NUMBER 67, DECEMER 1988 / JANUARY 1989
Scanned, OCR'ed, and proofed by Bob "Bacon" Bruhns WA3WDR
A Message From The Editor And Publisher
Our readers are bound to be wondering why AM P/X has been arriving so late the last few months. This "December" issue will not show up in the mail until sometime after the first of the year. We are presently running about a month behind. There are three reasons for this.
Firstly, there have been unusually heavy demands on my time. As many readers already know, I quit the radio/electronics profession several years ago, while retaining amateur radio strictly as a hobby. I am now employed as a foreign language teacher in the local public school system. Beginning this academic year, I have been teaching high school French at two separate schools located at opposite ends of the county -- a full time teaching load, plus at least one hour's travel time, five days a week. This, in addition to normal family responsibilities, leaves me, as editor and publisher, very little time to work on this newsletter.
Secondly, I am now essentially publishing AM P/X single-handedly. Originally, this publication began as a joint effort of interested AMers. Unfortunately, the logistics of having "helpers" who live hours of driving distance away, or with whom material must be exchanged via mail or UPS, made the joint effort impractical, so I eventually took over the entire operation myself, my only assistance being the girl I hire every month to help staple the copies and affix stamps and mailing labels.
Thirdly, the manuscript tray has been running near empty for several months in a row, with articles for publication slow in coming. I no longer have the time to write one or more articles myself every month in order to fill the pages -- and cannot put an issue together without something to put into it. So I have been forced to delay publication each month until enough material has accumulated to fill the upcoming issue.
I am frequently asked why I continue the obvious hassle of putting together this publication every month, when it might be more enjoyable to spend the time on something relaxing, like operating AM on the radio. Certainly, this is not for monetary profit, as the subscription fees barely add up to cover production and mailing costs. I feel there is a real need for this publication. Our hundreds of subscribers are proof that there is a demand for this product. AM phone has made a healthy rebound to re-establish itself as one of the numerous facets of amateur radio; yet this mode continues to come under daily attack by certain elements within the amateur radio community, and is virtually ignored by the major "establishment" amateur radio publications. An informed AM community is essential to the survival of this mode in amateur radio, and AM P/X provides a vital link to maintain a flow of news and information among radio amateurs with a serious interest in AM. AM P/X, along with the dedicated efforts of those involved with S.P.A.M. (which is totally separate from AM P/X), have contributed heavily to the slow but steady growth of AM during an era when there is so much talk of amateur radio being a "dying" hobby that is withering away due to lack of interest.
Although we have not been able to get AM P/X out on schedule in recent months, there are no plans to scale back publication from the current 12 issues per year. But rather than rushing to get in an extra issue to "catch up", this issue has been designated "December 88/January 89". This change will merely accurately reflect the date you will receive each issue -- each "year's" subscription will still consist of 12 more or less monthly issues. If we fall behind and the year is stretched to 13 months, then your renewal time will be delayed a month, as well.
While on the subject, let me bring up a couple of other related points. Because of limited time, I cannot handle requests for back issues. Leftover copies are no longer kept on hand; they are given away as free samples or distributed at hamfests to serve as "free" advertising. If you need a specific article or back issue, please feel free to ask another reader to Xerox a copy from his/her file of back issues. Also, renewals and address change requests continue to arrive minus the code number from the address label, making it virtually impossible to locate those entries among the hundreds on the mailing list, without laboriously going through the list entry at a time until the specific one is found. Time wasted searching through the mailing list is time which could be better spent improving the quality of the upcoming issue.
I wish to express my appreciation for the continued support from our readers, and I wish you all the best of seasons greetings, looking forward to 1989 as a prosperous year for the entire AM community.
Donald Chester, K4KYV, Editor and Publisher
Packet Racket on 29.05 MHz
A packet radio enthusiast has apparently taken upon himself the position of ringleader, with the sole purpose of taking over the middle of the 10 metre AM window with "packet racket." The signal can be heard at frequent intervals whenever the band is open, causing severe interference to AM operation on and near the frequency. This appears to be some kind of automatic beacon, with no CW ID. The signal is broad, taking up 20 KHz or more of spectrum, centered on 29.05 MHz. Rumors are that the station is located "out west" somewhere (presumably in the western U.S.) Many of those who have observed this signal say it sounds like a packet radio transmission. According to data in QST (see page 77, January '89, and page 54, September '87), this signal is not legal under FCC rules. Packet falls under the category of "data" transmission, and is treated as a form of RTTY. On the 10 mtr. band, RTTY and other digital modes are authorized only from 28.0 to 28.3 MHz. The only modes allocated on 29.05 MHz are voice (AM and FM, including SSB), CW, SSTV and facsimile. SSTV and FAX are forms of picture transmission, and the total bandwidths of these signals are limited by the rules to that of SSB voice. ARRL's Ad Hoc Committee on Amateur Radio Digital Communication recommends the use of 28.1023 and 28.1043 MHz for automatic message forwarding when propagation is favorable. Note that these frequencies conform to the RTTY subband. Apparently the interfering signal 's in violation of FCC regulations, and does not conform to the ARRL "band plan." Since this interference has continued unabated for several weeks, and unless the AM community takes action, this latest nuisance will continue to spread like a disease. If this signal is somehow legal under FCC rules (is anyone aware of a STA granted for data transmission on this part of the band?), these operators should be encouraged to center their operations around 29.20 MHz, at the boundary of the AM window. Otherwise, this apparently illegal signal should be identified, and if of U.S. origin, removed from this portion of the band by FCC action, if necessary. (How long would the FCC tolerate AM operation below 28.300?)
If any of our readers have further information on this situation, including news of any STA's (special temporary authorization), please forward to The AM Press/Exchange so that the AM community may be made aware of what is going and what measures must be taken to preserve the AM window on ten metres.
- Tnx Rick, K8NLV
When requesting a change of address, PLEASE include the code number on your mailing label so we can locate your current entry on the mailing list.
MEET THE AMers
Sally Dawson, KA8UVQ - Picture
This month we are pleased to introduce a newcomer to AM. Sally Dawson, KA8UVQ, lives in Winthrop, Maine. She got the "8" call while living in Cleveland, and kept it when she moved back to the home state. She calls it a "terrific tongue twister." Sally operates AM with a Viking Ranger running 45 watts to a double extended zepp antenna, and uses a Hallicrafters receiver.
Sally is the ARRL Section Emergency Coordinator for the Maine Section. She has held this position for 2-1/2 years, and is possibly the only female in an ARRL leadership position. She describes herself as a "modified radical feminist." She says, "I like being on both sides of the fence; guess that's just the rebel in me."
Sally holds an Extra Class license, and is a professional photographer by trade. She is a former instrumental music teacher and is still active as a musician. Sally is single, "30-something," no kids, and at the moment has 6 chickens and 14 Airdale terrier dogs (the dog population should drop back to 4 as soon as the puppies are sold).
Common Troubles With Common Power Suppliesfrom RADIO, June, 1937
If you are using the same power supply to feed both your class B modulator and final amplifier, it is highly important that you decouple the two with a choke and condenser. If this is not done, the second harmonic distortion will be excessive, greatly impairing the quality of your signals.
There are quite a large number of amateurs using class B modulation who are operating their final amplifier from the same plate supply that supplies the modulators. If proper precautions are not taken in the design of this power supply, it is very difficult to obtain high-percentage modulation of the final stage without the introduction of a bad second harmonic audio component. The inferior audio quality of a number of the class B modulated amateur phones can be directly traced to this condition.
This is caused by the fact that there is a very strong second harmonic component in the plate current drawn by the modulator tubes. Figure 1 illustrates graphically the reason for the existence of this component.
Figure 1A shows the plate current flow for each tube of the two-tube modulator as it would look from the two halves of the primary winding. Figure 1B, however, shows the combined plate current flow through the center-tap of the output transformer to the power supply for the same two cycles as were plotted in 1A. The dotted line through the center of the plot indicates the plate current flow as it would be integrated by the ordinary plate circuit milliammeter. The presence of this line also clearly shows the four cycles of second-harmonic energy flowing in the plate return of the modulator. Figure 1C indicates the supply voltage variations caused by the appearance of this second-harmonic variation in plate current across the filter condenser that by-passes this return to the power supply. This would be condenser C1 in the power supply shown in Figure 2. The amount of this variation is determined by the regulation of the power supply, the frequency that is being passed, and upon the size of C1.
To look at it from another angle, we see that during the half-cycle of conduction for each tube in the modulator the a. c. component of plate current flow (which of course is what we desire at the output) travels from the plate of the tube through one half of the primary winding and is by-passed to ground by this condenser C1. Hence, by this latter reasoning we see that this condenser should be as large as is practicable. If you wish to prove to yourself the veracity of the statement above, insert a choke between the modulator power supply and the lead that goes to the center-tap of the class B output transformer. If the stage is running truly class B, the output will fall to almost nothing and you will be unable to "talk up" the plate current on the tubes. If the stage is running AB, the output will fall off less, and if the stage is class A, it will not be affected.
So we see that by both lines of reasoning the condenser C1 should be made quite large. The actual value, of course, is not critical and will vary widely with different modulator systems and with the requirements placed upon them. For an example, with a pair of -03A's operating at 1250 volts under normal conditions, a 10 or 12 ufd., 1500 volt condenser would be satisfactory. This is for a minimum modulator resistance (as presented to the power supply) of the plate voltage (1250) divided by the maximum plate current (0.350 amperes) or about 3570 ohms. A higher-resistance modulator (higher plate voltage, lower maximum plate current) would require a proportionately smaller value of condenser. A lower resistance affair would of course require a larger value.
The values of condenser given above would be capable of by-passing lower audio frequencies than would be required in amateur work, but since this condenser does assist greatly in handling syllabic variations in power supply drain in addition to its regular filtering duties, the use of a large condenser at this point does tend to greatly stabilize the rig for voice work. Another and last point in this connection: a 10 or 12 ufd. condenser really costs but little more than a 4 ufd. condenser of the same make and voltage rating. The cost seems to vary roughly as the square root of the capacity.
Now to consider briefly the balance of the power supply: The rectifiers should of course be mercury vapor. The input choke should be a large one, preferably of the swinging variety, and capable of carrying the full plate current of the final stage and modulator. The power transformer should also be capable of handling this maximum plate current. The second choke, CH2, is used to further attenuate any second harmonic variations appearing across C1, and to provide the additional hum filtering required by the final amplifier. The condenser C2 serves a similar purpose to the final amplifier as C1 does to the modulator. It serves as a by-pass between the bottom end of the modulation transformer secondary and ground in addition to its filtering action. Consequently it should also be quite high in capacity. About half the capacity used at C1 will be found ample for most cases.
Rejuvenating Transmitting Tubes
With the price of transmitting tubes becoming utterly outrageous, it might be a good time to review the procedure for getting a bit more life out of those trusty old bottles. Many of you old timers are well aware that you can improve the emission of some tubes, but this has been lost to many newcomers.
There are two types of filaments/cathodes used in vacuum tubes. The first type is an oxide coated cathode. This type of cathode is coated with a combination of rare earth elements, and is highly efficient. The oxide coated cathode is used in almost all modern receiving tubes, and in transmitting tubes such as the 807, 6146, 8874, 4CX250, etc. This type of cathode runs at a dull red heat. Unfortunately, you cannot rejuvenate this type of cathode.
The type of cathode you can rejuvenate is the thoriated tungsten type, used in tubes such as the 805, 810, 833, and 4-65 through 4-1000 series tubes -- filamentary cathodes that operate with a bright yellow-white glow. The thoriated tungsten filament is made by dissolving a small amount of thorium into the tungsten filament material, which forms a layer of thorium on the surface about one molecule thick. It is this thorium which does the bulk of the electron emitting when heated.
When this thorium is depleted, either from years of use, or by an overload, the tube loses emission, and becomes 'flat' - which is a good term, since a weak tube will cause flat-topping in an SSB amplifier, or won't reproduce audio or modulation peaks in an AM rig.
The idea behind the rejuvenation procedure is to duplicate part of the cathode forming process that was used in the tube's manufacture by bringing fresh thorium to the surface of the filament from the interior. Please be advised that this procedure does not always work, especially with tubes that are really shot, and you do risk burning out the filament. If the filament does open on you, take solace in the facts that it was probably ready to go anyway, and your tube was no good to start with! I have never burned out a filament in any tube made by Eimac or RCA, by the way.
To get started, you need a filament transformer that puts out some 150% of your tube's filament voltage, a variac, and some means of connecting power to the tube; either stout clip leads, or a socket. Be aware that your tube will get HOT -- support it wisely, and don't drop it! Apply some 150% of the tubes rated filament voltage to the tube for ONE MINUTE ONLY, then reduce the filament voltage to about 110% of normal and run the tube like this for a couple of hours. This should boil up some of the thorium to the surface of the filament. Try the tube in your rig. It will most likely show increased emission by increased idle current in a modulator or a linear amp, or more output and plate current for given loading in a class C amp. I have found that if there's any good left in the tube, this will work. If the tube still is weak, it's really been worn or abused, and is probably beyond hope. You can repeat the procedure, and try again, but watch carefully. At some point all the thorium will be used up, and you'll see reduced emission when trying the tube. This means that the tube was beyond saving. Also, repeating the procedure is real risky to the filament. So you're on your own here!
Incidentally, it is possible to make a repair on a tube with an open filament -- sometimes. Apply some 200% of rated filament voltage to the tube's pins and shake it, tap it, and jiggle it around. Sometimes you can get the two broken filament ends to touch, and then they might weld together. BE CAREFUL! A sharp blow to the tube will cause it to break, with flying shards of glass everywhere. WEAR SAFTY GLASSES AND THICK CLOTHING!!! I have found such re-welded filaments to be unreliable, but if you're lucky, you might get a few more contacts out of it.
For further information on tube construction and rejuvenation, refer to the pre-WWII issues of the Editors and Engineers Radio Handbook.
NOTES ON FEEDLINES AND SWR
from MHz TIMES, RF Hill ARC via X-MITTERBased on a Sept. '87 program by W3ZC
tnx Amateur Radio News Service
1. At HF, any effort to reduce an SWR of 2:1 on any coaxial line will be completely wasted from the standpoint of increasing power transfer significantly.
2. Low SWR is not proof of a good quality antenna system, or that it is working efficiently. Low SWR where there shouldn't be low SWR indicates that something else is wrong.
3. SWR in the antenna system is determined only by the matching condition at the antenna and is not changed or brought down by any matching device such as a Transmatch installed at the input end of the transmission line. Low SWR obtained by using a matching device at the input indicates that the output of the transmitter and the input to the antenna system are matched. The SWR between the feedline and the antenna remains unchanged.
4. Adjusting the matching device (Transmatch) for maximum transmission line current creates a perfect mirror or conjugate termination for the reflected wave. The reflected wave, therefore, is totally re-reflected upon arrival at the transmission line input. The tuner provides the proper mismatch, canceling reactance to effect this action. The reflected wave is re-reflected in phase with the transmitter output wave, the sum of which constitutes the incident power.
5. If a suitable matching device (such as a Transmatch) cancels all of the reactance developed by a non-resonant length radiator and a random length feedline which is mismatched at the antenna feed point, the antenna system is resonant, the mismatch effect is cancelled, maximum current flows in the radiator, and all real power available at the feed point is absorbed by the radiator.
5A. The radiator of an antenna system need not be of self-resonant length for maximum resonant current flow.
5B. The transmission line length need not be any particular length.
5C. A substantial mismatch at the transmission line-antenna junction will not prevent the radiator from absorbing all real power available at the junction.
6. Reflected power does not represent lost power over that which existed in a matched situation, except for an increase in transmission line attenuation losses. In a lossless transmission line no power is lost because of reflection. Only when the matched line attenuation and the SWR are both high is there significant power lost from reflection. On HF bands using low loss cable, reflected power loss is generally insignificant. At VHF it becomes significant, and at UHF it is of extreme importance.
7. Total re-reflection of the reflected power at the transmission line input is the reason for its not being dissipated in the transmitter. It is conserved rather than lost.
8. Reflected power does not flow back into the transmitter and cause dissipation and other damage. Damage blamed on reflections is really caused by improper output coupling - not by SWR. Tube overheating is caused either by overcoupling or mistuned loading, or both. Tank coil heating and arc-overs result from a rise in loaded Q caused by undercoupling. With manipulation and/or the addition of a matching device (such as a Transmatch) proper output coupling can be attained no matter how high the SWR is. The transmitter doesn't "see" SWR at all. It sees an impedance resulting from an SWR.
9. Both coax and open-wire feeders can radiate, though not to any significant level, by re-radiating energy coupled from the antenna due to feeder positioning, and by feeding a balanced antenna with unbalanced transmission line. Transmission line radiation has no relation to the level of SWR.
10. Lowest feed line SW occurs at the self-resonant frequency of the radiating element it feeds, completely independent of feed line length.
11. SWR cannot be adjusted or controlled in any practical manner by varying the transmission line length.
12. SWR indicators need not be placed at the feedline-antenna junction to obtain a more accurate measurement. The accuracy limits of the common SWR meters indicate that SWR at any point in the antenna system may be determined by simple calculation involving the SWR at the point of measurement, the transmission line attenuation per unit length, and the distance from the measured point to the desired point.
13. If the SWR readings change significantly when moving the SWR meter a few feet one way or the other, it indicates that some other problem exists and not that the SWR is varying with line length. The SWR bridge need not be placed at half-wave intervals to obtain a correct reading.
14. A dipole cut to be self-resonant at 3.75 MHz and fed with either RG-8/U or RG-58/U will not radiate significantly more at 3.75 MHz than at 3.5 or 4.0 MHz for feeder lengths up to 200 feet, providing proper loading can be obtained.
15. With a Transmatch or a simple L-network at the line input, proper coupling can be attained over the entire band with any random length coax.
16. Changing the height of a dipole above ground, or lowering the ends of a horizontal dipole to make an inverted-V will have an insignificant effect on the amount of power reaching the antenna from the standpoint of attempting to reduce the transmission line loss due to SWR.
Radio Amateurs' Handbook (any recent edition).
The ARRL Antenna Book, 12th edition.
Maxwell, "Another Look at Reflections", QST Apr 1973/Feb 1974.
McCoy, "The Ultimate Transmatch", QST, July 1970.
McCoy, "To Use or Not to Use a Transmatch", CQ, Feb. 1986.
Goodman, "My Feedline Tunes my Antenna", QST, Mar 1956.
Johnson, "Transmission Lines and networks", McGraw-Hill, N.Y. 1950.
"Reference Data for Radio Engineers", 4th Edition, Federal Telephone and Radio Company.
MAKING AM THE GREAT NEW GUY ON THE BLOCKOrHOW YOU CAN GREATLY OVERCOMEPOWER LIMITATIONS ON AM
Copyrighted, 1989, by George A. H. Bonadio, W2WLRWatertown, NY 13601-3829Part 3
CORNER BLOCKAGES OF SIGNALS
Most of us recall old chassis wiring where a "buss bar" dominated the space and all the wiring was on right angle corners. Even today we see wiring diagrams as though that practice continues -- all corners at right angles. Wiring today, however, usually takes the shorter path, often with rounded corners.
Because of chassis space, the fields around these wires have not expanded "out to infinity". The surrounding magnetic and electric fields are almost entirely within the chassis. Hence, I see no significant problem therein.
However, when we bring signals out into radiating exposed antenna wires, these signals then have their fields expand outward for distances that are significant, compared to their wavelengths. These fields are, then, no longer confined to a few inches or less around a conductor. Significant standing waves develop.
Visualize an inverted "L" or Marconi Antenna. It leaves a low level shack, rises to a roof support and goes through a corner, then sags out to a distant insulator. That sharp corner, at the roof, is after the radiation fields have expanded.
In order for most of the energy that reaches the corner to go around the corner, the fields at the inside of the corner must collapse to insignificance. Depending upon the configuration of the corner and how it is supported, that corner may have a radius of only an inch because of the supporting insulator, or it may be down to almost nothing due to wire twisting at the corner.
This sudden change of field space produces tremendous changes in the impedance gradient at that corner compared to that impedance on the wire before and after the corner.
About 1955, I had a "Windom" Antenna in my attic. For lack of space, I put a square corner in the radiating element. The antenna did not work well. I put a two foot Bonadio Corner Jumper in shunt of that corner.
That produced a surprise. My neon bulb, a voltage indicator, snowed the same amount of brightness on all of the wires involved in and connected to that corner. However, my two volt lamp, by contrast, a current indicator, showed substantially all of the current in the wires to the corner was in the Bonadio Corner Jumper. I could not get a significant current indication from the wires in the corner that were shunted by my jumper.
Years later, my friend Jack showed me his small back yard with four sharp corners, on his 40 meter (CW only) antenna. He had difficulties in maintaining contacts due to his poor signal levels.
I recommended, to Jack, my Bonadio Corner Jumpers. I believe that I suggested three feet of wire with six inches for wraparounds for a two foot smooth curve around his corners. He did that. He claimed that he had to retune his antenna. He was very pleased with his improved signals. So, too, will you be.
One of the problems with Cubical Quad antennas is their sharp corners. If you put a shunt on the four corners, you will shorten the resonance wavelength considerably. The circular corners should have been put into the original designs. An outboard loading would be needed to restore the original wavelengths, and this is, again, another "crowding of a field" problem.
I recommend that antenna corners be shunted with a three foot long wire that uses two feet for a smooth curve and six inches at each end for soldering.
Further, on the Bonadio Corner Jumper, I recommend a nylon string to loop the corner support and the center of the shunting wire, for weather support. The new wire should be stiff. The shape should be the curve of a circle which would touch the shunt from solder to solder.
Even the modest corners in the center of a rhombic have been shown to work better by several wires being spaced vertically past those central corners. That is another way of reducing the corner problem that I have described.
Every installation is different.
Judging from his enthusiasm, Jack probably made over a +10dB improvement. I don't know how to predict how many dB your kinky antenna can be improved. Try it to find out.
Remember, this improvement is only for signals in radiating wires. It does not apply, for example, to the corner produced by a feeder wire (with its confined fields) connecting to radiating element wire. It applies only to a corner in between two radiating lengths of an antenna system.
All right, if you wish, you can call it a Bonadio Corner Shunt, instead, but use it anyway. It can get you dBs that are real, both going out and coming in.
If you have made the previous Part II improvement for +2dB, and say you salvage +4dB herewith, then you have +2 and +4 = +6dB, which is 4x (400% of) your previous ERP (Effective Radiated Power) in wattage. This also applies to receiving.
NORTHEAST AM SCENE
by Bill Wolf - KA2EEV
AM OUTLOOK FOR '89: The prospects of another good year for AM would seem to look very promising. Our activity level remains more consistent than ever and the recent DX propagation has enhanced AM awareness even to overseas hams who have been working us frequently on 10 meters. Combine this with Japanese manufacturers who have made transceivers available with "quality" sounding audio and the picture indeed appears to be in our favor. Regardless of these factors though, we are still faced with the approaching 1990 power regulations.
Dangerous Cathode Voltage: Right now there's a very ugly condition which presently exists here in the northeast primarily on 75 meters. That is, THE ENEMY WITHIN. It doesn't necessarily matter whether we're using a "rice box" or a homebrew kilowatt of AM... and it doesn't even necessarily matter how strong in numbers we are. What matters more importantly is the IMAGE being projected on AM by our stations. Sad to say there are a few within the fraternity who occasionally cause blotches and create a black eye for AM. Certainly there is plenty of room for flexibility to express our various personalities. Lately, however, there's been some "mud slinging" taking place on 75 meters in the form of childish name calling, accusations, and personal character defamation against other AMers! There's something seriously wrong here. At a traditional time of year for making resolutions let's begin to question just who we think we are and keep in mind the glass house from where we cast our stones! C'mon now guys, really. If there's someone on the air who you cannot come to agreeable terms with, and you dislike so intently, then simply avoid them! DON'T SPOIL THE BAND FOR THE REST OF US WITH YOUR SOUR GRAPES BY SPEWING OUT YOUR VICIOUS POISON! Some of you might say this is just a "localized" problem being cause by only a select few... so why bother making an issue out of it in these pages? Well, it's NOT just a local problem because several AMers have been affected throughout the northeast and it's causing division and hurt feelings. Many of you know exactly who and what is being referred to here but I've refrained from using any names or call signs at this point. It's too bad that this column had to kick off on such a negative note, but it's a situation which needed to be addressed realistically because it is currently relevant. Enough said for now.
BACK TO THE FUTURE: Getting back to the original theme ... the AM outlook does look pretty good with the start of another year. There are far more positive aspects going for us now as opposed to the few negative elements previously mentioned. The overview shows that AMers are flanked with technically competent and intelligently minded individuals. We also have a strongly structured S.P.A.M. organization which helps give us favor in the public eye. Even without SPAM, though, the AM community is largely self structured anyway since we all rally to the same common cause ... the preservation of our mode! Then of course you have right before your eyes probably the most vital link which bonds us together ... despite band conditions and distance between us ... we have the AM Press Exchange. Let's emphasize and work at these positive things and hope they'll give AM a stronger advantage during the next year.
Bill Wolf, KA2EEV, at his station
Attention AMers:Having difficulty deciding which rcvr to get for your "AM" station? Find information scarce for making that special choice? Then read on.A book with an extensive cataloging of the different models available over the last several decades is out and worth mentioning. I ran across it recently & found it to be interesting reading. Titled "Communication Receivers" and costing $14.95 (+$2.00 shipping), I bought it anyway. Lightly written, it offers some technical information, lists specifications, has pictures (unfortunately not every model) ranging in quality from fair to fairly good. It also covers a little of the history behind the companies and the people who made these wonderful devices. I think most will find it good reference material for the shack library and others will enjoy reminiscing over receivers they once had.
The sub-title says it all, "THE VACUUM TUBE ERA: 50 GLORIOUS YEARS".
Indeed it was!
It's available from:
P.O. Box 218
Norwood, Mass 02062
(Names omitted, past copy.)
FOR SALE: Gonset "Communicator 11" 2-metre AM transceiver, 12 V and 110 V. Good condition, clean, complete (all tubes and knobs). Instruction manual and crystals included. Please make offer, plus 25 lbs. U.P.S.
WANTED two capacitors, can-type for Heath DX-100, 125 mfd at 450 volts, or can someone tell me where I can get these?
1989 WINTERFEST(tm) Virginia (Vienna)--February 26, 1989.
Sponsor: Vienna Wireless Society 1989 Winterfest.
Time: Tailgate/Seller setup begins 6 AM, General Public 7:30 AM.
Place: Vienna Community Center, 120 Cherry Street, Vienna, Virginia
(off Route 123).
Features: Newly enlarged indoor exhibition area. Breakfast and lunch available.
WANTED audio transformers U.T.C. LS-49 and Chicago BD-2.
FOR SALE: KWM2 and PM2 power supply, plus over $200 worth of tubes. All for $350, so I can buy some more AM equipment.
WANTED, Heathkit HW22 (40 mtr) transceiver and power supply in good physical and operating condition, Harvey Wells TBS-50A 40 w. transmitter with tubes in good physical condition (need not be in operating condition), Millen rack mount 90800 transmitter-exciter with tubes in good physical condition (need not be in operating condx)
WANTED Receivers R7 and National NC-240D.
TRADE: 2 new RCA 810's for PL172 tube.
SELL: Johnson Ranger II, exc. cosmetic/electrical condx with manual and custom CoverCraft dust cover, $125. Johnson 275W Matchbox with directional coupler/indicator and manual, exc. $75. Johnson T-R switch with instructions, exc. $30. Johnson modulator for Adventurer (model 250-40) with manual (copy), exc. $20. Hallicrafters S-119 Sky Buddy II with manual, exc. $25. Heathkit GR-81 regen rcvr, exc. $25. Manuals for Hallicrafters SX-100 Mark 1A (copy), National SW-54 (copy), Squires-Sanders SS-1R and SS-1S (originals), $5 each. All prices firm. Pick-up only on Ranger II, all others plus shipping.
WANTED: Instructions and other information on a Harvey-Wells Model TBS-50D. I also have a Elmac A54 and two Heathkit two-metre transmitters that someone may want to restore.
MODULATION TRANSFORMER: I have a modulation transformer in a wood Thordarson box. It is marked on the box T-11M77 pri & sec variable multi-match. It is a little small for the box and someone wrote "300 watts" inside the box. Open frame, weighs 21 lbs. 3 terminals on porcelain insulators on one side at the top and 6 terminals, screw (8-32) type on bakelite strips on other side. Ham I picked it up from didn't know anything about it. Looks good condx, but have not checked it out. Who needs it?
WANTED: Central Electronics 20A exciter. Also would like info. on converting an HW-12 to 160m.
FOR SALE: HQ170A Hammarlund receiver 160 to 6 mtrs mint $125, power tubes 805's new $20 each, 813's $20 each, many components, modulation transformers, chokes, power transformers; miniature tubes $1 each, octals and loctals $2 each.
This is the AM PRESS:
An amateur radio publication dedicated to Amplitude Modulation.
This is the AM EXCHANGE:
Offering FREE ADVERTISING to enhance the availability of AM equipment and parts.
DISPLAY ADVERTISING: Rates upon request.
Edited and published by Donald Chester, K4KYV
NOTICE: The purpose of this publication is the advancement of Amplitude Modulation in the Amateur Radio Service, and there is no pecuniary Interest. Therefore, permission is hereby expressed for the use of material contained herein without permission of the publisher, with the exception of specifically copyrighted articles, provided that The AM Press/Exchange is properly credited.