AM radio

When I was a young lad, still impressionable I might add, I would listen to the big AM powerhouses at night with my little transistor radio.  I have eluded to this in previous posts.  I have also written an article for Radio World in which I suggest turning AM transmitter off at overnight hours to save money, with certain caveats.  I still listen to AM radio quite often.  I have a Kenwood R-2000 MF/HF receiver which, while not the best technical receiver, is the best-sounding AM receiver I have ever heard.  Its wide AM IF bandwidth is 6.5 kHz, which seems to work very well with the high-end pre-emphasis curves most good AM processors employ.  Music, especially oldies, which were recorded in AM’s hay day sounds spectacular.  There is no other AM radio that sounds as good as this unit.   Right now, the sun has just set and I am listening to WFED 1500 KHz in Washington DC.    They are airing a VOA program called “Issues in the News.”  It’s real red-meat radio.  We are 250 air miles from the transmitter site.

I think there is a place for AM stations, not just merely being satellite repeaters, but making a meaningful contribution to their communities of license.  Unfortunately, I am one of the few that thinks so.  For as long as I have been in radio, AM has been declining.  It is a matter of economics, most GMs would tell me.  That being said, the two three-letter call signs that I worked at were consistently in the top four in the rating book.  Clearly, live local programming was the key to this success.

The notion that they sound bad may or may not be true.  An AM station that has a properly tuned and matched antenna can sound very good.  Using a good receiver, one that has good fidelity, good selection and sensitivity can also increase listening pleasure.  Unfortunately, almost all AM radios being sold today have an IF bandwidth that is only slightly better than a telephone around 2-3 kHz.  This is because… I don’t know.  Originally receiver manufacturers began limiting bandwidth to reduce interference.  NRSC-2 was supposed to limit interference by reducing out-of-bandwidth splatter.  Apparently, the manufacturers didn’t get the word.

Who knows, as the FM band gets filled with shit (interference from adjacent channel IBOC, translators shoehorned in, LPFM’s on third adjacent channels) AM radio might be viable again.

Once the moneymen got a hold of the broadcasting industry, everything was geared toward making money.  Not that making money is wrong, it is certainly good to make a profit, however, with the margins on the FM stations, usually between 25-50%, AM stations were relegated to second place because their margins were much less than that.   Even so, many AM stations were initially profitable during the consolidation and still had some ratings.  Not so anymore.  AM stations also require more maintenance, because of directional antennas and all that is associated with those systems.  What a banker or an accountant sees when he looks at an AM radio station is a money pit.  And, if the station has been run into the ground, it is a money pit.

Still, a small AM at a fire sale price might be fun to rehab.  Launch some type of community radio format, put AM radio back where it was 30 years ago, solidly in the community.  It might be fun.

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5 thoughts on “AM radio”

  1. Many things that were supposed to make AM “better” have done the opposite, and I always look at the Government regulations with skepticism in this regard. Look at NRSC with its stupid Positive Peak limit that was supposed to reduce interference and make AM “better”. Anyone who understands Amplitude Modulation knows that the Positive Peaks do NOT contribute to interference at all. The positive peaks of an AM envelope can go as high as they can with more talk power, but the spectrum is based on the modulation frequency. So we have a stupid regulation that made some dummy feel good while the industry went through a lot of hoopla modifying their Volumax or other peak limiters to limit the positive peak to 125% for absolutely nothing good. The new Ampliphase transmitter that I baby-sitted in 1966 had oscilloscope waveforms of 160% on positive peaks with certain music, while the trapezoidal pattern showed just barely hitting 100 % negative modulation. This transmitter sounded great, but did need knowledgeable people that knew how to ‘tweak’ it. After fooling with it for awhile, I came to like it. But that was before NRSC. We had the new CBS “Twins”, (Audimax & Volumax), which I still believe were some of the best limiting chains that I have ever seen. As for the receivers, most automobile receivers were concerned with noises from generators, spark ignition, road and tire static to be sure. But new designs with synchronous detectors, and better electrical systems in autos would be welcome. Computers are a part of the noise, and the FCC in the last 20 years hasn’t been concerned with controlling noise but instead fostering it! Powell and his promotion of BPL ( Broadband Over Power Lines) is an example. Now another nail in the AM coffin is AMHD, which is about the dumbest thing I can think of as far as the Medium Wave Spectrum is concerned. And the FCC is supposed to be a “Spectrum Guardian”??
    AM Station prices are still over-priced in my opinion, but I agree with the admin, it would be to my liking and fun to pick one up cheap, fix it up and meet the challenge.

  2. I had an ampliphase transmitter in Harrisburg, it was not my friend. The problem with that transmitter was age, the exciter needed some major work. Other than this, as you pointed out, it needed to be attended quite often. That being said, it was fairly reliable as far as staying on the air, it just took a lot of work to keep it sounding good. I don’t disagree with NRSC per se, before NRSC-2 it was a free for all, which led to many of the receiver problems we have today. I think that NRSC, specifically the provision to cut off the frequencies above 10 kHz is needed.

    The FCC in general has been a friend to large corporations (consolidators) and basically does what they ask it to do. Crowding the AM band with far too many stations that create interference, deregulation, removing ownership limits, HD radio, and now putting more and more junk on the FM band. The commissioners have been doing the bidding of various special interests, regardless of the technical aspects of what they are doing. A good example of this is the HD radio power increase, which will cause interference on the FM band.

    Regarding modulation, I seldom run (or rather ran) an AM transmitter with more than 95% negative modulation and would let the positive modulation run at whatever level I could get out of it. Most modern transmitters would run about 125-130% positive peaks w/o difficulty. Older RCA and Gate type transmitters wouldn’t do that. AM HD radio, as well as HD radio in general, will likely fail. No matter what Ibquity does to promote it, it is only lipstick on a pig. Most radio groups won’t buy it because it is too expensive, can’t be used at night and doesn’t sound all that good anyway. Nothing sounds as good as a well tuned AM transmitter/antenna.

  3. I am curious if the admin had a 5 kW Ampliphase model BTA-5L. It had the later solid-state exciter which I hear had problems. My Ampliphase was the BTA-50H built in 1964 and delivered in early 1965, going on the air during the summer of 1965 to proof the 9 tower antenna array with dead carrier while the old BTA-5E remained on the air 20 kHz. higher in frequency. I was hired right out of high school in February, 1966 while a freshman in EE for weekend sign-on at the 50 kW site about 20 miles south of the BTA-5E site. I spent a lot of time looking the 50H over while at 10 kW early in the mornings before sunrise. The tube-type exciter was proven in the BTA-50G which went through many modifications. It was extremely stable. Personally, I believe the 50H was the best Ampliphase out of the entire run of these transmitters. The 50J and 5L used a new solid-state exciter that was pushed out the door with no track record, and I am told was very problematic. This is an instance where the tube design was far superior, but of course, the state of the art had shamed RCA into a poor design. The other thing I have heard about Ampliphase rigs is that they do not perform well below about 800 kHz. My unit was on 1130 and it worked real well. However, we had a trapezoidal pattern displayed on it continuously with a Techtronix 5 inch oscilloscope. The only problem I had with the beast was that it would shut down by itself without warning. And, it happened to me one time when of course I was out at Tower #5 reading base current. I opened the tuning house door, pulled out the shorting switch and zero current! I ran back into the transmitter building (about 500 feet away) and of course the phone was ringing off the hook with an irate studio engineer asking what I was doing! Luckily, I had the BTA-10U filaments still on from earlier, and switched over to it immediately. I re-started the 50H into the dummy load, and of course it came right up. I called the studio engineer and told him what had occurred and he then stated that the same thing had occurred earlier in the week! There were no storms, or anything that I could put my finger on as to the trouble. I switched back to the 50H and watched it closely for overloads, and of course there were none. After about an hour, I went back out to finish reading the base currents of the day array and there were no problems. When my shift ended, I mentioned it to the guy who hired me, and he said the same thing had happened to him on the day shift during the week. The following week when I came in, I noticed on the log that a 2D21 thyratron in the storm detection circuit was replaced, and that further close observance of the transmitter should be adhered to. There were no more problems, and apparently the defective 2D21 was the culprit. As far as Ibquity is concerned, it is simply terrible engineering for AM, and FM as well. An AM transmitter with full fidelity (50-10000 Hz.) and low distortion feeding a low Q load impedance is superior to Ibquity, and the only way to go. I believe Ibquity will be gone on AM soon, and hopefully FM also. As far as the positive modulation peaks on AM transmitters is concerned, many plate modulated transmitters are good for about 130% maximum, and I will never understand why the FCC came out with the 125% maximum. The few transmitters that were capable of higher positive peaks (like the 50H) were few, and were very narrow when tuned correctly. I could drive away from the site on my way home and be in the main lobe, tune off the sides of the carrier while listening to music with huge high-frequency content and the emission was extremely narrow. Of course with the trapezoidal pattern showing excellent linearity, it was proof in the pudding.

  4. I did indeed have the later model BTA-5 transmitter, I don’t remember the letter, it might have been an L. It was installed in 1976 or so, had the solid state exciter and was on 580 kHz, so basically, everything was against it. It was a six tower directional night, non-directional day. As I recall, the day tower was pretty broad, the night array was fairly narrow.

    I hope that IBOC for AM dies an inglorious death.

    I have been fooling around with a Tuned Radio Frequency receiver for AM based on a MK484 IC. It is an exceedingly simple design and yet sounds far, far better than any store bought AM receiver manufactured in the last 20 years. The TRF design seems to be selective, sensitive, stable, etc. One little 3 pin IC, some resistors and capacitors and off you go.

    People have been complaining about AM’s fidelity for years, it is not the technology itself, it is the crappy receivers that make it sound bad.

    Anyway, I’ll put some pictures up when I am finished.

  5. Your 580 kHz. Ampliphase would have been a BTA-5L series as my 1973 RCA catalog proudly displayed it. It used a real dud tube the 7094 which only RCA made to my knowledge. My preference was always high-level plate modulated AM transmitters because of the simplicity and stability into changing load impedances. Granted, they use heavy components, but your old BT-25 lasted long and gave faithful reproduction without much but tube replacements for nearly 50 years. That GE transmitter was a good investment for the owners of 1540 and brought in huge revenues during its time on the air. I hate to say it, but I’m not really impressed with the transmitters of today. Cheap switching power supplies, more reliance on microprocessors and firmware, along with special solid-state devices in a changing time frame that seems to relish buying a new transmitter every few years. In other words, a disposable piece of trash with a huge initial investment. If I buy a AM station, you may think I’m crazy, but I would run a personally rebuilt tube type transmitter with some modifications to improve transmission quality. That would be fun to play oldies that were most likely recorded with tube-type audio consoles, and now broadcast with a tube-type transmitter with attention to the goal of perfection in transmission quality. I have a hunch my station with my plans of web access (not streaming) and localism might just click with the general public. That would be fun to do in my mind.

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