MRCG – MRHS Operating Event 2013

The 18th Annual Muster of the West Coast Military Radio Collectors Group has just concluded on May 4th, 2013.  The meeting was set up at the California National Guard base in San Luis Obispo CA. A good time was had by all.

Featuring the usual (great!) technical presentations, Swap meet, field operating events and indoor & outdoor displays, the event covered a lot of topics. More on that later.

One special event was the transmission and reception of messages sent from the Maritime Radio Historical Society coastal station KSM in Bolinas CA.  Overlooking the Pacific just north of San Francisco, the MRHS operates the historic KSM radio facility located there.

For this exercise, KSM transmitted 2 different messages, one via CW and the other via RATT on their normally assigned commercial frequencies as detailed in our FRAG Order.  What was unique however was that these messages were encrypted for transmission using the M-209 Convertor that was used by US forces during WWII.  Additionally, each message transmitted by KSM was an actual WWII operational message that had been sent during that conflict.  The first message was sent by Merrill’s Marauders while conducting combat operations in Burma and the second by the US Navy’s Commander Task Force 36 operating in the Western Pacific ocean.

On the receiving end at Camp San Luis Obispo, an AN/GRC-109 “Special Forces” set was operated by Tim, N6CC, to receive the CW transmission with able assistance by Tom, WA6OPE.

GRC-109 used in crypto experiment

GRC-109 used to receive KSM encrypted transmission

Above, the GRC-109 in a re-purposed transit container, antenna and ground wire out the window; a PRC-25 standing by.

GRC-109 and the MRCG Net Control position

Above: Along with the GRC-109 we ran the PRC-25 on 51.00 as net control during our VHF field operating event. The PRC-6 was up on Guard Hill in a net that included RT-68’s, PRC-6’s and PRT-4/PRR-9 sets. We also used the signal mirror to pinpoint exact positions on the ground. The gray toolbox housed a two meter rig on 146.520 for local liaison and visitor talk-in. We also ran a field event which included GRC-9, WS-19, MAB, BC-611 and TCS equipment from remote sites.

Copying CW with the GRC-109 Set

Above: The CW receiving setup; copying the 5 letter cypher groups being sent in CW: The GRC-109 in operation; J-45 knee key (in the previous image) at the ready for the follow-on K6KPH/KSM comms..

The RATT transmission was received by a GRC-46 set operated by John, WB6AZP.  John gets an award for hauling out some serious “heavy metal”!  Notice his “secret weapon”?  I called it the C-Ration Heater….
Decryption of the messages was the task of Mark, NF6X using his M-209 Convertor; he educated all of us in its operation along the way.

John WB6AZP tuning up the T-195 transmitter

Above: John tuning the T-195 transmitter, the RATT terminals in the back. The GRC-46 receiving chores were handled by the R-392 receiver seen to the right of the transmitter.

John's GRC-46 Set at MRCG

Above: The hoses and ammo can are a very clever noise abatement “muffler” for the T-195’s formidable blower noise.

The KSM CW crypto message fared pretty well despite significant local noise from the nearby high voltage power lines with their radiated hash that competed with the desired signal.  Since each CW message was transmitted twice, we received the first transmission on KSM’s 8 MC frequency but then I had to switch to their 4 MC frequency in an attempt to outsmart the noise.  Due to the noise, a few letters of the 26 group (130 letter) message was lost on each frequency but when reviewed together and with Tom’s copy after the transmission, we had received “all” groups and letters.  Absent the noise, this would have otherwise been a very routine receiving exercise.

Using our best “Spycraft” techniques, the GRC-109 antenna was a random 40 foot piece of wire, out the window and then tossed over the roof of the building with a plastic water bottle used as a throwing weight. Pretty stealthy, pretty low, pretty horizontal: Perfect for this particular circuit.

Mark operating the M-209 to decrypt the KSM message

Above: Post-Op decryption of the CW message (with its one error) by Mark yielded the contents of the message after the ciphertext wound its way through the mechanical labyrinth of the M-209.  The decoded message (with corrected letter):


Our thanks to Merrill’s Marauders veterans at WWW.MARAUDER.ORG for the text of that original message.

The M-209 and KeyMat

Above: Mark’s complete M-209 Convertor with WWII M-210 message book and a reproduced Keypad for the ‘209.

The RATT situation fared a bit worse, also due to local noise but also by signal fading (QSB). The bulk of the 8 MC transmission was received but the critical beginning and end groups were lost in the noise and fading, unfortunately preventing that message from being decoded. The RATT system properly recorded 40 of the 67 Group message.

RATT receiving problems were probably aggravated by the use of a borrowed vertical antenna. With its low radiation and reception angles, a vertical would not have been the optimal polarization for 4 and 8 MC signals at 1300 local time, over that 200 mile path. Those signals were arriving from about 60-70 degrees above the horizon – perfect for a low “NVIS” horizontal wire but pretty much in the overhead “null” of the vertical.

Part of KSM RATT transmission recieved at MRCG

Above: A portion of the received RATT message on the terminal

A portion of the KSM cipher groups received by the RATT station

Above: Many Groups were received but the effects of noise and fading are evident at the beginning and end of this segment.

The M-209 “Key” was made public on Mark’s website WWW.NF6X.NET prior to the event and with worldwide coverage made possible by KSM, we are anticipating that many others successfully received and decoded the messages. Mark did receive an E-Mail from an enthusiast in Ohio who received and successfully decoded the RATT message and then posted on You Tube a video of his Model 19 teletype clattering away as proof of reception!  Well done!

As a follow-up to the exercise, we contacted station K6KPH (co-located with KSM) via CW using the GRC-109 and exchanged notes on the exercise.  K6KPH then sent MRCG a congratulatory CW Radiogram marking the end of this fun event.  Well done to all! Special thanks to the team at KSM for making this all possible.

Practice makes perfect – Wait ’till next year!