Naval Radio Transmitting Facility
Annapolis, MD 13-14 March, 1999
AMRAD LF Listening Test
Naval Radio Transmitting Facility
Annapolis, MD 13-14 March, 1999
Members of the Amateur Research and Development Corporation (AMRAD), a non- profit organization of radio amateurs went to the Annapolis Navy transmitting site. LF (Low Frequency) and VLF (Very Low Frequency) antennas there are no longer used by the Navy and were made available for some experiments by AMRAD. These experiments were designed to familiarize the members with some aspects of LF antennas that could not be observed with smaller home built antennas. Eventually, radio amateurs are expecting to gain access to LF that they now do not have and this work is seen as paving the way for the general population of radio amateurs and supplanting the knowledge gained from the current LF experimenters operating under FCC part 15 rules.
With the reduced interest in cold war LF technology by the military, the gaining of expertise by the radio amateurs is seen as building a pool of private expertise that could be called upon by the nation in the future should conditions like the cold war reappear.
Listening was at building 69 with a 300 foot tall Marconi type LF antenna. A large tuning coil in Building 69 was made with Litz wire over 1 inch in diameter. This coil was connected to the antenna lead for use with an automobile jumper cable. The antenna and coil combination are resonant just under 60 kHz. The combination was tuned with a series variable capacitor to between 120 and 200 kHz.
Receivers used included a Cubic R3030, a Hewlett Packard 312A wave analyzer, a Rycom selective voltmeter and a homebrew crystal set.
AMRAD was fortunate to have these antennas available to conduct these experiments. These antennas may further contribute to the body of LF transmitting antenna knowledge in the future as permission to operate the antennas for test transmissions can be obtained from Navy and the FCC.
Frank Gentges
Member
The usual suspects gather for the event. (L-r) Andre, N4ICK; Rob Bowers; Glenn, KA0ESA; Frank, K0BRA.
The antenna tuning building we occupied for the test was at the back of this former transmitter building, now a Navy Seabee facility. Thanks to the kind efforts of our host, John Schorpp, an NRTF employee, the Seabees Commanding Officer and the base Captain, for their courtesy.
At the antenna tuning building, John Schorpp re-attaches the lead-in wire from the large flat-top antenna. The Antenna, approximately 400 ft long, is suspended between two towers approximately 300 ft high.
Inside the tuning coil building, John lifts the safety grounding arm. Copper pipes, visible on the wall, connect the copper-covered ceiling to the floor ground system.
Connecting to ground was easy. The whole building is an RF cage and attaches to a massive radial system.
Frank, K0BRA, connects to the tuning coil, 30 turns, about 6 ft diameter, wound with 1.5 inch Litz wire.
Glenn, KA0ESA, listening with Hewlett-Packard 312 and Rycom 2174 selective voltmeters.
André, N4ICK, with his Cubic receiver.
Operating the Crystal Receiver
Richard O'Niell operating his famous three-stage crystal set.
Top view of crystal detector set. Left coil is antenna tuning, center is detector tuning, right coil is for nulling an interfering station. All three coils slide in a track to change coupling.
Additional photos of the NSS transmitter site are found at:
March 1999
The Usual Suspects
CBU 403
Lead In Attachment
Safety Ground
RF Ground
Tuning Coil
KA0ESA Receiving
N4ICK Receiving
Crystal Receiver
Tower Base Insulator