Posts Tagged ‘regenerative radios’
This past weekend's 'Barn Door' CLE' saw a lot of participation, in spite of the mid-summer doldrums and the universal nasty lightning noise.
After reading CLE-organizer Brian Keyte's interesting posting to the ndblist, describing his homebrew single transistor regenerative receiver, I was inspired enough to dig out the soldering iron and build one for myself.
The circuit widely described as a '1AD regen' was originally designed several years ago by crystal-radio guru Mike Tuggle out in Hawaii. Mike is widely known for his exquisitely designed "Lyonodyne" DX crystal radio, which inspired an entire decade of intense DX crystal radio building activity back in the late 90's.
|Mike Tuggle's 'Lyonodyne' DX Crystal Radio|
His '1 Active Device' medium-wave regen consists of a handful of simple components and a MOSFET that is up to the task. His design was, and still is, being duplicated by many throughout the NDB DX listening community.
|Mike's original 1AD regen|
Mike recently sent me the circuit diagram that he eventually settled with, showing two possible ways of extracting audio with the widely popular Bogen T725 output transformer.
My own version used Mike's output scheme on the right and the RF circuitry in Roelof Bakker and Steve Ratzlaff's modified version, shown below. I had to increase the tickler (feedback) winding from 4 turns to 11 turns in order to get any regeneration. With 11 turns, my regeneration kicked-in at about three-quarters from the end of the regen control. At some point in time, while testing, some of the leads from my Bogen T725 output transformer momentarily brushed against each other, smoking my FET. Upon replacing it with another BF966, the receiver was much hotter, with regeneration kicking-in very close to the start of the pot. I'm not sure if the first FET was already damaged or that there is enough variation from FET to FET (of the same type) to make some have more gain than others. Accidentally blowing up the FET proved beneficial in the end!
Although most users employ sensitive sound powered headphones with their regens, including myself, some use modern phones with an extra stage of audio, such as an LM386.
Although not nearly as pretty as Mike's regen, my own 1AD was built in an afternoon, just for the recent Barn Door CLE.
|My own MW 1AD regen|
I later added a calibrated dial plate, breaking the segment from 200kHz to 550kHz into two separate bands, with calibration ~ +/- 1kHz so that I pretty much new where I was tuning at all times. This allowed me to target specific beacons and wait for them to fade up.
When first published, Mike suggested the BF966 MOSFET seemed to work well and I purchased five of them with the intention of someday building a 1AD for the NDB band. The purchase came in handy, as today, the BF966 is no longer available. Apparently the similar, and still available BF998 works well (from tests done by Steve Ratzlaff) but is now in an SMD package at just 18 cents! No doubt there are dozens of MOSFETS that will do the job and at these prices, experimenting with various devices would be a very worthwhile project.
When operating, the regen proved to be surprisingly sensitive, and by using my 10' x 20' loop, I was able to put my local pest (AP-378 kHz and 1/2 mile away) into a deep null so that its huge signal was no longer blocking the top half of the NDB band. The null allowed me to hear beacons within a few kHz of the blowtorch signal as shown below:
I ended up with 70 stations logged, including a couple of Alaskans, in spite of the horrendous lightning noise on all three nights. Doing another 'Barn Door CLE' in the middle of the quiet DX season would be much more exciting and several 1AD users have indicated an appetite for such an event. If you put something together please let me know as having an army of 1AD's ready to go would be a great incentive to schedule another Barn Door weekend!
This coming weekend will see the 'Barn Door' CLE, mentioned in a previous blogspot here. Listeners are required to challenge themselves by listening on a receiver using a wide enough bandwidth that several kHz worth of signals can be heard at once.
The 'immersive' effect this wider bandwidth mode provides is much different than when listening with narrow filters and can make digging out IDs a lot more challenging. Throwing in some mid-summer lightning noise makes it even tougher, but if it were easy, it just wouldn't be much fun!
Many, including myself, will be using homebrew single MOSFET regenerative receivers, often called a '1AD' since they normally use just one active device. I've just finished testing my own version and have been able to hear some night time DX so hopefully the band will be quiet enough to hear some signals during the CLE.
From CLE organizer Brian Keyte, here are the details explained ... and good luck to all participants!
It is an opportunity to bring back to life basic kinds of receiver - anything with low selectivity which allows you to hear NDBs on several frequencies simultaneously - leaving the barn door wide open!
Listening with 'back to basics' equipment often gives very satisfying and unexpected results. It can also show us ways of improving our listening when operating more normally.
Our last Barn Door CLE was No. 209 in July two years ago.
Here comes our fifth 'Barn Door' CLE. Between us there will be a great variety of different receiver types in use.
Days: Friday 27 to Monday 30 July 2018
Times: Start at ## 11 a.m. on Friday 27th, your LOCAL time
End at ## 3 p.m. on Monday 30th, your LOCAL time
Frequencies: Centred on 360 kHz (see below)
NDBs: NOT MORE than 100 'normal' NDBs including any UNIDs
(That is not intended to be a target to reach)
We are all asked to listen with NON-SELECTIVE receivers - i.e. with a WIDE
filter or NO filter. Your 'barn door' should be open wide so you could
hear, at the same time, any NDBs 2 kHz away on both sides of your receiver
setting - E.g. NDBs on 348, 349, 350, 351 and 352 kHz with the receiver set
to 350 kHz.
## The extra daytime hours on the first and the last day might help some of
us planning to listen out of doors.
You could listen with:
1. A simple home-made receiver, such as a single transistor set with regen.
(e.g. based on the sets used by Mike, Finbar and others).
2. OR - an Ultralight receiver, maybe one converted to cover the NDB
frequencies with a modified aerial.
3. OR - an 'antique' receiver (e.g. Eddystone, R1155, Scott, etc.)
Perhaps you have something you've not switched on for many years?
4. OR - a normal receiver but with NO filtering, or using a WIDE FILTER,
(not less than about 2 kHz and no selection of an audio filter).
You choose how wide a RANGE of frequencies you will listen in, CENTRED ON
360 kHz. You could choose 350-370 kHz or 330-390 kHz or 260-460 kHz, etc.
(This allows each of us to choose a +/- range with enough NDBs to
match our equipment's capability. It will also allow our loggings to
be compared in the Combined Results, at least around 360 kHz).
Logs should show NOT MORE THAN 100 NDBs please (if more than 100, the
harvester program will 'drop' the loggings furthest from 360 kHz).
There are several extra targets you could set yourself - maybe the wide
bandwidth, the centre frequency of 360 kHz and the 100 loggings limit do not
challenge you enough!
You could listen only in daytime and/or away from home.
Or how about NDBs on 360 +/- 10 kHz or even +/- 5 kHz?
The Twente remote receiver in Holland could be interesting to use for the
whole of your (only) CLE log.
( Go to http://websdr.ewi.utwente.nl:8901/ and read the advice there:Select AM and 'MAX IN', enter e.g. 354.7 in the frequency box and change the
filter's limits to 2 or 3 kHz from the centre frequency on both sides )
We’ll summarise everyone's equipment on the first page of the combined
results, so please describe:
The RECEIVER/AERIAL you used and the FILTER(s) selected, if any.
If homebrew, please quote: the total number of active devices used – e.g.
1 for a single transistor stage ( 1AD ) - the transistor/valve types,
whether using regen., etc.
All the usual procedures for making logs apply:
Send your CLE log to NDB List, if possible as a plain text email and not in
Please show on EVERY LINE of your log:
# The full date (or Day No.) and UTC (the day changes at 00:00 UTC).
# kHz - the beacon's nominal published frequency, if known.
# The Call Ident.
Show those main items FIRST on each line, before other optional details
such as Location, Distance, etc. Please send your complete log with
CLE234 and FINAL in the Subject line.
Whether you are a first time CLE-er or a regular, make your log interesting
to everyone by showing your own location and your equipment details.
Do feel free to share any comments you have on this unusual event.
Joachim or I will send the usual 'Any More Logs?' email at about 17:00 UTC
on Tuesday 31st so that you can check that your log has been found OK.
Make sure your log has arrived on the List at the very latest by 08:00 UTC
on Wednesday 1 August. We hope to complete making the combined
results a day or so later.
However you choose to take part, we hope you will find your 'back to basics'
listening enjoyable and worthwhile.
P.S. NOT FOR YOU?
Listening without narrow filters is not going to revolutionise our hobby!
But there ARE some unexpected benefits and advantages:
1. Hearing several beacons on a few adjacent frequencies at the same time
becomes easier as you get practice at recognising them by listening to their
very different audio tones. At first, when listening to a random frequency
setting, you may hear just one or two beacons. But after listening for a
little while you realise that there are three - - four, maybe more, all of
them audible without altering any of the receiver controls.
It is a skill that gives satisfaction as you improve.
2. Hearing multiple beacons like that can be useful because, with no extra
tools, you can hear NDBs over a wide frequency range much more quickly than
usual, perhaps spotting the arrival of new UNIDs or the return of occasional
beacons. (To protect your hearing, keep your receiver gain controls fairly
low, except on very quiet frequencies).
3. With normal listening it is easy to miss any NDBs that have abnormal
carrier frequencies or non-standard offsets. With 'Barn Door' listening
they won't escape because everything is let through.
4. When using a wide filter, you may be surprised by hearing some Broadcast
Station signals (e.g. harmonics) among the NDBs and you will be able to
With a narrow filter, often you may not recognise an AM signal as audio
- it just sounds like nondescript 'hash' affecting a wide range of
frequencies around the central carrier.
Maybe listeners will report some other good things about their barn door
listening during the CLE - and probably some bad things too!
Do join in if you can.
From: Brian Keyte G3SIA ndbcle'at'gmail.com
Location: Surrey, SE England (CLE coordinator)
Don't forget that help and chat regarding NDB DXing can be had on the ndb group list here.
I've also published a new page on my website which contains more pictures and details of all phases of the project. The page also has a recording of the 40m CW band, made a few evenings ago, which really best demonstrates how the receiver is working.
In the meantime, much consideration has been given to the next project work ... it will be a return to my earlier lightwave experiments. During the recent visit here by Toby (VE7CNF) and Mark (VA7MM), both expressed interest in building some lightwave equipment (in fact ... 'parts' have been ordered!) to try some direct LOS work as well as to try some QRSS clear-air scatter / cloudbounce work. It's really exciting to see some new interest in this fascinating mode as the field for experimentation in both transmitting and receiving systems is quite vast.
My first task will be to build a 4" optical tube receiver or another boxed Fresnel-lens type for portable operation, here on Mayne Island, to see if I can scatter a signal to the other side of the island and detect it while operating in the field. There are a couple of nearly 600' peaks on Mayne which should provide a good shielding effect for testing ... maybe too good. Time will tell.
Work has begun on a new "summer project" (as well as re-shingling the woodshed and garden shed roofs) ... a 3-tube audiodyne receiver.
This one appeared in the January 1933 addition of QST (Rationalizing the Audiodyne by George Grammer) and then in subsequent Handbooks for a few years. It's the type of building I like to do, with lots of pre-planning before breaking out the tools, measuring all components carefully and refurbishing some of the 85+ year old parts.
So far, I've completed all of the shielding and drilling of critical holes ... all measured three or four times before taking the plunge. The only chassis available (Hammond or Bud) is about 1/2" smaller in width and depth, making everything just a little snugger, but still maintaining proportions.
I have no idea how it will perform but so far it's been a fun project. If it works well, even better yet ... but handily, it's given me a good excuse to avoid more important things, like the two roof projects!
Friday evening's 630m crossband activity was 'interesting' in many respects. Propagation, which had been improving slowly, chose to follow Murphy's Law. The K-index, holding at a quiet '1', rose to level '3' by the time our event had concluded, as the geomagnetic activity ramped up. Additionally, lightning pocketed various areas of the continent, making listening noisy for many.
From here on Mayne Island (CN88iu), good two-way CW crossband contacts were made with the stations in the following order:
- N7IO (Seattle, Washington)
- VE7CA (North Vancouver, BC)
- KK7UV (Missoula, Montana)
- NW7E (Bend, Oregon)
- KU7Z (Ogden, Utah)
- VA5LF (Saskatoon, Sakatchewan)
- K7SF (Portland, Oregon)
- VE7BKX (North Vancouver, BC)
- K6TOP (Los Gatos, California)
- ABØCW (Westminster, Colorado)
- NO3M (Saegerton, Pennsylvania)
- KB5NJD (Duncanville, Texas)
- W7MTL (Independence, Oregon)
- KØSBV (Tucson, Arizona)
- WB6DCE (Seaside, California)
- KO6BB (Merced, California)
- K6CLS (Palo Alto, California)
- WY3B (Kaneohe, Hawaii)
- AA7U (La Grande, Oregon)
I was also more than excited to exchange signal reports with Pennsylvania and Texas. Considering conditions, this distance was far beyond my expectation but both of these stations have very efficient, dedicated 630m antenna systems.
John, VE7BDQ, worked the following stations on crossband:
- VE7CA (North Vancouver, BC)
- W7DRA (Seattle, Washington)
- N7IO (Seattle, Washington)
- NW7E (Bend, Oregon)
- KK7UV (Missoula, Montana)
- KU7Z (Ogden, Utah)
- VA7JWS (Delta, BC)
- VA5LF (Saskatoon, Sakatchewan)
- WB6W (Oysterville, Washington)
- K5HK (Reno, Nevada)
- KØSBV (Tucson, Arizona)
- WY3B (Kaneohe, Hawaii)
It was gratifying to see all of these fellows making the effort to listen for our signals or to attempt the QSO.
This exercise taught me a few things about our new band.
- It is not necessary to have huge antennas and acreage to make this band work. Good solid contacts can be easily made with small backyard antenna systems.
- With good systems on both ends, transcontinental QSO's can be made.
- There really should be more interest by Canadian amateurs in their newest band as so much work has been put into securing this portion of the spectrum as a ham band. It was very disappointing not to work any stations in VE6, VE4 or VE3 land.
- There is already much interest in this band by U.S. amateurs, many of them anxiously awaiting the day that they can also call it a ham band.
I would like very much to continue this type of crossband activity to try and generate more interest in our new band. I'm presently considering a weekly, one-night crossband operation, similar to Friday's event, perhaps running for one hour per week. The main difficulty will be in getting the word out to those that might wish to participate.
|Courtesy Roelof Bakker PAØRDT|
Anyone experimenting with the LF regen circuits described by Mike Tuggle and Roeloff Bakker in my recent "Tuggle-Style LF Regens" blog, might be interested in some helpful 'building notes' posted to the Yahoo ndblist by noted NDB/BCB DXer and exceptional RF guru, Steve Ratzlaff, AA7U of La Grande, Oregon.
Mike uses a Siemens 1216 Mosfet that he obtained from junked TV UHF tuners, but that particular transistor is no longer available. My first thing was to purchase a variety of Mosfets of other types and test them on the bench to see if they might be suitable. I bought one or two of all the Mosfet types available from this non-eBay US seller, Scott Lowe. (He used to sell on eBay but now only sells through his own webpage. And while checking the URL I notice it's now listed as Mike Lowe instead of the previous Scott Lowe--I don't know why the change.)
So I got the dual gate Mosfet types 40673, BF981, 3SK88, MFE201, BF960, BF961, BF998, 3N211 to try. When I mentioned this project to Mike Tuggle he was extremely generous to send me one of his rare Siemens 1216 Mosfets to test along with some other Mosfets he'd been saving for years. Thanks Mike! I bought five BF966 Mosfets from an eBay seller in Italy, so I was able to test the same type Roelof is using too. (The eBay seller of the BF966's seller name is "radionova22" and current item number for five BF966's is 331079146309, for $1.00 plus shipping ($10 for me in Oregon). He shipped immediately, and it took about 10-12 days for me to receive the small padded envelope. My one experience with this seller was 100% positive.) Note that almost all, if not all, Mosfets are diode-protected on the gates, and are more or less insensitive to handling static damage. But most sellers will ship the Mosfet in a static-protective wrapping. The Italian eBayer does not do this. But the couple BF966's I tried in my sensitivity test worked fine, thus were not damaged by any lack of antistatic shielding. I always use antistatic methods if I build something with Mosfets or anything that might be sensitive to static damage, and I recommend you do the same. At the minimum that means sit perfectly still while you're handling the Mosfet, don't shuffle your feet. Try to touch a grounded object before handling the device. In the US that could be as simple as a wire attached to the third wire/ground on the AC outlet powering your soldering iron that you can touch first. More elaborate would be an antistatic mat and an antistatic wrist strap all connected to the third wire ground of the AC outlet. Most modern soldering irons use a 3-wire AC cord with the actual metal of the soldering iron connected to the third wire ground, but I don't recommend you try to touch the very hot metal soldering iron part to obtain your antistatic ground!
I built the LF regen toroid version that Roelof used, and used the diode source bias that Mike and Roelof used and used my existing USI soundpowered phones (also now rare to find) with the Bogen T725 audio transformer and tested each Mosfet on the bench for sensitivity. I used a calibrated signal generator at mid-band, 300 kHz, reducing level to the faintest level I could detect. Initially I used Roelof's Gate 2 separate bias circuit, but soon found that I got the same sensitivity with no separate Gate 2 adjustment needed (using Mike's circuit of tying both gates together) and that's what I used for all the sensitivity tests. What I found was that all the Mosfets were more or less equally sensitive, within a dB or two, if they would work in the circuit. Not every Mosfet would work, that is would give proper regeneration when the Regen control was varied, and detect a signal--a few types did not work at all. Perhaps they would work with separate Gate 2 bias but I didn't try that to see if they might work. The ones that did not work were the 3SK88, MFE201 and the 3N211 made by Siliconix. Mike's selection of Mosfets included a 3N211 made by Texas Instruments, and oddly that one worked fine and was equally as sensitive as the other Mosfets that did work. So the good news is if you select a Mosfet from the ones I tried that worked, then you don't have to worry about one Mosfet being more sensitive than another. That list is the BF960, BF961, BF966, BF981, BF998, 40673 (and Mike's own "unobtainable" Siemens 1216). Note the BF998 is a surface mount part, very tiny, and will require you to use magnification and some ingenuity in order to solder wires to it. I was able to solder thin #30 silverplated wire stripped from #30 wirewrap wire but it took a number of attempts to get the three wires on (both gates are tied together and both gates are on the same side of the package making it slightly easier). Using my sensitive USI phones I was able to get -135 dBm sensitivity--that was the faintest signal I could hear, for my sensitivity test for the Mosfets.
|Steve's Testbed Regen|
Perhaps I should say something about the units I'm using for sensitivity. "DBm" stands for "decibels referred to one milliwatt across 50 ohms". 50 ohms is the standard impedance for test equipment in non-telecommunications industry (75 ohms is the standard for telecommunications). The larger the number, in negative terms, the lower the signal from the generator to give the sensitivity in my tests. So, -135 dBm is 5 decibels lower (for my USI phones) than the next most sensitive phones, -130 dBm for the SH-091A phones. For power measurements in decibels, every 3 decibels (dB) change, the power is cut in half (or doubled if going up in power). So ideally for the 1AD you want to use the phones that are the most sensitive.
But in the real world of LF, the external noise is high even if you happen to live in a location of low AC noise, and my most recent tests have been to see if one of Ming's readily available phones would work about as well as my more sensitive USI phones.
Something else to consider is one needs to use an audio transformer with soundpowered phones, in order to match their relatively low impedance to the higher impedance of the output signal at the drain of the Mosfet. That's what the Bogen T725 transformer that Mike uses does, and the transformer that Roelof uses. But one of the phones Ming offers is a non-soundpowered type that already has relatively high impedance, the 4400 ohms phones. Using that, no audio transformer is needed, which simplifies the 1AD circuit, as long as these 4400 ohms phones are sensitive enough with the 1AD. I've been testing this 1AD configuration for the past 5 days, on real NDB signals from my antenna and believe that these phones are sensitive enough. So using them, one takes the output at the Mosfet drain and 0.001 uF bypass capacitor directly to one of the 4400 ohms phones leads and the other phones lead goes to the +9 volts (where the top of the Bogen T725 transformer would normally go).
I've been using my active whip antenna with my 1AD and that works very well. Roelof uses his standard Mini-Whip with his own 1AD. Mike uses a high impedance wire antenna for all his 1AD listening and has his own tuner he's developed to feed his 1AD consisting of a series inductor and variable capacitor with the antenna link on the 1AD. The inductor (about 2600 microhenries) has one end to the antenna and the other end to the 1AD antenna link with the other end of the antenna link to the series variable capacitor (about 1000 pF) with the other side of the capacitor to ground.
Scott Lowe's webpage has a bunch of electronics parts stuff. My own 1AD is currently using a custom two-section high capacity miniature polyvaricon variable capacitor that he offers. He has a knob to go with it as a separate item. I'm using the switched capacitor arrangement that Roelof shows in his diagram and the same fixed capacitors. The idea is to separate the NDB band into two sections and to reduce how far up in frequency the tuning goes. If you use a similar capacity variable capacitor, the two fixed values (300 pF and 100 pF) work well. You want some overlap in tuning for the two switched sections. My own 1AD has about 8-10 kHz overlap. You don't want "underlap" which means the lower section stops, say at 310 kHz, and the upper section starts at say, 315 kHz, which would leave a gap of 5 kHz where you couldn't tune the radio in that section. The Scott Lowe polyvaricon is labeled as "dual 335 pF and 20 pF plastic variable capacitor" that I'm using. He includes a sheet for the pinouts of the various sections. We only want to use the two 335 pF sections. I find this capacitor is (just barely) adequate for use in the 1AD, with the dual section switching arrangement. By that I mean I can turn the shaft and get enough resolution to smoothly tune in fine increments without jumping over frequencies. A larger knob than is offered would help, but the "larger knob" option that Scott Lowe offers (it's not really a large diameter knob!) works. It takes some careful tuning with thumb and forefinger but I don't have any major problems tuning. Of course a "proper" much larger variable capacitor, especially with a vernier drive, would be far more preferable (like Mike and Roelof use). But I'm suggesting that one could build a pretty inexpensive LF 1AD radio using readily available parts, using Ming's 4400 ohms phones which don't require an audio transformer.
I used toroid that Roelof gives in his article, FT140-61 with the specified turns. That worked fine. I had a smaller FT114-61 toroid I used and that worked equally well. In North America both these can be obtained from Diz at www.kitsandparts.com. (He also ships internationally.) I used #24 wire for the main coil on the FT140-61. For the FT114-61 I used smaller #30 silverplated wirewrap wire, with 88 turns, about 9 feet of wire. Regen winding 5 turns; antenna winding two turns. For both, I wound the Regen winding next to the ground end of the primary winding. Of course proper phasing is needed for the Regen winding.
Ming's eBay items can be found by searching for his seller name "mkmak222" in the advanced search options under "seller". The 4400 ohms phones I bought are called "NOS Military 4400 ohm Headset for Crystal radio, ham". The picture shows a banana plug on the end of the cord. He has another 4400 ohm headset also listed but I didn't try that--it has a phone jack on the cord--I don't know if it's the same sensitivity as this one. Current eBay item number for the one I tried is 161409812818; price is $24.99 plus shipping. (He also has a very good ferrite audio transformer with a wider range of taps than the Bogen T725, if you're using soundpowered phones.) Of course you can see all the items he sells by clicking on the "See other items" on any of his eBay ads.
I live about one mile from my local NDB, 296 LGD. It only causes some problems from extremely strong signal strength (which isn't adjustable on the 1AD) within about +/-25 kHz or less. Once the 1AD is set to proper regeneration the Q of the tuning inductor is high enough that outside that tuning range LGD isn't a problem. It can still be heard sometimes way down in the background until you tune far enough away. Even tuned very close to it, just the actual headphone level is the main problem. I have a BCB station about 6 miles away which is quite a bit stronger in actual signal level. That causes some mixing products here and there in the NDB range, but those are on some even 10 kHz frequencies. If you're in an urban area with a bunch of AMBC stations, perhaps you'd have more problems with the 1AD or may need to think about how to maybe add a lowpass filter in front of the set.
One last comment, about winding lots of turns on a toroid. I use a homemade stiff cardboard bobbin that I wind the wire on then use the bobbin to wind the actual toroid turns. This makes for fast winding where lots of turns are needed compared to pulling a long length of wire through the toroid core for each turn, without the bobbin. The bobbin I used is about 4" long x 1/2" wide with a 1/4" notch cut in each end where the wire is wound. (The bobbin width of course has to be narrower than the inside diameter of the toroid and the length is generally several inches or more, depending on size of toroid and length of wire/number of turns to be wound.)
Good luck with making your own 1AD if you decide to do so; I've tried to give some ideas on how you can buy current products that will work for a true 1AD configuration. Please let ndblist know of your results if you build one! "
Steve adds that so far, in just a few nights of casual listening (and under not so good conditions) he has logged 104 NDB's using a small homebrew active whip!
Thanks for all of the great tips Steve.
|Mike Tuggle's Lyonodyne 17 Crystal DX Tuner|
The challenge was too hard to resist for many and the contest was popular for several years running. Some of the inventive entries for individual years may be seen here. The contest logbooks also make for interesting reading and demonstrate the capability of some of these simple radios.
Although the contest has not been run for the past few years, there is still much interest and discussion of "1AD" radios on Dave Schmarder's "RadioBoard" forum.
Mike's LF tuner is a prime example as he uses it daily and continues to post some amazing DX to the Yahoo "ndblist" Group. His furthest ndb catch in North America with the regen has been "YY" in Mont Joli, Quebec.
Now, "YY" is a good catch for me, from B.C., but Mike is listening from Kaneohe, Hawaii !
You can read about Mike's original design here, while his latest version shown below, incorporates a dedicated LF antenna tuner.
|LF Regen (Courtesy Mike Tuggle)|
|LF Regen Schematic (courtesy Mike Tuggle)|
|Courtesy: Roelof Bakker, PAØRDT|
Roelof has also published a nice write-up describing the project which sparked a lot of "must build" discussion within the group.....even enough to make Mike get out his soldering iron and build the European-version!
As old and as simple as they are, regenerative receivers still hold much fascination amongst radio builders and dollar-for-dollar are amazingly good performers, especially on LF.