[Amps] *** SPAM *** Re: Pi-L Network

[Peter Chadwick]

Tom said:
>You aren't confusing a double L with a pi-L are you? You 
aren't assuming marine rigs used pi-Ls are you....when they 
actually commonly used double L's?<
No, I was thinking of 7.5kW and upwards transmitters, where frequency changing wasn't that common ( once on a frequency, it would be there for hours, and each tx was likely to only need about 6 channels anyway), wideband antennas such as rhombics were used, and the max SWR at the tx was limited to 2:1 max.
The HF marine bands are about as narrow as ham bands (in some cases much narrower), so the amount of retuning between band ends is in practice negligible. The exception is the MF band: in theory (and for Type Approval purposes in Europe), transmitters were required to operate over 1.605 to 3.8MHz, but in practice, after WW2, frequencies used were mainly limited to 2.009 at the bottom (International ship-ship) up to around 2.8 or 2.9 MHz. For Type Approval, the antenna load was 10 ohms in series with 250pF. In AM days, there were some Greek fishing boat frequencies above 3MHz, but not many - there was some (but very little real demand) requirement to cover up to 4.2MHz

73
Peter W6/G3RZP