Paul Thurst – Page 2 – Engineering Radio

Golos Ameriki

The Voice of America; expended goodwill edition.

Radio Liberty and Radio Free Europe were The main sources of Western information behind the Iron Curtain during the Cold War. While the VOA, RFE, and RL used HF, there were also FM relays in the mix. If you wanted to know what the US Government’s position was on any topic, VOA, RFE, and RL were the information sources.

I wrote several articles about this in the past:

So what happened? Why has the current administration shuttered those services?

There are several good reasons why many government broadcasters have reduced or eliminated shortwave:

Fewer people care about the US Government’s position
Changes in geopolitics
Reduced listenership to HF Shortwave Broadcasts due to technical difficulty
Large double-sideband AM transmitters are expensive to operate and maintain and therefore are a target for reducing expenses
HF transmitter sites require a lot of land and physical infrastructure, which is also expensive to maintain
New distribution technology is easier for the end user and less expensive to operate

Many people, particularly young people, do not know the difference between an over-the-air broadcast and an internet stream. Buying a special receiver, putting up some indoor or outdoor antenna, then tuning around several different frequency bands to find something worth listening to, seems like a lot of work. These days, there are few shortwave broadcasts worth listening to, especially in the English language.

The BBC greatly reduced HF distribution of The World Service starting in 2005, favoring more internet-based distribution. Radio Canada International completely went off the air in 2012, scrapping its extensive transmitter site in Sackville NB in 2014. Radio Australia signed off in 2017. Deutsche Welle mostly left the HF band in 2011 while reducing its FM in 2016. The Voice of Russia ended HF broadcasts in 2014.

The only state-owned shortwave broadcaster that has expanded is Radio China International.

VOA Greenville B has some very old transmitters. The newest units date from the late 1980s or early 1990s. The oldest are the two original Continental 420As, dating from 1960, and are original to the building. When I visited there in 2017, two transmitters were on the air, the BBC and the AEG broadcasting at half power to Cuba and Africa respectively. The rest were shut down. The Continentals were difficult to change frequencies on because of the Doherty modulation. The GEs were long in the tooth, but at least serviceable due to the stock of spare parts from site A. I think the overseas sites in the Philippines and Sao Tome are similar.

Many have pointed out, and rightly so, the Internet censorship issue. Terrestrial radio broadcasting is often the best or only way to circumvent the suppression of information. Kim Elliot pointed this out in his Radio World article “Why we need Shortwave 2.0” All of those points are valid.

What can be done? Implementing DRM30 as a worldwide HF broadcasting standard would be a step in the right direction. DRM30 can send ancillary data, including Radiogram type news bulletins. DRM30 is much more energy efficient than DSB AM because there is no carrier, which wastes half or more of the transmitted power on a carrier that contains no information. Instead of a giant transmitter site, with curtain arrays, a more distributed transmission system with several frequencies on the air at the same time uses lower-powered transmitters, simpler antenna systems such as Rotating Log Period Arrays (RLPA), or non-directional vertical towers. This would require some changes to the FCC rules, but now is the time for that.

TV’s ATSC 1 has something called a “Transport Stream ID,” (TSID) which is a unique number assigned to each broadcaster. Wide-band SDRs are capable of scanning across many HF bands. Implementing something similar for DRM30 HF broadcasts would not be that difficult. Shortwave Listeners just program the HF TSID to lock onto the digital broadcast of their choice, if it is available. This would make HF Broadcasting available to most non-technical people looking for information. Most of this can be done with existing technology. However, DRM still (almost 2 decades later) lacks receivers. There is a development on that front as well: RF2Digital support module. The point is that there are many good ways to improve the technology, keep HF broadcasting relevant, and bypass attempts at internet censorship.

What will be done?

The General Electric T1000C Stereo Receiver

My parents had one of these units on the side table in the dining room. My father put up an FM antenna outside on the roof so he could listen to more stations. In the early 1960s, there were not as many around as there are today. Our house was on the wrong side of a hill for the NYC stations, although Peekskill seemed to come in just fine. What is fascinating to me is the timing and cost. These stereos were made in 1963, not long after the Zenith/General Electric FM stereo system was adopted and first broadcast on WGFM (now WRVE) in Schenectady, NY (June 1, 1961). Not every FM station rushed out to install the new system.

General Electric T1000C Stereo receiver marketing

For a bit of a reference, $180.00 in 1963 is worth $1,868.65 in 2025. At that time, my father was an installer/repairman for New York Telephone. My mother was not working and six of us lived under one roof. That was quite a bit of money for an AM/FM radio.

The radio was normally tuned to 100.7 WHUD, which initially went stereo in 1972. Other stations that could be received: WGFM, WROW-FM, WSPK, WEOK-FM (now WPDH), and WGFH (later WINE-FM now WRKI).

General Electric T1000C stereo (Walnut cabinet)

I purchased this one on eBay for $70.00. It turns on (in fact, it did not turn off), there is a hum, the pots are scratchy, etc. However, if I tune it to one of the local AM stations, I can hear music under the loud 60-cycle hum. In other words, it works! So, I spent time fixing all the defects and enjoyed some nostalgia. According to this date stamp, the wood enclosure was made in January 1963. I would think the rest of the unit was made about the same time, which means this is one of the first radios in this model. This may have been manufactured in Bridgeport, CT, or Syracuse, NY. The serial number is missing from the back of the chassis.

The main source of the hum appears to be this capacitor, which clearly has seen better days.

The on/off problem was the selector switch, which stuck in the on position because it was gunked up with dried-up lubricating oil and dust. I cleaned it with denatured alcohol and DeOxit.

The parts list included about $15 worth of capacitors, $1 for a new rectifier diode, a $7 telescoping FM antenna from Amazon, and $6.32 for two PLT 12 6.3 volt miniature lamps for dial light.

All of the tubes look to be the original GE units. After the recap, I turned it on and there was nice sounding AM, but no FM. The FM RF section has a triple triode (V2) which is the AFC, 10.7 MHz Oscillator, and mixer. This tube was loose in its socket and needed to be reseated. After that, everything worked.

All of the pots were scratchy. I cleaned them with DeOxit and worked them back and forth many times. After a while, they all are working.

FM Stereo receiver MPX decoder block diagram

I found a Sam’s Photofact (basic service manual) on this set. What is very interesting is the schematic for the multiplex receiver. This section decodes the L+R/L-R signals and produces the stereo audio. Unlike modern FM stereo receivers, in which the broadband multiplex signal is fed into one side of a chip and the discrete L/R signal comes out of the other side, the signal path through the various processing stages can be followed.

The broadband MPX signal comes from the IF stage via wire #27. The signal is amplified by V6. The L+R (20 Hz to 15 KHz) or mono signal goes through a low-pass filter L17/C40; the 3dB cutoff should be around 16-17 KHz. The L-R and 19 KHz pilot goes to wire 34, thence through a high-pass filter C37/L16/C38; the cutoff should be 20 KHz or so. The L-R and 19 KHz pilot are Amplitude Modulated subcarriers on the FM signal. Wire 38 routes the MPX signal to V6 which recreates the 38 KHz subcarrier by doubling the 19 KHz pilot. This is filtered by a bandpass filter C13/L14. The L-R and the 38 KHz subcarrier are sent to the product detector.

Diode product detectors X4 and X5 (1N541) demodulate the lower sideband (23 – 37.98 KHz) and the upper side band (38.02 – 53 KHz) respectively. Those signals are summed in the matrix subassembly K4 with the L+R. Mathematically, the results are:

The Left and Right audio is then sent to the first audio stage V7 through a deemphasis network. If no 19 KHz pilot is detected, no 38 KHz carrier is recreated and this stage remains silent. In other words, you have to find an FM station in mono first, then flip it to stereo to see if there is enough signal to decode the L-R. One of the limitations of the first generation of FM stereo receivers. Newer versions of this set have a stereo light, or “Stereo Eye” so the listener knows when stereo reception is possible.

The front of the cabinet is covered with glass, which I cleaned with soapy water. The glass has part of the gold leaf trim rubbed off. I think this radio got a lot of use.

I let the knobs soak in soapy water overnight then cleaned them off with an old toothbrush. I believe that this radio was once in a smoking environment, based on the amount of yellow, gooey substance covering everything. I ended up disassembling the entire unit to clean it. I used a paintbrush and the shop vac to get all of the dust out of the cabinet.

The speakers and speaker cones are in good condition. The speaker cabinets needed a little work; in both cabinets, the fronts (the part that is seen when both speakers are “closed”) were popping off. I had to glue a bit of wood back together and fix the metal holding brackets. The cloth on the speaker side is a little faded.

General Electric T1000C restoration complete

The wood finish is in good shape with a few scratches and dings. I decided to use Howard Restore-A-Finish. This is not the same as stripping and refinishing but rather repairing the existing finish. There was a water ring on top of the cabinet, which was removed with the Restore-A-Finish and light use of steel wool.

Three power supply capacitors, held down by a ty-base glued to the chassis

Reassembly went about as expected. I glued these tie bases to hold up the new capacitors.

The receiver is fairly sensitive and the dial is accurate. There is an alignment procedure in the repair manual, but I think everything is working as it should. I have spent enough time trying to fix things that are already working to know that for a 1963 tube receiver, this is good enough. Perfection, as they say, is the enemy of everything else.

So, how does it sound? Pretty darn good, as it turns out. I am working on a brief YouTube video with some religious music (I’ll post it when it is done). On the FM side, I can get WAMK, WBPM, WKXP, WJUX, WDST, WPDH, WFSO, and WPDA clearly with the whip antenna on the radio. AM, I hear WGHQ and WJIP.

I can hear the old man now, humming along to his favorite tune…

The Bext TFC2K broadband FM antenna

FM Broadband antennas are a compromise because they generally have less gain than tuned antennas, are more complicated, and take up more space. However, this antenna has none of those issues. The gain and radiation pattern appears to be almost the same as a tuned three-bay FM antenna.

We are finishing up an antenna project in Pittsfield, MA, this week.

The project involved replacing a Shively 6812 tuned to 95.9 MHz (WBEC-FM) with the TFC2K so that the W277CJ 103.3 MHz (WUPE) translator located on the roof of the 14-story Holiday Inn on West Street could be moved to the studio location. In this case, having the translator in-house will save significant rent. The new antenna will continue to serve as a backup facility for WBEC-FM when the main site is off the air for whatever reason.

The input power per bay is based on the antenna’s input connector. In this case, each bay has a 7-16 DIN connector and the power divider is a 7/8 inch EIA flange. Thus the maximum input power for this setup is 5.5 KW. The licensed output for both facilities is far below that.

According to the manual, this antenna should be spaced at 0.85 wavelength, which is frequency-dependent. I chose a frequency halfway between the two (103.3 – 95.9)/2+95.9 = 99.5 MHz. The formula from the Bext general antenna manual is:

D = (300/F) x 0.85

Where
D = the distance between center of radiating elements (booms)
F - Frequency in Mhz.

Thus, D = (300/99.5) x 0.85 = 2.56 meters (or 8′ 5″)

As this is a series excited AM tower, some type of broadband isolation coil is needed to cross the base insulator. This one is simply a large coil of 7/8 inch coax, likely with a capacitor across the outer conductor to create a resonant LC network.

To me, it looks like a water heater. Since the ground is frozen solid, we made a temporary stand. We will have to come back in the spring to create a permanent stand or perhaps a unistrut mount to the wall of the ATU building.

In the rack room, the transmitters are combined into a Bext FDCSDC2 star point combiner.

Broadband sweep shows a good match across the entire FM band. I will be interested to see how it performs with respect to the Shively single bay 6812 on the roof of the hotel (103.3 W277CJ).

Return loss, Bext TFC2K 3 bay FM antenna

The return loss looks good on both 95.9 and 103.3 MHz. The interference noted in the sweep is from local FM stations including the main transmitter for 95.9 MHz.

Weather related broadcast issues

We just finished our 3rd annual February ice storm. It is becoming somewhat of a tradition in these parts. After shoveling the driveway this morning, I sat down to enjoy my nice hot coffee. While doing that, I figured I would check some of the transmitters to see how things were going. That is when I noticed this:

The reflected power is much higher than normal indicating potential issues with the antenna deicers. I knew something was wrong after a quick call to the Burk, which stated the deicers were on. A quick double-check showed that the reflected power had increased by another 75 watts, so a nice drive to the transmitter site was in order.

Indeed, the controller had turned on the antenna deicers.

Using a clamp on amp meter, I saw almost no current on either leg of the 240-volt circuit. In the meantime, the backup antenna had 2 amps on each leg, which is normal. Then I noticed this:

The relay on the right shows signs of overheating.

I moved the Main Antenna circuit over to the aux antenna relay to get things going again. The current on each leg of the main circuit is 4.2 amps. Over the next 45 minutes, the reflected power returned to normal.

Other transmitter sites to the north in Albany have had similar issues. Unfortunately, those antennas do not have heaters or radomes. Thus, the only remedy is reducing power until the transmitter stays on.

I also noticed that when there is an antenna problem, the station does not sound as good as it normally does because of the bandwidth restrictions adding distortion in the frequency domain.