Radio Digest (July 1924-Apr 1925)

July 26, 1924 RADIO DIGEST -Illustrated England's New Unidyne Radio Receiver Part III — Radio Frequency Hook-Up IT MAT seem funny but the moment any new circuit appears, there is an immediate response in the form of numerous letters requesting the circuit with more tubes added. Naturally this has not been the case "over here" in the case of the Unidyne because of the tube problem, but the English inventors appear to have anticipated the demand from their fans by promptly giving details of a circuit employing a stage of Radio frequency amplification in conjunction with the detector. This circuit used in conjunction with a stage or two of audio frequency amplification as shown in Figure three of last weeks article, should prove to be a popular all-around hook-up. As might be anticipated, English fans refuse to give up regenerative, features even when Radio frequency is employed, so we have the tickler from the plate circuit of the detector tube, inductively coupled to the antenna coil as shown in Figure 5. Details of the Circuit The series condenser in antenna circuit is a variable with vernier (.0005 mfd. capacity). The antenna inductance has 75 turns and the tickler 100 turns. These can be honeycomb or spider web coils. Even a variocoupler with the proper number of turns will be suitable. In the Radio frequency transformer, the following suggested construction is offered. The primary should be made of 75 turns of number 22 double cotton covered wire wound in a single layer on a 1 % inch diameter tubing. The secondary has 85 turns of the same size wire on a 2 inch tube. The primary is then fastened inside of the secondary. Both windings should run in the same direction. The plate and grid connections should be made at opposing ends of the two windings. Rather than the grid circuit, the primary is tuned by means of a .00025 variable condenser. A .00025 mfd. fixed grid condenser is used. The detector circuit has the usual variable grid leak. The inventors lay particular stress on the fact that this grid leak must be of CARTER Portable Jack $1.50 Make your loud speaker portable by using a Carter Portable Jack for extending to other rooms, out on the porch or garden. Take one with you on your vacation. Any dealer can supply ~ J^adLi By Harry J. Marx VRoMEB G<u>. Figure 5 high quality. It's resistance range should be from 500,000 ohms to 5 megohms. This variation should be reasonably uniform. Many so called variable grid leaks fail to do this entirely — further, their range seldom covers the limits specified. In this circuit, the grid return of the first or Radio frequency amplifier tube is to the negative filament. The inner grid as usual is conneced to the positive filament lead in both tubes. In the detector circuit, the grid return is to the positive filament terminal. The use of a phone condenser appears to be optional in as much as no positive instructions covering same are offered. Radio Becomes New Weather Forecaster Your Radio set is a good weather forecaster, and as soon as you come to understand it, you will be able to predict atmospheric conditions with remarkable accuracy. With experience it is quite an easy matter actually to predict the forthcoming weather by carefully noting the type of the static signals heard in the telephones due to unwelcome Radio waves of atmospheric origin."*' Thunderstorms, of course, produce the worst form of interference. They make their presence known by "clicks" and "cracks" in the telephone. These static disturbances are a source of great annoyance to Radio I ,■' , si to' m % <• Build a FADA 5 tube Neutrodyne Receiver Ton can assemble one in a few hours. For distance, selectivity and loud speaker volume there's nothing better. The FADA 5-tube Neutrodyne outfit No. 167-A contains everything needed — the finest Neutrodyne parts that can be purchased. The FADA "How to Built It" book makes everything as simple as A, B, C. Buy the original FADA No. 167-A in the sealed package, $65.60. F. A. D. ANDREA, INC. 1581 Jerome Ave. New York FLa d i o t THE LAST WORD IN AERIALS The Greatest Improvement in Radio Within the Fast Year Here it is at last — the very thing you have been looking for — a Non-Directional Aerial that can be used anywhere and on all makes of receiving sets. No longer is it necessary to string unsightly wires or be bothered with cumbersome aerials that pick up only from certain directions. THE PORTABLE GLOBE AERIAL, as the name indicates, is not only portable but collapsible, ornamental and, above all, mechanically perfect, bringing in messages no matter where from or how far away. It is the Only Aerial That is NonPatent Directional Pending U No. 690459 Quick installation is another feature. It can be installed and used on the roof, hung out of the window, or in any room at home, at the office, in hospitals, on trains or ships, or out in the woods and summer camp, especially adapted for tourists. In its operation it is more selective and tunes much sharper and clearer with less static. The Portable Globe is the only Aerial to use in congested cities and crowded apartments where usually the interference is great, but which interference with the Globe is entirely eliminated. It is made of the finest I'hosphor Bronze Spring wire with the Duco water and weatherproof finish attractive as well as serviceable — a wonderful value, featured at a price within the range of everyone. Order Today — Satisfaction Guaranteed Send in your order now. Be among the first to show your friends the latest and greatest improvement in Radio. Send money order or will ship C. O. D. $ jO— 00 Parcel post pre paid to door. your The Portable Globe Aerial Co. OPEN 1602 Locust Street, St. Louis, Mo. CLOSED "An Attractive Proposition to Jobbers and Dealers Who Order in Quantities." engineers who are ever endeavoring to design circuits and devices to overcome these malicious oscillations. Those who possess crystal detectors with their receivers will notice that during atmospheric disturbances of this nature the resulting static "clicks" will paralyze the crystal and will necessitate exploring of a fresh sensitive point with the usual "cats whisker." Squalls before and during their throes of violence will produce a low rushing sound in the telephones, increasing in intensity to a crescendo as the storm reaches its maximum. This phenomenon is generally accompanied by a heavy static or electrical charge on the antenna, so that ft iS quite possible to obtain sparks of considerable dimensions between the aerial and the earth. It is of further interest to note that the direction of incoming squalls can be located by means of the Radio direction finder, static signals having a marked direction along the path of the squall. Snowstorms produce a similar disturbance in the telephones as that due to squalls, although the intensity of these static signals are not so strong and do not impair reception to the same extent. Wind storms will frequently affect a tube receiver in such a manner as to bring about a continuous alteration of the tuning of the installation, causing signals to fade. Then again, there may be a tendency for the circuit to commence oscillating at an audible frequency. These effects are noticed when the lead-in wire from the aerial is brought down the side of the house, the wind causing the same to swing to and from the wajl, bringing about an altered capacity. In the Sahara and other points on the globe where the phenomena of sand storms are a local occurance, Radio receivers are likely to be seriously hampered by these meteorological outbusts. The small particles of sand, during their hurtling through the air on the wings of the wind, become highly charged with frictional electricity which in turn is passed on to any aerial which happens to be in its path. The result is a heavy rushing sound in the telephones and intermittent "clicks." Although not actually granted the government of South Africa has finally definitely promised a Radiocasting license to the Associated Scientfic and Technical Societies of Johannesburg, for a Radiocasting station to be installed in that city. A*2rOO,ooo.oo Company 2/* Stands Squarely Back |V of Every^Phone (Plus a/euf cents postage Send No Monev Order by mail if your dealer cannot supply you and we will ship immediately. Written 5-day money back Guarantee with each set. Our next year's production schedule of two million phones UNDOUBTEDLY places us as the Worlds Largest Headset Makers THE TOWER MFG. CO. 98 Brookline Ave. Boston Mass. Stop the Leaks! Save all the energy in the antenna for your detector tube. This Coto Compact Air Condenser with Vernier is so perfectly insulated that losses are reduced to a minimum. Type 3505 .asssSJSTOBs*^ Type 3510 .0005 Mfd. Plates are of silver plated copper soldered in place for lasting adjustment. If your dealer fails you, write us, giving his name and address and list of Coto parts yon need. COTO-COIL CO. 87 WiHard Ave., R. I. Providence, BRANCH OFFICES Los Angeles, 329 Union League Bldg.; Minneapolis, Geo. F. Darling, 705 Plymouth Bldg.; Atlanta, C. P. Atkinson, Atlanta Trust Co. Bldg.; CANADA. Perkins Electric Co., Ltd., Montreal, Toronto, Winnipeg. * !