The AM PRESS/EXCHANGE
ISSUE NO. 76                         October, 1989


Status Of The AM Power Issue

The legal power limit for AM is scheduled to be cut in half beginning June 2, 1990, as a result of the FCC's decision to redefine the power limit in terms of peak envelope power. The FCC stated that it was not their intent to change the actual power limit, but to change the method of measurement. Because of a fluke in the mathematics of modulation theory, this change in fact reduced the AM power limit, and the FCC refused to write an exception into the rules to maintain the existing power limit for AM, because this would "unnecessarily complicate" the wording of Part 97. Instead, they grandfathered the old DC input measurement for AM until 1990, and promised to reconsider the issue at that time "if there appears to be any justification to so so."

Since that original decision was made, there have been numerous changes in personnel at the FCC, Including at least three new commissioners out of the five member FCC. We now have the possibility (but no guarantee) that a new Commission with a new agenda might re-examine a decision made by their predecessors. However, unless the amateur community actively exerts some pressure, the most likely action the FCC will take will be to simply sit on the matter and do nothing, letting the power reduction go into effect as planned. The Commission must be reminded by the AM community of its commitment to reconsider.

It will be highly desirable for ARRL to actively support our cause, in the form of a League supported petition for rulemaking. If the League is unwilling to actually submit such a petition, the second best hope would be League support of a petition submitted by individual members of the AM community. Our first step, already in the works, is a letter-writing campaign to the ARRL Division Directors, asking for the League's help in preventing the loss of a privilege presently enjoyed by U.S. amateurs (the present AM power privileges). If the League is unwilling to actively support us in this effort, then it is essential that they at lease offer passive support, that is, not oppose our cause.

Several readers have forwarded copies of letters to their Directors. The reply from Southwestern Director WA6WZO, a SPAM member, was lukewarm, at best: "...I do not see the need (to prevent the AM power reduction), particularly since AM uses more bandwidth than SSB. Also
I doubt we could get the needed support from other ARRL Directors or any large part of the ham community in general. If you can show me support from (other) Directors ... I will be happy to give it more thought... Nevertheless, I will bring the subject up...at the EC (Executive Committee) meeting... I do not see the need to keep (vintage amateur equipment) on the air if they are operated illegally. Surely, we would not want spark gap transmitters to again become legal to use."

A more positive response came from Joel Harrison, WB5ICF, in response to the letter reprinted on page 2, September AM P/X. Mr. Harrison said he contacted Headquarters and discussed the situation, and he feels optimistic that the grandfather clause could be made permanent. He also indicated that he would bring up the issue at the EC meeting.

However, statements by Mr. Bill Cross, an engineer working for the FCC's Private Radio Bureau, cast some doubt about the possibility that the FCC would agree to permanently grandfather the old DC input limit. Mr. Cross reportedly stated that the DC input method of power measurement was hazardous to FCC personnel, who would be required to probe into unfamiliar rigs to measure lethal voltages, and that the Field Operations Bureau had been strongly opposed even to the "grandfather clause" in Part 97, wanting to immediately impose the p.e.p. limit to AM when the power rule change first went into effect.
We will at least have a foot in the door at ARRL if the issue is brought up at the EC meeting. In order to gain widespread support among the Directors, ALL AM'ers who are League members must contact their Division Director. There are fifteen Division Directors (see page 8, any recent issue of QST). EVERY ONE of these Directors must receive SEVERAL well thought out letters, firmly demanding, in a friendly and positive manner, that ARRL support the interests of all its members, including those who operate AM.

Here are some ideas to keep in mind when contacting ARRL Directors and others on this subject:

1. The AM power reduction was not the result of any petition or request by the amateur radio community; the idea was entirely concocted by the FCC as they exercised their own unique brand of logic.

2. The FCC clearly stated in the original rulemaking proposal that it was not their intent to change the actual power limit, but to simply change the method of measuring transmitter power.
 
3. ARRL opposed the AM power reduction, and requested that the grandfather clause be made permanent. The FCC denied the request.

4. A 3 dB power reduction would limit the communications capability of AM stations under poor band conditions frequently encountered particularly on 160 where much of the present day AM activity takes place. But more importantly, the planned power reduction will render many existing amateur transmitters illegal or obsolete unless expensive modifications are performed, which may include replacement of the costly plate transformer. Nevertheless, the FCC admits that under most conditions, the 3 dB reduction would have negligible effect on the actual transmitted signal.

5. The FCC did in fact promise in writing, when Docket 82-624 was adopted, that they would reconsider this issue in 1990 before putting the power reduction in effect.

6. AMers are not seeking special privileges, but are resisting the loss of a privilege enjoyed by all U.S. amateurs. The FCC is about to make something illegal that has been permitted since the earliest days of amateur radio. Another freedom is being chipped away by federal bureaucrats.

7. We are not bringing into question the issue of input power vs. output power for the legal limit. An output power limit which maintains the existing maximum power level for AM would be completely satisfactory. This could be defined in terms of the approximate maximum carrier output power or p.e.p. output, which can legally be generated under the present rules.

FCC Party Line: Levelling The Playing Field

Bill Kleronomos, KD0HG, recently contacted Bill Cross, an engineer at the FCC's Private Radio Bureau, to discuss the impending reduction in the AM power limit. Mr. Cross replied that 1500 watts p.e.p. was selected as the limit for all modes in amateur radio in an effort to "level the playing field for all amateurs." A few years ago John Johnston, also of the Private Radio Bureau, made an identical statement to Ed Bolton, WA3PUN, at a Washington, D.C. area hamfest. Neither Johnston nor Cross were reported to have cited any engineering data that shows that peak envelope power is relevant to the purpose behind having a power limit in the regulations of the various radio services: to limit the interference-causing potential of a signal. An AM signal does not produce more interference in an amateur band just because it reads 3000 watts p.e.p., while a SSB signal of the same average power output reads only 1500 watts p.e.p., and an FM signal reads 1500 watts steady carrier output. Why has the FCC not been willing to back up their claim of the relevance of p.e.p. with documented engineering data?

Mr. Cross went on to question the "traditional amateur spirit" in the AM community because we greeted the power cut with opposition rather than by a resolve to improve and innovate to overcome this "slight handicap."

A detailed account of Bill's conversation with Mr. Cross appears in the October issue of Electric Radio.




Keep Those Articles Coming

In recent months we have had good response from our readers in the form of article manuscripts; we now have a good supply of articles on hand for future issues. Nevertheless, this supply will quickly become depleted unless we continue to steadily receive more articles each month. Especially needed are construction articles on transmitters, modulators, speech equipment, audio processing equipment, AM receivers and accessories, where-to-find-it information, restoration and modification/enhancement of all types of equipment, modifications and techniques to improve audio quality while maintaining good communications effectiveness, vintage equipment and radio history, state-of-the-art AM techniques and equipment, basic AM radio theory, interesting historical and AM radio personalities, news and political opinion, tips on good fleamarkets and hamfests, classic components for constructing authentic vintage homebrew equipment, classic tube-type equipment, the latest in solid-state, and anything else you believe might be of interest to AM P/X readers.

We are less interested in antenna articles at the moment, but please feel free to submit an article on this subject if you think you really have something unique that would interest our readers. Articles on link coupled finals, open wire tuned feeders, balanced line antenna tuners, and other alternatives to the pi-network-to-coax feed system and the "transmatch" are especially wanted.

Once you have submitted an article, please do not assume it was rejected for publication simply because it does not appear in the next issue or two of AM P/X. Articles and photographs are not necessarily published in the same chronological order in which we receive them; they are chosen each month on the basis of how well they fit into the space available, how well they relate to other items in the same Issue, how well they give the issue a good balance, what has appeared in recent past issues, and what we conceive as of immediate interest to our readers. First priority is news of urgent interest to the AM community such as the power limit issue. Often, hot news items at the last minute displace photos and articles we had planned to run. Longer articles tend to take longer time to appropriately fit into an issue for publication. We sometimes run articles that have been sitting in the tray for a year or more.

Several months ago we received a lengthy but well-written article, and just the month we had planned to run it, the exact same article appeared in another amateur radio publication. It was pure luck that we managed to see a copy of that publication before the issue went to the printer. Please indicate if you plan to submit the article to other publications. Some publishers become very upset when their articles appear simultaneously in other newsletters and magazines. This may not be inappropriate or cause any problems, but each publication running the same article has an obligation to clear with the other before articles run simultaneously. If you are not sure your article is going to be published, check with the publication you submitted it to first before sending a duplicate to another magazine. One hint: if you plan to submit an article to several publications, re-write the text for each one so that the information is presented differently, and be sure to use different titles. (This applies to articles, not "Open Forum" type letters; if you can get several publications to publish your letter-to-the- editor, more power to you.)

Finally, if you are dissatisfied or bored with the articles appearing in AM P/X, don't just gripe about it over the air. Write up the kind of article you would like to see, and it will in all probability appear in a future issue.
AMer Receives Citation For "Broadcasting"

Irb Richardt, W2VJZ was recently cited by the FCC for allegedly violating Sections 97.113(a) and 97.113(d)(3) by "making one way transmissions directed to no particular station or stations and involved in subjects not related to amateur radio."

According to the citation, on July 16, 1989, at 2257-2330 GMT, Irb was calling a long CQ, interjecting comments about freedom of speech, the U.S. Constitution, liberty and justice, and excerpts from a publication called the Spotlight. Despite the fact that he stood by every five minutes or so and listened for callers, the FCC monitors decided Irb had committed a violation of the rule against broadcasting: "It appears that W2VJZ continued broadcasting until such time as another station answered one of his calls." However, the text of the citation specifically includes a call by N2IFY at 2319Z, with a two way exchange of communications, all within the time period of 2257-2330 when the FCC claimed W2VJZ was in violation of the rules. The text of the citation continues, "((QSO continues back and forth and W2VJZ reads more, and they both discuss it and give their views/opinions etc.))"

In a letter to The AM Press Exchange, Irb stated: "...perverted and deluded 'hams' seem undisturbed about the destruction of the U.S. Constitution, but they follow me with a vengeance and break in to tell hams who respond to my CQs with 'Don't talk to him. That was an illegal CQI'!  They say that it is illegal to call 'CQ brotherhood, CQ the fraternity - no Factions, Cliques or Classes, CQ the real voice of America - amateur radio, CQ The Press Exchange, CQ the Spotlight, CQ Freedom of speech, CQ the U.S. Constitution, CQ liberty and justice for all, CQ Christians, CQ Americans etc. Yet they then go out and call CQ ARRL, CQ DX, CQ classy contest, CQ Union of Soviet Socialists etc.!"

In his official reply to the FCC, Irb included the following statement: "Many years ago I framed and hung in my casting-abroad studio a print-out of a 'one way' broad-cast by the corporate ARRL radio station W1AW, because certain elements were claiming that we-the-people individual radio broad-casters were not allowed to do likewise.
"I have since heard many broad-casts from another corporate radio station of the IARN, K1MAN, and after their Sunday evening 'one way' broad-casts conclude I pick up their frequency and commence to cast my radio waves through the air. Amongst other things I respond to the K1MAN broad-cast which is usually quite provocative and includes letters to and from Mrs. (President) Bush, to and from USSR Premier Gorbachev etc..."

EDITOR'S NOTE: This whole matter of amateur "broadcasting" and "bulletin" stations has long been a delicate issue. Evidently, the FCC presently interprets the rules to mean that one way Broadcasting is OK as long as the subject matter is limited to amateur radio topics. However, there is one loophole open to anyone who wants to "broadcast" non-ham subject matter.

It can be made perfectly legal by simply joining up with a like-minded amateur radio partner and making the broadcasts in the form of two way dialogues between licensed amateur stations. Ideally, both stations would have strong signals with wide coverage areas and be located in the same geographical region of the country. As long as both stations comply with the rules on station ID, music, profanity, etc., the FCC would have to go far out on a limb to cite two amateurs in legitimate QSO for the subject matter content of their conversations.
Saga of the AM Power Reduction: Documents Available

You have heard plenty about the 1990 AM power reduction over the air, and you have read about it in the pages of AM P/X and other amateur radio publications. You may wonder why some AMers are so concerned over this issue, especially since it actually affects only a minority within the minority AM community, those of us running over 500 watts DC input to plate modulated transmitters. Most amateurs have not seen the actual FCC documents related to Docket 82-624, but have received only second hand information.

Without fail, those who read through the official government documents and see first hand the seedy manner in which the AM community is treated by FCC officials, immediately develop a sense of outrage and frustration. Unfortunately, because of the length of these documents (22 full pages), the material would more than completely fill an entire issue of AM P/X, and therefore we have run only selected excerpts from the official documents, and summarized accounts of the proceedings.

We feel more AMers would become motivated to actively participate in the campaign to retain the existing power limit, so AM P/X is making the entire proceedings available upon request.
(Web editor's note - these are no longer available; this issue is from 1989.)


FCC DOCUMENTS AVAILABLE
(Web editor's note - these are no longer available; this issue is from 1989.)

This packet of documents includes:
(1) The original FCC Notice of Proposed Rulemaking.
(2) The Report and Order officially adopting the p.e.p. limit.
(3) Petition for Reconsideration submitted by Donald Chester, K4KYV, Editor and Publisher of AM P/X.
(4) Memorandum Opinion and Order rejecting all the Petitions for Reconsideration submitted.

A copy of the complete set of documents, printed at our expense, will be sent to anyone upon request. Please include $1.00 in cash or postage stamps to cover the costs of postage and the mailing envelope. (Web editor's note - these are no longer available; this issue is from 1989.)



OPEN FORUM


Editor, The AM Press/Exchange:

Great article on the W8ZO estate! The description on the AM Swap Net got me into the old Dodge van and on the road to Ypsilanti the next morning. I planned to get there early Saturday to have first pick, but my alternator blew out in Ontario, so I had to stay over. I got to W8ZO past noon to find another Dodge van filling up with racks. A family of hams (at least 3 sons) from Marion, OH had glommed onto the 2 KW rigs (20 & 80 m.). This was OK, as I wanted to supplement my T-368E which does not cover 15 and 10 metres. I looked in vain for a 15 m. rig. The T-55/838 rig looked like 10 m. I could not resist the 7' tall Motorola police rig (FM, 2- metres), an RME DB22A and VHF152, HT-37 and BC1267. I found a few extra T-55's, 838's (new in JAN boxes) for the 10 m. homebrew rig. Both sons helped haul it all up and I was back on the road for a smooth 600 miles home, thinking about those great 125' Baul-Knox towers and just exactly what that big bottle was in the KW rig in the back room.

Twelve days go by and I just had to call Ypsilanti. Nothing had been sold since I left. Back I went this time arriving late PM and sleeping over at the gate. Woke up to a blue sky and those red towers and antennas overhead. What inspiration! Looked through the 5 KW transmitter in the yard for a modulation transformer. Must be in the bottom somewhere hidden by dozens of chokes, caps, etc. Should have brought my ox-acet. torch. Maybe next time!

I helped myself to the homebrew 160 m. rig (single 8005) probably built as a pair, but changed when band power was reduced... a beautiful and strange small-size rack perfectly symmetrical in appearance jammed full of all sorts of odds and ends. It was working and was hooked up fully as was the "10 m." Also took the mystery 851 rack with no modulator. Good thing too as the thing was heavy enough with that 1400 watt Thordarson (1900 primary v-a). I looked up the 851 in the C-E book, and it should make a nice rig and I hope to complete it someday. Part of the fun of all this is trying to figure out what W8ZO had in mind or what setup he used, especially with all those antennas and feeders.
Finally, I hauled out the mystery rack with Lampkin FM mod monitor, Bendix freq. monitor, BC-639 2m. (FM?) receiver, Motorola (10 m. AM?) rcvr, Thordarson mike amp, and three Thordarson speech amps. Best yet, we found original books for all the commercial gear I'd bought.

So thanks again. I thought the readership would like to know where all the old goodies went. By the way, Jeff (W8ZO's son) is keeping the old 203A 160 m. rig with bakelite panels for his antique radio collection. When I left, the only rig remaining is the old 807 type (cannibalized somewhat). There is also a 75A4 available for $300 and a HT37 for $75, both units in nice condition.

The family in Marion OH will enjoy the two KW rigs, and the five racks I got will grace my new shack and inspire me to get my code up and get a license. I've been into ham radio since 1955 or so, but never got a ticket.

William Dudan
R.D. # 1
Cambridge, N.Y. 12816




Editor, The AM Press/Exchange:

Many thanks for the fine article on Dad's equipment (W8ZO Estate), in the AM P/X. I had very good response from that, and also from your advertising on the air. Most all the racks were gone even before the article came out. The only thing left is a couple receivers (75A4 for $300 ? - Ed.) and one or two racks. Once again, thanks for the help in moving the equipment; it was greatly appreciated.

Sincerely,
Jeff Gault
2571 Seminole, Ann Arbor, MI 48103
(303) 973-6445 or 434-0490




Editor, AM P/X:

It seems to me that Docket 82-624 was a challenge to the AM fraternity. What argument could we make for our exemption from its peak power limit? Unfortunately, many reactions are quite belated. It may already be too late to affect the Part 97 rewrite, but this ought to be done anyway: I CALL ON THE AM COMMUNITY TO CLEAN UP ITS ACT, AT LEAST AT THE TECHNICAL LEVEL.

Not to be negative, but I figure it's going to be real tough to get the FCC to allow AM stations to operate according to anything like the old IKW DC input rules. They will probably act to close the upside-down-tube loophole inherent in the DC input limitation. They will went to take the easiest path, which will be to maintain the planned 1.5 KW PEP limits. Unless something changes, we will have to give them an easier path, and/or massively justify a complicating exception to the general power limit rules. Anything that makes this task any harder is bad news for us.

Amateur AM is an exceptional training ground for broadcast and recording engineers. And, as Ed, WA3PUN, has said, many new hams have been SWL's who discovered amateur radio by tuning across AM stations on the bands, and an understanding of AM is the basis for an understanding of all other modes of modulation. Working with AM at the level of DSBRC, synchronous detection, etc., gives a unique insight into the workings of advanced communications systems such as are used in digital data modems, satellite communication, etc - fields of electronics which are far from obsolete! So there is some justification for AM into the next century. But what about power?

Ultimately, it's a question of interference. Generally, the radio regulations have been designed to ensure a minimum interference environment to the various services, with the highest priority users enjoying the least interference.

AM as such is no more of a problem for users of other radio services than CW, FM, SSTV, SSB, etc. It may be argued that an AM signal would produce a little more neighborhood RFI because of its higher peak power, but a difference of 3 to 6 dB would probably not affect the situation. Changes of 10dB or more are necessary for a perceived change in most cases.

Because of the rectification effect, RFI from AM, CW and SSB can be more troublesome than RFI from FM - but nobody would call for conversion of all amateur radio to FM operation.

The RFI susceptibility of the affected equipment is not the fault of amateur radio. However, the FCC gets all these complaints, and they don't want to be bothered, so they just impose quiet hours or something. It's much easier to muzzle a non-profit amateur than it is to force manufacturers and importers to equip their products with RF filtering and shielding.

An AM signal does not produce more interference in an amateur band just because it's 300OW PEP (or more) instead of 1500. if i t produces more interference, it's because of the bandwidth it occupies. At best, it will be twice as wide as clean SSE. At worst .... well, I regularly hear amateur AM stations with significant splatter 10 to 20 KHz away from the carrier, and usually this is not because of superior hi-fi audio. Some amateur AM stations overwhelm anything within about 10 KHz of the carrier, producing heavy and unnecessary interference, while other equally strong stations, on AM and SSB, are clean and make good radio neighbors. Yes, we went to dominate our channels, but it behooves us to contain ourselves, especially when the bands are crowded. Nearby groups don't all jump on the frequency and complain, but it's not because they're happy - and when they do complain to us, we usually just tell them to hit the road.

Every petition which may be made to ban AM, reduce its power, reduce its bandwidth, etc, reduces the chance that AM may be exempted from the 150OW PEP limitation. It's too late to prevent them altogether, but we may be able to reduce the damage if we can clean' up our technical act, which we ought to do anyway. What I'm saying is that we ought to make our rigs able to concentrate their firepower in a realistic bandwidth such as 8 KHz. As it is now, the northeast 3885 AM group typically splashes from 3877 to 3893, and everybody from 3870 to 3900 knows when we're fighting SSB, which is about every night, because OUR splatter QRMs them. Meanwhile, the SSB clowns we're fighting are relatively clean!

And why shouldn't they come and fight us? We clobber them whether they are on our frequency or not. By moving in on us, they can at least fight back. And their strike is more selective than ours. All right, so we're going to fight them; must we punish a dozen other groups as well? It doesn't make sense to me. It sure doesn't make friends on the air or at the FCC.

Demand and pressure for spectrum space continues to increase. Some years ago, the standard business radio FM deviation was reduced from 15 KHZ to 5 KHz to reduce bandwidth, so that more users could fit onto the crowded bands. Right now, some SSB hems (the vast majority of amateur HF voice operators) are calling for the outright banning of AM on the HF amateur bands, because of bandwidth. The FCC probably doesn't want the burden of enforcing such regulations, so this will probably not happen. still.... Communications Canada evidently has a 6 KHz bandwidth limit for amateur AM right now - and, significantly, the CHU standard time and frequency broadcasts use single-sideband with carrier.

I think it behooves us to demonstrate that AM is not a problem. Perhaps if we can do this, we will not face as much opposition.

Robert E. "Bacon" Bruhns, WA3WDR


MEET THE AMers

Bob Dennison, W2HBE is shown beside his homebrew 35 watt 160 metre rig. The tube line-up is as follows: 1852 VFO, 42 crystal oscillator/buffer, 807 class C final, 6SJ7 speech amp, 6J5 driver, pushpull 6L6-G class AB1 modulator. The rig has automatic modulation control with fast attack/slow decay, used in conjunction with a modulation monitor.
Bob is a member of SPAM.

"If I look tired in the photo, it's because the XYL broke her arm and I'm doing the cooking, shopping, laundry, etc. But I still keep my Monday night sked with my friend Jack, whom I introduced to ham radio back in Salina, KS in 1936."



ELECTRET CONDENSER MIKE WITH EQ FOR AM TRANSMITTERS
BY BEN GIORGI, K1PTS


1. The circuit shown in the wiring diagram will improve the audio of most AM transmitters.  However, it will not do much for those transmitters that are designed with restricted audio unless all of the stages of the complete modulator have been upgraded.

2. The AM Press Exchange has provided many of the required changes that have been submitted by AM fellow hams.  This article does not cover those specific changes.  However, I will mention the four major areas that will affect good AM audio quality.  (1) Final modulator stage, (2) driver stage, (3) speech amplifier stage, (4) microphone and speech processing stage.  These stages form the audio stage or train, and deficiencies in any of these four stages can cause problems and reduce the overall AM quality.

3. Let's assume that the above-mentioned (1), (2) and (3), have been examined, and are in good shape.  We can now improve the audio system by wiring an electret condenser mike as shown.  Although the part list shows Radio Shack part numbers, any equivalent component that you may have on hand can be used.  The first thing to do is to check your shack for an old discarded mike stand.  Then check for any equivalent parts that you might have in accordance with the first list shown.  When all of the needed parts are on hand, the assembly and wiring can begin.

4. Physical Assembly

4A. Check the base of the mike stand to see if all parts will fit, including the battery and the switch.

4B. Drill a hole and mount the switch.

4C. Check for access for cables CA1 and CA2.  If the mike stand has high bumper foot mounts installed on the bottom, no access hole is needed.  If a cable entrance hole is required, drill one clearance hole in the base of the mike stand for cables CA1 and CA2.

4D. Open the front mike screen, and remove any old mike element or wiring.

4E. Install a piece of foam cut to fit the shape of the mike head installation area.  (See Note 1 on the wiring diagram.)

4F. Check to see if the new electret mike element will fit into the mike head installation area and behind the mike screen.  Upon completion of the above, wiring of the electret mike circuit can begin.

5. Wiring (Refer to wiring diagram.)

5A. Connect and solder B+ circuit including R, a 10K resistor.  (See Note 2 on the wiring diagram.)

5B. Connect and solder C2 (47uF capacitor) across BAC (the battery connector).

5C. Connect and solder the black wire of the BAC to the switch.

5D. Connect and solder the center conductor of the shielded mike cable to the positive side of capacitor C1.  Connect and solder the center conductor of cable CA1 to the negative side of capacitor C1.  Connect and solder jumper W2 between these cable shields.  Connect and solder wires W3 & W4.  Install connector P1 on the end of cable CA1.

Always observe the waveform changes on a scope after any new audio adjustments.  Note: the amount of increases of highs and lows that can be insterted by the EQ will depend on the rest of the transmitter audio chain, as mentioned in paragraph 2.  For instance, poor or limited frequency response that may exist in any of the audio chain stages will produce distortion upon increases of lows or highs or both.

I believe the microphone presented here is a worthy project, since it is simple and inexpensive.  Extensive tests that were made prove it to be an excellent quality AM microphone, having audio frequency response adjustment parameters that are necessary for high quality AM transmitters.  Final note: the EQ shown may not be available.  However, an equivalent can be substituted.



The Electret "Condenser" Microphone
(Application Note)
Mike Koscak, WA1MTZ


Often I have been asked, "How do you hook up that thing?  I tried it, but it didn't give enough audio, or it sounded muffled!"

There are basically two types of small electret microphones that show up in the market these days... One type has two pins that exit from the bottom. The other type has a short shielded lead and a seperate lead to power the unit. The output impedance is 1-2k ohm, so a means to match impedance may be required in your case. The simplest thing would be to use a transformer, or you can use an active circuit. These mics are very low cost, Hi-Fi, and physically small, so that it is easy to retrofit any existing mic element. The mic with the separate wire has an internal amplifier, and accepts a wide range of voltages. The two-pin unit must be voltage-limited.

These electrets don't exhibit as much low frequency "proximity" effect when speaking at a close distance as most directional dynamic mics, but they will not tolerate high sound pressure, as they are prone to distortion when subjected to such. Fig. 1 is a simple setup that is used in conjunction with an Elmac AF-67.  C1, C2, R1 and R2 are used to filter the automobile D.C.  Fig. 2 is a universal hookup useable with any Hi-Z input, or a low-Z balanced input if a transformer is used. Fig. 3 is highly amplified!

Walk away from the rig and still be heard, or stick it out the window to broadcast the birds, or the cat's purr-motor!



EXCHANGE
(Contact information removed; this issue is from 1989)


WANTED: Top cover for R-388/51J receiver, front panel for RCA AR-88 receiver. Call collect, or write.  Howard, W3HM

AM ROCK CRUSHER for sale or trade. The famous "One Ton Kilowatt" is a 1949 B&W BC339N with external homebrew modulator. The BC339N has exciter with VFO for driving single 813 driving pr. 833A's. Modulator is pr. 6C5's driving pr. 211's driving pr. 833A's, with commerical grade UTC transformers and chokes. $500 (firm) or swap for mint Collins T-368 or 30K__. Send SASE for photos and other data. SERIOUS INQUIRIES ONLY. Mike Carroll, NI4N

WANTED: UTC S-62 filament transformer and National R-175 or R-154 RF choke. James T. Schliestett, W4IMQ

WANTED: Manual for Heathkit DX-100B. Will pay for shipping and copying. Marty Drift, WB2FOU/5

WANTED: Schematic for maring transceiver, Pearce Simpson, Bimini 50. Also wanted: 2 to 3 mhz marine transceiver (tube type or hybrid) for conversion to 160 and 75 ham use.  Blase, W7JSJ

WANTED: Mint Heath Twoer, Tener, and CB-1.
FOR SALE: Lafayette HA410 (10 M AM) in super-clean condition with 10 crystals, AC/DC cables, mobile mount, manual, mike. $110 shipped. Lafayette HA460 (6M AM) in very nice condition with 5 crystals, AC/DC cables, manual, desk mike. $75 shipped. Another HA460 in good condition with AC cable, manual, mike. $50 shipped. Will consider trading Lafayette rigs for mint Heath gear. Harry Schools, KA3B

FOR SALE: RME DB22A preselector.  540 kc - 42 mc in 4 switchable bands. This is the later version with grey wrinkle case. (Original?) chrome metal tuning knob. Circuit consists of 2 6BA6 tuned RF stages with built-in power supply. Good physical condition and worked when recently checked out, but paint has some scratches. No manual. $30 plus shipping.
WANTED: UTC LS-18 high level 500/600 ohm line to pushpull grids input transformer, LS-49 Class-B driver transformer, Chicago BD-2 driver transformer.  K4KYV

FOR SALE: TMC SWR-1K/power meter $75, UTC S-22, Stancor A3895 Modulation Transformers new $35 ea. Elmac AF-67 $50.
WANTED: TV-2, 852 and 75TH tubes. Parker, W1YG

WANTED: AM transmitter to go with my Collins 75A-3. Since TVI is a concern I would need a late model rig of some kind, such as Viking Ranger I or II, or 32V-3, or other rigs built in the television era. Particularly looking for Johnson Viking Ranger II clean, in very good working condition, with manual. K8LZF, Tom Russel

WANTED: 32V2 or 32V3 Collins transmitter in working condition that is not all butchered up. Gary Elliott, K7OX

FOR SALE: Two 19 inch enclosed AEK enclosures black wrinkle finish, one is 34" high, other 37", $50 each. Dow coaxial relay 119 volts $20 each, limited supply. Powerstats and variacs 15 amps at 110 volts $50 each. Tubes type 7C5 new boxed $2 each no limit. Inquire on others. Levy (the tube man) W5QJT



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.

Subscriptions $10 per year (12 issues) in North America.  Classified ads (AM related) free of charge to subscribers and nonsubscribers.  Display advertising and foreign subscription rates on 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.