Posts Tagged ‘homebrew’
Wellbrook Loop Plans
July 23rd, 2014 | 
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| My present 9.5' active loop |
During last winter's DX season I built and played with a number of different preamps for use with my (almost) 10' diameter shielded loop. I had been hoping to get the Burhans Preamp to play-nice above 500KHz so that I might use it for DXing the broadcast band with my new Perseus SDR radio. By bypassing the preamp's LPF, the level of BCB signal delivered by the 10' loop was just too much for the preamp's JFET front end to handle with the consequence being various strong intermod products showing up at several places inside the band. Several different toroidal input transformers produced varied results but none were satisfactory. Although I didn't try it, a smaller aperture loop might do just fine with the LPF removed and even better if there were no blowtorch BCB signals in the vicinity. My particular location, on the east coast of Mayne Island, looks directly across Georgia Strait to several 50KW BCB transmitter sites near the points of nearest landfall. Luckily, this direction is usually in the loop's null when pointing in my favorite target direction of SE/NW for the central U.S. Even so, it would be nice to not have to worry about loop orientation in order to guarantee intermod-free performance.
I did have much better success on the BCB using a version of the PA0RDT active antenna preamp, modified with transformer input to match the shielded loop's low impedance to the JFET amplifier input.
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| Courtesy: Aldo Moroni |
Gain of the system was adjusted by swamping the transformer's output with various levels of 'R' until there were no signs of intermod products with the loop pointing away from the Vancouver blowtorch signals. The end result was a preamp that had good performance throughout the BCB, even with the big loop, as this recording of French language station, CJBC (860KHz) in Toronto(identifying as 'Radio Canada') demonstrates.
....but unless the loop was oriented in my favored SE/NW direction for most North American targets of interest, there were still a few frequencies that produced some very low-level intermod products. Again, had the loop been just slightly smaller, I think this preamp would do a great job as a wideband loop amplifier for the BCB and above. Although still usable down at 540KHz, performance dropped off rapidly as I went lower in frequency and was not considered usable for the LF NDB band. Perhaps more inductance in the input transformer as well as higher value coupling capacitors would improve LF performance. There is still room for further development of this circuit for LF use with a medium-sized shielded loop.
I recently ordered and received a Wellbrook ALA-100LN loop preamp, which I am anxious to install for the upcoming DX season. With its front-end of 8 JFETS in push-pull parallel, the Wellbrook boasts extremely good strong-signal handling capability within the BCB and below.
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| Please visit: http://www.wellbrook.uk.com/ |
My present plans call for a new and lighter loop frame, this time using PVC tubing in some sort of H-frame. I will aim to make the loop as large as possible while keeping within the Wellbrook's circumference limit of about 21m. Mid-summer doodling has produced one possible front-runner but no final decisions have been made.
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| 10' x 20' LF / BCB Loop |
I always savour the design and 'what-if' phase of any new project and the new loop is no exception. Any other ideas for possible frame configurations would be most appreciated.
SMD Kits
I've been intrigued for some months now by the proliferation of SMD parts kits widely available from Asian manufacturers being sold on E-Bay. Resistor, capacitor and inductor kits, containing significant numbers of standard-value parts and in various sizes are being offered at attractive prices. With many sellers throwing in free-shipping, I find myself being tempted more and more to press the "Buy Now" key and fear that I will not be able to hold out much longer.
I have had limited experience with SMD parts, when building a small 40m QRP transceiver several years ago called the SMK-1. As I recall, it had 72 SMD parts....the bigger ones, 1206 size. I recall finding the assembly and soldering of these SMD parts to be somewhat tedious and less than enjoyable. I usually only soldered a half dozen parts at one sitting. After a few weeks of periodic assembly, I was delighted to see the circuit come to life once power was applied as I was definitely not looking forward to trouble shooting the board! Perhaps my technique of fluxing and the method of holding the component in place with a homebrew 'third-hand' device was not ideal or maybe my soldering iron was not properly sized for the job but I do have a desire to try it again.
A 630m transverter, now planned out, would really lend itself nicely to SMD construction but realistically, the only size I would consider is 1206 at the smallest.
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| Courtesy: www.emeraldinsight.com |
Why I am really contemplating the purchase of more SMD parts is somewhat vexing to me....perhaps it is simply my 'concrete-sequential' thinking style making me lust after all of these tiny parts, with all of them so neatly organized in their holders, begging to be brought to life by my own hands. Or maybe I just want to prove that my 66-year-old eyes and hands are still capable of working with these things. Vintage Radio Reading
I really love old radio magazines, especially those from the 30's, but to purchase any original copies today is very costly. If you grew up in the 50's or earlier and became hooked by the magic of radio as I and thousands of other kids did, then you no doubt recall the plethora of great monthly magazines devoted to 'radio'. Now, thanks to AmericanRadioHistory.com, most of those great old hobby magazines of the past can be viewed online and enjoyed once again.
Just a few of the many magazines available are: Radio Craft, Short Wave Radio, Radio, Radio World, White's Radio Log, Popular Radio, Popular Electronics and Radio Amateur News, later to become Radio News.As a pre-teen short-wave listener in the late 50's, I couldn't wait to get my hands on the latest edition of Popular Electronics, stuffed with its latest SW broadcast news, frequency lists and DX stories.
Thanks to David Gleason's work, I always have several of my favorite classics downloaded to my I-Pad's bookshelf for offline reading. With hundreds of recent updates this spring, there appears to be a lifetime of vintage reading now available!
As a builder of vintage-style radios, particularly transmitters, I can often find new inspiration from the magazines particularly devoted to ham radio. If your workshop library is lacking in vintage reference material, you need look no further than this site for a vast source of building inspiration....transmitters of all description along with receivers from crystal tuners to complex multi-tube designs.
So many of these early publications were the brainchild of Hugo Gernsback, a prolific writer and editor of both technical and science fiction magazines but sometimes blurring the boundaries of each! I suspect that his wide variety of radio publications had some significant role in the way radio so quickly transformed the world. Even in the 50's, long after the 'golden years' of radio, it was not uncommon to still see radio antennas on most houses, at least in my neighbourhood!
If you haven't visited this wonderful resource yet, I'm sure you will be amazed at what you find.
A 1935 Style QSL
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| '29 Style Card |
When I next became interested in mid-30's style construction, I decided it was time for another 'era-appropriate' card to match the transmitters. I began searching the web for vintage cards from the mid-30's and soon zeroed in on a card that I found particularly attractive...and from Canada as well.
Once again, Dennis came to the rescue and worked enthusiastically with me to try and duplicate the features and look of the VE4 card that I wanted.
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| '35 Style Card |
I think he did a super job once again and this past winter the new cards have gone out at a furious pace as I worked many new stations, all on 10m CW with my 6L6 Tri-Tet-Ten.
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| 6L6 Tri-Tet-Ten |
If you or anyone you know might be interested in a vintage style card (or any type of card) please get in touch with Dennis. I cannot speak highly enough about him and the quality of his work. You won't be disappointed.
E-Bay, China, and Free Shipping!
I recently had the choice of buying from Chinese suppliers when shopping around for a new Rigol oscilloscope but must admit that I whimped-out when it came time to buy and chose to buy from a U.S. dealer who would also honour the warranty. I did end up paying slightly more, considering shipping and exchange rates but I do not regret my choice.
I have however made some smaller purchases from China, in an attempt to 'test the water'. I have seen some very attractive pricing on many homebrew-related goodies that would cost much more if purchased in North America and I reasoned that buying a few lower priced items would be a good way to test the quality. Politics aside and with a tiny bit of guilt, over the past few months I have purchased:
2 packages of HSS 1mm drill bits for PC work @ 25 cents each from
I happily admit that in all cases, I have been very pleased with not only the quality of the items received but also in the service. With the high cost of shipping anything to Canada, I find the 'free shipping' for all of these items to be particularly attractive.
Although all of these items are available from many e-Bay sellers in China, I think it pays to carefully search feedback records before purchasing. In many cases, a high rating does not always tell the story. I look for high volume dealers that have very few complaints within the past year. Check what complaints are being made...if it is the quality of what is being sold, then go elsewhere, as some dealers do a high volume of selling junk while others have only single-digit or even zero negative feedback.
It will still be some time, if ever, before I feel comfortable buying any high priced items from China but if you were brought up in the 50's, you will probably recall when buying from Japan was an invitation for disaster and look how that turned out!
There’s a new radio hobby magazine in town!
Recently, a number of hobby radio magazines have either retired, or have merged into a digital mix of several. Filling that void is the new The Spectrum Monitor, a creation of Ken Reitz KS4ZR, managing editor for Monitoring Times since 2012, features editor since 2009, columnist and feature writer for the MT magazine since 1988. Ken offers this digital, radio communications magazine monthly. The web site is at http://www.thespectrummonitor.com/
The Spectrum Monitor magazine – get your’s, today.
Ken, a former feature writer and columnist for Satellite Times, Satellite Entertainment Guide, Satellite Orbit magazine, Dish Entertainment Guide and Direct Guide, is also contributing editor on personal electronics for Consumers Digest (2007 to present). He is the author of the Kindle e-books “How to Listen to the World” and “Profiles in Amateur Radio.”
The Spectrum Monitor Writers’ Group consists of former columnists, editors and writers for Monitoring Times, a monthly print and electronic magazine which ceases publication with the December, 2013 issue. Below, in alphabetical order, are the columnists, their amateur radio call signs, the name of their column in The Spectrum Monitor, a brief bio and their websites:
Keith Baker KB1SF/VA3KSF, “Amateur Radio Satellites”
Past president and currently treasurer of the Radio Amateur Satellite Corporation (AMSAT). Freelance writer and photographer on amateur space telecommunications since 1993. Columnist and feature writer for Monitoring Times, The Canadian Amateur and the AMSAT Journal. Web site: www.kb1sf.com
Kevin O’Hern Carey WB2QMY, “The Longwave Zone”
Reporting on radio’s lower extremes, where wavelengths can be measured in miles, and extending up to the start of the AM broadcast band. Since 1991, editor of “Below 500 kHz” column forMonitoring Times. Author of Listening to Longwave (http://www.universal-radio.com/catalog/books/0024u.html). This link also includes information for ordering his CD, VLF RADIO!, a narrated tour of the longwave band from 0 to 530 kHz, with actual recordings of LW stations.
Mike Chace-Ortiz AB1TZ/G6DHU “Digital HF: Intercept and Analyze”
Author of the Monitoring Times “Digital Digest” column since 1997, which follows the habits of embassies, aid organizations, intelligence and military HF users, the digital data systems they use, and how to decode, breakdown and identify their traffic. Web site: www.chace-ortiz.org/umc
Marc Ellis N9EWJ, “Adventures in Radio Restoration”
Authored a regular monthly column about radio restoration and history since 1986. Originally writing for Gernsback Publications (Hands-On Electronics, Popular Electronics, Electronics Now), he moved his column to Monitoring Times in January 2000. Editor of two publications for the Antique Wireless Association (www.antiquewireless.org): The AWA Journal and the AWA Gateway. The latter is a free on-line magazine targeted at newcomers to the radio collecting and restoration hobbies.
Dan Farber ACØLW, “Antenna Connections”
Monitoring Times antenna columnist 2009-2013. Building ham and SWL antennas for over 40 years.
Tomas Hood NW7US, “Understanding Propagation”
Tomas first discovered radio propagation in the early 1970s as a shortwave listener and, as a member of the Army Signal Corps in 1985, honed his skills in communications, operating and training fellow soldiers. An amateur Extra Class operator, licensed since 1990, you’ll find Tomas on CW (see http://cw.hfradio.org ), digital, and voice modes on any of the HF bands. He is a contributing editor for CQ Amateur Radio (and the late Popular Communications, and CQ VHF magazines), and a contributor to an ARRL publication on QRP communications. He also wrote for Monitoring Times and runs the Space Weather and Radio Propagation Center at http://SunSpotWatch.com. Web site: http://nw7us.us/ Twitter: @NW7US YouTube: https://YouTube.com/NW7US
Kirk Kleinschmidt NTØZ, “Amateur Radio Insight”
Amateur radio operator since 1977 at age 15. Author of Stealth Amateur Radio. Former editor,ARRL Handbook, former QST magazine assistant managing editor, columnist and feature writer for several radio-related magazines, technical editor for Ham Radio for Dummies, wrote “On the Ham Bands” column and numerous feature articles for Monitoring Times since 2009. Web site: www.stealthamateur.com.
Cory Koral K2WV, “Aeronautical Monitoring”
Lifelong air-band monitor, a private pilot since 1968 and a commercial pilot licensee since 1983, amateur radio licensee for more than 40 years. Air-band feature writer for Monitoring Times since 2010.
Stan Nelson KB5VL, “Amateur Radio Astronomy”
Amateur radio operator since 1960. Retired after 40-plus years involved in mobile communications/electronics/computers/automation. Active in radio astronomy for over twenty years, specializing in meteor monitoring. Wrote the “Amateur Radio Astronomy” column for Monitoring Timessince 2010. A member of the Society of Amateur Radio Astronomers (SARA). Web site: www.RoswellMeteor.com.
Chris Parris, “Federal Wavelengths”
Broadcast television engineer, avid scanner and shortwave listener, freelance writer on federal radio communications since 2004, wrote the “Fed Files” column for Monitoring Times.http://thefedfiles.com http://mt-fedfiles.blogspot.com Twitter: @TheFedFiles
Doug Smith W9WI, “The Broadcast Tower”
Broadcast television engineer, casual cyclist and long distance reception enthusiast. “Broadcast Bandscan” columnist for Monitoring Times since 1991. Blog:http://americanbandscan.blogspot.com Web site: http://w9wi.com
Hugh Stegman NV6H, “Utility Planet”
Longtime DXer and writer on non-broadcast shortwave utility radio. Former “Utility World” columnist for Monitoring Times magazine for more than ten years. Web site: www.ominous-valve.com/uteworld.html Blog: http://mt-utility.blogspot.com/ Twitter: @UtilityPlanet YouTube: www.youtube.com/user/UtilityWorld
Dan Veeneman, “Scanning America”
Software developer and satellite communications engineer writing about scanners and public service radio reception for Monitoring Times for 17 years. Web site: www.signalharbor.com
Ron Walsh VE3GO, “Maritime Monitoring”
Retired career teacher, former president of the Canadian Amateur Radio Federation (now the Radio Amateurs of Canada), retired ship’s officer, licensed captain, “Boats” columnist and maritime feature writer for Monitoring Times for eight years. Avid photographer of ships and race cars.
Fred Waterer, “The Shortwave Listener”
Former “Programming Spotlight” columnist for Monitoring Times. Radio addict since 1969, freelance columnist since 1986. Fascinated by radio programming and history. Website: http://www.doghousecharlie.com/
Thomas Witherspoon K4SWL, “World of Shortwave Listening”
Founder and director of the charity Ears To Our World (http://earstoourworld.org), curator of the Shortwave Radio Archive http://shortwavearchive.com and actively blogs about shortwave radio on the SWLing Post (http://swling.com/blog). Former feature writer for Monitoring Times.
Practical Wireless with the LM386 unleashed
“Improving the LM386 Audio Amplifier” is the title of always inspiring Rev. George Dobbs G3RJV’s column in this month’s Practical Wireless. George talks about the basic amplifier with a voltage gain of 20 (26 dB) and how it is straight forward to increase gain to any value up to 200 (46 dB). The article then shows how it can be built dead-bug style.
Then he goes on to talk about various ways to improve the circuit such as for hiss reduction and even higher gain. In that connection he also mentions my article “Unleashing the LM386” from SPRAT in the Autumn of 2003. That circuit was an enhanced version of the high-gain circuit of Kazuhiro Sunamura JF1OZL. Basically it increases the gain to up to more than 70 dB, enough for it to drive a loudspeaker. My circuit also adds bandpass filtering. All this is achieved by adding only 5 passive components to the basic amplifier. The circuit was recently revisited in SPRAT by Johnny Appel SM7UCZ. He added a 40 dB Darlington pair preamplifier for even further gain.
The bandpass filtering (not low pass as the article says) is due to the series resonance of 100 uF and 1 mH which happens at about 500 Hz making it a nice CW filter.
It was good to see my article revisited as I think the idea deserves to be better known and to be considered in more LM386 amplifier circuits. The same goes for the improved muting circuit of the LM386 using pin 7. I developed both in the period when I was interested in minimal transceivers like the Pixie 2 and in true QRP spirit was interested in how to achieve much with as few as possible components.
One thing which is not mentioned in Practical Wireless is that the circuit may be used in such a way that it really squeezes out every grain of amplification of the poor little LM386, so the warning I wrote when I wrote an introduction to “Unleashing the LM386” for the blog (see link below) is worth repeating:
One word of warning is prudent here. As the 200 ohm pot approaches zero ohms, the amplification becomes so large that the series resistance of the 1 mH inductor and the ESR (equivalent series resistance) of the 100 uF capacitor in combination with the open loop gain of the LM386 will determine gain. Some of these values are unspecified for standard components and may vary a lot. Therefore such a setting is not recommended for use in mass-produced circuits. However for a hobbyist’s one-of-kind circuit it should be fine.
A poor copy of the last of the three pages of the Practical Wireless article, where the high gain options are discussed, is shown.
See also:
- Unleashing the LM386, introduction to article in SPRAT, No 116 (Autumn 2003)
- Using pin 7 of the LM386 to reduce BCI and add side tone to Pixie 2, based on article in SPRAT, No 113 (Winter 2002)
