MRHS Newsletter No. 45
Dedicated to True Believers Worldwide
Special Night of Nights Edition

16 June 2014


Newsletter back issues click HERE                                        MRHS Web site click HERE

FLASH!

USCG WILL PARTICIPATE IN NIGHT OF NIGHTS!
NEW USCG STATION ON THE AIR!
KPH, KFS, KSM, WLO AND KLB WILL BE ON THE AIR!

Event Date: 12 July 2014 Pacific Daylight Time
First Transmission form MRHS Stations: 5:01pm Pacific Daylight Time 12 July, 0001Z 13 July 2014




> Historic coast stations KPH, KFS, KSM, WLO AND KLB will return to the air


> RCA "H Set" Transmitter 298 will be on the air

> 1942 Press Wireless PW15 transmitter will be on the air

> USCG Coast Stations NMC, NMQ and NMW will be on the air

> K6KPH will be listening for calls and signal reports

  

> Join us in person or on the air!

  

But wait, there's more:

 

> Marconi author Calvin Trowbridge Jr. book talk and reception  

  

> Fantastic exhibit at Bolinas Museum for 100th anniversary of Marconi operations

  

> Listen to "An Ode to Morse Code", the story of Night of Nights 

  

> MF antenna filter saga

  

>  Preserving the RCA BL298H set transmitter with heat  

  



Clearly we have a lot to cover in this issue.  But before we dive in we'd like to solicit your support for our activities like Night of Nights and the ongoing maintenance and repair of the transmit and receive stations and their associated antenna fields.  Any donation you can make will be very deeply appreciated and will go directly to support our efforts.  Just click on the button below.

 

 

Make a Donation

 Thanks!

 

 

 

 

 Night of Nights 2014!   

 

 Morse code... 

 

It's just beeps in the air. Yet on 12 July 1999 some very tough looking grizzled old radio pioneers had tears in their eyes as the last commercial Morse code radiogram was sent. It was the end of an era. And as the last beeps faded away into the static they witnessed the end of the career to which they had devoted their lives.

 

These men - and some women - had stood watch over the airwaves on shore and at sea. Theirs was mostly the business of maritime commerce. But when their ship was in peril they were called upon to send the most electrifying three letters in radio, S O S, knowing that all their fellow radio operators would press their earphones close to get every scrap of information and bring aid to their stricken ship.

 

Once, our coasts were dotted with great Morse code radio stations, all communicating with ships at sea. They're all gone now... all except one, the one they called the Wireless Giant of the Pacific, located at Point Reyes.

 

On that sad day in 1999 another event took place. The Maritime Radio Historical Society (MRHS) was formed. We made it our life's work to honor the men and women of wireless by restoring that wireless giant. One year and one minute later the giant's voice once again spanned the oceas as we picked up the thread and kept the faith with our colleagues of the air.

 

Every year since, in an event that became known as the Night of Nights, Morse code station KPH has returned to the air, joined by KFS and the station of the MRHS, KSM.

 

This year our friends and colleagues at USCG station NMC have labored mightily to bring that storied call sign back to life on Morse code for the evening along with NMQ in Cambria, CA..

 

And, for the first time on Night of Nights, station NMW in Astoria, OR will be on the air as well. 

 

Stations WLO and KLB will join us again as hey have in years past. 

 

This is a global and local event.  Hundreds of listeners around the world will be waiting with their earphones on, waiting for the signals of the great station to once again arc over the dome of the Earth to their receivers.   

 

You can be with us in person!   

 

Dozens of people will join us at the RCA receiving station in the Point Reyes National Seashore to watch as the signals are transmitted by hand using vintage telegraph keys.   

 

A guest operating position will be available so bring your key and 'phones or use ours and operate K6KPH.  No license required!  So if you're an ex-commercial op who never became a ham here's your chance to sling some Morse again.  Or if you hold a current commercial radiotelegraph ticket you can operate KPH, KFS and/or KSM and have your license endorse to that effect.    

 

Chief Operator Richard Dillman at Position 1

 

Date: Friday 12 July 2014 Pacific Daylight Time 

 

Location: RCA receiving station, 17400 Sir Francis Drake Blvd., Point Reyes National Seashore   

 

Click HERE for a map of the location from Google Maps 

 

Time: Doors open at 3:00pm pdt, first transmission 5:01pm pdt (0001gmt 13 July)

 

Refreshments: Served

 

Photographs: Encouraged

 

Tours: Given

 

None of this would have been possible without the trust and vision of the Point Reyes National Seashore.  The only reason these facilities were spared the bulldozer that visited all the others is that they are on park land.  And the only reason they have been restored to operation is that the PRNS staff understood their importance and trusted the MRHS to restore them to life.  

 

We will send last minute changes and signal reports by Twitter.  You can join Twitter free at:

https://www.twitter.com

and follow us at @Radiomarine

MRHS Stations

Sixteen transmitters will be on the air from the MRHS transmitter site in Bolinas.  That doesn't include transmitters held in ready reserve in case of failure.  Members of the crack MRHS Transmitter Department and the H Set Team will be on hand to assure that all goes well.

> KPH:

Frequency            Transmitter                  Antenna

500/426                Henry MF-5000D        Marconi T
4247.0                  RCA K Set                  Double Extended Zepp
6477.5                  RCA K Set                  Double Extended Zepp
8642.0                  RCA L Set                  Double Extended Zepp
12808.5                RCA L Set                  H over 2
17016.8                RCA L Set                  H over 2
22477.5                RCA H Set                 H over 2

The restoration of the H set has been chronicled in past issues of the Newsletter.  It will return to revenue service for the first time in decades for Night of Nights.  See Newsletter No. 38 for information about and photos of this magnificent transmitter.

> KFS

We want to offer our sincere thanks to Globe Wireless for the help and support they have provided for our project since the very beginning.

Frequency
            Transmitter                     Antenna

12695.5                Press Wireless PW15   H over 2
17026.0                Henry HF-5000D            H over 2

> KSM

Frequency           Transmitter                     Antenna

500/426               Henry MF-5000D            Marconi T
8438.3                 Henry HF-5000D            Double Extended Zepp
12993.0               Henry HF-5000D            H over 2
16914.0               Henry HF-5000D            H over 2


Verification card for K6KPH.  A similar card is available for KSM.  Both were designed by Paul Shinn

> K6KPH

K6KPH ops will monitor the frequencies below as propagation and the number of available operators permit.

Frequency           Transmitter                    Antenna

3550.0                 Henry HF-5000D           Double Extended Zepp
7050.0                 RCA L Set                     Double Extended Zepp
14050.0               Henry HF-5000D           H over 2
18097.5               Henry HF-5000D           H over 2
21050.0               Henry HF-5000D           H over 2

> Reception Reports

Reception reports and verification requests for the MRHS stations listed above may be sent to:

Maritime Radio Historical Society
PO Box 392
Point Reyes Station, CA 94956
USA

> Station Telephone

The receive site may be contacted by phone on 415-669-9646


USCG Stations


NOTICE!

This may very well be the last time ever that USCG stations can be heard on the air using A1A (Morse) emission.  As new equipment is installed the hardware and wiring for Morse has been progressively removed.  And the personnel who knowledgeable in the art retire or are reassigned.  So be sure to listen for these stations.

Many USCG personnel at all levels are responsible for bringing these stations back on the air for Night of Nights 2104.  We want to particularly thank ET1 Mike Leska for taking the lead for this year's project.

NMC/NMQ verification card from Night of Nights 2014

> NMC
(Transmit Bolinas, Receive Pt. Reyes)

Frequency            Transmitter                         Antenna

448.0                    Nautel ND2500TT/6           173' monopole tower
472.0                    Nautel ND2500TT/6           173' monopole tower
500.0                    Nautel ND2500TT/6           173' monopole tower
6383.0                  Rockwell-Collins RT-2200  Omni-directional
8574.0                  Rockwell-Collins RT-2200  Omni-directional
17220.5                Rockwell-Collins RT-2200  Omni-directional

NOTE regarding NMC/NMQ/NMW MF transmissions.  Only one MF transmitter will be in service at each station.  Morse transmissions will be made on an as-available basis from each station as USCG operators must also accommodate scheduled NAVTEX transmissions.


> NMQ
(Transmit Cambria, CA, Receive and Control Pt. Reyes)

NMQ Transmitters

Frequency
            Transmitter                  Antenna

448.0                    Nautel ND2500TT/6    Inverted L
472.0                    Nautel ND2500TT/6    Inverted L
500.0                    Nautel ND2500TT/6    Inverted L


> NMW
(Transmit Astoria, OR, Receive and Control Pt. Reyes)

Capacitive top hat transmitting antenna at NMW


Frequency            Transmitter                   Antenna

448.0                    Nautel ND2500TT/6    Capacitive top hat
472.0                    Nautel ND2500TT/6    Capacitive top hat
500.0                    Nautel ND2500TT/6    Capacitive top hat


> Reception Reports


Reception reports and verification requests for the USCG stations listed above may be sent to:

Attn: OSCS Phil Marsh
USCG CAMSPAC Point Reyes
17000 Sir Francis Drake Blvd.
Point Reyes Station, CA 94956
USA

Shipcom LLC Stations

All thanks to Rene at WLO and CJ at KLB for the work they do each year to bring these stations back on the air.  They are true radiomen.



> WLO 

2055.5
4343.0
8658.0
12992.0
16968.5

> KLB

488.0
500.0
8582.5

> Reception Reports

Via email (for both stations) to: wloradio@wloradio.com
 
> Calling Channels

All commercial and USCG stations listed above will listen for calls from ships on 500kc and on ITU Channel 3 HF:

4184.0
6276.0
8368.0
12552.0
16736.0
22280.5


Listen on these frequencies if you want to copy both sides of ship to shore contacts.


> Commemorative Messages

Was your father, uncle or grand dad a commercial op or amateur operator?  Would you like to send a commemorative message in their honor over KPH, KFS and KSM?  We have sent several of these messages in past events and they were all very moving.  If you would like us to send such a message this year please send it to us no later than Wednesday 9 July pdt so we can be sure to include it.  Sent it to info@radiuomarine.org



> Marconi author Calvin Trowbridge Jr. Book Talk and Reception

Make it  full weekend of radio with this event the day after Night of Nights

Date: Sunday, July 13
Time: 2 pm to 5 pm
Location: Red Barn Classroom at Bear Valley.  Directions.
Phone: 415-464-5125



Description: Meet the author of Marconi: Father of Wireless, Grandfather of Radio, Great-Grandfather of the Cell Phone, The Story of the Race to Control Long-Distance Wireless. He will speak about Marconi's empire building, the competition and patent wars, and the fast pace of invention and technology change as the potential for radio became understood in the early 20th century. Books will be available, enjoy a chat with the author and complimentary refreshments.


> Fantastic exhibit at Bolinas Museum for 100th anniversary of Marconi operations

 

 

 

 

The Marconi trans-Pacific stations in West Marin went into service in February 1914 with a transmit site in Bolinas (still in use today) and a receive site at Marshall.

 

Carola DeRooy of the Point Reyes National Seashore and Jennifer Gately of the Bolinas Museum combined efforts with many other to produce a truly wonderful exhibit at the Bolinas Museum commemorating this event.   

 

Marconi & Sarnoff at Rocky Point, tube display including water cooled tube, submarine spark transmitter on display

 

The exhibit includes a great display of power tubes, the submarine spark transmitter donated to the MRHS as described in Newsletter No. 41, a great assortment of keys and bugs, an IP501A receiver and much more. 

 

The museum is located at 48 Wharf Road in Bolinas.  The hours are Friday 1:00 - 5:00, Saturday 12:00 - 5:00, Sunday 12:00 - 5:00    

 

Richard Dillman, Carola DeRooy and Denice Stoops at exhibit opening

 

  

> "An Ode to Morse Code", the story of Night of Nights   

 

 

 

Julie Caine is a producer at public radio station KALW in San Francisco.  In 2013 she produced a wonderful radio program about Morse code and Night of Nights.  

 

Click HERE to listen to "An Ode to Morse Code". 

 

 

> MF antenna filter saga  

 

KSM uses a Marconi T antenna for MF reception.  This is a great antenna - almost too great as it pulls in all sorts of broadcast signals.  Plus it feeds a house made preamplifier that can be easily be driven non-linear by strong signals.  To prevent problems there is a selectable frequency filter at the base of the antenna that's remote controlled from Position 1.  The filter and its housing served well but eventually the salt air took its toll.  That's where Bill Ruck of MRHS Maintenance stepped in.  He rebuilt both the filter and the case.  Let's listen now as we hear Bill say...

 

KPH's MW receive antenna at RS has for a long time been a "Marconi T" antenna.

 

The problem with maritime band MW reception is that just above the maritime band is the AM Broadcast band with many high power (mostly 5 kW and a few 50 kW) stations nearby. A good maritime MW receive antenna is also a good broadcast MW receive antenna.

 

The KPH home-built MW multicouplers overload from broadcast stations so a filter was added to the receive system to allow good maritime reception without overloading.

 

The filter assembly had five fixed frequency series L - C filters plus a direct selection connected via a 6 pole single throw coaxial relay. This relay is commonly used at RS for receiver input selection from the SW multicouplers.

 

The assembly was housed in a galvanized steel box on the pole at the feed of the "Marconi T" antenna in what used to be the "C" antenna field.

 

The first experience with the filter was when the Operations Department complained that one of the filters did not work.

 

A trip to the antenna and filter was in order. I found the box, pried the lid off, and removed the relay / filter assembly. Back at RS it was easy to spot the bad filter because there were two wires in mid-air and no capacitor. Likely a nearby lightning strike had blown apart the small capacitor. An identical replacement was found in the shop, installed, and the filter frequencies adjusted with a spectrum analyzer and tracking generator.

 

Re-installing the filter I added single pole Molex pins and sockets so that the relay / filter assembly could be removed without field soldering. At that time it was readily apparent that the galvanizing had worn off and the bottom of the box was mostly rust.

 

This worked for a couple of years until again the Operations Department complained that one of the frequencies did not work. In the field one could see that about half of the bottom of the galvanized steel filter box was missing. The relay / filter assembly was removed and returned to the shop.

 

Filter box and filter as found

 

This time the cause was sufficient rust on the relay clappers to restrict the motion sufficiently so that the contacts were never pushed together. The rust was filed off of the clappers, the contacts were good, and the relay / filter assembly was returned to the box. An attempt to seal the box with 2" wide 10 mil black tape was made, although it was hard to get the tape to stick to the box.

 

A couple of months later again the Operations Department reported one of the frequencies did not work. In the field the tape had fallen off, more of the bottom of the box had rusted out, and rust and corrosion was evident inside on the relay / filter assembly.

 

Original filter assembly, rear

 

The assembly was returned to the shop. The rust on the relay clappers was filed off again and this time a coat of clear nail polish was applied to slow down the rust. Once the polish had dried the assembly was returned and all filters worked.

 

It was clear that this design was at the end of its life. Many discussions were held to determine the course of replacement. One idea was to replace the switched single frequency filters with a single fixed low pass filter; perhaps with a second notch filter to remove the high power broadcast stations near the bottom of the dial.

 

The Operations Department wanted to keep the historical fabric intact even though there are clear advantages to the fixed low pass filter.

 

Ye Olde Junque Boxe was scrounged for parts. I found six 24 VDC single pole NO reed relays. Reed relays have the advantage that the contacts are totally sealed in a glass tube. They can not handle much current, but they would be more than acceptable for a receive application.

 

We also had saved parts from the KMI antennas when they were cut down and found from that salvage a good fiberglass water-tight box with feed insulators in the shop.

 

The plan was to fabricate a whole new filter assembly and replace the rusted out box and rusted and corroded relay / filter assembly.

 

Two enhancements were added. The first was a static drain choke. The "Marconi T" antenna is either floating when no relay is selected or DC isolated when a filter is selected since the filter is a series L - C filter. Surplus Sales of Nebraska had an appropriate coil that could be used as a static drain choke.

 

The second enhancement was a spark gap external to the filter box. A suitable gap was fabricated from -20 brass all-thread mounted to the antenna and ground insulators.

 

Five new adjustable inductors were also purchased from Surplus Sales of Nebraska for the filters.

 

The relays and filters were fabricated on an aluminum plate that would mount internally in the fiberglass box. Since the reed relays are sealed inside of the coil it is impossible to observe them LED status indicators were added showing which relay had +24 VDC.

 

The relay coil DC connections on the existing filter assembly were with the standard RS style S-308 CCT Jones plug but I wanted a connection that did not need field soldering. An 8-140 barrier strip was used so that crimp lugs could be used to terminate the control cable.

 

New filter assembly in new enclosure

 

The relay assembly had a binding post input terminal and a BNC output connector. A short BNC to N female chassis jack RG-58C/U coax cable was used to connect the filter to the outside world.

 

The control cable got a weather tight strain relief.

 

Some discussion was made over how waterproof the assembly could be. The box itself is well sealed but the two insulators (antenna and ground) could leak. The insulators were sealed with a drop of silicone RTV inside the insulator and the rubber washer was liberally coated with silicone grease but these seals may not be perfect. Finally we decided to use a vent so that if water did get in the box would not fill up with water but drip out. Hoffman makes water-tight electrical boxes and they make an appropriate vent accessory and one was purchased. A " threaded hole was made for the vent.

 

The next design issue was how to mount the new filter box. The box is designed to mount to a flat bulkhead but in the antenna field it has to mount to a round wood pole. After some thought a simple mounting bracket could be fabricated from strut. However, since the location is close to the ocean, standard zinc-plated steel strut would start to rust the day it was installed. Galvanized steel strut is available but the cut ends would rust, even after a coat of zinc-rich "cold galvanize" paint. The decision was to use stainless steel strut. I was staggered to find out how expensive this material is but it will last forever. All of the hardware used for this project was stainless steel.

 

A template was cut matching the box dimensions and mounting holes. The stainless steel strut was cut to length and drilled appropriately. The mounting bracket assembly was put together and checked for dimensions.  

 

All was tested and ready for installation.

 

Saturday November 9, 2013, the installation work commenced. Operations were possible by bypassing the filters although with the antenna directly connected to the coax there was a lot of IM and noise on the maritime frequencies. The old box was removed with no issues (it basically fell apart) and the new mounting bracket attached to the wood pole with " stainless steel lag screws. The filter assembly bolted to the holes in the bracket. The antenna connection was made with a new lug on the down lead. The filter ground connection and mounting bracket ground connection were tied to the existing ground lead on the pole. The control cable was cut to length, crimp lugs installed, and landed on the barrier strip.

 

New filter mounted on pole

 

Then the "Welcome to KPH" moments started. Checking with Position 1 selecting various filters the relays did not work. Turns out after some head scratching I remembered that while every other relay at RS uses the black wire for DC minus the filter relay used the red wire for DC minus. In the process of sorting this out the +24 VDC got shorted to the DC minus and the fuse for that switch blew. It took a little time for Chief Operator Dillman to find the blown fuse and replace it. Now 5 of the 6 relays worked. We will return to the bad relay later.

 

Good engineering practice is to use Type N RF connectors but the existing coax cable had a UHF male connector so an adapter was used at the output connector. But Chief Operator Dillman reported no signals at Position 1. More investigation revealed that the box thickness was sufficient to keep the N male connector from mating properly with the N female chassis bulkhead connector. A short BNC cable was used to bridge the cap between the filter output BNC and a BNC-UHF adapter to the existing coax. Now Position 1 could hear signals. The cable and connectors were taped up to make them weather-tight as an "OK temp" solution.

 

The next weekend I investigated the one relay that was not working. At the relay box I could not measure any voltage on that control wire but if I lifted that lead I could measure a volt or so into my VOM. Back at Position 1 I could measure a full +24 VDC. Likely conclusion is that this wire in the control cable is broken at one point. Fortunately the control cable is a 9-conductor #18 AWG cable and we only need 7 wires. The plan is to switch out the bad wire with the spare conductor. This is easy at the filter box but the other end of the control cable is soldered to a xmas tree block which makes it hard to rewire.

 

On another trip a barrier strip was added at the multicoupler and relay box and the control cable was cut and terminated at the barrier strip.

 

By this time it was winter and the MF Marconi T feed is located at a low point in the field. It fills with water and lacking a small boat or hip waders we had to wait until it dried out. Late rains kept the lake filled but when it dried out a trip was made to swap the wires at both the multicoupler terminal strip and filter terminal strip. The "blue" wire was swapped with the spare "orange" wire and that filter position works now.

 

Completed assembly

 

Chief Operator Dillman also reported that the 500 kc filter was not operating. When checked in the field it was working. Measuring the voltage at all six positions revealed that at five of the relays the voltage was about volt higher than at the 500 kc position. At this time we suspect that the "white" wire for the 500 kc relay was going bad. This is a concern because the control cable has nine conductors. Seven are necessary. The "blue" wire is already known bad which leaves eight conductors. The "black" wire is used as a source of +24 volts that is not necessary so the "white" wire can be swapped with that wire. That leaves us with a known failing control cable and no spare wires.

 

We're now looking for a donation of about 500 feet of at least seven conductor #18 AWG wire suitable for outside use, something known as Out Side Plant (OSP) cable in the telephone world.

 

Finally we need to come up with a solid mechanical coaxial connector at the filter box. The plan is to fabricate a spacer on the outside of the box to mount a plate with the N bulkhead connector. This will allow full engagement of the N Male cable connector.

 

The Operations Department is prepared to stipulate that Bill Ruck is indeed a God. 

 

 
> Preserving the RCA BL298H H-Set Transmitter With Heat

When we began our project the salt atmosphere in the transmitter gallery was virtually the same as that outside.  The "modern" (1990 vintage) Henry transmitters had been abandoned for two years.  There was standing water inside them from condensation.  The classic transmitters from the 1950s had been abandoned for ten years.  The controls were frozen and the doors couldn't be opened.  When we did open them we find staggering amounts of rust and corrosion.

When you're running transmitters H24 as RCA did the heat keeps them moisture free.  We now run the Henry transmitters only once a week, the classic transmitters even less frequently.  So when the H Set Team completed their stupendous restoration of 298H they wanted to make surethe classic gem did not once again become a victim of salt air and moisture.  Here's the story of how they did it, told by Greg Farrell of the H Set Team:  

Superintendent Cicely Muldoon pits restored T298H on the air for Night of Nights 2013 

Many of you are already familiar with the work the venerable H-set team did to restore the RCA 20 KW SSB T3 "H-set" transmitter and get it back on the air. It was a huge team effort, with countless trips to Bolinas (BL) and thousands of hours of volunteer time spent working on it, over a 3 year period. It's dedication occurred on July 12, 2013. What I will be covering in this article, is the design and implementation of a heating system, to help preserve the transmitter between operating cycles, which could be days, weeks, months, by keeping the interior hardware above dew point.

We were very conscious of the fact that the marine climate at Bolinas is tough on transmitters. After 30 years of service and 20 years of sitting idle, the salts in the air that had accumulated and precipitated where electric and magnetic fields were strongest inside while it was in operation, had turned much of the exposed metal,wiring, hardware and electronic components into corroded relics. With all the effort put into the restoration, how could we ensure that history wouldn't repeat itself again, either in the next 10 years or next 1000 years?  The work we had done was to restore and preserve a National Treasure of the Wireless Communication Age. We sure as heck didn't want to see it turning into a corroded hulk again!

The humidity on the coast at Bolinas runs high most of the year, between 80%-99%, with a dew point that runs in the mid 50's most of the time. Dew point is defined in Wikipedia, "as the temperature at which the water vapor in air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. At temperatures below the dew point, water will leave the air."

The prevailing on-shore winds off the Pacific Ocean, move tons of NaCl molecules over the land, and anything that is exposed or that moves air will get exposed continually with molecular salt.  We knew we needed heat to keep the transmitter above the dew point, especially during the winter months, while it was sitting idle between operations.  The RCA transmitter building 2A is not heated, and gets quite cold inside at times.

We knew we needed to get heat inside the transmitter cabinet, but in particular, heat into the sensitive RF Power Amp/Modulator Assembly. With limited funds, we needed to come up with a solution that was not only inexpensive, practical and durable, but also one with no moving parts, or parts that could easily fail due to fatigue, age or corrosion. 

 

Several options were investigated, including high-grade commercial/industrial heaters, strip heaters, cabin heaters etc.  Finding a suitable thermostat was another challenge. Most thermostats commercially available are not designed to operate indefinitely in a harsh marine environment.  

On the way home one day from Bolinas, riding with Bob Dildine and Larry Nutting, I asked the question, "What if we used power resistors?"  They have no moving parts. Their resistance and power (heat) output is rated specifically. All they need is electricity. Sealed, they will produce a known value of power in watts in perpetuity as long as AC current is available to them. 

The thermostats selected had to be sealed, durable and able to survive the salty air.  After investigating possible sources, I settled on using one made by a company named SENASYS, model 2570L334 (L-1671) . Sealed, it is designed for use in extreme environments. This particular model closed (power on) at 60 degrees F (15.5 C) and opened (power off) at 70 degrees F (21.1 C).  And they were cheap! Price was $9.75 each, so I ordered two with one for back-up. 

For the resistors, we selected a DALE RH-250 250W 120 OHM 5% power resistor, readily available and cheap ($7 each on eBay). They produce a nice even predictable level of heat when mounted to 3/8" aluminum plate. We decided to mount them in series using thermal compound, to operate at approximately 55-60 watts at 1/2 amp for nice, gentle continuous  operation.

DALE 120 Ohm resistor 
 
Larry Nutting, assisted me in the overall design, locating and selecting a suitable aluminum mounting plate at a local salvage yard, drilling and tapping holes, along with testing and validation prior to finalizing the design and installation. The plate had to fit the bottom of the PA assembly exactly, and its mounting holes had to align where screw holes already existed to attach the large PA bottom cover. One of guiding rules during the restoration project was to avoid unnecessary cutting or hole drilling, to keep the transmitter as original as possible when it ceased operations in the early 1990's. The thermostat was mounted to the outside of the PA assembly against one of the side covers. Fleece covers were used to cover the top cabinet vents, so when the transmitter is offline the vents are covered to reduce heat loss out the cabinet itself (it has plenty enough openings already without the vents being left open!). 

Testing was done both on the bench and inside the transmitter day.

During bench testing, the plate would warm to a nice 130-135 deg F and pull a steady 500 ma. @ 120 VAC.  Field testing with the plate assembly mounted inside H-Set # 355, measuring ambient temperature after four hours the probe inside the PA Assembly read 77 deg F (25 C) but this was in May 2012.

Early bench testing of resistors 
 
Installation in #298 took place September 15, 2012 during a very difficult time for me, as my father had come down with terminal cancer and passed a month later.

Further temperature measurements were taken during November 2012: inside PA assembly 67 F (19.4 C), inside main cabinet 61 F (16 C) ambient. On a very cold day in February 2013 (we'd had a long cold spell all throughout January into February), I measured transmitter gallery ambient at 51 F (10.5 C), inside main cabinet 52 F (11.1 C), inside PA unit 57 F (13.8 C) ambient with the metal anywhere from 52-89 F depending on where you took the reading with the Raytek Raynger ST2 "gun". Dew point was at 51 F (10.5 C). The heater was doing its job!

Since there is no power on to the transmitter "after hours", external 115VAC power was brought in initially with an extension cord, due to time constraints, with a later project to upgrade and install a direct line up through the floor in conduit to the transmitter. That project is currently underway. In fact, the H-set heater design has proved so successful, that MRHS has decided to direct wire all the RCA "L" and "K" set transmitters in the gallery and install Dale resistor heaters. At some future time, we may run heaters into some of the unrestored RCA H-sets.

Heaters mounted to bottom of PA assembly 
 
In addition to the PA Assembly Dale power resistor heaters, two 60 watt infrared reptile heaters (they emit no visible light) were installed to add supplemental constant heat inside the open cavern of the transmitter cabinet. A temporary neon lamp is employed to indicate when the PA heater is on or off as governed by the SENASYS thermostat control. Longer-term, a front panel neon indicator light will be utilized to indicate external 115VAC power is on into the cabinet, in addition to the one employed for the PA assembly heater.  John Felton helped design and install a similar power resistor heater solution, to keep the downstairs PA plate transformer warm and dry. Unwanted moisture and salts are considered evil things for HV plate transformers.

 

The PA assembly heater has been in use since September 2012 with no major issues. BL298H stays toasty warm and dry inside even on the coldest, dampest days at BL.  It is a treat to open the cabinet door when I am out there and feel the warmth inside, and know that this transmitter might just be operable 500 years from now.


Greg Farrell
K6SRO

  

 

> MRHS Merchandise

 

 Support the MRHS and look cool at the same time. Such a deal!  We've got hats, mugs, T shirts, belt buckles and bumper stickers, all with variations of the MRHS logo.  Get a hat and mug for yourself and a put yourself in solid with the XYL by getting her a MRHS hoodie.

 

Click on the images to go to the True Believers Store

 

 

 

 

 

 

 Just click on the images above to go to the MRHS True Believers store and browse our offerings.  Thanks!

 

   

 

Whew!  Okay, that's it for this issue.  Thanks for reading.  We very much look forward to hearing you on the air or seeing you in person on Night of Nights.  Until then we wish you the best of luck and fair winds & following seas.

 

73,

 

MRHS