Saturday, July 30, 2011

Vintage Germanium on 20m

Some months ago a surprise package turned up in my mailbox. An anonymous donor had sent me three wonderful, old germanium transistors. The 2N170 and a pair of 2N107's (all date-coded December 1956) were still in their original plastic tube packaging.

A thin booklet, Type 2N107 Transistor Circuits for Experimenters  [and] Amateurs, was also included. The circuits shown in the booklet appear to be aimed at the rank beginner: audio amplifiers, code practice oscillators and the like. However, the "Simple Radio Receiver" caught my eye (lower right-hand corner below). 

This was exactly the sort of project that captivated me in my early youth. Growing up in St. Louis, Missouri in the late 1960's, I enjoyed listening to baseball and ice hockey games on KMOX, and pop music on KXOK, using a wide variety of simple homemade AM radio receivers. Although there's nothing much of interest to me on the broadcast AM radio dial these days, I have a nostaligia for the simple circuits that marked my first steps in amateur radio. By the way, this same circuit also appeared in the first (1957) through the seventh (1964) editions of the General Electric Transistor Manual.

While I'm not now interested in listening to broadcast AM radio, a direct-conversion receiver suitable for copying CW only requires the addition of a beat-frequency oscillator (BFO) to the above receiver circuit. With sufficient BFO drive the germanium diode can be made to function as a commutating (switching) mixer. On the other hand, a single diode mixer has several notable disadvantages; perhaps the worst is the relative lack of AM signal rejection. This type of mixer also creates more spurious frequency energy and the port-to-port isolation is quite inferior as compared to more advanced designs. 

Nevertheless, the more I thought about it the keener I became to find out how well a lad might have done with such a basic radio in the late 1950's...on 20m perhaps? Fortunately, all it took was a pleasant evening to find out.

The circuitry on the left-hand side of the proto-board in the above photo carries a crystal-controlled (14.059kHz) beat-frequency oscillator made from a Philco surface barrier transistor (1959 date-code). This oscillator generates 13mw of RF output power. A miniature 50 Ohm potentiometer acts as the oscillator load and BFO input signal power splitter.  

Yes, that's a cat's whisker and galena detector working as the switching mixer in the above photograph! Alternate mixer diodes are shown in the foreground. The left-hand diode is a classic, large glass 1N34A made by Sylvania in the early to mid-1950's. To the right is a red plastic-packaged 1N66 (date-coded March 1957) diode made by Raytheon. This was Raytheon's equivalent to Sylvania's hot selling 1N34A.

Here's the circuit that I'm using (BFO details are not shown).

C1: 130pF
C2: 1.2nF
C3, C4: 10nF
C5: 1uF (although it's not necessary I used a non-polarized capacitor)
C6: 18nF
R1: 270k Ohms (optimum value depends upon the transistor used)
L1: ~1uH, slug-tuned, 14.5t, tap 6t from ground-end, 9 x 16mm)
L2: 470uH molded RF choke
HP: high-impedance magnetic
D1: 1N34 or most any point-contact diode arrangement 
Q1: 2N107, PNP germanium transistor (mine is date-coded Feb. 1957)

Signals were heard as soon as I powered-up my new receiver. I began using the Sylvania 1N34A as my mixer diode. When things became quiet on the QRP calling frequency I substituted my RF bench signal generator for the crystal-controlled BFO, in order to roam around the band. After logging a dozen or so DX calls I switched first to the Raytheon 1N66, and finally to the cat's whisker and galena. The galena appeared to be at least as sensitive as my vintage commercial diodes in this application.

The catch of the night came with the cat's whisker and galena installed when I copied F6HFX running 5w from the southwest of France! A station in Florida that Pierre was working had a fairly rough copy, judging from the number of repeats requested. The Floridian lost him several times before throwing in the towel. Pierre's signal was also coming and going here, but with spells of decent copy in between. 

Another station heard with the galena was G3HGE. Tom had a huge signal here for well over an hour. It was a real pleasure to copy him sending with his old bug. Some of you may recall his company, TW Radio; a history of which may be found by clicking here

A few of the DX stations heard include: OZ0TX, PA3CJP, 4O8A (big sig), OK2AN, YT2ISM, OK4RQ, G3VMW, DM4IM, DL0KWH, LY5A, CR7ACS, and DF8GI (579 on the galena). Altogether, I filled two sheets of notebook paper with the callsigns heard that evening. I heard a number of weaker domestic stations calling CQ (with no answer) near the QRP calling frequency; presumably some of which were running 5w or less. 

A few more technical details...

The impedance looking into the base of the 2N107 AF amplifier is 2740 Ohms. Ic = 388uA, Ib = 10.7uA, Vc = 1.49Vdc, voltage gain = 44.3dB, power gain = 36.1dB

The injected BFO signal level is ~1Vpp at the diode. The 14MHz BFO "backwave" radiation measures 4uW at the antenna terminal.

Some images taken from the 1957 Radio Shack Catalog are shown below. Included are listings for the Sylvania 1N34A and Raytheon 1N66 diodes, as well as the General Electric 2N107 transistor. The 2N107 might have been a bargin in 1957 at $0.99, but adjusted for inflation the equivalent cost today would be $7.95. Even "low-end" electronic components were relatively dear in those days!

The 2N43, 43A, 44, 45 and 2N107 transistors were graded products from the very same fabrication line. In fact, what was to become the 2N107 had been discarded as rejects until the "bean counters" at GE could be convinced that electronic hobbyists might find them useful.

This transistor line was introduced in September of 1953; the first alloy junction devices ever produced. John Saby was the lead developer of these historical transistors, however, the alloy junction process itself had been invented at GE in 1950 by Hall and Dunlap for use in rectifiers. 

Given the semiconductor surfaces were not passivated, or otherwise protected from the environment, GE found it necessary to evacuate their early transistor envelopes to nearly vacuum tube levels. This explains the metal "pinch" found at the top of these early "top hat" transistors.

Finally, the datasheet power gain listed for the 2N107 is 38dB. I'm tickled to find that my 2N107 is still producing 36dB some 54 years later. Having now myself reached the age of 54, I only wish that my original "specs" would have held up so well!


Tuesday, July 19, 2011

Sputnik QSO Party Transmitter Prototype

Here is my Sputnik QSO Party transmitter prototype. The RF output power is 450mW with 70Vdc @ 14.4mA on the V2 anode. The V2 screen (G2) current is 1.6mA. The V1 anode current is 1.05mA with 45Vdc @ 176uA at the screen (G2). These little vacuum tubes are capable performers, however, for long-life operation it's important to heed the maximum electrode ratings as shown on the datasheets (links given below). 

The simple MOPA (Master-Oscillator -> Power-Amplifier) vacuum-tube radio transmitter circuit shown below was well-known in the mid-1950's. A crystal-controlled Pierce oscillator drives a Class-C PA. The PA grid bias is derived from rectified PA grid current (thus; never run the PA stage without the oscillator drive signal present!).

The CW keying and transmit/receive switching circuitry are not shown in the circuit below. Please click here to listen to a strong-signal recording of the original Sputnik-1. The oscillator signal bleed-though during "key-up" intervals is clearly audible. This implies that the oscillator stage was allowed to run continuously. Presumably, only the power amplifier (PA) stage was keyed on/off. As such, I plan to only key my PA stage (via the anode supply or perhaps using grid-block keying). My oscillator will be switched off only while I'm receiving signals. 

Parts List
C1:     85pF S.M.
C2:   100pF S.M., 100V
C5: 1000pF, 100V
C6:     10nF
C3,4,7:  10nF, 100V
C8:    2200pF, 250V
R1:    27k
R2:    68k
R3:   100k
L1,2:  67uH 
L3:  3.3uH
VC1:   5-35pF
VC2:   20-150pF
X1:  21.060MHz, ESS Type HC49
V1:  1sh24b (1j24b or 1Ж24Б) ex-Soviet sub-miniature "rod tube"
V2:  1p24b  (1П24Б)      "                     "                      "

  1. Ground the internal shields (V1 pin 3 and V2 pin 4)
  2. A low-pass filter may be required between the Pi-network impedance matching circuit and the antenna. I have not yet checked the RF output spectrum, however the inherent Pi-network 2nd harmonic attenuation is only ~28dB.
  3. The value of C1 may have to be adjusted for your particular circuit layout. This capacitor helps both to maintain the optimum level of oscillator feedback and provide the proper loading capacitance for the quartz crystal resonator.
  4. I had somewhat better results with V2 pin 1 (the filament common terminal) negatively polarized. 
 The drawing below shows the original Sputnik 1 keying plan for normal conditions; 0.3 seconds on, 0.3 seconds off. While the 40.002MHz transmitter was off the 20.005MHz transmitter was on, and vice versa. This helped to hold the battery load steady.

    DL3JIN has made a wonderful job of his Sputnik Sender; details of which may be found here. Well done, Peter!

    Roger, G3XBM and Andrew, G6ALB posted details of their Sputnik-1 transmitter project here

    Here's a short video on the topic of these Soviet "Rod Tubes" (dig the Cosmonaut on the intro screen!). Of these amazing sub-miniature vacuum tubes, Dmitri Faguet writes (post #12)

    "The 1j24b is a universal ultra low power miniature HF pentode designed in the mid 1950’s as part of the series of so-called Rod Tubes, invented by Russian engineer and academic Valentin Avdeev, who worked at a special vacuum tube research and manufacturing plant code named “No.617”, located in Novosibirsk, Russia during and after WWII. For many years, Rod Tubes became the backbone of Soviet military and aerospace electronics, with more than 200 million Rod Tubes manufactured without any modifications for nearly four decades from 1950’s to 1990’s. All Rod Tubes were low power battery operated pentodes with one or two thin 1.2 V filaments, and with other rod-type electrodes rigidly located at very small distances from each other."

    David, NM0S, is building his Sputnik clone into a metal earth-globe. How clever!



    Sputnik-1 and Amateur Radio
    Sputnik Declassified: Nova, 2007 documentary
    Spaceflight Magazine: Vol 49 November 2007 
    Volkssternwarte Muenchen; thanks to DL4ZAO for the excellent link!
    Sputnik Model Plans; from The Arizona Model Aircrafters 
    October Sky (required viewing for Sputnik QSO Party participants ;o)
    The Top Ten Sputniks
    Dr. Asif Siddiqi's Research Pages; my thanks to Chris, OE3HBW
    More Sputnik-1 Info; Tnx to OE3HBW
    Pull Apart the PS-1; Tnx to OE3HBW  

    Friday, July 15, 2011

    F6HKA via D-Cell DX

    Back home now (and using a new D-Cell battery!)...F6HKA replied to my CQ on 15/7/11. Bert began with 400w on his end but quickly dropped down to 5w. I had a perfect, 549 copy of his signal with my 20m receiver made from a diode mixer and a one-transistor audio frequency amplifier. His, "VY FB INCREDIBLE" CW exclamation translates to a Milliwatter's "home run." :o)     

    Bert emailed later, "Your 85mW doing a very nice job and your report was really 559." We had a very solid contact lasting some ten minutes....a wonderful QRP/QRPp QSO!

    Saturday, July 9, 2011

    D-Cell DX Results

    DL/AA1TJ/p/QRPp near Friedrichshafen (photo by DL3PB)

    Dear Friends,
    Our trek across Austria, our trip to Friedrichshafen, Germany and our visit with family in Northern Italy are all now the happiest of memories.


    A total of seven 20m CW QSOs were made along the way using a single D-cell battery for the entire, month-long trip. The RF ouput power was 75mW at the outset but by the time we reached Italy it had fallen to just over 50mW. As if to compensate, the propagation improved considerably once we arrived in Italy.

    I first operated from a hillside just west of Perg, Austria on the 10th of June. I was pleased when ON6QP answered my CQ and we exchanged 589/529 reports. Rene was located near Liege, Belgium. 

    On June 13 we climbed out of the Danube valley and entered the Kürnbergerwald, just west of Linz. There we came upon the ruins of a Roman watch tower located high above the river. The six meter square tower was thought to have been manned by a crew of six; whose duty it was to stand vigil for invaders and relay messages using both visual and acoustic means. An earlier tower was reinforced on this spot during the Marcomannic Wars which took place in these regions, circa A.D. 174 (the opening battle scene in the film, Gladiator, was supposedly set amid this conflict). 

    The very idea of operating my QRPp rig from the ruins of this ancient Roman signal tower sent shivers up my spine. Alas, I made no two-way contacts from this spot, however my signal was catured by two Reverse Beacon Network (RBN) stations located in Finland and Norway! 

    On June 15th the Donausteig walking path led us to the ruins of Schaunberg Castle, dating from A.D. 1160. We ate our lunch in the chapel, beneath the spot where the altar must have once stood. Afterwards I flung my antenna out from the top of the remains of the 32 meter high tower and settled down to try my luck again on 20m CW. Again, I made no QSOs but I did receive two RBN hits from the OH6BG receiver in Finland. 

    Nine and a half walking days out of Grein, Austria we rounded a corner to find the fairy-tale city of Passau set before us. It was a moment I shall never forget. It had been a 27km day of dodging thunderstorms; running across open fields for shelter and standing beneath farmhouse eaves munching brotchen with Milka chocolate. We had decided to splurge for two nights in a lovely hotel that in the past had hosted both royal families and the first man to walk on the moon. We appeared before the desk clerk tired and muddied from the knees down...but what an adventure it had been!

    Three days later we met up with DL3PB and his wife in Friedrichshafen. Together we had a  wonderful time on the shore of Lake Constance until the big hamfest was over some days later. Thank you Peter and Petra! 

    We took the ferry across to Romanshorn, Switzerland on a Sunday morning; arriving at the railroad station only moments before a vintage Swiss steam locomotive pulled into the station. What a treat! A hydrofoil took us across the length of Lago Maggiore to Arona, where our family met us for more than a week of visiting and sight-seeing. 

    I set up my radio twice in Italy with my 10m end-fed wire dropped from the second floor balcony. On 1 July I worked G3JPX/QRP (579/449), DL1ARH (569/439) and ON4TJ (589/559). On 4 July I worked DJ0GD/p/QRP. Peter was field-testing his FT817 @ 3w into a 3 meter whip antenna from Moers, near Cologne. He reported "all ok Mike no problem to copy." Peter was 559-569 on my end.

    Afterwards I worked SM3YQX/4 (589/559) near Mora, Sweden and F8DGY (589/579!) near Paris. 

    Upon my return to Vermont my RF output power measured 52mW; down from my initial 75mW output due to the drop in battery voltage. Although I hadn't worked the Americas from Europe as I had hoped, I've no complaints whatsoever. My thanks to W1PID, AA1MY, DL3PB and everyone else who kindly listened for my signal. 

    Mike, AA1TJ