Tuesday, February 28, 2012

What has been happening?

Anyone looking at my blog could be forgiven for thinking that I had dropped off the face of the earth for a while, has nothing been happening in my world?

Well, the answer is that a LOT has been happening and all at once. My daytime job has become busier and there have been several non-radio projects at home that needed to be completed. All this has kept me away from Amateur Radio blogging even though I have spent more time on the computer than usual.

In between projects I did manage to stumble across this video of Rear Admiral Grace Hopper explaining just how "long" a nano-second is and what it looks like. This has relevance to radio as we're usually well aware of frequency and wavelength but don't usually spend too long thinking about speed.

From Wikipedia : Rear Admiral Grace Murray Hopper (December 9, 1906 – January 1, 1992) was an American computer scientist and United States Navy officer. A pioneer in the field, she was one of the first programmers of the Harvard Mark I computer, and developed the first compiler for a computer programming language. She conceptualized the idea of machine-independent programming languages, which led to the development of COBOL, one of the first modern programming languages. She is credited with popularizing the term "debugging" for fixing computer glitches (motivated by an actual moth removed from the computer). Because of the breadth of her accomplishments and her naval rank, she is sometimes referred to as "Amazing Grace." The U.S. Navy destroyer USS Hopper (DDG-70) was named for her, as was the Cray XE6 "Hopper" supercomputer at NERSC.

Thursday, February 23, 2012

Morsemail and LCWO.net

The time has come when I can't put off learning Morse code any longer, With an interest in vintage amateur radio and the impending restoration of a Heathkit AT-1 I'm going to need to use CW sooner or later.

So I have been checking out resources for learning Morse code and stumbled across two that really intrigue me.

The first is LCWO.net, a web browser based Morse code learning tool that is usable on any internet connected computer. It is available free of charge and there is no software to install. LCWO.net keeps track of where you are in your lessons and where you need to concentrate your effort. The Koch method is the primary tool available but they also offer code group practice, callsign and plain text training modes along with a service to convert text to Morse MP3s for download and use offline.

Once you are on the way to CW proficiency and want to communicate with others you can always fire up a rig and get on the air ... What if you don't have a rig or need a confidence boost before 'going live'?

Well, you could always send Morsemail using the Morsemail client from http://brasspounder.com:8873/.

Morsemail is, "A simple text format that encodes mark and space times to make it possible to send Morse coded messages via email" but a recently added feature allows for QSOs using a internet repeater hosted on brasspounder.com. You can use a mouse or actual key wired to the mouse or joystick buttons to send CW which can be emailed or sent through the repeater live.

Now I just have to carve out the time to sit down and use these resources!

Tuesday, February 21, 2012

DIY Magnetic Loop Antenna - Part 2

Part 1 of the DIY Magnetic Loop Antenna covered mostly theory and materials so now its time to move on to designing the magnetic loop antenna (MLA).

If you have priced a commercially made MLA you'll see prices start at $400 and keep going up, and up. If they cost so much you would think they must be difficult to build or use expensive parts, right? Well, it is certainly possible to spend more and get a higher quality MLA but a low cost MLA will still work very well.

For the purposes of this article we'll assume that you want to build a loop to cover the 20-10M bands. I'll run through the calculations required to build the MLA.

The required information for the MLA calculator is:
  1. Length of the loop
  2. The conductor diameter
  3. Frequency/s of operation
  4. Input power to the antenna
Lets pick some starting values
  1. We don't really know the best length of the loop at the moment so I'll pick 9 feet circumference as a starting point (It'll still fit in the trunk of my car)
  2. Since we seem to be having better luck with sunspots now I'd like to try 10M so we'll start with 29 Mhz as the highest frequency we'll use.
  3. I have some copper pipe left over from an ice-maker install, it is 1/4 (0.25) inch in diameter.
  4. Input power to the loop will be 100W.
Using the 66pacific.com calculator we get the following:
The comments section informs us that, "The specified conductor length is not idea" and we can go on to read that, "To avoid self-resonance, the conductor length for a small transmitting loop antenna should be less than 1/4 wavelength (less than about 8.23 feet at the specified frequency of 29 MHz)."

Well, I don't want the wire in the loop to resonate by itself, its designed to resonate in combination with the capacitor. Lets make the loop 8 feet in circumference and while I'm at it I'll make it out of 3/4 (0.75) inch copper pipe for better conductivity.

Lets see what we have now:
Well, that seems to have fixed the self resonance issue and we've managed to bump up the antenna efficiency to 91% from 82% ... not a huge increase ( About 0.5 dB) so I could use either diameter copper tube in this case. Everything looks good so far!

How about the 20M band, at 14 MHz how do things look?
So, the specified conductor length is not ideal but the comments section says were under the 1/4 wavelength at 17 feet. What is also tells us is that, "For highest efficiency, the conductor length for a small transmitting loop antenna should be greater than 1/8 wavelength (greater than about 8.52 feet at the specified frequency of 14 MHz)." 

That is OK, we know that the MLA is going to be less efficient somewhere in its range and the suggestion of 8.52 feet is close enough to our 8 feet we can ignore it. The 42% efficiency is not the greatest but -3.6dB is about half an S-Unit down so I'll live with that.

Just for fun I changed the copper pipe back to 1/4 inch and the efficiency dropped to 20% (-7 dB) so I think I'll stick with 3/4 inch. It makes more of a difference at lower frequencies since more current is flowing through the loop!

In order to tune the loop between 14MHz and 29MHz we look at the Tuning Capacitance value in the last two calculations above. At 29 MHz the tuning capacitance required is 19 pF and at 14 MHz it is 83 pF. 
This is well within the capacitance range of a normal air variable capacitor and in fact a larger capacitor with a maximum capacitance of 160 pF would allow you to reach the 30M band with reduced efficiency. 

Its important however to look at the voltage across the capacitor in our last two examples. At 29 MHz we'll see a Capacitor voltage of 2,562 volts RMS and at 14MHz we'll see a Capacitor voltage of 3,664 volts RMS.

What does this mean? In order to know what kind of capacitor would be best we need to know the absolute maximum voltage it will have to withstand before it arcs between the closest conductors. If the voltage is high enough it will 'leak' between the plates of the capacitor by breaking down the air between them and directly passing an electric current ... we don't want this to happen.

The breakdown voltage of air is around 3000V per milimeter (39/1000 of an inch = 1 mm). The voltage above is shown as RMS (Useful for power calculations) but we need to know the peak value which is higher and determines the maximum voltage. The peak voltage = RMS x 1.414 or 3664 x 1.414 = 5181 V peak. 

A peak voltage of 5181V will require a minimum spacing of 1.7 mm (peak voltage / breakdown voltage per mm) between the closest conductors in the capacitor. That would rule out an old air spaced variable capacitor from a vacuum tube radio but you could still use a wide spaced variable capacitor from an antenna matching unit or transmitter. A vacuum variable capacitor would be great (watch the minimum capacitance) or a home-made capacitor would also be fine provided you checked the breakdown voltage of the insulating material.

What if all you have is a capacitor with insufficient plate spacing for that voltage? If you reduce the output power to 35W then the voltage across the capacitor will decrease to 2168 V RMS which is 3066 V peak( 2168 x 1.414) This voltage requires a 1 mm plate spacing which is easily achievable with surplus capacitors. At QRP power levels (5 W) the voltage falls to 1160 V peak and requires only 0.39 mm between the plates, suitable for practically any variable capacitor!

The value of 3000V / mm is only an approximation and if possible use a capacitor rated for a higher voltage than you expect to run to prevent damage to your radio. Modern rigs have great protections circuits but they shouldn't be relied on.

Next post I'll cover building the loop and coupling it to your transceiver. Hopefully you found this information useful and if there are mistakes or inaccuracies you'll drop me a line and set me right.

Friday, February 17, 2012

DIY Magnetic Loop Antenna - Part 1

Do you live in a neighborhood with a restrictive antenna policy and despair of having a useful HF antenna?

Can you solder or know someone who can?

A magnetic loop antenna may be the answer and they are not as difficult to build as you might think. Like getting on the air for the first time or taking your license exam there is a certain amount of uncertainty when you first approach magnetic loop antennas, there are a few new ideas to grasp. However, thanks to other hams like Steve AA5TB there are tried and tested designs, calculators & building methods that are known to work and that you can follow.

At the heart of every radio and MLA (Magnetic Loop Antenna) is the resonant circuit. The combination of an inductor (a wire has inductance, but a coil of wire has more) and a capacitor (two conductors separated by an insulator) in a circuit will resonate or 'ring' at a certain frequency. Sound vibrations at a certain frequency can cause a piano string to vibrate in sympathy and a vibration of the correct radio frequency will cause a resonant circuit to electrically vibrate in sympathy.
Since there is no such thing as a free lunch, the sacrifice you make with a MLA is that it needs to be re-tuned whenever you change frequency on your transceiver. The frequency range over which it is resonant is very small, typically only a few hundred kilohertz at the most.

The materials you can get your hands on is going to decide the capabilities of your MLA. Ideally you'll have a loop made from a conductor with very low resistance (usually copper) and a capacitor that can handle high voltages. A variable capacitor is required if you want to use your antenna on multiple frequencies but you can use or make a fixed capacitor if you operate on one frequency, for Eg PSK31.

A MLA calculator like the Excel spreadsheet from Steve AA5TB or this web page from 66pacific.com will help you to decide what size components you'll need to make your antenna.

The four pieces of information required are:

  1. What frequency or frequencies do you wish to transmit on?
  2. How large do you want the loop to be (It should have a circumference less than 10% of the design frequency wavelength, both calculators help you figure this out)
  3. The diameter of your conductor (Three quarter inch (0.75 inch) copper pipe is a good start)
  4. How much power you want to use (The voltage across the capacitor is proportional to the input power to the MLA)
A MLA of a certain circumference will be more or less efficient based on the frequency you transmit at. It is worth changing the loop size in the calculator to get the best efficiency possible in your favorite band. 
For example, my 30-10 Meter loop is 8.5 ft in circumference and 23% efficient at 10.1Mhz but 91% efficient at 28Mhz. This represents a difference of about 6dB or 1 S-Unit.

The diameter of the conductor determines its resistance and this becomes important due to the large current flowing through the loop. Large diameter copper pipe is better since the radio frequency current flows primarily on the outside of the conductor rather than the core. Typical 3/4 inch plumbing pipe is a good balance between low resistance and weight, Heliax coax is good for portable antennas where the loop has to be rolled up into a compact space.

Probably the most problematic part of the MLA is the tuning capacitor. While everything else can be found in your junk box or on a shelf at the local hardware store the capacitor takes a little more digging. Ideally it should be variable from a minimum to a fairly high capacitance (0-300 pF would be good) it should also be able to withstand high voltages. If you are planning to run 100W then you could expect at least 4000 volts across the capacitor. This is not as bad as it sounds as it takes 3300 volts to jump just 1mm or .04 of an inch.

Ideally you could purchase a vacuum variable capacitor, the Rolls Royce of high voltage variable capacitors. You would expect to pay anywhere from $100 up when buying a 10 - 500 pF unit on Ebay and a LOT more if you buy new. If that is the way you want to go then great, you're all set. If not then read on ...

There are several alternatives to the vacuum variable capacitor that will work almost as well. The primary concern now becomes resistance and plate separation. For QRP power levels you can use the tuning capacitors from old vacuum tube radios, the type that have a set of fixed metal plates and a set of moving plates that mesh into them.
For higher power there are two other types of capacitor that are suitable. 
One is the split-stator capacitor, so called because each terminal of the capacitor is connected to a stator that is electrically isolated from the other and the frame. The rotors and shaft form the rest of the circuit so there is very low resistive loss and no sliding contacts.
The other type is called a butterfly capacitor due to the shape of the rotor plates. In this type the stator plates are placed opposite each other with the butterfly rotor in between. When each of the butterfly "wings" are fully meshed between the stator plates the capacitor is providing maximum capacitance, when rotated 90 degrees the wings are completely un-meshed and the capacitor is providing minimum capacitance. Because of the construction of butterfly capacitor there is a higher minimum capacitance that should be noted when planning the frequencies your loop will cover.
If all else fails then you can construct your own variable capacitor. The idea is to have two conductors separated by an insulator, the larger the area of the conductors and the better the insulator the higher the capacitance. Sliding metal plates, trombones of copper tube and even Coke cans have been used as variable capacitors.

A fixed capacitor can be created out of coaxial cable if you intend to operate on one frequency and a table of approximate capacitances for different types of coax is included here, click to enlarge the table below.

You can cut a length of coax a bit longer than the length suggested by the table above and trim it to frequency once it is attached to the loop. Make sure there are no stray pieces of braid between the shield and the center conductor as the voltage rating is determined by the spacing of the two closest conductors.

Part two of this post will continue with calculating the antenna dimensions and performance.

One important thing to remember ... If you don't have access to the best materials then use what you have and improvise. If you don't have copper pipe then use coax or heavy wire. If you don't have a high end variable capacitor then use what you can find and keep the power levels QRP. The only antenna that is a complete failure is the antenna you never get around to building.

Wednesday, February 15, 2012

Now I understand - Phase Locked Loops

Every now and then I come across great books or videos that explain a concept in such a way that it becomes immediately obvious what is going on. I'm a great believer in learning by demonstration or even better, learning by doing.
I came across another explanatory video recently that I thought was too good to keep to myself. It covers a topic that was a complete mystery to me: Phase Locked Loops. We utilize them in almost every modern transmitter and receiver yet most people I have talked to view them as a black box that, fortunately, does its job well and usually without interruption.
The video below does a good job on opening the black box and showing just what makes phase locked loops ... well, lock.

Monday, February 13, 2012

What is the AM-6155/GRT-21 ?

FAA AM-6154/GRT-21 Amplifier
From the website of N1RWY

The FAA used the AM-6154 and 6155 amplifiers in the early 1980's as ground-to-air AM transmitters. The 6154 was designed to cover 118-136 MHz and the 6155 to cover 225-400 MHz. Both models were set to 50 watts output, and amplified an AM exciter.

Both models were rack-mount, 7" high, 19" wide, and about 24" deep; they weigh about 75 pounds and have an internal AC power supply that can be used on 120/240 VAC. They are built so they have a slip-in RF drawer that contains the RF amplifier itself. The main chassis holds the power supplies and a small blower. No T/R switching is included. Because they are intended to be used with the exciter, the amplifier circuitry expects to get some DC control signals from the exciter which have to be simulated by some modifications.

The reason the amplifiers are so interesting to V/UHFers is because they are capable of outputting over 400 watts on 2, 222 or 432 MHz with only a few hours work and almost no extra parts. This is because they use the 8930 tube (or the Amperex equivalent, the DX-393), which is basically a 4CX250R with a 350-watt anode. 50 watts average power of AM is actually four times that power peak; or 200 watts; and these things were designed to do that all day, every day. That's why they used such a high-power tube for only 50 watts output power.

The RF drawer of either model can be modified for ANY of 2, 222 or 432; but as it comes from the factory, modifications HAVE to be made for any of the three bands. In general, the mods involve redesigning the RF grid circuit to be more efficient and to tune one of the ham bands. The plate circuit in either model can be used on any of the three bands, although use at 400 watts on 432 MHz places a big strain on the stock plate DC choke and plate blocking capacitor, which almost always have to be reworked for serious 432 MHz use. They have apparently proven able to withstand high power on 144 and 222 MHz without modification, although the mods do not hurt.

The power supply chassis is composed of three smaller drop-in chassis, an additional metering PC board, and a 400 Hz 120VAC blower which is powered by a DC-to-AC converter (one of the three drop-in chassis). The high-voltage power supply uses a very compact and lightweight transformer, a dual-section oil-filled filter capacitor, two screen voltage dropping resistors and a string of three zener diodes to regulate the screen voltage. Another drop-in chassis houses the filament transformer which also provides grid bias power and another winding to provide power to the DC-to-AC converter which drives the very small, compact 400 Hz blower (which is able to cool the large tube due to the high speed, 5500 RPM, of the blower).

A front-panel-mounted meter with 12-position switch is also wired to a PC board which contains circuitry that originally monitored the output power and antenna VSWR in addition to the blower current, filament voltage, grid, screen and plate voltage, and plate current. The RF drawer contains a directional coupler and low-pass filter which are almost always removed from the output of the amplifier (and sometimes rewired to the input side) because they don't handle 400+ watts very well.

So, where can you get one?    
Most of the amps are sold by Fair Radio in Lima Ohio. They advertise in QST. Sometimes they can be found at hamfests and there have been reports that a few have been picked up from government surplus sales. Fair Radio asks $235 for the AM-6154 and $285 for the 6155. (Based on early 1997 figures) Fair Radio has by far provided the lion's share of them, probably well over a couple thousand to US hams alone.

They are extremely popular among US V/UHFers and usually command a $300+ price tag, whether modified or not (because the shipping alone totals around $35 for UPS Ground!). Recent estimates by Harry Brown, W3IIT of the Packrats, are that there are OVER several hundred in the Philly area alone; and Ev Tupis, of the Rochester VHF Group, estimates ALMOST that many in northwestern NY state! They're great amps - not 8877's but the price is hard to beat.

[ Thanks to Steve, KO0U/1, and Harry, W3IIT, for the summary and history of these fine amplifiers. ]

Sunday, February 12, 2012

Heathkit's first amateur transmitter - Heathkit AT-1

The Heathkit AT-1 represents the commercial embodiment of the simple Master Oscillator Power Amplifier (MOPA) transmitter using a crystal controlled 6AG7 oscillator plus a 6L6 final output tube.

Although it was possible to design and build a simpler transmitter, the goals of output power and stability could become mutually exclusive when trying to operate with only one tube. For a novice class license holder of 1951 the Heathkit AT-1 represented a solid performing rig that would be relatively easy to construct and operate.

The Novice remained the primary entry license until the Morse code requirement was eliminated for Technician licenses in 1990. On HF it permitted code transmissions only, with a maximum power of 75 watts, (input to the transmitter's final amplifier stage) on limited segments of the 80, 40 and 15 meter bands.

For $29.50 and the loan of a few tools you could get some use out of that new novice license
The earlier MOPA circuit from the ARRL handbook of 1941 below shows a layout remarkably similar to the circuit of the AT-1 although it is designed for plug in coils rather than the band-switching arrangement of the later Heathkit transmitter.
MOPA transmitter using a 6L6 and an 807 as the power amplifier (ARRL Handbook 1941)
For a little added complexity MOPA transmitters generally offered better stability of frequency and keying waveform than single tube crystal controlled or self exited rigs. The straight forward design of the AT-1 should have looked familiar to novice class hams after studying the ARRL handbook or other radio publications.
Heathkit AT-1 Circuit diagram showing band-switching arrangement and link coupled output
Once the novice had upgraded his license the AT-1 could be expanded by the addition of the Heathkit VF-1 variable frequency oscillator to allow transmission on any frequency within the allowed band.
The Heathkit VF-1 Variable Frequency Oscillator
The VF-1 covered 160-80-40-20-15-11-10 meters and used an OA2 voltage regulator tube to provide a stable voltage for the oscillator. Ceramic coil forms, solid construction and high quality components were used to help increase stability.

It was recommended that to correctly couple an antenna to the AT-1 you would use an antenna coupler such as the Heathkit AC-1 which also included a low pass filter.

The Heathkit AC-1 Antenna Coupler. Designed to attach to a single wire by the insulated post on the front panel.
Heathkit AC-1 Antenna Coupler circuit diagram
Although Heathkit did not produce a AM modulator for the AC-1 there is provision for modulator connection on the rear panel. The earlier ARRL manuals have several suitable circuits for modulators that would work with the AC-1. Most functioned by driving a modulation transformer with the output from an audio power amplifier. The secondary of the modulation transformer would be carrying the DC plate supply for the power amplifier tube plus or minus the instantaneous voltage of the audio waveform. By changing the plate voltage to the final amplifier tube the radio frequency output would be controlled by the amplified audio frequency resulting in amplitude modulation.

Saturday, February 11, 2012

South Texas Balloon Launch Team launches balloon aimed at China

My daughter and I made the short trip to the No Label Brewing Company in Katy TX to watch the South Texas Balloon Launch Team launch a helium balloon aimed at Nanjing China. Thanks to Tom AE5QB for letting us know about this event!

To track the balloon in real time go to : http://aprs.fi/?call=a%2FKT5TK-11&_s=mb

From the press release of the South Texas Balloon Launch Team:

The South Texas Balloon Launch Team is pleased to announce the upcoming launch of its twenty-eighth, helium-filled, unmanned balloon in twenty one years. The purpose of this flight is to establish a world record for distance by floating a balloon from Katy, Texas to Nanjing, China.

The balloon will be released at approximately 3 P.M. CST on Saturday, February 11, 2012. The site of the launch is at the western end of the No Label Brewery complex at 5373 First St., Katy Texas, near the old rice grain silos.

The public is invited to this free event, with a special invitation to science students and teachers. Free helium-filled balloons will be available to the first 100 students. Sorry, no pets allowed in the balloon area.

The balloon payload package weighs only about five ounces (150 grams) and contains a high altitude GPS tracking system and a VHF amateur radio transmitter. To conserve weight and battery life, no camera equipment will be on board. The maximum altitude is expected to be above 100,000 feet, with horizontal speeds between 100 and 150 MPH. The balloon size will increase from about five feet to about 39 feet at maximum elevation. Recovery of the payload package is not expected.

Individuals may follow the balloon's progress on the Internet by logging onto APRS, filling in the "track callsign" field with "kt5tk-11", and change the "show last" to 24 hours.

The South Texas Balloon Launch Team is composed of about twenty active amateur radio "Ham" operators from a variety of occupations who donate their time and expertise.

We appreciate the continued support by No Label Brewing Company for our amateur radio projects.

Thursday, February 9, 2012

Now I understand - Standing Wave Ratio (SWR)

There are great books out there that explain radio principals in a plain and straightforward manner. Many are vintage military manuals whose primary aim was to give a functional understanding of the theory involved without getting caught up in the interesting but ultimately unnecessary details.

Modern material on the other hand can sometimes miss the mark of providing a functional understanding in favor of trying to completely address the high level theory and leaving practical matters to be addressed later ... or perhaps never.

The AT&T training video certainly hits the mark when it comes to explaining and showing the properties of radio waves. It shows how they are affected by termination and changes in impedance, what resonance looks like, how terminated and non-terminated lines reflect waves and much more.

Material like this is well worth the time of anyone who has an interest in radio or electronics.

More video are available from the AT&T archives here : http://techchannel.att.com/showpage.cfm?ATT-Archives

Wednesday, February 8, 2012

Virtual Tour of W1AW, the Hiram Percy Maxim Memorial Station

Virtual W1AW Tour on Sunday, February 12 at 5 PM EST (2200 UTC)

Join W1AW Station Manager Joe Carcia, NJ1Q, on a virtual tour of W1AW, the Hiram Percy Maxim Memorial Station, the Amateur Radio station at ARRL Headquarters in Newington, Connecticut. Carcia will lead this tour via a live webcast on . Anyone with an Internet connection will be able to watch the tour here.

W1AW - The Hiram Percy Maxim Memorial Station

"We want viewers of this live Internet tour to feel as if they are actually at W1AW," Carcia explained. "If you came to W1AW in person, you would see the same things that we are going to show on the virtual tour: The three operating stations, the W1AW workshop, the transmitter racks that we use to send out our bulletins and use for the code practice transmission, the control console and Old Betsy, Hiram Percy Maxim's personal spark gap transmitter."

Al Petrunti, KA1TCH, of the New Day Group, will follow Carcia as he leads viewers through the station. ARRL Staff members, including Media and Public Relations Manager Allen Pitts, W1AGP, and Chief Operating Officer Harold Kramer, WJ1B, as well as local television weatherman Geoff Fox, K1GF, will also be on hand at W1AW during the tour.

"Hams around the world know of W1AW, and thousands have made contacts with this impressive station -- but most hams never get to see it," Pitts said. "Thanks to Al Petrunti's group, we hope that folks enjoy seeing what's at the other end of the signals. As in all live broadcasts, you never know just what might happen. We invite you to join us." Pitts is producing the live web tour.

From the ARRL Letter, available at http://www.arrl.org/arrlletter?issue=2012-02-09

The Power of Making

A brilliant video detailing the power of making through a triptych of views into the workshops of makers.

A three screen film installation for the Power Of Making exhibition. A collaboration between the V&A and the Crafts Council, this exhibition presents 100 crafted objects in a cabinet of curiosities that explores traditional and time-honoured ways of making, as well as innovations taking place around the world.

Visit the Victoria and Albert Museum at http://www.vam.ac.uk/

Tuesday, February 7, 2012

The KN-Q7A - A new 40M SSB 10W transceiver kit

Amateur radio kit builders have had greater opportunities to construct high-end equipment thanks, in part, to more economical production processes. Online services allow kit manufacturers to farm out circuit board production to large workshops where jobs are batched together into larger production runs with significant cost savings. A number of suppliers are now willing to sell in smaller amounts while maintaining low costs due to automated on-line processing. The end result has been an increase in the number of kits available of significant complexity including rigs with using sideband, digital signal processing and software defined radio.

One new SSB rig kit is the KN-Q7A available from Adam Rong BD6CR/4, designed by Shi Ke BA6BF. The KN-Q7A is a 40M SSB transceiver in a compact case with VXO tuning and 10W power out. This style of rig would be ideal for back-packing, camping or as a compact emergency transceiver.

It would be interesting to see how this would pair with the NUE-PSK Digital Modem for a ultra-compact portable PSK31 station if the VXO could be made to tune to 7.035 MHz

The KN-Q7A - 40M with VXO SSB 10W
The KN-Q7A is available directly from http://crkits.com/ or from their US distributor http://www.qrvtronics.com/HAM-Radio

Price for the KN-Q7A kit is $125 USD, a suitable microphone is available for an additional $25 USD.


• Dimension: 153 mm x 97 mm x 40 mm, not including protruding features
• Weight: 500 g or 1.1 lbs
• Power Supply: 12~13.8 V, 3 A
• Current consumption: 30 mA in RX and about 2 A in TX @ 13.8 V
• RF output: about 10 W PEP @ 13.8 V
• Spur suppression: better than -43 dBc
• Sensitivity: better than 0.5 μV at 10 dB SNR
• IF filter: 6 pole crystal ladder filter + 1 pole post IF amplifier crystal filter
• IF bandwidth: about 2.0 kHz
• IF frequency: 8.467 MHz or 8.192 MHz, depending on the selected tuning range
• Frequency tuning range: about 20 kHz in VXO type. Five options: 7.050~7.070 MHz,
7.080~7.100 MHz, 7.145~7.165 MHz, 7.200~7.220 MHz, or 7.280~7.300 MHz
• Connectors:
• Speaker output: 3.5 mm connector, mono output
• Microphone input: 8-pin, can be configured to be compatible with electret
• Antenna connector: SL-16 type (M or SO-239 type equivalent), rear panel mount
• Controls:
• IF Gain Control: act as volume control
• Tune Control
• On board RF Attenuator trimmer to eliminate broadcast interference

Sunday, February 5, 2012

Radio Kits that Teach

There continue to be great kits produced that aid in learning the fundamentals of radio theory and construction. Two that I really admire are the Elenco radio trainer kits, available in both AM/FM and AM only versions. They do require some soldering so, if you haven't soldered before, I would recommend a soldering starter kit like the AmeriKit Learn to Solder Kit or similar. The AmeriKit costs around $15 and includes a basic soldering iron.
Possibly the best part of the radio kits are the detailed instruction manuals that step through the theory behind each section as it is constructed. This is more than just a assemble and go kit, the aim is to come away with an understanding of how radio signals are turned into intelligible audio.
Both Elenco kits are available from a variety of retailers, you can source your own or I will include links to Amazon if you prefer.

Elenco AM / FM Radio Kit - $30
Elenco AM Radio Kit - $18

Although this probably sounds like an advertisement for the Elenco kits I'm not affiliated with Elenco, I just happen to like their kits and educational gear.

Friday, February 3, 2012

Winter Field Day 30 - 10 Meter Loop

This is a very rough diagram of the magnetic loop antenna I built for Winter Field Day. The tuning capacitor is a military surplus 150mmf (150pf) air variable with a worm and wheel drive. It also has a anti-backlash mechanism for very fine control.
The main loop is made of 1/4 inch annealed copper tube 8.51 feet long. Half inch pipe would have been better but quarter inch was easier to work .. and it was what I had. Both ends of the loop terminate at the tuning capacitor with soldered connections for the lowest loss possible.
The coupling loop has a circumference that is 1/5 that of the main loop. In this case it is 1.7 feet. It is located opposite the tuning capacitor and can be moved or squashed slightly to adjust for best SWR.
The one improvement that immediately comes to mind would be to terminate the connection to the coupling loop in a SO-239 connector rather than the short length of coax I used.

I have plans for remote tuning and automatic tuning but it remains to be seen if I can get the time & resources to bring those to completion.
A short length of heavy wire is used to connect one side of the tuning capacitor to the loop, the other was bolted and soldered to the body of the capacitor. As the tuning cap had been sitting for several decades a shot of Deoxit restored the connection between sliding contacts after I noticed that tuning was erratic while using an antenna analyser.
The supports for the loop are made from the ham's best friends : white pvc pipe and zip ties. Holes were drilled to keep parts from moving.

Wednesday, February 1, 2012

Incredible materials : Ultra dense plastic - Malleable at just 150F

Ham radio folk have been home brewing, inventing and crafting before most Makers were a gleam in their parents eye but that doesn't mean we can't learn from those industrious Maker guys. One area that is receiving more and more attention has been new and innovative construction materials.
Most of us are familiar with the concept of cutting a plastic chopping block up to make insulators but what would you do if you needed to create a molded part or something more complex? Injection molding is expensive for one off parts and anything more complex than drilling a hole also requires a substantial investment in machinery.
A new material that goes by several names (Shapelock, InstaMorph) is malleable at just 150 degrees Fahrenheit (66 degrees centigrade) and cools to an ultra-dense plastic similar to nylon.
It can be molded with your hands when heated and machined with low speed tools when cool.  I couldn't find specific details but I imagine it has similar dialectic properties to nylon which would make it suitable for a wide range of radio and electronic applications. Perhaps you'll be the first to add this material to your arsenal of home brewing tools?
Check out the demo below which shows how easy this material is to mold using simple tools or just your hands. You can get Polycaprolactone under several different brand names such as Friendly PlasticInstaMorph or Shapelock from a number of different suppliers or search for it on Amazon.