Ron wrote: >For emergency use, the famous "Gibson Girl" hand-cranked lifeboat >transmitter only put out about 5 watts amplitude-modulated CW (MCW) on 500 >kHz and had, under the most ideal conditions, an end fed wire 100 or 200 >feet long (attached to a box kite or balloon). Frequently it was much, much >shorter, depending upon weather conditions. Such a setup was considered to >have a working range of up to 200 miles.
>It seems that 600 meter communications using a very short antenna and >moderate power should be entirely practical over tens of miles in the >daytime and perhaps hundreds of miles at night. MF communications in the 410 to 512 kHz band, prior to worldwide abandonment of maritime Morse in 1999, was fascinating to monitor. I always kept a receiver on 500 kHz in my station at night. It was amazing what could be heard over very long distances, even when the receiver was hundreds of miles inland. The US military's hand-cranked Gibson Girls (SCR-578, later the AN/CRT-3) emergency 600m transmitters were carried in almost every military aircraft that had liferafts. In Pacific Theater WWII submarine "lifeguard" duty (looking for downed aviators), the rescue subs always monitored 600m in case a downed aircrewman was using his Gibson Girl. There was also a two-way system intended for use by the distressed party in Arctic rescue efforts, consisting of the SCR-578 transmitter and a dry battery powered AN/CRR-1 MF receiver. There was also a large variety of larger maritime lifeboat receiver-transmitter units (also hand-cranked) like the RCA ET-8053 and MacKay 401-A that transmitted and received Morse on the 500 kHz (2 watts) and 8364 kHz (5 watts) distress frequencies. These were all vacuum tube radios, although late in the maritime Morse era some of these lifeboat radios introduced some solid state technology. The ERP of such 2 watt 500 kHz transmitters under the best of circumstances must had been well under 100 mW, yet many decades of experience proved these devices to be effective. My point is that quite a lot of experience and historical importance is attached to very low power operations in the old maritime MF band. I'd love to see a part of the band be allocated world-wide to amateur operations. I believe that there will be some surprises at what can be accomplished, especially at night, when/if amateurs start re-discovering these low MF bands. Six hundred meters and up, anyone? Mike / KK5F ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
