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.
73,
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.

Sunday, June 10, 2012

Telefunken Match

It might seem odd that I'd go out of my way to  purchase a broadcast band AM receiver, given that I won't allow a factory-made ham rig into my shack. What's more, I'm not the "collecting type" and I don't listen to broadcast band AM radio.


Nevertheless, I've long admired the design of this particular "transistor radio," and when one was found going "für einen Apfel und ein Ei" I found it impossible to resist.

The Telefunken Match was an early project by the well-know German/Italian designer, Richard Sapper.

My Telefunken Match arrived in the lower half of its original box packing, along with the instruction manual. A corroded battery holder coupled with a spot on the leather case was obviously the result of the radio having been stored away with the batteries installed at some point in time (notice the spot on the instruction manual as well). Otherwise, the radio is in nearly perfect aesthetic condition.


Applying a current-limited 6Vdc supply to the radio only produced a soft hiss in the loudspeaker. A schematic diagram pasted to the inside of the radio (complete with proper node operating potentials) made it an easy task to pin-point the problem. Here's a scan of the schematic.

 
The 2nd IF amplifier transistor was found to be shorted from base to the emitter; a Telefunken AF172. I happened to have a spare AF138 device on-hand, which has similar specifications. The radio came to life once the replacement transistor was installed. The alignment was found to be only slightly off. The sensitivity is excellent, although the noise level is somewhat higher than what one would normally expect from this type of radio. Although I haven't yet gotten around to isolating this issue, I suspect that at least one of the transistors has become noisy and needs to be replaced.

My receiver tunes from 495 to 1870kHz (the slide-rule dial calibration is spot-on). Using only the internal ferrite antenna I had no problem copying W1AW's evening code practice session on 160m (1802.5kHz). My bench signal generator provided the beat-frequency-oscillator with no connection needed to the radio. Broadcast band AM stations filled the dial, roughly a third of which were French language stations transmitting from nearby Quebec.

Here is a scan of the original (October 1966) instruction manual.