Sunday, June 16, 2013

A Single-Stage Heterodyne VFO

A heterodyne VFO is normally constructed using a minimum of three distinct circuit blocks, namely: a VFO, a crystal-controlled oscillator and a mixer. I've managed to pare it down to two stages in the past: a VFO followed by a self-oscillating, crystal-controlled "converter," but I always knew my "minimalist devil" would ultimately be satisfied with no more than one stage.

Past attempts were thwarted due to excessive oscillator interaction. But at last I seem to have stumbled over a reasonably well-behaved "all-in-one" heterodyne VFO circuit. The result employs a VFO configured as a common-collector Colpitts oscillator. Simultaneously, a crystal-controlled Colpitts oscillator works in the common-base mode. The passive oscillator component values selected reflect the need to roughly equalize the two oscillator energies.  

The crystal-controlled oscillator frequency was dictated by the contents of my junkbox; 16.877MHz, in this case. The VFO tunes from 2.877 to 2.777MHz, in order to cover the bottom 100kHz of the 20M band.  

I used a 2N3904 throughout most of the design process. Once the circuit worked to my liking I swapped this modern device for a 1950's-vintage, Germanium surface-barrier transistor. Aside from some component tweaks (R1, especially) the circuit behaved much the same. 

The frequency stability seems quite up to the task in my underground shack, however, I wouldn't think of operating this transmitter under the noonday sun. The Germanium transistors, compounded by the primitive DC biasing technique would likely spell disaster. The VFO isolation is commendable for such a simple circuit.

A tuned RF amplifier, primarily comprised of a second, vintage Germanium transistor, produces an RF output of slightly more than 2mW. The worst spurious frequency output power (at 16.877MHz) measures -26dBc (~5uW). While I intend to add a second RF amplifier stage, I was curious whether or not I could make a contact at 2mW. 

My answer came last evening when I returned K5TF's CQ. He replied straight-away with a 439 report from Atlanta; a distance of 937m/1508km. An avid QRP-op himself, Dick joined my happy-dance with, "WOW 2mW AMAZING." Indeed, it's the lowest power I've used to make a long-haul contact thus far. He missed one exchange from me due to QSB, otherwise, he appeared to enjoy a fairly good copy throughout most of the seven-minute QSO. Dick operates an Elecraft K2 at 5W to a Hexbeam. I had a steadfast - 589 - copy of his signal on my two-transistor regenerative receiver. Enjoying my new-found frequency agility, I subsequently roamed the CW band for several hours, calling the stronger DX stations but without success. 

Still, I was happy with my one QSO. Besides, the transmitter worked well enough to placate my minimalist least for now ;-)

20 June 13: Worked W4TZM in the NAQCC Milliwatt Sprint! (589/559, 1330km @ 2mW) 

    Parts List

R1:  2.2MegOhm
R2:  560 Ohms
R3:  3.3k Ohms
R4:  220 Ohms
R5: 470k Ohms
C1, C2:  1nF (s.m.)
C3: 1.67nF (s.m.)
C5: 120pF (s.m.)
C6: 560pF (s.m.)
C7, C13: 47nF
C9: 0.47uF
C10: 678pF (s.m.)
C11, C12: 15-60pF 
T1: 11 turns / 3 turns, junkbox iron-powder toroidal core
T2: 15 turns / 1 turn, junkbox iron-powder toroidal core
X1: 16.877MHz (junkbox "uP" quartz xtal)
Q1: Philco T1657, Germanium surface-barrier transistor, circa 1959
Q2: Philco 2N502, ditto above    


Tuesday, June 11, 2013

A New Vanguard

Last week I received a surprise package from Jack Ward, curator of the online, Semiconductor Museum. I was astonished to find inside seven examples of the transistors used in the original Vanguard-1 satellite beacons.

Please click here to view Jack's excellent, recent posting concerning these historical devices.

This early run of diffused-base Germanium transistors was made by Western Electric, primarily for use by the US military. For example, in the May, 1959 issue of CQ Magazine, Donald Stoner suggested various substitutes for prospective "Vanguard" circuit reproductions, given the original devices were unavailable to amateurs. If this was the case only fourteen months after the launch of Vanguard 1, I reckoned it would be nearly impossible to find them over 50 years later. As such, it seems an incredible stroke of luck that led Jack to these rare artifacts in the estate of an engineer who'd once been tasked to stress-test them.

Unfortunately, time was not kind to six of the seven transistors that I received. Five of the seven devices had at least one defective P-N junction. The 6th device produced very little HF gain. Fortunately, the 7th device, a GF-45011, is a strong performer. The GF-45011 was originally used in the one-stage, solar-powered, Vanguard-1 beacon transmitter.

I used the one functional GF-45011 to reproduce the original Vanguard 1 transmitter as closely as possible. It's similar to my previous attempt using a substitute surface-barrier transistor. Needless to say, I handled the GF-45011 device with extreme care! Of course the original operated at 108MHz, whereas my circuit works at 14MHz. Moreover, the original solar-powered transmitter produced an RF output power of 5mW, whereas mine produces 38mW. The transmitter, seen below, is comprised of only 11 components. The precious, still-functioning transistor is appropriately gold-plated!

I paired this new transmitter with a 0V1 regenerative receiver (MPF102/2N3904), connected my 41m end-fed wire (at 10m) and began calling CQ on 14.060MHz. 

Ninety minutes passed without so much as a nibble, but a
t 2118z I suddenly heard GW3YDX calling me. 579/519 reports were quickly exchanged. Ron subsequently copied my QTH as well as my transmitter output power. His 5w signal was an easy copy in the two-transistor regenerative receiver...a solid QSO from Vermont, USA to Four Crosses, Wales; albeit, my one and only contact for the day!

The next day W4OP in North Carolina answered my CQ. Dale reported in a follow-up email that my 38mW signal had briefly peaked at 589. I twice heard K5ACO calling me through heavy QRM but we didn't manage to complete the contact. Tnx all the same, OM!

On the following day my call was answered by two Georgian QRP stations: K5TF and W4DU. The contact with K5TF turned into a very pleasant rag chew lasting a quarter of an hour.

I'd like to express my sincere gratitude to Jack Ward for his thoughtful generosity. It was a tremendous thrill to recreate the Vanguard 1 transmitter down to the original - now extraordinarily rare - transistor type. My thanks as well to everyone who listened for my signal in recent days.

Mike, AA1TJ

Thursday, April 18, 2013

Talking to France Via My Electric Razor

I nearly threw away my worn out Braun 5569 electric shaver a few months ago. On second thought, I decided to at least check it for usable components before I disposed of it. It occurred to me a short while afterwards that it might be fun to attempt to convert whatever was inside it into an amateur radio

I got around to opening it up last week. It was mostly built using surface-mount technology (SMT), but at least it used discrete devices vs. a custom-made IC. A waterproof coating made salvage difficult, but careful surgery with a razor blade allowed me to remove all five SMT transistors and half-a-dozen diodes; one of which was a 5V Zener.

The transistors were soldered to bits of copper-clad "carriers" along with flying leads. One transistor didn't survive the transplant operation. The one non-SMT transistor, an NPN power device, refused to oscillate above 1MHz. The remaining three NPN and one PNP transistors appeared to function well enough at 14MHz that I thought I'd have a go at building something for 20m.

My first idea was to build this Japanese 10/6m DSB rig for 20m using a 14.3MHz computer crystal from my junk box.

After the standard amount of tinkering the transmitter appeared to be operational. Two of the tiny Silicon diodes taken from my electric razor matched well enough to produce a decent carrier null in the single-balanced modulator. I used a pair of NPNs in a push-pull PA stage. A forward-biased diode taken from the razor was used to set the PA bias. The RF CW output was ~90mW. An electret mic from an old telephone drove the PNP SMT transistor in the AF amplifier. The VXO provided a tuning range of 8kHz.

Unfortunately, switching the transmitter to the direct-conversion receiver mode produced the expected result. The 100kW, Nashville-based, WWCR, on 13.845MHz swamped the amateur phone signals. Placing a "balancing" pot in line with the the SBM diodes helped considerably, but not enough to completely eliminate the interference. Past experience tells me that at my QTH a narrow, triple-resonator, BPF is needed between the antenna and these simple diode mixers. I decided to pull the DSB rig apart and build instead a 20m CW station.

I built a 0V1, common-base, Colpitts autodyne regenerative receiver using two of the NPN SMT transistors. The Q-multiplied RF resonator easily shrugs off interference from the high power commercial shortwave transmitter. 

The transmitter begins with a variable quartz crystal-controlled oscillator (VXO) made from the third NPN transistor. The final PNP SMT device was used in a common-base, RF power amplifier (PA). The transmitter VXO tunes from 14.055 to 14.061MHz using an xtal cut for the QRP calling frequency. The oscillator free-runs on transmit; only the PA is keyed. The RF output power is 75mW. A 7th order lowpass filter (LPF) holds the harmonics below -45dBc.

The current draw is 1mA on receive and 12mA on transmit using a 9Vdc battery as my power supply.

The bread-boarded transmitter appears in the above photo. The LPF is on the left-hand side, followed by the PA and quartz-crystal oscillator. Two of the transistors taken from the electric razor can be seen in this photo.

Here's a close-up of the two-stage receiver. The regenerative detector is on the left-hand side of the board, followed by one stage of audio amplification. The variable capacitor at the left tunes the receiver from 14.000 to 14.075MHz.

I was pleased to have worked four stations with this setup on April 17, 2013.

W4SX GA 569/339 K2 @5W
KB0PCI MN 569/339 12w
KD4ESO AL 579/559 100w
K5EST MO 569/559 5w

Coming up to the house later in the day I found three Reverse Beacon Network receivers had made captures of my 75mW signal. Oddly enough, all three were located in Europe.

On April 18, I worked three stations; my transmitter still driving an end-fed wire antenna with 75mW of RF power.

N0UR MN 449/229
W4SX GA 579/449
F6DCD France 559/519 K2 @ 5W

F6DCD very kindly called again 35 minutes later to inform me that my signal was still audible near Strasbourg. Denis increased my signal report to 529. Needless to say, I was ecstatic to have "crossed the pond" with the transistors taken from my old electric razor.

On 19 April I received an email from F6DCD

Hello Mike,
I was really pleased to contact you with your 75 mW. I heard you calling on frequency during 1 hour and more. Your sig was really nice on my K2.

Vy 73/72,
Denis, F6DCD

Tuesday, April 9, 2013

"Sputnik-1" Radio Beacon Schematic Found!

The search for the schematic diagram of the world's first orbiting radio beacon transmitter is finally over! 

Отчет о разработке бортовой радиостанции первого советского искусственного спутника Земли /прибор Д-200/. Репринтное издание. - М.: «ИД Медиа Паблишер»,2012.- 122 с., ISBN 978-5-903650-23-1

Published in 2012, this book is a report on the development of the radio beacon transmitter (D-200) that was carried into orbit by Sputnik 1, on October 4, 1957. 

Boris/RU3AX reviewed this book in the April, 2013 edition of the Russian magazine, Radio. His review features the schematic diagram of one of the two radio transmitters carried aboard Sputnik 1. Please click here to open a PDF file of his article.

I would like to thank Oleg/RV3GM and Sergey/UA3ALW for bringing this wonderful news to our attention. 

Wednesday, January 16, 2013

A New Sputnik from the Czech Republic

OK1DPX, has made a wonderful job of his Sputnik transmitter reproduction. Plug-in modules allow for multi-band operation. He even included an on-board vacuum tube multivibrator (beep-beeper). Petr details his work in the current, Bulletin of the OK QRP Club. Please click here to download his article (presented by permission).

Congratulations and well-done, Petr!

Friday, July 13, 2012

Simplicity's Reward

On July 9, I answered a CQ from KB8BWE using my Vanguard 1 station setup. Charlie came back to me straight-away with a 529 report. Unfortunately, my signal subsequently dropped into the noise. While it didn't qualify as a full-fledged QSO, nevertheless, I was pleased to learn that he was operating with three watts into a three-foot diameter loop antenna. The full details of his station arrived in his follow-up email

"...I was using a 3’ diameter magnetic loop called the “Alexloop Walkham” from here:

The loop itself is a piece of RG213 coax. I had just received it in the mail that morning, and was trying it out on the deck behind my house. It all folds up into a laptop-sized case.

The rig is a TenTec 4040 (Youkits HB-1B) 4-band QRP rig that I got at Dayton this year." 

I have, these past twenty-five years, worked and lived atop Mt. Mansfield; Vermont's highest peak. My task there is to maintain a powerful commercial television transmitter that is coupled to a huge antenna. For all of that, it might seem curious that having my 25mW signal copied by a guy sitting on his deck in Ohio with a 3' loop antenna would be the thing to send a chill up my spine. In fact, my passion for radio minimalism has long since spoiled me for anything else. :-)     

"Simplicity is the final achievement. After one has played a vast quantity of notes and more notes, it is simplicity that emerges as the crowning reward of art."  Frédéric Chopin

Saturday, June 30, 2012

Vanguard 1 Satellite Transmitter Reproduction

Last week I aired a reproduction of the Vanguard 1 (TV-4 or "Test Vehicle 4") satellite beacon transmitter on the 20m CW band. The original 6.4" diameter satellite (Premiere Khrushchev famously referred to it as "the grapefruit satellite") carried two, one-transistor "Minitrack" beacon transmitters. One transmitter was powered by seven mercury cells and produced an RF output power of 10mW on 108MHz. The second transmitter produced 5mW on 108.03MHz from energy provided by a small photovoltaic array.

Philco surface-barrier transistors were used in the early beacon prototypes. However, diffused-base PNP germanium transistors produced by Western Electric were found to be more reliable when thermally and vibrationally stressed. The engineers eventually settled on a GA53233 for the battery transmitter. The solar-powered transmitter was equipped with a WE45011. An early Minitrack beacon transmitter prototype using a Philco SBDT-12 surface-barrier transistor provided an output of 10mw with an RF output power/DC input power efficiency of 20%. The same transmitter equipped with a GA53233 transistor produced an identical RF output power at 30% efficiency. 

The original circuit operated on the 5th quartz-crystal overtone, whereas my version works on the fundamental resonant frequency. Otherwise, I've tried to reproduce the circuit as faithfully as possible. My reproduction sports a Philco 2N504 MADT (surface-barrier transistor) manufactured in September of 1959. It produces 25mW with an efficiency of 38%. The -8.4Vdc collector supply line is keyed to provide CW transmissions. My antenna is a 44m end-fed wire, supported at a height of 10m.

The two left-hand photos shown below appeared in the May, 1959 edition of CQ Magazine. The article was written by Don Stoner, W6TNS (SK), as part of his regularly featured, "Semiconductors" series. The circuit of my reproduction appears on the right. The output signal connection shown in the CQ Magazine schematic appears to lack a proper impedance match to 50 Ohms. To this end I settled on a simple capacitor divider network. The article expresses a hope that the solar powered beacon would continue to function for several hundred years. In fact it expired after 75 months of operation.

My component values

L1: 10uH molded RFC
L2: 470uH molded RFC
R1 220 Ohms
C1, C2: 10nF
C3: 15pF silver mica
C4: 75pF silver mica
C5: 300pF silver mica
T1: 13 turns on slug-tuned, 5mm dia. former; 2 turn coupling
X1: 14.060MHz quartz crystal
Q1: Philco 2N504, date-code 5937 (September 1959)

The schematic shown below was taken from a Jet Propulsion Laboratory report dated September 6, 1960, and titled, "Juno Final Report: Re-entry Test Vehicles and Explorer Satellites." The text for this figure reads, "The beacon transmitter as flown in early rounds is shown schematically in Fig. 25. Power measurements from the actual flight configuration shows that all the beacons radiate approximately 10mW."   

The circuit shown above is very similar to the schematic illustrated in W6TNS's 1959 CQ Magazine article.  

Here's a photograph of my bread-boarded transmitter. Please note the early, "silver-bullet," Philco transistor package. The transmit/receive antenna changeover and receiver muting functions are provided by the green DPDT relay along with the time-delay circuitry at the right of the relay. A Pico Keyer appears in the top-left of this photo. 

My 0V0 regenerative receiver, built from a single subminiature Raytheon QF721 pentode, is shown below. The illuminated filament shows up clearly in this photo. 

W4OP was first to notice my unannounced presence on the 20m QRP calling frequency. Dale emailed after our QSO.

Hi Michael,
That was fun! I first heard you on my SG-2020 rig, but did not have a paddle handy, so I fired up the K3. I don't ever recall having QRN on 20M, but it was  bad. Without it, you were 579 and even with it, 569 towards the end of the QSO. I just happened to be QRV on 060 listening when I heard your CQ's. Not bad for a 25mW signal from (I think you said) a Philco transistor.
Dale W4OP

Later in the day I worked K4DP (599/559) in Covington, VA (929km).

Two days later my CQ was answered by VE9TTT at the northern end of the Bay of Fundy. Fortunately, the QSO turned out better than one would think given my 309 report. We kept it going for 13minutes and Paul ended up copying everything that I sent. 

The next day I met W4OP for a second time on 20m; this time in a prearranged "sked." Dale reported that my signal was 579, peaking occasionally at S-8. He was kind enough to make an audio recording of my signal following our contact. You may listen to my 25mW signal as received by Dale at a distance of 1329km by clicking here.

An audio file of the original Vanguard 1 satellite beacon signal may be heard here. Information on this recording may be found here.

You can watch the March 17, 1958 blast-off of the Vanguard 1, and listen to the control room banter on the US Navy's site located here.

NASA has a wonderful write-up on the Vanguard Project. Check out this snip from the chapter on the TV-0 launch...

"Rain was falling when an hour after midnight, 8 December 1956, the countdown reached its final seconds. A variety of difficulties had plagued the final launching procedures. Snarls at the range telemetry building and at Central Control had necessitated two holds, the appearance of a ship in the waters of the impact area, another. Nerves were jumping in the crowded control room of the blockhouse, with Colonel Gibbs, the Air Force's conscientious project officer, shouting dire predictions at Bob Schlechter, the man in charge. "It's gonna blow up, Bob," Gibbs kept insisting. "Cancel! It'll never fly!"

But it did fly. Lifting off at 1:05 a.m., TV-0 achieved an altitude of 126.5 miles and a range of 97.6 miles. One of the objectives of the launch was to test Vanguard's newly developed Minitrack transmitter. With this in mind Mengel's tracking team had devised and Martin had installed in the vehicle a special Minitrack package. At T+120 seconds, two minutes after launch, the triggering device of the package-a timer-powered two bellows-contained squibs, causing them to ignite and expand, thereby withdrawing a releasing key and allowing a compressed spring to extend and eject a small sphere equipped with "roll-up" antennas and enclosing a Minitrack transmitter. Without difficulty the ground receiving units at AFMTC, the Laboratory's Mark II tracking station among them, picked up the little oscillator's plaintive beep as the ejected package descended into the sea."

Some of you will recall the launch of TV-3 didn't go so well; what Pravda christened, "Flopnik."

And here again in "living" color

Amazingly, following the tremendous explosion the little "grapefruit" satellite was found lying near the base of the launch pad. The turnstile antenna elements were cock-eyed, but it was still transmitting! You can see it on exhibit today at the National Air and
Space Museum
in Washington D.C..

The little satellite successfully carried aloft by TV-4 is the oldest man-made object in space. As of today it has logged over 213,600 orbits and traveled a distance of 11.6 billion km, or 77AU.