MRHS NEWSLETTER No. 11
13 August 2011
Readers have commented that the previous Newsletters, with white letters on a black background, were hard to read and hard to print. As as you see we've taken heed and reversed the print and background colors.
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Visit the MRHS Web Site
There's a lot more on the Web site than we can cover in the Newsletter. Take look at our "Incredible Radio Tales" section for great stories of radio and radiomen. The "Historic Coast Stations" section has information and never before published photos of coast stations that have now become silent. And the "Coast Stations Recordings" section has a ton of off-air recordings from stations around the world. There's a lot more too. Take a look.
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Transmitter No. 298 Update
When we last left transmitter 298 (a RCA T3 20kW independent sideband "H Set" transmitter designed for point to point work - see Newsletter No. 10) we saw the wonderful restoration work that had been done by the "H Set Team", a group of dedicated volunteers, current and former HP engineers. But some problems were mentioned as well, problems that might be expected when bringing a powerful transmitter back on line that had been dormant for decades.
Now comes Mr. Bob Dildine of the H Set Team to report on the progress that was made on Saturday 11 August.
WARNING: Lots of transmitter geek information included below.
Saturday as a productive day at Bolinas.
Steve Pazar and I went out to continue troubleshooting the H-set. The objective was to check for parasitic oscillations and track down the cause of the excess plate current we've been seeing.
Here's what we found.
When we first turned on the transmitter to check for parasitics, we noticed that the total plate idling current drifted up over the course of 5 minutes or so for no apparent reason. After some experiments that included swapping tubes and monitoring the individual cathode currents we found that the 4CX5000 that was rebuilt by Econco (s/n 4GC73) for this project was the culprit.
Its cathode current started out at 0.7 amps and increased to 0.95 amps in less than 10 minutes of operation. The other tube is a new one from Eimac (s/n JEG197) and its cathode current remained constant at 0.55 amps. This was with 4,500 volts on the plate, 1,300 volts on the screen, and -325 volts on the control grid and with no RF drive. We checked for parasitic oscillations using an HP 8554 spectrum analyzer connected through an attenuator to the sampling loop on the transmitter's output. This is before the low pass filter. No indication of oscillations were found up to about 1500 MHz.
There were no other indications such as erratic tuning either. Then we installed a pair of well used 4CX5000's that were pulled from KPFA's transmitter about 35 years ago. Cathode current on these were 0.55 amp and 0.6 amp and these currents were steady and unchanging with time. We tuned up at 22 MHz and were able to see about 4,700 watts output for an input power of 6,900 watts, an efficiency of about 68%. Output power was measured with an RF ammeter in series with the 600 ohm dummy load but we're not sure of the ammeter's calibration.
|Bob Dildine (L) and Steve Pazar (R) watch the meters intently as they tune up transmitter 298 |
In the meantime, Steve Hawes connected the H-set to the station's keying network and we had it sending the KSM traffic into the dummy load. We looked at the output waveform wave shape and it looked pretty good, with reasonable rise and fall times. Next time out we'll do a more careful measurement.
So it was a pretty productive day.
To all those who have clicked on the donate button in the past we offer a heartfelt thanks. Your support is tremendously appreciated.
We know not everyone is able to undertake a project like the restoration of H Set 298 or is close enough to be able to participate directly in MRHS projects. But even if you can't volunteer you can help assure that projects like this wonderful restoration can continue.
If you're a True Believer and can make a contribution to The Cause it will be most appreciated. And remember, we're all volunteers so 100% of your contribution goes directly to purchase the items needed to keep the transmitters and receivers working and the antennas in the air.
Mystery Station on Mt. Tamalpias
Mt. Tamalpias is a reference point for the San Francisco Bay Area. Vintage postcards and some literature show that a wireless station once existed there, allegedly for communications with Hawaii. But the wooden towers were poorly installed and they soon blew down.
Solid information about this mystery station has been hard to find. But Fred Runner has recently written with the results of some of his research on the station along with the best photo of it we have yet seen.
Enlarged look at Pacific Wireless Telegraph's radio towers on Tamalpais's Middle Peak, shows detail: a better look at the funicular railway, "Pie Ville" (San Rafael turn) and the buildings created by Pacific Wireless.
In 1905, just 4 years after Marconi sent his first transatlantic message, two 300-foot wooden radio towers are erected at middle peak by the Pacific Wireless Telegraph Company for communications with Hawaii and perhaps Japan. They are blow down the following year on December 10, 1906 and never rebuilt.
It is unclear if they were ever successful (A very detailed letter at the Library of Congress website notes funicular had an incline of 37.4 per cent. Steepest part of scenic railway was just above pie ville at 7%.)
Note foot path that runs to the left from pie ville. It's where Ridgecrest Blvd. will be built in 1925.
West Peak is on the left, today the site of the RADAR dome. West Peak WAS the highest peak on Tam, at 2604 feet. The Air Force bulldozed the peak in the 1950s when they built the first RADAR station there.
This article with a map drawn in 1987 by Marin County historian Dewey Livingston gives the best information we have seen about the station. Do you know more? Please let us know if you do. Our email address is firstname.lastname@example.org
Mr. and Mrs. America and all the ships at sea... let's go to press with the KSM and K6KPH report for Saturday 11 August 2012...
As we announced in the last Newsletter, K6KPH was unavailable last weekend so we don't have a contact report. However Transmitter Supervisor Steve Hawes stepped up to provide CW and RTTY press and weather transmissions via KSM for the day.
This is probably a good time to mention that we hear regularly from True Believers who provide KSM reception reports by radiogram and email. One of the most faithful is Marsh Hall. Here's his report from Southern California for last weekend:
Good morning KSM group.
I hope all is well up there it is very HOT here. Here is a signal report for Sat. Aug. 11, 2012
at 2230 Z 1130 PSDT . You were sending news about " first students in the cadet program"
and other news for mariners.
4.3505 MHZ. Q5 / S5
6.4740 MHZ. Q5 / S9
8.4383 MHZ. Q5 / S5
12.9930 MHZ. Q4 / S3
16.914 MHZ. Weak QSB
22.4458 MHZ. Very weak
6.2280 MHZ. Good copy
8.4330 MHZ. Very good copy
12.6310 MHZ. Fair copy Fast QSB
Thanks to all of you for keeping the signals on the air.
If you'd care to send a signal report we'd enjoy hearing from you. Our email address is email@example.com
NOTE: KSM and K6KPH will be active on Saturdays only until further notice.
Until next week we wish you fair winds and following seas.
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