, and then built the power supply section of the RF board so that I could power up and test the UI board. Chris has a very helpful document on the mcHF webpage that steps through the process of installing the bootloader and uploading firmware to the CPU on the UI board. So after only about 4 hours of work I had a functional UI board.

mcHF (7)Next I completed the remainder of the RF board, which was fairly time consuming since winding toroids and transformers is a tedious operation. Documentation exists for how to wind the transformers, however, the only information regarding the toroids is on the RF board schematic which details how many windings each core requires. Extra attention should be paid to stripping the enamel wire used for the toroids and transformers. Even though I diligently sanded off the outer coating and thought that I had solid solder connections to the board, I did not do a good enough job on two of the toroids which prevented the radio’s operation on the 80M band. After desoldering and re-sanding the wires I achieved a good electrical connection and consequently 80M functionality.

mcHF (10)mcHF (11)This portion of kit construction is somewhat confusing because there are a ton of possible mods for the various transformers that can improve performance of the final power amplifier. I decided to build mine in the default configuration which results in a solid 5W output on 80M-12M and about 4W on 10M. When modified, users report 10 or more watts of power output. The only modification I made was with regard to the SWR bridge where RG-178 coax is used in place of a single winding of enamel wire. Construction details for many of these mods are available in a document on the Yahoo group produced by Clint, KA7OEI who has done considerable work on both the hardware and software of the mcHF.

mcHF (18)Although not technically a mod, I did add a resistor that is regarded as “optional” on the UI board schematic. This resistor provides power for when an electret microphone is used. Since I would be modifying an Icom HM-36 I had lying around to work with the mcHF, I needed to install this resistor in order for the microphone to function. For this I used a standard 1/4W resistor since I had on of the correct value in my junk box and just soldered it to the surface mount pads. In order to avoid shorting with nearby components I carefully shaped the resistor’s leads and used electrical tape to insulate between the parts.

mcHF (5)mcHF (6)After completing construction of the boards, I turned my attention to completing the radio as a whole. The first step of this was to construct the shield plate between the boards. For this I used a thin mcHF (12)sheet of aluminum that I hand cut, drilled and nibbled according to a pattern available on the mcHF website. I then test fit and assembled the board and shield sandwich to check for proper clearance. When I was satisfied I completed the assembly using 5mm standoffs.

mcHF (19)mcHF (17)If you look around the web you will see a lot of people who have built the mcHF using the same case. This case is sold by Artur, SP3OSJ from Poland for about $63. If you email him at asnieg@epf.pl he will give you the details for how to order. The case comes with all of the knobs and buttons as well as a small piece of acrylic to protect the LCD display. The front panel is pre-machined, however, the endplates are left to the builder to complete. I also had to file some of the button holes to allow smooth operation and I had to sand the acrylic to fit the opening in the case.

mcHF (8)mcHF (9)Since the case serves as the heatsink for the power supply circuitry as well as the final amplifier transistors, a good mechanical connection between the components and the case is necessary. To mcHF (13)mcHF (14)accomplish this I soldered brass #4-40 nuts to the heatsink fin on power supply and amplifier components. I then drilled holes in the case to match where these nuts line up when the case is mcHF (15)assembled. When bolts are inserted and tightened, the electrical components are pulled tight to the wall of the case. In order to achieve a properly aligned connection, I had to grind away a small amount of material where the final amp transistors contact the case (note the hole I drilled in the wrong location due to my inability to follow the old rule of measure twice drill once). The last step in construction was labeling the buttons and ports, which I did using vinyl self-adhesive labels and my laser printer.

The final adjustment before testing the transmitter involves setting the proper bias for the final amplifier and then setting the transmitter gain for each band of operation. Documentation for these adjustments is on the Github Wiki. Basically you set the bias in one of the mcHF’s menu settings while keying the transmitter with no audio present as you watch the current draw of the radio. The transmitter gain is also a menu setting. These adjustments can be accomplished with an ammeter and a RF power meter.

mcHF (16)Finally, after probably 20 hours of work I put my mcHF on the air. After adjusting my microphone gain I made a contact on 40M SSB. I then plugged the transceiver into my PC and fired up WJST-X. Following the guide on the Github Wiki I was able to get rig control working and made a half dozen contacts using JT65 on the 30M band using nothing but the mcHF and my laptop. The next day I checked into my local 10M SSB net and received good signal and audio reports from the other regulars who are familiar with my voice.

Overall I have to say that I am incredibly happy with the mcHF kit. It has been a great learning experience and the radio itself is an incredibly capable and configurable device that offers a lot of bang for your buck. I plan to use the mcHF quite a bit in the future and look forward to any future firmware updates. I also hope that this kit leads to other similar kits in the future that can help get more hams back to building equipment.

I highly recommend this kit for anyone with some electronics experience. While the documentation has not been collected into one easily digestible package, the kit itself is actually very straightforward to put together and I was able to get it on the air with only a cheap multi-meter and an RF power meter. It is also an incredible bargain for such full featured radio; I spent under $500 total for the kit, case and other ancillary parts (not including the microphone) which is not bad at all when you compare this to what is available commercially.

Update – New Knobs, Bootloader & Firmware (August, 2016)

After using the mcHF for a few months I decided to look for some new knobs since the smaller ones included with the case I purchased aren’t ideal. I found some on Mouser that come in various colors and are designed to work with the “D” shaped shafts of the mcHF’s encoders. They have a nice soft rubber feel and the colors help to differentiate which knob is which. Each knob cost under $1, so this was a very economical upgrade.

Recently Andreas DF8OE, who is the main developer for the mcHF, released version 2.0 of the mcHF bootloader. The updated bootloader allows the use of the larger USB Type A port for firmware upgrades using only a USB Flash Drive. This eliminates the need for the proprietary software that was required to update the firmware in the past and solidifies the open source development of the mcHF going forward.

Andreas also released version 1.2 of the firmware for the mcHF. The new firmware has a number of feature improvements and bug fixes including better spectrum display performance and system responsiveness overall. Other future upgrades are in the works and I look forward to what the new features will bring.

Slim Jim Antennas

2 Meter Slimjim (2)2 Meter Slimjim (1)I am a big fan of the J-Pole antenna style and have built a few of them in the past (see here and here). Electrically the J-Pole is a half wavelength antenna that is end-fed by a quarter wavelength stub to achieve a feed point impedance of 50 Ohms. The Slim Jim is very similar except that there are two half wavelength segments with the second folded next to the first. This arrangement makes them ideal to be constructed from 450 Ohm ladder line. This also allows them to be incredibly compact and portable since they can be rolled up very easily.

2 Meter Slimjim (4)2 Meter Slimjim (3)I found a very useful calculator that gives you all of the dimensions needed to build a Slim Jim or a J-Pole from ladder line (you will have to convert from metric to imperial units yourself). Using this calculator set for 146 MHz (the middle of the 2 meter band), I assumed my 450 Ohm ladder line had a velocity factor of 0.91 and cut it to a length of 56 inches (not including the 0.5 inch on each end to be stripped and soldered together). I then cut the half wave radiator 36.75 inches from the top and the quarter wave matching section 18.375 inches from the bottom. This left a gap of 0.8 inches between the two. The 50 Ohm feed point was calculated to be about 1.8 inches from the bottom, however, using my antenna analyzer I found the the feed point should be 2.1875 inches from the bottom. With a piece of RG-8X feedline soldered at the feed point this antenna has an SWR under 2:1 across the entire 2 meter band. To complete the antenna I drilled a 0.25 inch hole at the top so that the antenna can more easily be hung from a mast or a tree or clipped to a wall if used as an indoor antenna.

This type of antenna is a very economical way to build a VHF or UHF antenna. It also has a considerable amount of gain compared to a standard quarter wavelength vertical and is just as easy to build and transport.

6 Meter Collinear Antenna

6 Meter CollinearI have been wanting to get on the 6 meter ham band for some time now, but I just never got around to it. Most people say that you should use a beam antenna for 6 meters, but I like to keep my antennas simple and cheap by using wire as the basis for everything. As part of my search for a good wire antenna for 6 meters I came across an article in QST from February 1997 called “Wire Gain Antennas for 6 Meters”. The article describes three different designs: the long-wire, the collinear array, and the Sterba curtain. After reading the article I decided I wanted to try building the collinear antenna because it has more gain than the long-wire while also being smaller and easier to build than the curtain.

6 Meter Collinear Antenna-4KI built my collinear array in the same manner as the article, using insulated 14 AWG wire and 450 Ohm ladder line. I cut mine for 50.1 MHz. For the 4:1 balun at the feed point, I used the balun I built recently. To securely mount the balun I used a DX Engineering Wire Antenna Balun Mounting Bracket. These brackets are specifically designed to mount to the type of enclosure I used for my balun, and they make a perfect feed point for a wire antenna. One of the benefits of 6 meter antenna experimentation is that you don’t need a lot of materials or space. This antenna when finished is only about 38 feet long and requires less than 15 feet of ladder line.

After getting the antenna in the air and the coax terminated I did some testing with my transceiver and the antenna exhibits around a 1.3:1 SWR at the design frequency and easily stays under 2:1 from 50-51 MHz. In theory this antenna should have a gain of 4-5dB over a dipole, so I am really looking forward to my first band opening to give this thing a try.

Update:

After playing with this antenna during a few band openings and not hearing many stations I realized that while this antenna is of a good design, it would work best when at a greater height than I can achieve at my location. It would also help if I was able to erect a couple of them to be able to shift the directivity of the array. Not being able to accomplish either of these goals I decided to take down the array and move on to another antenna design for 6 meters that better fits my operating capabilities and the size of my property.

Baluns & Ununs

Anyone building antennas will come across designs that either recommend or require the use of a balun or unun. The design and construction of these components can get quite complex and are beyond the scope of this blog and my own knowledge. In short these devices act as impedance transformers from balanced loads to unbalanced loads (balun) or from unbalanced loads to unbalanced loads (unun). They can also be used as a common mode choke to eliminate any RF on a coax feed line’s shield. That said, it is actually quite easy to construct your own baluns and ununs and to learn something in the process. You can also save a considerable amount of money.

1-1 Balun (2)1-1 Balun (1)Amidon sells a good starter kit for building baluns and ununs. It includes everything you need including a book with dozens of designs with various impedance transforming characteristics. 1-1 Balun (6)1-1 Balun (3)I used this kit to make a 1:1 balun. Since the kit uses 14AWG wire, it should be capable of handling 2KW of power continuously. This is overkill for me since I will never be putting more than 100W through the balun. The 1:1 balun is essentially a choke that blocks current flow on the shield of the coax feed line. It is constructed using 10 bifilar wraps on the toroid core using approximately 4 feet of wire.

For other projects I decided to use the same FT-240-K core with 18AWG wire covered in 16AWG PTFE insulation. While the 18AWG has less power handling capability, it should be more than adequate for 100W usage as well as being cheaper and easier to work with.

4-1 Balun (2)4-1 Balun (1)The first balun I made using these materials was a 4:1 current balun. This balun is intended to transform a 200 Ohm load for use with a 50 Ohm coax feed line. This type of balun is commonly used in 4-1 Balun (3)Off-Center-Fed dipole antennas because the feed-point is placed at the location on the antenna where the impedance is approximately 200 Ohms on multiple bands. I intend to use this balun as part of a 6 meter collinear antenna that I am building. The balun is constructed using two sets of 8 bifilar wraps on the toroid using approximately 8 feet of wire. Each pair of windings is then wired in series with the other pair. This design can be thought of as two 1:1 baluns wired in series and in fact an alternate design of this balun uses two separate 1:1 balun cores wired in series to achieve the same affect.

9-1 Unun (2)9-1 Unun (1)Next I made a 9:1 unun for use with an end-fed antenna I am building. End-fed antennas exhibit very large impedances and consequently require considerable impedance transformation to 9-1 Unun (3)get the feed point within the range of an antenna tuner. Unlike a dipole, an end-fed antenna is unbalanced and therefore an unun is used instead of a balun. This design uses 8 trifilar wraps on the toroid using approximately 6 feet of wire. Each wrap is then wired in series to create the desired impedance transformation.

1-1 Line Isolator (2)1-1 Line Isolator (1)I also made another 1:1 balun. The main difference here is that I constructed it using two SO-239 connectors because I intend it to act as a coaxial feed line isolator. My plan is to use this in conjunction 1-1 Line Isolator (3)1-1 Line Isolator (4)with the 9:1 unun as part of my end-fed antenna project. The idea here is that a section of coax from the 9:1 unun acts as the counterpoise for the end-fed antenna and the line isolator is used to choke the RF current in the shield of the coax and allow the remainder of the feed line to continue to the antenna tuner without risk of radiating RF.

For all of these projects you can see that I used colored electrical tape to mark the various windings. This is essential to keeping track of the wiring and assuring that the windings are wired together correctly. For all of these I also used standard NEMA 4X 4″x4″x2″ plastic electrical boxes which are cheap and commonly available. I also used 10-32 stainless steel hardware for the antenna connections and silver-teflon SO-239 connectors.