From: military-radio-guy Full-Name: Dennis R Starks To: military radio collectors#1 Fcc: Sent Date: Wed, 26 Nov 1997 13:51:53 Subject: Military Collector Group Post, Nov.26/97 Message-ID: <19971126.135057.9559.13.military-radio-guy@juno.com> X-Status: Sent X-Mailer: Juno 1.38 Military Collector Group Post, Nov.26/97 Index: The SSTR-1; From the Horses Mouth Part III, Further Reflections Concerning The SSTR-1, By Dean Cortright POWER FOR AIRCRAFT AND MILITARY RADIOS; by John Mackesy VK3XAO HUMOR; *********************************************************** The SSTR-1; From the Horses Mouth Forward, Regretfully, this is the last of this series, & of the material that I have. While it is possible that other accounts were preserved, if so, they are unknown. Did I not say in a prior comment, "I'm left wanting for more, much more!" You can now see why? Dennis Starks; MILITARY RADIO COLLECTOR/HISTORIAN military-radio-guy@juno.com -------------------------------------------------------------------------------------------------- Part III, Further Reflections Concerning The SSTR-1, By Dean Cortright Hank Shore was on the design of the SST-1. Earl Anderson later worked on the circuit and constructed the first prototype. Design of the SSTR-1 was influenced to a certain extent by examination of the British clandestine radio equipment. I remember that within a month or two of my arrival in Commo Division (and soon after Hank had appeared), we received a copy of the British underground suitcase radio which had been obtained when HQ was set up in the UK, well before George Graveson was there. I assume that Steve Simpson or someone else on the ball thought to ask for it. It didn't have the exact shape factor we used but it was approximately the same; in three pieces: the transmitter, receiver, and power supply. Their power supply had an assortment of plugs for different European AC outlets, and this was helpful. Also, it had some different kinds of crystal holders. That got use into the universal crystal sock which was designed to accommodate whatever type of crystal holder we thought might be encountered. I think they also had a hand-crank generator which we also got into. However we did decide to get some standard voltage spec so we could use what was available. rather than having something built. Power supplies were kicked around a lot. We decided on 115/230 volts and a switch which altered the primary so it could be operated with two windings in parallel for 115, and in series for 230 volts. The transformer cores were designed to handle either 60 or 50hz. Later we found a rather light core that would operate from 400hz as well. The circuit would also accommodate a small gas-driven generator in addition to operation in aircraft. Direct current operation was for six volts which was the standard vehicle voltage in those days. This all took more space , so we made the power supply case a bit wider. Then we had a suitcase made to hold it all, plus crystals and some tools so one could change the plugs, etc. There was also space for a separate key, if available, and the signal plan. The idea for the rotating coil as a loading system came after the first models were built, but I don't remember exactly when that took place. Manufacture was split up at first, with transmitters built one place, the receivers another and the power supply still another. The first rotating coil design was attempted using a GLASS coil form made by Corning. I remember going to their plant to work with them, but they couldn't hold the required tolerances, and after a lot of delay, admitted that. Then we went to cast ceramics and that worked quite well. The final production design was a little beauty. The people that worked with Hank Shore were Maddy Rehm (who was an active ham, and worked for RCA Communications in New York), and Walt Bostwick, who was a customer engineer, traveling from one plant to another do to expediting, etc. Later when Maddy went overseas, Claude Leather did some of the coordinating work in DC. The receiver tuning was a bit touchy. We worked a lot on that and finally got a design which kept the tuning capacitor and coils all on one sub-assembly for greater stability. Also, the range was increased, tuning 2 through 24 mhz or thereabouts. In the Official War Report of the OSS, reference was made to an "earlier model" receiver. I think it was something which was turned out on a Signal Corps contract. I remember seeing one; it was housed in a wooden box about 15 by 15 inches, covered with naugahyde, or something like that. With those high voltage filaments tubes, the inside of the box got plenty hot if it was left on for any length of time, and that contributed to frequency instability. ------------------------------------------------------------------------------------------------- ed) Note the recurrent references in these accounts of "six volts being the standard vehicle voltage of the day", & the unit of measure "Hertz", as apposed to cycles. Both these, especially the later would indicate these accounts were compiled 'after' the late 1960's, as this is when Hertz became the standard unit of measure for frequency. By 1957 12vdc had become the standard vehicle voltage for all domestic automobiles, and later for those of foreign origin. The gas-operated generator Mr. Cortwright refers to is in strange sequence including mention of 400hz power supplies etc. Can we surmise that this generator was of 110vac 400cps ops, rather than the common multi voltage DC types in use elsewhere? This would provide for a smaller lighter unit, with more versatility in it's application. Though this chapter provides some additional information on the "earlier model" set, and 'parts' of that description do match that of known types. The use of high voltage heaters, or parallel RF output tubes still does not jive with those we know about. Nor could the complete radio set utilizing parallel output tubes/30 watts power output described by Mr Ranney in part 1, be contained in the cabinet 15 x 15 described by Mr Cortwright. Then too there is the strong possibility that more than one "earlier model set" was encountered by these authors & those providing material for Kermit Roosevelt (War Report of the OSS). We know that MANY different radio sets went through the hands of the OSS, or it's predecessor the COI, both in the early day's & later as equipment was considered for use. And that several of these early sets were indeed issued as expedients prior to the advent, standardization, & sufficient availability of the SSTR-1 . They came from various avenues including the British, the Signal Corps, & already available civilian types including some that had been in use by U.S. Forestry for years. Some of these were actually used, many more were dismissed outright. As we can see with this volume of prospective, & varied equipment being inspected by numerous persons, that we could have different accounts of different sets, or at least some very understandable confusion. While I have good reason to beleive I know what the "earlier model" set described by Mr Cortwright, & Mr. Roosevelt were(both being different radios). That described by Mr. Ranney in Part 1 remains a mystery. Towards the end of Part III in Mr Cortwright's account, we find reference to "first models", a successive developments where receivers, & transmitters are improved. The text discribes a rotating coil in the transmitter, & an "Oscillator sub-assembly" in the receiver, also haveing an "increased frequency range of 2 through 24 mhz or thereabouts". It is known that variants of SSTR-1 existed at least up to model "E", these emprovements are not incorperated in the serviving examples, nor are they included in the later model replacement, the SSTR-5. These receiver improvements do however exist in the RS-1/GRC-109 who's development we know began before the end of WW-II. I submit then that Mr Cortwright may then have been giving us a chronology of the 'breed of radio & their developments', rather than just that of the SSTR-1. Several other SSTR type sets were also built & is shown by official documents disclosing OSS purchase expenditures, these variants have never been encountered or described, perhaps these improvements were incorporated in those sets. More recent evedence exist to further support this theory, & will be addressed in further issues along with some other questions that have been submitted by our readers. Hopefully the information presented in these accounts will provoke further input that will serve to enhance our understanding. ***************************************************************** POWER FOR AIRCRAFT AND MILITARY RADIOS; by John Mackesy VK3XAO mack@melbpc.org.au Unlike domestic radios, all aircraft radio equipment is powered by something other than 115/240V 50/60Hz. This also applies to a significant proportion of military ground equipment. For the collector who wishes to restore these (often complex) systems to their full operational glory, exotic power requirements can be a major difficulty. There are 2 solutions to the problem: 'conversion', and 'roll-your-own' power. 'Conversion' generally means techniques like re-arranging filament wiring, outboard B+ supplies, and reworking internal power supplies. When done to a high standard, conversion can produce very acceptable results. Unfortunately, not all equipment lends itself to this approach, particularly devices which contain servomechanisms and/or position indicators. 'Roll-your-own' power usually means 24-28V DC and/or 115V 400 Hz AC. A high proportion of mobile (transportable, vehicular) equipment uses 24V, this being a common standard for military vehicles (and heavy vehicles generally). Aircraft use 24-28V DC extensively, many larger aircraft also using 115V 400 Hz AC power systems. 400 Hz is used to reduce the iron requirement in generators, motors and transformers, as 400 Hz devices needing much less iron to be resonant, than its 50 Hz counterpart. This all reducing weight, & during WW-II iron, when supplies were critical. Some military ground equipment also uses 400 Hz power. Most receivers (and low power transmitters) will not need more than 150W (total), so power sources are reasonably manageable. Typical examples (in the writer's collection) are the WW2 vintage Bendix MN-26 & SCR269 Radio Compasses and the '50s Marconi AD7092 Auto Direction Finder. More grandiose devices tend to require more power, especially higher powered transceivers. The Collins 618S-1A Airborne HF Transceiver is an example of this. A sample of typical power requirements appears below: EQUIPMENT 24-28V DC 115 VAC 20 MN-26 RADIO COMPASS 3.0 A NIL20 SCR-269 RADIO COMPASS 1.0 A 100W (320-1000 Hz) 20 AD7092D ADF 3.0 A 6.0W20 618S-1A (Receive) 3.0 A 160W 618S-1A (Transmit) 30.0 A 160W There are a few devices (usually test equipment) which will operate over a wide range of power supply voltages and frequencies. A common example is the British AVO CT-160 Valve Tester, which can be used between 50-250V and 50-500 Hz AC. DC power sources, usually based on a simple transformer-rectifier arrangement, are relatively straightforward and inexpensive. Some equipment will operate satisfactorily on 'raw' DC, but well-smoothed regulated power is desirable for most applications. A point to remember is that although the DC requirement may be quite modest (4 - 6A), cold filaments and dynamotors tend to look like dead shorts at switch-on. For 400 Hz AC power generation, an inverter (usually 24-28VDC in, 115VAC out) is the most practical solution. Inverters are widely used in aircraft with modest AC power requirements, where the bulk, weight and complication of an engine driven AC generator is not justified, and for standby purposes. Until the '60s the aircraft inverter was an electromechanical device (a combined DC motor and AC generator), commonly called a rotary inverter. These have now been largely displaced by the 'static inverter', solid-state, much lighter, more efficient and reliable. As a result rotary inverters have become available at reasonable prices.20 A 150W inverter takes care of most things, with a 28V DC input current of about 12A. Rotary inverters are not particularly efficient, rotate at high speeds (typically 8000 RPM) and have a large cooling air requirement. Internal fans move the air, the overall construction being very similar to a siren - so is the noise, usually a high-pitched resonant whine. Solid-state inverters have much higher efficiency (and better regulation) with much less noise. In my situation, 27.5V DC power is supplied by several small (2 - 10A) regulated supplies. For AC power, the main source is a 190W Eclipse Type 778 rotary inverter, with a '60s 770W Rotax Type S3303/2 for occasional higher power operations. The Rotax inverter is surprisingly quiet (modern fan design!) and is a type originally used in Argosy and Canberra aircraft. A 1.2KW 115/208V 3-phase inverter is 'in progress'. There is also a 'Nova' Frequency Changer (solid-state), 240V/50Hz in, 208/115V 400Hz @ 1Kw out. This was sidelined for a number of years due to its RF hash-generation tendencies, but after a recent intensive noise-suppression campaign is now the primary AC source..20 Notes: (1) 400 Hz is the nominal AC frequency. Most equipment is specified for operation between 380 to 420 Hz. (2) Some equipment is specified for use on aircraft with "frequency wild" AC power systems, where the frequency may vary between 320 and 1000 Hz. (3) Although 115V 400 Hz is the generally accepted standard, other voltage/frequency combinations may be encountered, e.g. 80V 1600 Hz, 115V 800 Hz. (4) Static inverters are available with sine wave or square wave output, sometimes both.20 (5) Disadvantages of 400 Hz power are a significant line impedance (not a problem on the aircraft scale) and a pervasive 400 Hz background whine. The latter is particularly annoying when it gets into the audio. (6) The means whereby an engine operating at varying RPM can drive an AC generator at a fixed output frequency is technically fascinating, but sadly, outside the scope of this (necessarily brief) article. ed) My thanks to John for his much needed contribution. And to the area of aircraft equipment specifically as there has been an obvious neglect of our/my attention to this field. Typically, a 100 watt, dynomotor driven transmitter can draw as much as 135amps for a split second until the thing gets spinning. This can spell immediate death to a solid state regulated power supply, even one capable of relatively high current output. One remedy used by an old friend is to strap about 1 farad(yes that's a bunch) across the output terminals of his 40 amp regulated supply. The capacitors start the dynomotor spinning, & once this is done, the current needed usually drops to a manageable 35 amps. This system has yet to fail with any load it's been used with. High current supplies were also available for such power mongers as the T-195 for operation from AC mains. This was a monstrous thing, unregulated, & had a no load output of over 60 volts. If the companion R-392 were turned on before or without the transmitter, it would be instantly fried because it's low current drain could not pull down this extreme no load voltage. Many early supplies will act in the same manor so use extreme caution, & common sense when trying to utilize them. ***************************************************************** HUMOR; For those of you interested, this is the current make up of a Marine Corps Rifle Squad SSG Squad Leader Lance Corporal Automatic Rifleman Private Still Camera Operator Private Motion Picture Camera Operator Private Television Camera Operator Private Extra film carrier Private Extra film carrier Private Extra film carrier Private Extra film carrier Private Camcorder battery charger, spare battery carrier Lance Corporal Document Shredder Private Assistant Document Shredder, Paper feeder Private Rifleman, duties uncertain -------------------------------------------------------------------------------- COMPUTER PROBLEM REPORT FORM From Your Friendly Technical Support Staff 1. Describe your Computer problem: ________________________________________________________________ 2. 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