History is one of my interests. Working in Radio over the years, there is plenty of interesting history that surrounds the first electronic mass media. My parents grew up in the depression/WWII era. For them, radio was a vital information source. Listening to FDR’s fireside chats about the economy and the progress toward recovery was a friendly voice reassuring them that times were indeed difficult but they would get better. Then the shock of the Pearl Harbor attack on December 7th rippled through the airwaves on a Sunday afternoon. These are the life long memories of my mother, who is now 92.
Preserving some of this history for following generations, who take the free flow of information for granted, is a worthwhile cause. Thus, I want to visit, then write about the many Radio Museums around the country. Each is a little bit different with its collection and interpretation of radio history.
Over the Christmas/New Years holidays, my SO and I went on a road trip around Western North Carolina and Virginia. We visited the Asheville Radio Museum along the way.
One thing that I found interesting is the People’s Radio. This was from Nazi era Germany (1933-45).
Folks Radio
This radio only had medium wave and was designed only to receive radio stations from Nazi radio stations. In order to possess a radio, a permit from the government was needed.
Nazi German Broadcast permit
Having a radio receiver without a permit would lead to an arrest and possibly being sentenced to death. In addition to that, getting caught listening to a non-Nazi radio station would result in arrest, imprisonment and later in the war, possibly death. It was no trivial matter.
Atwater Kent console with Philco table top receiver
Older radios were often treated as a piece of furniture. My parents both said that evenings were often spent sitting in the living room listening to the radio. Radio dramas were performed live and included programs like Amos ‘n’ Andy, Mercury Theater of the Air, Jack Benny, Ed Sullivan, The Lone Ranger, The Fleischmann’s Yeast Hour, Calling all Cars, The Answer Man, Dick Tracy, Death Valley Days, The National Barn Dance, to name a few.
Early tabletop radios were powered by batteries1935 Zenith Stratosphere 1000Z console radio Zenith Promotional Materials
The top of the line console radio was the Zenith Stratosphere 1000Z. The porcelain cat was a notable feature for these radios.
The Asheville Radio Museum holds Amateur radio license W4AFM. They have a decent display of vintage Amateur radio gear.
Old Amateur radio circa 1915Collins 30-S-1 HF Linear AmplifierAN T-74/CRT-3 life boat transmitter
This is a WWII era life boat radio which transmitted on 500 KHz and 8,280 KHz. It was powered by a hand crank and could send an automatic SOS or a CW message could be sent manually by the key button. The round door on the front contained a wire antenna. After 1947, the HF Lifeboat frequency was changed to 8,364 KHz, which remained in use until about 1992.
There are several other displays on early telephones, the proximity fuses developed during WWII and so on.
The Asheville radio museum is located in room 315, Elm Building, A-B Technical Community College, 16 Furnihurst Drive, Asheville, NC.
Special thanks to Stuart Smolkin for coming in on his day off to give us a tour.
This is not a new idea, many people have discussed it in the past. The National Radio Systems Committee (NRSC) has a guidance paper, NRSC-G102 which gives a detailed explanation of why synchronized AM carriers are beneficial. There was even a move by some to have it included in the AM revitalization plan of a few years back. The NAB opposed this idea, saying it would be too expensive. That is unfortunate because out of all of the revitalization initiatives, GPS locked carriers had the best potential for an actual technical improvement. While it may be expensive for some very old tube type transmitters, for more modern solid state transmitters, GPS referenced carriers can be implemented as little as $200.00 US.
The FCC rule (73.1545(a)) for AM Carrier frequency specifies:
AM stations. The departure of the carrier frequency for monophonic transmissions or center frequency for stereophonic transmissions may not exceed ±20 Hz from the assigned frequency.
40 Hz is quite a bit of movement on a 20 KHz AM (18 KHz in ITU region II and III) channel. The reason for trying this is simple; there are many co-channel and first adjacent channel AM stations which at night, interfere with each other.
Typical AM spectral mask
Above is a typical spectrum analysis of an AM station on 940 KHz. This was a 10 minute peak hold for an NRSC-2 spectrum mask measurement. The carrier is approximately 20 dB greater than the audio, which means that most of the interference between co-channel AM stations is created by the carriers beating against each other. By locking carriers to the same reference, that carrier interference will be greatly reduced. NRSC-G102 goes into great detail on the listenability of interfering stations with synchronous AM carriers (Page A-3).
Stations drifting off frequency also cause greater adjacent channel interference.
Almost all transmitters made in the last 30 years have an option to use an external frequency generator or 10 MHz reference. The required drive levels vary. The easiest way to implement this is by using a GPS locked programmable frequency source such as the Leo Bodnar LBE-1420. It can be programmed to any frequency from 1 Hz to 1.1 GHz, has a frequency stability of 0.000001 PPM (10-12), and an output level of 3.3 V peak-to-peak. This drive level is not enough for some transmitters. For those situations an additional amplifier such as a Mini Circuits ZHL-3A+ is needed.
Here are a few AM transmitters that except an external RF source including a GPS disciplined oscillator.
Nautel J-1000
An external RF source can be plugged into the EXT RF IN connector (J-6) on the Remote Interface board. The source must be on the carrier frequency ± 5 Hz and have a peak-to-peak voltage of between 5 – 15 V (sine wave or square wave), 50 ohm impedance.
Nautel J-1000 external RF input
An external 10 MHz signal can be connected to the RF synthesizer board 10 MHz REF INPUT (J2). The external 10 MHz frequency reference must be precisely 10.00 MHz and have a peak-to-peak voltage of between 2.2 – 8.0 V (sine wave or square wave).
Jumpers on the Remote Interface Board and RF synthesizer board need to be configured appropriately for each source. Consult the manual pages 3-9 and 3-11.
Nautel ND series
An external RF source can be connected to ABA1J1 on the external interface board. The RF drive must be on the carrier frequency ±5Hz with level of between 5 – 12 V peak-to-peak (sine wave or square wave) and have a 50-ohm impedance.
Nautel ND-1 remote interface board
Do not remove the crystal from the RF Drive board as the PDM frequency for the modulator is derived from it.
To select the RF drive source for the transmitter the links on the RF Drive board need to be changed. Consult the manual pages 3-3 and 3-14.
Nautel XL series
An external 10 MHz signal can be connected to the RF synthesizer board 10 MHz REF INPUT (J2). The external 10 MHz frequency reference must be precisely 10.00 MHz and have a peak-to-peak voltage of between 2.2 – 8.0 V (sine wave or square wave).
Nautel XL-12 10 MHz reference input
An external RF frequency source can be connected to the Exciter Interface board, J7. The external drive signal must be between 5 – 12 volts peak-to-peak (sine wave or square wave). Consult manual pages A1 and B4.
Nautel XL-12 external RF input
Nautel XR series
An external RF source can be connected to the remote interface board’s digital EXT RF IN (J6). This replaces the internal carrier frequency oscillator for one or both exciters (A/B). The external RF source must be the carrier frequency, within ± 5 Hz, have peak-to-peak voltage between 5 – 12 V (sine wave or square wave). Consult the manual pages 7-1.
Broadcast Electronics AM2.5 – AM10A, AM5E
The transmitter has an external RF input on the top of the unit (EXTERNAL RF INPUT). The input is designed for an external stereo generator or reference oscillator with a signal level from 5 to 15 volts peak-to-peak. To use this input, program jumper P7 on the exciter circuit board in position 1-2. Consult the manual page 2-19.
Broadcast Electronics AM500 – AM1A
The transmitter has an external RF input on the ECU rear-panel (EXTERNAL STEREO RF INPUT (J1). The input is designed for an external stereo generator or reference oscillator with a signal level from 5 to 15 volts peak-to-peak. To use this input, program jumper P7 on the exciter circuit board in position 1-2. Consult the manual page 2-20.
BE AM1A external RF input
Harris Gates AM series
An external RF source can be plugged into J-1 on the Oscillator board. The source must be on the carrier frequency ± 20 Hz and have a peak-to-peak voltage of 5 volts. Frequency source selector P-6 must be set to external. Consult the manual, Oscillator Board Schematic.
Harris DX series
An external frequency generator can be connected to J2 on board A3. Jumper P5 should be set to either 20K ohms or 50 ohms depending on the source impedance. Jumper P6 can be set to either external source or automatic source selection. The drive level needs to be 4 to 4.5 volts peak-to-peak square wave for high impedance inputs or 0 to +25 dBm for 50 ohm impedance sources. Consult the manual, page A-2.
Newer DX series oscillator boards which have automatic source selection will fail over to the internal oscillator if anything happens to the externally generated RF signal.
Harris DAX
An externally generated carrier frequency or 10 MHz reference signal can be connected to connector J11 for the external carrier or J10 for the 10 MHz reference on the External I/O board. External carrier or 10 MHz reference must then be enabled via the VT100 screen. The external carrier frequency or 10 MHz reference must be above 2.0 volts peak-to-peak. Consult the manual page 3-15.
Harris 3DX
An externally generated carrier frequency can be connected to J12 (RF CARRIER) jack on the external IO board. The drive levels need to be 4 to 5 volts peak-to-peak, square or sine wave. On the carrier frequency +/- 5 Hz. The input is impedance is selectable for either 50 ohms or 10 K ohms.
An externally generated 10 MHz reference frequency can be connected to J10 (10 MHz REFERENCE). 10 MHz reference level needs to be 1 to 5 volts RMS, square or sine wave. The input impedance is selectable for either 50 ohms or 10 K ohms.
Programming for these options is done on the exciter setup page. Consult manual page 2-43.
Harris SX series
SX series transmitter have either an oscillator board or a frequency synthesizer board. Both will accept an external frequency source. The oscillator board is A16J1 and it needs a 5 volt peak-to-peak carrier frequency signal. Frequency source selector P-6 must be set to external.
The frequency synthesizer board external frequency input is also J1, however, it requires a 10 volt peak-to-peak signal. Frequency source selector P-6 must be set to external.
Conversion table for various RF power levels into a 50 ohm impedance
Volts, Peak-Peak
Volts, RMS
dBm
mW
2.2
0.77
10.8
12
3.3
1.23
14.35
27
5
1.76
17.9
62
10
3.5
23.9
250
12
4.24
25.5
360
15
5.3
27.5
562
20
7.07
30
1000
A 10 MHz reference input is preferred over direct carrier frequency generation simply for the ease of implementation. With direct carrier frequency generation, the frequency output of the GPSDO needs to be double checked. One misplaced digit and severe damage to the transmitter can result.
AM Tube type transmitters, plus early solid state transmitters such as the Harris MW1A may have instructions for implementing AM stereo. Since the AM stereo exciters generated the carrier frequency, those instructions would be a good guide on how to connect an external frequency generation source. However extensive modifications may be needed to the oscillator section depending on the transmitter.
Honestly, this is cheap enough that I think all new AM transmitters should come with this from the factory.
Any radio station’s on air signal is its biggest marketing tool.
What sounds bad:
Over use of compression (gain reduction)
Over use of high frequency EQ
Over “equalization” on all frequencies
Over modulation
Overly aggressive composite clipping
Improper use of FM pre-emphasis
Poorly tuned transmitters (tube type)
Poorly matched antenna systems (all types)
Poor quality audio input
Over use of bit reduction on the STL
Analog STL’s that are off frequency
Playback of bad audio recordings
What sounds good:
Moderate use of compression to bring up audio levels for in car listening
Using equalization that suites format (e.g. more mid-range for all talk, more bass for urban, etc.)
Properly adjusted processor output levels for the correct modulation levels
Setting the pre-emphasis correctly
Tuning tube type transmitters for minimum distortion
Tuning antennas for adequate impedance and bandwidth
Making sure that audio input levels are correct, the audio is properly distributed and terminated with the correct impedance
Using STLs that have enough throughput that either no bit reduction or minimum bit reduction is used
Regularly check analog STL frequencies and re-adjust as necessary
Get rid of all bad audio recordings in the automation/playback system. Make sure that new files are from good sources and/or are re-recorded correctly
I took a little road trip between Christmas and New Years (Happy New Year!). I cannot help myself, I ended up tuning around the radio to see what was on. Suffice to say, I found the usual formats and a few locally focused stations. What struck me was the sound of some of the stations. While most sounded acceptable, if not somewhat generic, there were a few that had ear splitting, headache inducing audio. These stations were often over modulating and way over processed. It would have been better if there were no processing at all.
That got me thinking, what is or rather what should be the point of audio processing? Way back in the day, there were loudness wars. These were often program director ego induced efforts to sound louder than the competition because if you were louder, it meant you had more power. As listeners tuned their analog car radios from station to station, the signal that “jumped out” was mostly likely to attract more listeners. At least that was the way it was explained to me in the by a program director in the late 1980s.
We are no longer living in a listening environment where loudness is of huge importance. The number of audio sources has increased greatly; iTunes, Amazon Alexa, Spotify, Tune in, Pandora, YouTube Music, Sirius XM, iHeart, and AM/FM radio. Audio levels can be anywhere and listeners have gotten into the habit of raising or lower the volume as needed. Outside of program directors (or whatever they are called these days) offices, loudness means next to nothing. If you asked an average audio consumer how loud their program sounded, they would not likely know how to answer you.
I believe what most people are looking for is an enjoyable listening experience. The most important quality of any type of audio processing is that the product sounds good. The problem is “sounds good” is very subjective. Perhaps a better term would be technically sounds good. The audio should be free from distortion and artifacts of CODEC bit reduction. Overdone AAC or HE-AAC has this strange background swoshy platform behind everything which is headache inducing. Instruments should sound as they do when heard live. In other words, Susan Vega’s voice in the original Tom’s Diner should sound like Susan Vega.
Next would be compensating for difference levels in program material. A bit of gain reduction so that those in mobile listening environments can hear all of the program material. Finally, some format specific equalization can be useful. That is it. Moderate use of various audio processing tools can certainly accomplish those things. Like everything else, too much of a good thing is bad.
The public TV viewers in the St. Lawrence Valley get an updated transmission system. I recently finished installing this GatesAir ULXTE-6 transmitter in South Colton, NY. That is way up on the very northern fringes of the Adirondack Mountains. It replaces the Thales CCT-U-TDU2 8KW UHF TV transmitter, which was installed around 2004, early on during the analog/digital TV conversion.
WNPI-DT coverage map
South Colton, NY is home of Sunday Rock. According the the historical marker:
This glacial bolder (erratic), twice preserved by local citizens, marks the gateway to the “Great South Woods.” In frontier days it was said that there was no law or Sunday beyond this point. May all who pass this way continue to enjoy the beauty of the mountains.
Sunday Rock, South Colton, NY
This in the northern end of the lake effect snow belt, where the average yearly snowfall tops 6 to 10 feet. Sometimes there is continuous snowfall starting in November and ending when Lake Ontario finally freezes in late January or February.
Back to the business at hand; the new transmitter placed:
ULXTE-6 transmitter
The 25 KW heat exchanger was placed where the old analog heat exchanger was:
25 KW heat exchanger
This system uses 1 1/4 inch flexible tubing, which is easier to work with than the 1 1/2 inch steel reenforced tubing.
ULXTE-6 HTF tubing run
Measuring the Comtech mask filter with the network analyzer:
New mask filter mounted on the old dielectric mask filter stand:
New Comtech mask filter
This arrangement allows for the reuse of the two coax patch panels, on for antenna/dummy load, the other for main antenna/backup antenna.
3 inch rigid line between the transmitter and filter
Post mask filter RF signal analysis using a Rohde Schwarz ETL:
The GatesAir equipment always has good performance parameters.
The carrier frequency is measured using the pilot. In this case, both exciters have the GPS reference connected and working. I think the ETL OCXO might be 11 Hz low.
