AM transmitter – Engineering Radio

The Energy Onix Pulsar transmitter

Engineering Radio: The Oh Dear God Edition.

I have been tasked with fixing one of these glorious contraptions. Aside from the usual Energy Onix quirks; design changes not reflected in the schematic diagram and a company that no longer exists, it seems to fairly simple machine. Unfortunately, it has spent its life in less-than-ideal operating conditions.

Energy Onix Pulsar 1000 in the wild. Excuse the potato quality photo — Energy Onix Pulsar 1000 in the wild. Excuse the potato-quality photo

Upon arrival, it was dead in the water. Found copious mouse droppings, dirt, and other detritus within and without the transmitter. Repaired the broken start/stop switches, fixed the RF drive detector, replaced the power supply capacitors, and now at least the unit runs. The problem now is the power control is unstable. The unit comes up at full power when it is first switched on, then it drops back to 40 watts, then after it warms up more goes to about 400 watts and the audio sounds distorted. This all points towards some type of thermal issue with one of the power control op-amps or another composite device.

After studying the not-always-accurate schematic diagrams, the source of the problem seems to be the carrier-level control circuit. This is based around a Fairchild RC4200AN (U10 on the Audio/PDM driver board) which is an analog multiplier chip. That chip sets the level of the PDM audio output which is fed into the PDM integrator circuit. Of course, that chip is no longer manufactured. I can order one from China on eBay and perhaps that will work out okay. This all brings to mind the life cycle of solid-state components. One problem with the new technology; most solid-state components have a short production life, especially things like multiplier chips. Transmitters are generally expected to last 15-20 years in primary service. Thus, transmitter manufacturers need to use chips that will not become obsolete (good luck with that), or purchase and maintain a large stock of spare parts.

In the meantime, the chip is on its way from China. Truth be told, this fellow would be better off with a new transmitter.

Decommissioning transmitters

I was at a transmitter site a few days ago scrapping a Continental 814-R1 transmitter and started thinking (always a dangerous thing) about how many of these units I have decommissioned over the years. It turns out, quite a few:

Make/Model	Year new*	Year removed	Station	Disposition
GE BT25A	1948	1994	WPTR	Donated/scrapped
Gates BC5P	1960	2004	WWLO	Donated
Harris MW5A	1982	2000	WLNA	Scrapped
Gates BC1T	1961	2001	WLNA	Donated
Harris FM20H3	1972	2001	WYJB	Scrapped
RCA BT1AR	1960	2001	WROW	Donated
Harris BC1G	1972	2001	WDFL	Abandoned
Harris FM20H3	1971	2005	WHUD	Scrapped
BE FM30A	1988	2005	WHUD	Cannibalized
Harris FM5G	1972	2008	WSPK	Scrapped
Mc Martin BF3.5K	1976	2011	WCTW	Scrapped
RCA BTF-10ES	1978	2011	WRKI	Scrapped
Gates BC1T	1964	2011	WINE	Scrapped
Continental 315F-R1	1985	2013	WVMT	Donated
Collins 813F	1975	2014	WKXZ	Scrapped
RCA BTA1AR	1965	2014	WCHN	Scrapped
Collins 813F2	1978	2015	WKXZ	Scrapped
Collins 830D-1A	1968	2014	WKXZ	Scrapped
Harris FM20H3	1972	2013	WYJB	Scrapped
Harris BC5HA	1973	2013	WROW	Scrapped
Harris FM10H	1971	2013	WMHT-FM	Scrapped
Harris FM2.5H3	1973	2015	WEXT	Scrapped
Mc Martin BF3.5K	1972	2014	WSRK	Scrapped
CCA FM5000G	1980	2015	WTBD	Scrapped
RCA BTF1E	1972	2016	WZOZ	Scrapped
QEI 695T3.5	1996	2015	WBPM	Scrapped
QEI 695T5	1996	2015	WBPM	Scrapped
Harris HT3.5	1997	2015	WUPE-FM	Scrapped
Harris Z5CD	1997	2015	WXPK	Cannibalized
Energy Onix SSA1000	2000	2015	WDHI	Cannibalized
Harris MW1	1982	2016	WPUT	Abandoned
Mc Martin BF1K	1982	2016	WSUL	Scrapped
Mc Martin BF3.5K	1982	2016	WSUL	Scrapped
Continental 814R1	1980	2016	WDBY	Scrapped
Broadcast Electronics FM35A	1986	2017	WEBE	Cannibalized
CCA FM-1000D8	1973	2018	WDLA	Scrapped
Collins 828E	1978	2018	WSYB	Scrapped
Gates BC-1H	1971	2018	WHUC	Scrapped
Gates BC-1J	1954	2019	WBEC	Scrapped
Gates BC250GY	1969	2019	WSBS	Scrapped

*In some cases the “Year New” is a guess based on when the station went on the air. Before you write me and say “But model XYZ transmitter wasn’t made until 19XX, I did not look at every nameplate and write all the information down as I did this.

Like everything else, there is a process to this.

First of all, if the transmitter was made before 1978, the possibility of PCB capacitors and transformers exists. In the case of the GE BT25A, massive amounts of PCBs needed to be disposed of properly. According to current federal laws, ownership of PCBs and PCB-contaminated items cannot be transferred. Thus, the transformer casings were cleaned out and taken to Buffalo to be buried in a PCB-certified landfill. Otherwise, most other transmitters, such as the RCA BTA-10, may have a few PCB capacitors in them and perhaps the modulation transformer. Those items can be disposed of by calling an authorized environmental disposal company like Clean Harbors.

The rest of the transmitter is stripped of any useful parts. Things like vacuum variable capacitors, rectifier stacks, blower motors (if they are in good condition), HV power supply contactors, unique tuning parts, whole control and metering boards, tube sockets, etc.

The remaining carcass is then disassembled and hauled off. I got a guy that will do this for relatively little money. He takes the transmitter back to his warehouse and cuts it up, sorts all of the various metals out, then takes it to the scrap yard. This includes things like cutting all of the windings off of transformers and power supply chokes, sorting out the brass and copper tuning parts, etc.

Village seeks repayment from Energy Onix

This saddens me a little bit. Apparently, the Village of Valatie, NY is seeking repayment of a $500K loan from Transmitter Manufacturer Energy Onix. Since the passing of Bernie Wise, the company has basically folded.

The village may foreclose on the building if necessary, said Mayor Diane Argyle.

Located at 1306 River St., Energy-Onix was founded in 1987 by broadcast pioneer Bernard Wise, who is known for bringing the “grounded grid” to radio broadcasting. The company designed, manufactured and sold radio transmitters and tubes.

More from the Columbia-Greene Register Star.

Sadly, there goes support for many Energy Onix and CCA transmitter still in the field. I know of several of those old CCA transmitters that are still cranking away, 40 or more years after they rolled out of the factory in Gloucester, NJ. I have tried, several times, to call Energy Onix since Bernie passed last year and the phone goes unanswered. I wonder if we could pick up the the field support and service for these units. I wonder if there are any spare parts left at the old factory building?

Broadbanding an AM antenna

Many articles have been written on the topic and it is still a black art to some. Making a Medium Frequency (MF) antenna that has enough bandwidth to pass 10 KHz audio can be challenging, to say the least. The VSWR out to +/- 15 KHz carrier needs to be kept at a minimum and the power needs to be evenly distributed between the two sidebands. This can become problematic with complex Directional Arrays or towers that are tall or short for their operating frequency.

When we were working on the WFAS-AM tower in White Plains, NY, it became apparent to me that something was not right. The tower is skirted and now holds the antenna for W232AL, a 250 watt translator broadcasting the WPLJ HD-2 channel. After installing the FM antenna, some tuning of the AM antenna was required and this is the graph of the resistance and reactance curves:

WFAS 1230 KHZ, ATU output resistance and reactance

This looked very similar to the resistance and reactance curves before the FM antenna work was done. Red line is resistance, the blue line is reactance. I think it had been like this for a long time. While it is not terrible, it is not that good either. As alluded to in a previous post, some re-working of the ATU was needed. After some trial and error, this is the circuit that we ended up with:

WFAS 1230 KHZ White Plains, NY ATU schematic

Not quite what I expected, however, it was designed with the parts on hand, excepting the vacuum variable output capacitor, which was donated by me. That part was key in making the proper adjustments.

After my redesign and tune up of the ATU, this the resistance and reactance curves at the input terminal of the ATU:

WFAS 1230 KHz resistance and reactance after ATU modification

The graphs have a slightly different format, but you get the idea. The red line is resistance, the blue line is reactance and the green line is overall impedance. The resistance is symmetrical about the carrier as is the reactance. Truth be told, I think there is a little more that can be had here, but for now, there is no reason to go any further. I made the initial measurements at the input of the ATU and confirmed them again at the output terminals of the transmitter. When we turned the transmitter back on, I noticed that the modulation index had dropped by about 15 percent. I think the reflected power was getting back into the RF sample and fooling the mod monitor. I also noticed that the high end in particular sounded much nicer.

The ATU building is a little cramped and it is hard to get a good picture. The vacuum variable capacitors were salvaged from a scrapped AM transmitter years ago. The tower is 202 degrees tall, which is also a factor. It will be interesting to see what seasonal changes there are with snow cover, mud, etc.

Overall, this was a fun project.